WO2025255485A1

WO2025255485A1 - Natural carbon-enhanced composite materials and systems and methods for their manufacture

Info

Publication number: WO2025255485A1
Application number: PCT/US2025/032680
Authority: WO
Inventors: Jason Patrick Trembly; Yahya Taha AL-MAJALI
Original assignee: Ohio University
Current assignee: Ohio University
Priority date: 2024-06-07
Filing date: 2025-06-06
Publication date: 2025-12-11
Anticipated expiration: 2026-12-07
Also published as: WO2025255485A9

Abstract

An NC-enhanced composite material including a natural carbon and a resin. The natural carbon is a majority, such as greater than 50%, by weight of the NC-enhanced composite material. The resin is a thermoplastic or a thermoset material. The composite material being between 10 wt.% to 50 wt. % of the NC-enhanced composite material. The NC-enhanced composite material may be in one or more forms, such as a filament, a pellet, a 3D-printed composite material, and a carbonized NC-enhanced 3D-printed material. The NC-enhanced composite material includes a lubricant in an amount of 1 wt.% by 5 wt.% by weight of the NC-enhanced composite material.

Description

Natural Carbon-Enhanced Composite Materials and Systems and Methods for Their Manufacture

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63/657,432 filed on June 7, 2024, the disclosure of which is expressly incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] Exemplary embodiments of the present invention relate generally to systems and methods for natural carbon (NC)-enhanced composites and carbonized structures, and more specifically NC-enhanced composites and carbonized structures suitable for use in additive manufacturing.

BACKGROUND OF THE INVENTION

[0003] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0004] Additive manufacturing systems and methods arc commonly used to manufacture complex components using inputs such as thermoplastic-based composites or thermoset-based composite materials. These thermoplastic-based materials and thermoset-based materials can be mixed with one or more filler material to modify the properties of the end materials and reduce the amount of thermoplastic or thermoset materials needed to form the end product. These systems and methods are applicable in a variety of circumstances, such as manufacturing prototypes, manufacturing complex parts, or manufacturing custom parts across a variety of industries, such as building/construction, automotive, and aerospace.

[00051 It would be desirable to use natural carbon (NC) materials — such as coal, reclaimed coal waste, coal-derived carbons, and mixtures thereof — as filler materials in thermoplasticbased materials and thermoset-based materials used in additive manufacturing. Not only are NC materials widely available and inexpensive, but their use as fillers in thermoplastic -based and thermoset-based composites might improve the mechanical, thermal, and flammability performance of the resulting composites. In addition, the use of NC as a filler may reduce the negative externalities of burning these materials as fuel. Accordingly, there is a need for a system and method for producing NC-enhanced thermoplastic-based materials and NC-enhanced thermoset-based materials therefrom at scale that is cost-effective.

SUMMARY OF THE INVENTION

[0006] Certain exemplary aspects of the invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be explicitly set forth below.

[0007] A first aspect of the invention is directed to an NC-enhanced composite material comprising a natural carbon, wherein the natural carbon comprises between 50 wt.% to 90 wt.% by weight of the NC-enhanced composite material; and a thermoplastic resin, wherein the thermoplastic resin comprises between 10 wt.% to 50 wt. % of the NC-enhanced composite material, wherein the NC-enhanced composite material comprises a material selected from the group consisting of an NC-enhanced filament, an NC-enhanced pellet, an NC-enhanced 3D- printed composite material, and a carbonized NC-enhanced 3D-printed material. In one embodiment, the natural carbon comprises between 55 wt.% to 90 wt.% by weight of the NC- enhanced composite material, the NC-enhanced composite material further comprising a lubricant, wherein the lubricant comprises between 1 wt.% by 5 wt.% by weight of the NC- enhanced composite material. Alternatively, the lubricant comprises between 1 wt.% and between 1.5 wt.% by weight of the NC-enhanced composite material.

[0008] In one embodiment of the first aspect of the invention, the NC-enhanced composite material further comprises an additive, wherein the additive comprises between 1% and between 20 wt.% by weight of the NC-enhanced composite material. In one such embodiment, the additive comprises a material selected from the group consisting of a process aid, a binder, a chemical foaming agent, an anti-foaming agent, a lubricant, and a combination thereof. In one such embodiment, the additive comprises a material selected from the group consisting of a fiber, an additional filler, a coupling agent, a thermoset resin, a crosslinking agent, a metal, inorganic material, and a combination thereof. In one embodiment, the natural carbon comprises a material selected from the group consisting of coal, reclaimed coal waste, coal-derived carbons, and a combination thereof. In one embodiment, the thermoplastic material comprises a material selected from the group consisting of PLA, PETG, HDPE, PA 12, and a combination thereof. In one embodiment, the thermoplastic material comprises HDPE. [0009] In one embodiment of the first aspect of the invention, the natural carbon comprises between 80 wt.% and 90 wt.% by weight of the NC-enhanced composite material.

[0010] In one embodiment of the first aspect of the invention, the NC-enhanced material is an NC-enhanced filament or NC-enhanced pellets. In one embodiment, the NC-enhanced material is an NC-enhanced 3D-printed composite material. In one embodiment, the NC- enhanced material is a carbonized NC-enhanced 3D-printed composite material.

[0011] A second aspect of the invention is directed to an NC-enhanced composite material comprising: a natural carbon, wherein the natural carbon comprises between 50 wt.% to 90 wt.% by weight of the NC-enhanced composite material; and a thermoset resin, wherein the thermoset resin comprises between 10 wt.% to 50 wt. % of the NC-enhanced composite material, wherein the NC-enhanced composite material comprises a material selected from the group consisting of an NC-enhanced composite slurry, an NC-enhanced printed composite material, a crosslinked NC-enhanced printed composite material, and a carbonized NC-enhanced printed composite material. In one embodiment, the NC-enhanced composite material further comprises an additive, wherein the additive comprises between 1% and between 20 wt.% by weight of the NC- enhanced composite material. In one such embodiment, the additive comprises a material selected from the group consisting of a process aid, a binder, a chemical foaming agent, an antifoaming agent, and a combination thereof. In another such embodiment, the additive comprises a material selected from the group consisting of a fiber, an additional filler, a coupling agent, a thermoplastic resin, a crosslinking agent, a shear-thickening agent, a shear-thinning agent, a metal, inorganic material, and a combination thereof.

[0012] In one embodiment of the second aspect of the invention, the natural carbon comprises a material selected from the group consisting of coal, reclaimed coal waste, coal- derived carbons, and a combination thereof. In one embodiment, the thermoset resins comprises a material selected from the group consisting of epoxy resin, polyester, a phenolic resin, a bismaleimide resin, and a combination thereof.

[0013] In one embodiment of the second aspect of the invention, the natural carbon comprises between 80 wt.% and 90 wt.% by weight of the NC-enhanced composite material. [0014] In one embodiment of the second aspect of the invention, the NC-enhanced material is an NC-enhanced composite slurry. In one embodiment, the NC-enhanced material is an NC- enhanced 3D-printed composite material. In one embodiment, the NC-enhanced material is a crosslinked NC-enhanced 3D-printed composite material. In one embodiment, the NC-enhanced material is a carbonized NC-enhanced 3D-printed composite material.

[0015] A third aspect of the invention is directed to a method of manufacturing an NC- enhanced composite material selected from the list consisting of an NC-enhanced filament, an NC-enhanced pellet, an NC-enhanced 3D-printed composite material, and a carbonized NC- enhanced 3D-printed material, the method comprising: melt mixing an NC material and a thermoplastic resin to form an NC-enhanced composite material formulation; and extruding the NC-enhanced material formulation as a material selected from the group consisting of an NC- enhanced filament and an NC-enhanced pellet. In one embodiment, the method further comprises cooling the NC-enhanced filament or the NC-enhanced pellet.

[0016] In one embodiment of the third aspect of the invention, wherein extruding the NC- enhanced material formulation comprises extruding an NC enhanced pellet, the method further comprises additively manufacturing an NC-enhanced 3D-printed composite material using the NC-enhanced pellet as an input. In a further embodiment thereof, additively manufacturing the

NC-enhanced 3D-printed composite material comprises FGF additive manufacturing. In a yet further embodiment, the method further comprises carbonizing the NC-enhanced 3D-printed composite material in an inert atmosphere to produce a carbonized NC-enhanced 3D-printed composite material.

[0017] In one embodiment of the third aspect of the invention, wherein extruding the NC- enhanced material formulation comprises extruding an NC enhanced filament, the method further comprises spooling the NC-enhanced filament.

[0018] In one embodiment of the third aspect of the invention, wherein extruding the NC- enhanced material formulation comprises extruding an NC enhanced filament, the method further comprises additively manufacturing an NC-enhanced 3D-printed composite material using the NC-enhanced filament as an input. In a further embodiment thereof, additively manufacturing the NC-enhanced 3D-printed composite material comprises FDM additive manufacturing. In a yet further embodiment thereof, the method further comprises carbonizing the NC-enhanced 3D-printed composite material in an inert atmosphere to produce a carbonized NC-enhanced 3D-printed composite material.

[0019] In one embodiment of the fourth aspect of the invention, the method further comprises adding at least one additive to the NC-enhanced composite material formulation prior to melt mixing.

[0020] A fourth aspect of the invention is directed to a method of manufacturing an NC- enhanced composite material selected from the list consisting of an NC-enhanced composite slurry, an NC-enhanced 3D-printed composite material, a crosslinked NC-enhanced 3D-printed composite material, and a carbonized NC-enhanced 3D-printed composite material, the method comprising: mixing an NC material and a thermoset resin to form an NC-enhanced composite slurry; and degassing the NC-enhanced composite slurry. In one embodiment, the method further comprises adding at least one additive to the NC material or the thermoset resin prior to mixing.

[0021] In one embodiment of the fourth aspect of the invention, the method further comprises additively manufacturing an NC-enhanced 3D-printed composite material using the NC-enhanced slurry as an input. In a further embodiment, the method further comprises crosslinking the NC-enhanced 3D-printed composite material using the NC-enhanced 3D-printed composite material as an input and an external heat source.

[0022] In one embodiment of the fourth aspect of the invention, the method further comprises additively manufacturing a crosslinked NC-enhanced 3D-printed composite material using the NC-enhanced slurry as an input, wherein additively manufacturing comprises using a heated print head to crosslink the NC-enhanced composite slurry during the additively manufacturing step.

[0023] In addition to the novel features and advantages mentioned above, other benefits will be readily apparent from the following descriptions of exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a pail of this specification, illustrate embodiments of the invention and, with a detailed description of the embodiments given below, serve to explain the principles of the invention.

[0025] FIG. 1 is a flow diagram showing a system and method for producing an NC- enhanced composite material in accordance with an embodiment of the invention.

[0026] FIG. 2 is a diagram of an extruder 200 in accordance with an embodiment of the invention. [0027] FIG. 3 is a flow diagram showing a system and method for producing an NC- enhanced composite material in accordance with an embodiment of the invention.

[0028] FIGS. 4A-D are graphs showing the tensile strengths (MPa) and elastic moduli (GPa) for NC-enhanced composite materials containing bituminous coal as a filler and (A) a PLA thermoplastic; (B) a PETG thermoplastic; (C) a HDPE thermoplastic; and (D) a PA12 (Nylon) thermoplastic.

[0029] FIGS. 5A-D are graphs showing the flexural strengths (MPa) and flexural moduli (GPa) for NC-enhanced composite materials containing bituminous coal as a filler and (A) a PLA thermoplastic; (B) a PETG thermoplastic; (C) a HDPE thermoplastic; and (D) a PA12 (Nylon) thermoplastic.

[0030] FIG. 6 is a graph showing the coefficient of thermal expansion for NC-enhanced composite materials containing bituminous coal as a filler and (A) a PLA thermoplastic; (B) a PETG thermoplastic; (C) a HDPE thermoplastic; and (D) a PA12 (Nylon) thermoplastic.

[0031] FIG. 7 is a graph showing the heat deflection temperature for NC-enhanced composite materials containing bituminous coal as a filler and (A) a PLA thermoplastic; (B) a PETG thermoplastic; (C) a HDPE thermoplastic; and (D) a PA12 (Nylon) thermoplastic.

[0032] FIG. 8 is a pictorial representation of coal-plastic composite (CPC) samples that were 3D printed in the horizontal orientation with 100 % linear infill at 0-90° alternating raster angles. [0033] FIG. 9 is a picture of 3D printed HDPE-based CPC samples (with 50 wt.% coal) that exhibited reduced warping compared to unfilled HDPE prints.

[0034] FIGS. 10A-D are a set of graphs showing glass transition temperatures (T_g) and melt temperatures (T_m) of the (a) PLA-based composites, (b) PETG-based composites, (c) HDPE- based composites, and (d) PA12-based composites. T_g values of the HDPE composites were below the DSC testing window (i.e., < 30°C). Samples were tested under nitrogen at a heating rate of 10°C/min.

[0035] FIGS. 11A-D are a set of graphs showing C_p values of the CPCs at 50 °C, 60 °C, 70 °C, 80 °C, and 90 °C for the (a) PLA-based composites, (b) PETG-based composites, (c) HDPE- based composites, and (d) PA12-based composites. Samples were tested under nitrogen at a heating rate of 10 °C/min.

[0036] FIGS. 12A-D are a set of graphs showing the thermal conductivities of (a) PLA- based, (b) PETG-based, (c) HDPE-based, and (d) PA 12-based composites. Thermal conductivity was determined at 23 °C.

[0037] FIGS. 13A-D are a set of graphs showing the thermogravimetric analysis (TGA) and derivative TGA (DTG) curves of the CPCs including (a) PLA-based composites, (b) PETG- based composites, (c) HDPE-based composites, and (d) PA12-based composites. The TGA and DTG curves of 100 % P8 coal are shown for comparison. PLA, PETG, and HDPE tests were conducted at a heating rate of 20 °C/min, and PA 12 tests were conducted at a heating rate of 5 °C/min. All tests were performed under air.

[0038] FIG. 14 is a graph showing the decomposition temperatures of the CPCs at 5 % (Ts %) and 50 % (T50 %) weight loss and the maximum decomposition rates of the CPCs. TGA tests for the PLA, PETG, and HDPE composites were conducted at 20 °C/min, and PA12 tests were conducted at a heating rate of 5 °C/min. All tests were performed under air.

[0039] FIGS. 15A and 15B are the 2D P8 coal model proposed by Solomon (a) was converted into a 3D supercell (b) containing 20 units of the Solomon model. In (b), hydrogen, carbon, nitrogen, oxygen, and sulfur atoms are indicated. [0040] FIGS. 16A-D are the atomistic models of (a) PLA, (b) PETG, (c) HDPE, and (d)

PA 12 generated using ChemDraw®. The atoms present include carbon, hydrogen, oxygen, and nitrogen.

[0041] FIGS. 17A-C are pictures of the representative PLA CPC filaments having (a) 100% PLA (b) 70% PLA 30% P8 coal (c) 60% PLA 40% P8 coal.

[0042] FIGS. 18A-C are pictures of the representative PETG CPC filaments having (a) 100% PETG (b) 70% PETG 30% P8 coal (c) 60% PETG 40% P8 coal.

[0043] FIGS. 19A-E are pictures of the representative HDPE CPC filaments having (a) 100% HDPE, (b) 59% HDPE 40% P8 coal 1% lube (c) 49% HDPE 50% P8 coal 1% lube, (d) 39% HDPE 60% P8 coal 1% lube, and (e) 29% HDPE 70% P8 coal 1% lube.

[0044] FIGS. 20A-C are pictures of the representative PA 12 CPC filaments having (a) 100% PA12 (b) 80% PA1220% P8 coal (c) 70% PA12 30% P8 coal.

[0045] FIG. 21 is a picture of a 3D printed PLA composite sample with 30 wt.% P8 coal.

[0046] FIG. 22 is a picture of a 3D printed PETG composite samples with 40 wt.% P8 coal.

[0047] FIG. 23 is a picture of a 3D printed HDPE composite sample with 60 wt.% P8 coal.

[0048] FIG. 24 is a picture of a 3D printed PA12 composite sample with 30 wt.% P8 coal.

[0049] FIG. 25 is a picture of 3D printed HDPE-based CPC samples (shown with 50 wt. % coal) exhibiting reduced warping compared to unfilled HDPE prints.

[0050] FIG. 26 is a picture of a representative microstructure of the HDPE-based composite filament with 60 wt.% coal showing no porosity or agglomeration.

[0051] FIGS. 27A-C are pictures of PLA CPC filament microstructures having (a) 100%

PLA (b) 70% PLA 30% P8 coal (c) 60% PLA 40% P8 coal. [0052] FIGS. 28A-C are pictures of PETG CPC filament microstructures having (a) 100% PETG (b) 70% PETG 30% P8 coal (c) 60% PETG 40% P8 coal.

[0053] FIGS. 29A-E are pictures of HDPE CPC filament microstructures having (a) 100% HDPE, (b) 59% HDPE 40% P8 coal 1% lube (c) 49% HDPE 50% P8 coal 1% lube, (d) 39% HDPE 60% P8 coal 1% lube, and (e) 29% HDPE 70% P8 coal 1% lube.

[0054] FIGS. 30A-C are pictures of PA12 CPC filament microstructures, (a) 100% PA12 (b) 80% PA1220% P8 coal (c) 70% PA12 30% P8 coal.

[0055] FIG. 31 is a graph showing representative composite tensile stress-strain curves with fractured surface SEM images showing particle pull-out (circle) and coal particle fracture (arrow) failure mechanisms.

[0056] FIG. 32A-D are graphs showing UTS and elastic modulus (EM) of 3D printed (3DP) and compression molded (CM) composites, including (a) PLA-based composites, (b) PETG- based composites, (c) HDPE-based composites, and (d) PA12-based composites. Error bars represent the standard error.

[0057] FIGS. 33A-D are graphs showing FS and FM of 3DP and CM composites, including

(a) PLA-based composites, (b) PETG-based composites, (c) HDPE-based composites, and (d) PA12-based composites. Error bars represent the standard error.

[0058] FIGS. 34A-D are graphs showing Izod impact resistance of 3DP and CM composites, including (a) PLA-based composites, (b) PETG-based composites, (c) HDPE-based composites, and (d) PA 12-based composites. Error bars represent the standard error.

[0059] FIG. 35 is a graph showing Shore D hardness of CM composites, including PLA- based, PETG-based, HDPE-based, and PA12-based composites. Error bars represent the standard error. [0060] FIG. 36 is a graph showing the normalized Fourier amplitude for the sulfur K-edge EXAFS spectra of the P8 coal model.

[0061] FIG. 37 is a model showing bond-breaking sites found in the coal model at 200 °C. The bonds break at the region with weaker noncovalent bonds (hydrogen bonding). The hydrogen bonds hold the different subunits of the different coal macromolecules together. The chemical structures of the cleaved subunits are indicated in different colors: C105H88O10N2S2 (green), C42H34O4 (teal), and CwHieO (magenta).

[0062] FIG. 38 is a series of snapshots showing the starting and final configuration (after 5 ns) of PLA-coal composite.

[0063] FIG. 39 is a series of snapshots showing the starting and final configuration (after 5 ns) of PETG-coal composite.

[0064] FIG. 40 is a series of snapshots showing the stalling and final configuration (after 5 ns) of HDPE-coal composite.

[0065] FIGS. 41A-C are a series of simulated models and graphs showing hydrogen bonding in the simulation models and FTIR spectra of PA12 composites. A snapshot before and after bonding is shown in (a) and (b) representative double hydrogen bonding between the (1) oxygen and (2) nitrogen in the amide group in PA12 (-NH-C=O-) and (3) oxygen in the phenolic group (ph-OH) of the coal. The FTIR spectra of PA12 composites are shown in (c). In (b), all hydrogen atoms except the polar hydrogens have been deleted for clarity.

[0066] FIG. 42 is a chemical mechanism diagram showing a proposed mechanism for the hydrogen bonding observed in the PA12-coal composite resulting from the high polarity of the amide linkages along the polyamide chain. [0067] FIG. 43 is a graph of tensile properties of 3D-printed NCPC, CFC, and WPC formulations compared to unfilled HDPE.

[0068] FIG. 44 is a graph of compression properties of 3D-printed NCPC, CFC, and WPC formulations compared to unfilled HDPE.

[0069] FIG.45 is a graph of flexural properties of the 3D-printed NCPC, CFC, and WPC formulations compared to unfilled HDPE.

[0070] FIG. 46 is a graph of impact resistant properties for 3D-printed NCPC, CFC, and

WPC formulations compared to unfilled HDPE.

[0071] FIGS. 47A and 47B are images of a test hexagon for a 70 wt.% Keystone 325 — HDPE formulation.

[0072] FIGS. 48 A and 48B are images of a positive overhang test and a negative overhang test, respectively, for a 70 wt.% Keyston 325 - HDPE formulation.

[0073] FIG. 49 is an image of a bridge test for a 70 wt.% Keyston 325 - HDPE formulation.

[0074] FIG. 50 is an image of a wind turbine blade tooling part for a 70 wt.% Keystone 325

- HDPE formulation.

[0075] FIGS. 51 A and 5 IB are images of a test hexagon for a 55 wt.% Keystone 325 - PETG formulation.

[0076] FIGS. 52A and 52B are images of a positive overhang test and a negative overhang test for a 55 wt.% Keystone 325 - PETG formulation.

[0077] FIG. 53 is an image of a bridge test for a 55 wt.% Keystone 325 — PETG formulation.

[0078] FIG. 54 is wind turbine tooling for a 55 wt.% Keystone 325 - PETG formulation.

[0079] FIG. 55 is a wall design part for a 55 wt.% Keystone 325 - PETG formulation.

[0080] FIG. 56 is an image of material from a 4 mm nozzle. [0081] FIG. 57 is an image of a hexagonal test print with 8 inch square sides.

[0082] FIGS. 58 and 59 are images of a negative overhang test and positive overhang test, respectively, with a 2 mm nozzle.

[0083] FIGS. 60 and 61 are images of a negative overhang test and positive overhang test, respectively, with a 4 mm nozzle.

[0084] FIGS. 62A and 62B and 63 A and 63B arc images of a bridge test with a 2 mm and 4 mm nozzle, respectively.

[0085] FIGS. 64A and 64B are images of a negative overhang test and a positive overhang test with a 6 mm nozzle, respectively.

[0086] FIG. 65 is an image of a bridge test with a 6 mm nozzle.

DETAILED DESCRIPTION OF THE INVENTION

[0087] One or more specific embodiments of the present invention will be described below.

In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation- specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. [0088] Exemplary embodiments of the present invention are directed to natural carbon (NC)- enhanced composite materials as well as systems and methods for producing said materials.

Related components and manufacturing methods are also included. Relative to the known art for producing composite materials for use in additive manufacturing, exemplary embodiments may include NC-enhanced materials having improved or similar- physical characteristics such as strength, stiffness, impact resistance, extrudability, resistance to thermal degradation, cabonizability, resistance to moisture, resistance to mold, resistance to mildew, and/or resistance to flammability. Relative to the known art, exemplary embodiments may also satisfy the need for the use of different carbon sources, carbon chains, and/or carbon sizes.

[0089] With reference to FIG. 1, a system 100 for producing an NC-enhanced composite material is shown. The system 100 may include an optional melt mixer 102 configured to receive a natural carbon material and a thermoplastic resin and implement a melt mixing step. Alternatively, the extruder 200 (see FIG. 2, described further below) may be capable of implementing a melt mixing step. In such embodiments, the optional melt mixer 102 may not be necessary and may be omitted from the system 100. If the system or method does not include the optional melt mixer 102, the extruder 200 may be configured to receive the natural carbon material and the thermoplastic resin.

[0090] The natural carbon material includes at least one carbon-based material, and may comprise a mixture of a plurality of carbon-based materials. The at least one carbon-based material may be selected from the group consisting of, by way of example and not limitation, coal, reclaimed coal waste, coal derived carbons, waste coal, oxidized coal, carbon black, coke, coke breeze, coal-derived carbon foam dust, petroleum coke, pitch, biochar, lignin, lignocellulose, charcoal, and other suitable materials containing carbon. The carbon-based material may be or include an industrial product or byproduct that is predominantly carbon such as, for example, coke (e.g., petroleum coke), coke breeze, pitch, or other suitable carbon-based industrial byproducts. Those of ordinary skill in the art, however, will recognize that “coke” may refer to substances other than petroleum coke; coke could also refer to, for example, coal- derived coke (e.g., metallurgical coke or foundry coke), an industrial product (e.g., metallurgical coke), an industrial byproduct (e.g., coke breeze), or other coal-based materials. An example of waste coal may comprise coal and optionally inorganic materials (e.g., soil). An example of oxidized coal is coal which has been exposed to oxygen or oxygen containing atmosphere at a sufficient temperature to induce oxidation of the coal surface, but not to include devolatilization of the material. Further examples of waste coal may include, for example: fine coal refuse, waste coal slurry, tailings, or settling pond material; coarse coal refuse or hollow fill material; intermediate prep plant streams or middlings; fly ash with intermixed carbon (loss on ignition); and refined carbon materials derived from the above waste streams. Examples of biochar may be derived from woody biomass, non-woody biomass, animal/human waste, and algae. In a preferred embodiment, the natural carbon material comprises coal, alternatively reclaimed coal waste, or alternatively coal-derived carbons.

[0091] Exemplary embodiments may also implement various types of coal chemistry. For example, since the natural carbon material is not meant to be burned, natural carbon material may comprise any level of other materials including volatile matter, macerals, sulfur, ash, minerals, impurities, hardness (e.g., Hardgrove Grindability Index), etc., which may facilitate the use of materials that otherwise have little or no alternative value. In exemplary embodiments, the type of natural carbon material may be selected based on one or more properties of the NC- enhanced composite material such as, for example, mechanical properties, fire resistance, oxidation resistance, other relevant properties of an NC-enhanced composite material, or a combination thereof. In exemplary embodiments where natural carbon material contains both carbon-based materials and other materials, the carbon-based material may account for greater than or equal to 90% by weight of the natural carbon material.

[0092] Exemplary embodiments of the natural carbon material can include particles of varying sizes. The natural carbon material may have a particle size that is determined or selected by using one or more separators (not shown) configured to implement a size separation technique such as, for example, mesh separation or sieve separation prior to the natural carbon material entering the melt mixer 102. When using a mesh or sieve to separate particles out by size, natural carbon material particles must have at least one dimension smaller than the mesh opening in order to be able to pass through said opening. In one such embodiment, particle sizes of the natural carbon material may be less than or equal to 120pm, alternatively less than or equal to 50pm, or alternatively less than or equal to 20pm. Additionally, more than one mesh can be used in series to select for a range of particle sizes by selecting particles both having a size smaller than the larger mesh openings and having a size larger than the smaller mesh openings. In one such embodiment, particle sizes of the natural carbon material may range from 1- 120pm, alternatively range from l-50pm, alternatively range from l-20pm, alternatively range from 20- 50pm, alternatively range from 20-120pm, or alternatively range from 50- 120pm.

[0093] If the size of the natural carbon material is substantially bigger than the mesh openings, the separator configured to implement a mesh separation step may be preceded by a pulverizer (not shown) configured to implement a pulverization step. The pulverizer may be used to reduce the particle size of the natural carbon material by, for example, grinding, crushing, milling (e.g., a hammer mill, a ball mill, etc.), other suitable particle size reduction techniques, or a combination thereof. The particle size of the or the natural carbon material may be estimated based on a duration of pulverization for the natural carbon material.

[0094] If the natural carbon material has a moisture content too high for processing or the end product, the natural carbon material may be dried prior to processing in the system and method 100. In one embodiment, heated air may help dry the natural carbon material, before, during, or after optional pulverization, removing water therefrom as water vapor. In one embodiment, the natural carbon material is subjected to the heated air until most or all surface moisture is removed. Determining that most or all surface moisture has been removed can be accomplished by, for example, subjecting the natural carbon material to the heated air at a given temperature or temperature range for a duration or duration range known to eliminate most or all surface moisture, analyzing the mixture of gases exiting the natural carbon material to determine the ratio of heated air to water vapor, using another means of determining the amount of moisture in a gaseous mixture, or a combination thereof. In one embodiment, the natural carbon material may be subjected to heated air at a temperature of at least 100°C for a duration between 1-30 minutes. In another embodiment, the natural carbon material may be subjected to the heated air or inert gas at a temperature between 100-350°C for a duration between 1-30 minutes. In one embodiment, the natural carbon material has less than or equal to 5% moisture by weight. In an alternate embodiment, the pulverized natural carbon material has less than or equal to 2% moisture by weight.

[0095] The thermoplastic resin may be selected from the list consisting of polylactic acid (PLA), high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS), nylon, polycarbonate (PC), polyethylene terephthalate glycol copolymer (PETG), polystyrene (PS), polyvinyl chloride (PVC), styrene, polybutylene (PBT), polyethylene terephthalate (PET), polyethylenimine (PEI), polyether sulfone (PES), polyphenylene ether (PPE), polyphenylene sulfide (PPS), some other suitable thermoplastic monomer/polymer, or a combination thereof. In one embodiment, the thermoplastic resin is or includes PLA. In one embodiment, the thermoplastic resin is or includes PETG. In one embodiment, the thermoplastic resin is or includes HDPE. In one embodiment, the thermoplastic resin is or includes nylon. In a further embodiment thereof, the thermoplastic resin includes nylon 12 (PA 12).

[0096] In embodiments including the optional melt mixer 102, the natural carbon material and the thermoplastic resin are first combined, then agitated while applying heat to form a melted NC/thermoplastic mixture. The agitation step may be implemented by using known methods of mixing or agitating particulate matter including, for example, kneading, stirring, rolling, vibrating, compressing, some other method for mechanical agitation and mixing, or a combination thereof. In one embodiment, the agitation step is implemented using a screw to rotate the material along a heated pathway. The heat applied to the mixture may vary based on the natural carbon material used, the thermoplastic resin used, the size of the particles, time, or other factors. In one embodiment the heat applied to the system during the melt mixing step is between 160-300°C. The time necessary to thoroughly mix and melt the natural carbon material and the thermoplastic resin may vary based on the natural carbon material used, the thermoplastic resin used, the size of the particles, temperature, or other factors. In one embodiment, the melt mixing step takes between 5-10 min.

[0097] In embodiments not including the melt mixer 102, the extruder 200 is configured to receive the natural carbon material and the thermoplastic resin, then implement a melt-mixing step as described above. In one such embodiment not including the melt mixer 102, the extruder 200 may implement the agitation step by using one or more screw to rotate and mix the material as it advances along a heated pathway.

[0098] In embodiments including the melt mixer 102, the extruder 200 is configured to receive the pelletized NC/thermoplastic mixture from the melt mixer 102. The extruder 200 may comprise any known extrusion system such as, for example, a single screw extruder, or a twin screw extruder. In a preferred embodiment, the extruder 200 is or includes a double screw extruder.

[0099] The extruder 200 may be configured to implement a filament extrusion step, a pellet extrusion step, or a combination thereof. In embodiments wherein the extruder 200 is configured to implement a pellet extrusion step, the NC-enhanced composite material may comprise an NC- enhanced pellet or a plurality thereof. In one such embodiment, the NC-enhanced pellet or plurality thereof is the end product of the system or method 100. In another such embodiment, the NC-enhanced pellet or plurality thereof is an intermediate product that is further processed into an end product (discussed further below). In embodiments wherein the extruder 200 is configured to implement a filament extrusion step, the NC-enhanced composite material may comprise an NC-enhanced filament or a plurality thereof. In one such embodiment, the NC- enhanced filament or plurality thereof is the end product of the system or method 100. In another such embodiment, the NC-enhanced filament or plurality thereof is an intermediate product that is further processed into an end product (discussed further below).

[00100] One or more optional additives may be added to the natural carbon material to improve the manufacturing of at least one of the NC-enhanced composite material and/or to improve the performance of the NC-enhanced composite material. With regard to improving the manufacturing of the NC-enhanced composite material, the one or more additives may include, for example, a process aid, a binder, a chemical foaming agent, an anti-foaming agent, a lubricant, another suitable additive for improving the manufacturing of an NC-enhanced composite material, or a combination thereof. With regard to improving the performance of the NC-enhanced composite material, the one or more additives may include, for example, a fiber, an additional filler, a thermoset resin, a coupling agent, a crosslinking agent, a metal, inorganic material, other suitable additives for improving performance of the NC-enhanced composite material, or a combination thereof.

[00101] In one embodiment, the one or more additives includes a process aid such as, for example, a binder (discussed further below), a fiber, a metal, or a combination thereof. In a further embodiment thereof, the binder may include, for example, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid, methyl acrylate, and combinations thereof, polyvinylidene chloride latex, styrene-butadiene latex, carboxylated acrylonitrile butadiene rubber, carboxylated butadiene copolymer rubber, styrene-acrylic emulsion polymers including resin supported emulsions, vinyl-acetate based polymers such as vinyl acetate ethylene copolymers and vinyl acrylic latex, nitrile latex elastomers, nitrile-butadiene elastomers, polybutadiene elastomers produced from 1,3-butadiene elastomers, dicyclopentadiene-based elastomers, ethylene propylene dicyclopentadiene -based elastomers, neoprene binder, natural rubber binder, water-based polyurethane elastomers, starch/dextrin-based binders, protein/casein- based binders, silicone-based binders, other suitable binders, and combinations thereof. In one embodiment, the one or more additives includes an additional filler such as, for example, saw dust or other similar organic particulate matter. In one embodiment, the one or more additives includes a chemical foaming agent such as, for example, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, azodicarbonamide, hydrazocarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylene tetramine, toluenesulfonyl hydrazide, p,p’- oxybis(benzenesulfonylhydrazide), azobisisobutyronitrile, barium azodicarboxylate, other suitable chemical foaming agents, or a combination thereof. In one embodiment, the additive includes an antifoaming agent such as, for example, an oil-based anti-foaming agent (e.g., a mineral oil, a vegetable oil, or another oil that is insoluble in the carbon foam), a silicon-based antifoaming agent (e.g., a polymer with a silicon backbone, a hydrophobic silica, silicone glycol), an alkyl polyacrylate, some other suitable additive that reduces or inhibits foaming, or a combination thereof. In one embodiment, the one or more additive includes a lubricant such as, for example, a solid lubricant (e.g., a lamellar solids such as graphite, PTFE, etc.), oil-based lubricants, water-based lubricants, silicone based lubricants, other suitable lubricants, or a combination thereof. In one embodiment, the additive includes a fiber such as, for example, a carbon fiber, a carbon nanotube, a metal fiber, an inorganic fiber, some other suitable fibrous material, or a combination thereof to improve performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a thermoset resin such as, for example, an epoxy resin, polyester, a phenolic resin (e.g., Bakelite, Novolac, Catalin, etc.), a bismaleimide resin, a fluoropolymer resin, some other suitable thermoset resin, or a combination thereof. In one embodiment, the one or more additives includes a coupling agent such as, for example, maleic anhydride. In a further embodiment, maleic anhydride is used as a coupling agent in the NC-enhanced composite material including HDPE and/or PLA as the thermoplastic resin. In one embodiment, the one or more additives includes a crosslinking agent such as, for example, dialdehydes (e.g., glutaraldehyde (GA), phthalaldyhyde (OP A)), hydrazides, alkoxyamines, isocyanates, carbodiamides, some other suitable crosslinking agent, or a combination thereof. In one embodiment, the one or more additives includes a metal or metal fiber made of, for example, steel, iron, aluminum, chromium, titanium, cobalt, lead, nickel, manganese, molybdenum, copper, gold, silver, beryllium, magnesium, rhodium, tungsten, zinc, an alloy including one or more of the aforementioned metals, or a combination thereof.

[00102] One or more of these additives may be added to the natural carbon material and thermoplastic resin to define a composite material formulation. In exemplar)' embodiments, the one or more additives collectively are included in an amount less than or equal to 20% by weight of the composite material formulation, or alternatively in an amount less than or equal to 10% by weight of the composite material formulation, or yet alternatively in an amount less than or equal to 5% by weight of the composite material formulation, or still alternatively in an amount less than or equal to 1% by weight of the composite material formulation. In one embodiment, the one or more additives includes a process aid in an amount between 0-7% by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In an alternate embodiment, the one or more additives includes a process aid in an amount between 0.05-3% by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In yet another alternate embodiment, the one or more additives includes a process aid in an amount between 0.05-1.0% by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In one embodiment, the one or more additives includes a chemical foaming agent to improve the manufacturing of the NC-enhanced composite material. In one embodiment, the one or more additives includes a lubricant in an amount between 1-5% by weight of the composite material to improve the manufacturing of the NC-enhanced composite. In an alternate embodiment, the one or more additives includes a lubricant in an amount between 1-1.5% by weight of the composite material to improve the manufacturing of the NC-enhanced composite. In one embodiment, the one or more additives includes a fiber in an amount between 0-7% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In an alternate embodiment, the one or more additives includes a fiber in an amount between 0.05-2% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In yet another alternate embodiment, the one or more additives includes a fiber in an amount between 0.05-1.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a thermoset resin in an amount between 1-10% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a crosslinking agent in an amount between 0.5-5.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes at least one of a metal or a metal fiber in an amount between 0.5-5.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a coupling agent in an amount less than or equal to 5% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material.

[00103] One or more of these additives may be added to the natural carbon material to impart or enhance a property of the resulting NC-enhanced composite material such as, for example, the strength, the electrical conductivity, the thermal conductivity, stiffness, resilience, modulus of elasticity, density, impact resistance, or a combination thereof. In one embodiment, the one or more additives includes a metal or metal fiber such as, for example, steel, iron, aluminum, chromium, titanium, cobalt, lead, nickel, manganese, molybdenum, copper, an alloy including one or more of the aforementioned metals, or a combination thereof that enhances the strength of the NC-enhanced composite material. In one embodiment, the one or more additives includes a metal or metal fiber such as, for example, copper, gold, aluminum, silver, an alloy including one or more of the aforementioned metals, or a combination thereof that imparts or enhances electrical conductivity of the NC-enhanced composite material. In one embodiment, the one or more additive includes a metal or metal such as, for example, copper, gold, aluminum, silver, beryllium, iron, magnesium, molybdenum, nickel, rhodium, tungsten, zinc, an alloy including one or more of the aforementioned metals, or a combination thereof to impart or enhance thermal conductivity of the NC-enhanced composite material. Metal fibers may be used in addition to or instead of ordinary metals (e.g., metal particles) to increase the strength of the resulting NC-enhanced composite material over a comparable embodiment only using a metal. [00104] The NC-enhanced composite material formulation may comprise between 50- 90% natural carbon by weight, alternatively between 60-90% natural carbon by weight, alternatively between 70-90% natural carbon by weight, or alternatively between 80-90% natural carbon by weight. In one embodiment, when the amount of natural carbon in the NC-enhanced composite material formulation exceeds 55%, a lubricant is included, alternatively lubricant is included in an amount between 1-5% by weight of the composite material formulation, or alternatively lubricant is included in an amount between 1-1.5% by weight of the composite material formulation. The NC-enhanced composite material formulation may comprise between 5-50% thermoplastic by weight, alternatively between 5-40% thermoplastic by weight, alternatively between 5-30% thermoplastic by weight, or alternatively between 5-20% thermoplastic by weight. [00105] The extruder 200 may be configured for continuous production of an NC- enhanced composite material from the NC-enhanced composite material formulation. With reference to FIG. 2, the extruder 200 has a feed hopper 222 configured to receive the NC- enhanced composite material formulation and configured to permit entry of materials received into a barrel 224. The barrel 224 includes a at least one auger 226 that is coupled to a motor 228, wherein the motor 228 is configured to rotate the at least one auger 226. The at least one auger 226 is configured to convey the NC-enhanced composite material formulation received from the feed hopper 222 toward a die 248 when rotated by the motor 228.

[00106] The extruder 200 includes a plurality of heating elements 230 that are configured to heat the barrel 224 and the NC-enhanced composite material formulation as it travels therethrough. In one embodiment, the extruder 200 includes one or more optional cooling fans 232 that are configured to remove heat from the barrel 224 and the NC-enhanced composite material formulation as it travels therethrough. In one embodiment, the extruder 200 includes one or more optional sensor such as, for example, an optional pressure transducer 234 configured to determine the pressure within the extruder 200, an optional thermocouple 236 configured to determine the temperature within the extruder 200, an optical sensor (e.g., Raman, IR, etc.), another similar sensor, or a combination thereof. In one embodiment, the extruder 200 includes an optional vent 238 that is configured to reduce pressure within the barrel 224 when opened. In one embodiment, the extruder 200 includes the die 248 configured to shape the NC-enhanced composite material as it exits the extruder 200. In one embodiment, one or more pullers (not shown) configured to enhance conveyance of an NC-enhanced composite material away from the extruder 200 may be positioned downstream from the die 248. In one embodiment, the extruder

200 includes more than one component selected from the list consisting of the one or more optional cooling fans 232, the one or more optional pressure transducer 234, the one or more optional thermocouple 236, the optional vent 238, and the one or more optional pullers (not shown). In an alternate embodiment, the extruder 200 includes one or more cooling fan 232, one or more pressure transducer 234, one or more thermocouple 236, and a vent 238.

[00107] With reference to FIGS. 1-2, in embodiments including the optional vent 238, any volatile gas(es) produced while processing the NC-enhanced composite material formulation can be removed from the extruder 200 when the optional vent 238 is opened and may be sent to an optional flare tank 104. Alternatively, any volatile gas(es) removed from the extruder 200 when the optional vent 238 is opened could be sent to a separate collection tank (not shown). In such an embodiment, the volatile gas(es) collected in the separate collection tank can be cooled to collect condensable hydrocarbons. In a further embodiment, any incondensable hydrocarbons collected in the separate collection tank (not shown) can be removed therefrom and sent to the flare tank 104. In one embodiment, no volatile gases are produced while processing the NC- enhanced composite material formulation.

[00108] Generally speaking, the extruder 200 functions by receiving NC-enhanced composite material formulation at the feed hopper 222, conveying the NC-enhanced composite material formulation through the barrel 224 downstream towards the die 248, and extruding the NC-enhanced composite material at or after the one or more die 248. While conveying the NC- enhanced composite material formulation through the barrel 224, the one or more heating elements 230 are configured to heat the NC-enhanced composite material formulation. Portions of the barrel 224 may be substantially free of oxygen, allowing for pyrolysis of the NC-enhanced composite material formulation when heated. In one such embodiment, an inert gas is flowed through the extruder 200 along with the NC-enhanced composite material formulation. The inert gas may include, for example, nitrogen gas, helium gas, argon gas, neon gas, carbon dioxide, steam, or a combination thereof. In one embodiment, the inert gas is flowed through the extruder 200 such that the inert gas enters the extruder 200 at or near the feed hopper 222 and is flowed towards the die 248 together with the NC-enhanced composite material formulation. In an even further embodiment, the inert gas is collected at or near the die 248. In a yet further embodiment, the inert gas collected at or near the die 248 and is recycled back to or near the feed hopper 222. Alternatively, portions of the barrel 224 may be exposed to air while processing the NC-enhanced composite material formulation under heat. In one such embodiment, the barrel 224 may be exposed to air at standard pressure.

[00109] As shown, the feed hopper 222 is tapered such that the point of entry into the barrel 224 is smaller than the point of entry into the feed hopper 222. It should be understood that this is a non-limiting example of the shape of the feed hopper 222, and that other embodiments of the invention may include a feed hopper having another shape. The feed hopper 222 may be configured to control the rate at which materials, such as the NC-enhanced composite material formulation, enter the barrel 224. In one embodiment, the feed hopper 222 may include an optional gating component (not shown) configured to open and close entry to the barrel 224. In an alternate embodiment, the feed hopper 222 includes an optional feed auger (not shown) configured to deposit materials, such as the NC-enhanced composite material formulation, into the barrel 224 at an adjustable rate. The feed hopper 222 may be configured to mix materials received, such as the NC-enhanced composite material formulation, prior to entry into the barrel 224. In one such embodiment, the feed hopper 222 includes an optional agitator

(not shown). [00110] As shown FIG. 2, the barrel 224 may be a cylinder that has a length and an inner diameter configured to receive the at least one auger 226. The at least one auger 226 has a shaft 202 and a flighting portion 204 extending radially from the shaft 202 toward the barrel 224 that spirals along at least a portion of the length of the shaft 202 to define a flighting length. In one embodiment, the diameter of the flighting portion 204 (i.e., the flight diameter) is selected to minimize the gap between the flighting portion and the inner diameter of the barrel 224.

[00111] The shaft 202 of the at least one auger 226 may have a diameter that varies across the length of the shaft 202. With reference to FIG. 2, the at least one auger 226 is a single stage auger wherein the shaft 202 has three portions: a first portion 206 proximate the feed hopper 222; a second portion 208 immediately downstream from the first portion 206; and a third portion 210 immediately downstream from the second portion 208. As shown in FIG. 2, the third portion 210 is proximate the die 248. In one embodiment, the first portion 206 has a diameter smaller than the diameter of the third portion 210, whereas the second portion 208 has an increasing diameter along the length beginning at the end of the first portion 206 and ending at the beginning of the third portion 210.

[00112] It should be understood that the invention is not limited to augers 226 as shown. In one such embodiment, the extruder 200 may include one or more auger 226 having a uniform shaft diameter (not shown). In another such embodiment, the extruder 200 may include a two stage auger (not shown). It should also be understood that the invention is not limited to embodiments having only a single auger 226. For example, the extruder 200 may include a plurality of augers (not shown) such as, for example, a counter rotating twin screw extruder, a co-rotating twin screw extruder, a cascade extruder having a plurality of augers in series, or a combination thereof. In one embodiment of the invention, a co-rotating twin screw extruder is used (not shown) to improve the resulting NC-enhanced composite material. The barrel 224 and/or the at least one auger 226 may be selected, at least in part, based on the ratio of the length to diameter (i.e., an L/D ratio), wherein the length corresponds to the length of the at least one auger 226 having the flighted portion and the diameter corresponds to the diameter of the flighted portion. In one embodiment, the L/D ratio of the barrel 224 and/or the at least one auger 226 is greater than or equal to 10:1 and less than or equal to 40: 1. In an alternate embodiment, the L/D ratio of the barrel 224 and/or the at least one auger 226 is greater than or equal to 20: 1 and less than or equal to 24:1. In another alternate embodiment, the L/D ratio of the barrel 224 and or the at least one auger 226 is greater than or equal to 30: 1 and less than or equal to 40: 1. [00113] The plurality of heating elements 230 may be configured to heat the pulverized carbon to a threshold temperature necessary to form the NC-enhanced composite material when extruded. Together with the at least one auger 226, the extruder 200 may be configured to implement the melt mixing step. In one such embodiment, the plurality of heating elements 230 are configured to maintain the temperature of the NC-enhanced composite material formulation between 160-250°C. In an alternate embodiment, the plurality of heating elements 230 are configured to maintain the temperature of the NC-enhanced composite material formulation between 250-300°C. Heating the NC-enhanced composite material formulation may cause or contribute to plasticizing the NC-enhanced composite material formulation within the barrel 224. In one embodiment, the NC-enhanced composite material formulation may become a fluid during conveyance toward the die 248. The extruder 200 may optionally include one or more cooling fan 232 that are configured to regulate the temperature within the barrel 224 by removing excess heat from the system. In one such embodiment, the one or more cooling fan

232 is configured to remove heat based on one or more of the thermocouples 236 reaching a threshold temperature. The one or more cooling fans 232 may be used to recycle heat to other parts of the system and method 100 such as, for example, the melt mixer 102. In an alternate embodiment, the optional one or more cooling fan 232 may be replaced with a water cooling system (not shown).

[00114] Depending on the embodiment, the plurality of heating elements 230 may be used to heat the NC-enhanced composite material formulation to a temperature or temperature range based on fluidity properties of the NC-enhanced composite material formulation. In one such embodiment, the plurality of heating elements 230 might be used to maintain the temperature above a softening temperature, alternatively at least 10°C above the softening temperature, still alternatively at least 20°C above the softening temperature, or yet further alternatively at least 30°C above the softening temperature. Without being bound by theory, it is believed that failure to maintain the temperature of the pulverized carbon and any additive above the softening temperature of the NC-enhanced composite material formulation may lead to premature hardening or setting of the pulverized carbon material within the extruder 200, thereby reducing or preventing the extrudability of the NC-enhanced composite material.

[00115] In an alternate embodiment, the plurality of heating elements 230 and optionally the one or more cooling fan 232 may be used to maintain the temperature of the NC-enhanced composite material formulation below a solidification temperature of the NC-enhanced composite material formulation, alternatively at least 10°C below the solidification temperature, still alternatively at least 20°C below the solidification temperature, or yet further alternatively at least 30°C below the solidification temperature. Without being bound by theory, it is believed that failure to maintain the temperature of the pulverized carbon and any additive below the solidification temperature of the NC-enhanced composite material formulation may lead to premature hardening or setting of the pulverized carbon material within the extruder 200 thereby reducing or preventing the extrudability of the NC-enhanced composite material.

[00116] In another alternate embodiment, the plurality of heating elements 230 and optionally the one or more cooling fan 232 may be used to maintain the temperature of the NC- enhanced composite material formulation above a softening temperature of the NC-enhanced composite material formulation and below a solidification temperature of the NC-enhanced composite material formulation. In one such embodiment, the plurality of heating elements 230 and optionally the one or more cooling fan 232 may be used to maintain the temperature above the softening temperature and below the solidification temperature, or alternatively above the softening temperature and at least 10°C below the solidification temperature, still alternatively above the softening temperature and at least 20°C below the solidification temperature, or yet further alternatively above the softening temperature and at least 30°C below the solidification temperature. In another such embodiment, the plurality of heating elements 230 and optionally the one or more cooling fan 232 may be used to maintain the temperature at least 10°C above the softening temperature and below the solidification temperature, alternatively at least 20°C above the softening temperature and below the solidification temperature, or still alternatively at least 30°C above the softening temperature and below the solidification temperature. In yet another embodiment, the plurality of heating elements 230 and optionally the one or more cooling fan 232 may be used to maintain the temperature at least I0°C above the softening temperature and at least 10°C below the solidification temperature, alternatively at least IO°C above the softening temperature and at least 20°C below the solidification temperature, still alternatively at least

20°C above the softening temperature and at least 20°C below the solidification temperature, or yet further alternatively at least 30°C above the softening temperature and at least 30°C below the solidification temperature.

[00117] As shown, the die 248 includes a plurality of plates 240, 244 configured to shape the NC-enhanced composite material as it exits the extruder 200. In such an embodiment, the die 248 may include a first plate 240 having a first plate opening size 242, wherein the first plate 240 is positioned upstream from a second plate 244 having a second plate opening size 246, wherein the second plate opening size 246 is smaller than the first plate opening size 242. In an alternate embodiment, the die 248 may include a greater plurality of plates, and each of the plates may have a plate opening size smaller than any plates upstream from it. By way of example and not limitation, the die 248 might include 3 plates, alternatively less than or equal to 5 plates, or still alternatively less than or equal to 10 plates. In another alternate embodiment, the die 248 may only have a single plate (not shown).

[00118] While within the extruder 200, the elevated temperature and pressure may be sufficient to keep any volatile organic components (VOCs) dissolved within the NC-enhanced composite material formulation. The at least one volatile gas may include, for example, carbon dioxide, one or more gases originating from the chemical foaming agent, some other volatile gas, or a combination thereof. Additionally, any water present in the pulverized carbon foam may be removed as water vapor along with the volatile gas. In one embodiment, the optional vent 238 is opened to release any VOCs and/or water vapor within the NC-enhanced composite material formulation to reduce the foaming when the NC-enhanced composite material exits through the die 248. In one embodiment, any VOCs and/or any water are removed and collected at a flare tank 104 (discussed further below). [00119] The shape of the NC-enhanced composite material formed in this process is at least partially dependent on a cross-sectional shape of the die 248 (not shown). The cross- sectional shape of the die 248 may be selected based on the desired shape of the NC-enhanced composite material. In one embodiment, the die 248 has a circular cross-sectional shape (not shown) to form an NC-enhanced rod (e.g., an NC-enhanced filament). In an alternate such embodiment, the die 248 may have a rectangular cross-sectional shape. It should be understood that these are non-limiting examples of how the die 248 may be used to shape the resulting NC- enhanced composite material, and that a die 248 having another shape may be used depending on the end product formed. In one embodiment, the die 248 is configured to produce an NC- enhanced filament. In another embodiment, the die 248 is configured to produce an NC- enhanced pellet.

[00120] The extruder 200 may be capable of shaping the NC-enhanced composite material into a shape having a desired diameter and/or length. The diameter of the NC-enhanced composite material shape may be determined at least in part by the diameter of the cross- sectional shape of the die 248. The NC-enhanced composite material may be formed into a shape having a diameter configured to be used in a 3D printer, alternatively configured to be used in a Fused Deposition Modelling (FDM) 3D printer. In one such embodiment, the NC- enhanced composite material produced by the extruder 200 has a diameter between approximately 1.7 mm and 2.9 mm, alternatively between approximately 1.7 mm and between 1 .8 mm, or alternatively between 2.8 mm and 2.9 mm. Alternatively, the NC-enhanced composite material produced by the extruder 200 has a diameter of approximately 1.75 mm, or alternatively approximately 2.85 mm. [00121] The rate at which the NC-enhanced composite material exits the extruder 200 at or near the die 248 may depend in part on a pulling process implemented using the one or more product pullers (not shown). The one or more product pullers may include, for example, a gear wheel, a roller, a belt, mesh, some other similar device, or a combination thereof. In one embodiment, one or more of the product pullers may be configured to pull the NC-enhanced composite material in the direction generally downstream from the die 248.

[00122] With continued reference to FIG. 1, the NC-enhanced composite material (e.g., the NC-enhanced filament and/or the NC-enhanced pellet) is received by the cooling system 106 to reduce the temperature of the NC-enhanced composite material. The cooling system 106 may comprise, for example, one or more fans, an ice bath, a water cooling system, some other suitable means of reducing the temperature of the NC-enhanced composite material, or a combination thereof. In one embodiment, the cooling system 106 is configured to reduce the temperature of the NC-enhanced filament to room temperature, or alternatively between 40-50 °C.

[00123] Following the cooling system 106, in embodiments where the extruder 200 produces an NC-enhanced filament, the NC-enhanced filament may be received by an optional spooler 108. The optional spooler 108 may be configured to coil the NC-enhanced filament so that it can be more easily handled or carried. In one such embodiment, the optional spooler 108 is configured to pull the NC-enhanced filament away from the extruder 200, thereby increasing the throughput of the system and method 100. In one embodiment, the optional spooler 108 is configured to create a coil of the NC-enhanced filament having a diameter between 1.7 and 2.9 mm. [00124] The NC-enhanced composite material, following the optional spooler 108 and/or the cooling system 106 (for embodiments not including the optional spooler 108), may optionally be received by the optional 3D printer 110. In one embodiment, the 3D printer 110 is configured to implement an additive manufacturing method such as, for example, fused deposition modelling (FDM) additive manufacturing, fused granulate fabrication (FGF) additive manufacturing, or some other type of additive manufacturing using a solid material input. In one embodiment, the 3D printer 110 is used to produce an NC-enhanced composite material, specifically an NC-enhanced 3D-printed composite material, having a shape or form designed for a specific purpose such as, for example, a prototype tool/product, tooling, a fixture, complex parts, a custom part, building components, vehicle components, or any other 3D printable material. In one embodiment, the NC-enhanced 3D-printed composite material is the end product of the system or method 100.

[00125] Following the optional 3D printer 110, the NC-enhanced 3D-printed composite material may be received by an optional pyrolysis kiln 112 configured to receive the NC- enhanced 3D-printed composite material for further processing. The optional pyrolysis kiln 112 may be kept at an elevated temperature for further treatment of the NC-enhanced 3D-printed composite material. In one embodiment, the optional pyrolysis kiln 112 is used to carbonize the NC-enhanced composite material. In such an embodiment, the optional pyrolysis kiln 112 is kept at an elevated temperature between 600-1700°C. In another embodiment, the optional pyrolysis kiln 112 is used to calcinate the NC-enhanced composite material. In one such embodiment, the optional pyrolysis kiln 112 is kept in a controlled environment at a temperature between 600-750°C, alternatively between 750-1150°C, or alternatively between 1150-1700 °C.

The controlled environment necessary for calcination may include a non-oxidizing environment such as, for example, heating in the presence of at least one inert gas such as those described above for the extruder 200.

[00126] Subjecting the NC-enhanced 3D-printed composite material to the elevated temperatures in an inert atmosphere at the optional pyrolysis kiln 112 may also serve other functions such as, for example, flaring VOCs from the NC-enhanced 3D-printed composite material to produce one or more volatile gases, further drying the NC-enhanced 3D-printed composite material (i.e., releasing water as water vapor), other treatments of the NC-enhanced 3D-printed composite material, or a combination thereof. In one embodiment where the elevated temperatures cause flaring of at least one of the VOCs within the finished foam product, at least one volatile gas (e.g., CO2) is produced and collected and collected as a value-added pyrolysis product. In embodiments where an inert gas is used in the optional pyrolysis kiln 112, such as in a carbonization process as described above, the inert gas may be separated from one or both of the volatile gases and/or the water vapor. In a further embodiment thereof, the inert gas may be recycled at one or more of the extruder 200 and the optional pyrolysis kiln 112 while the least one of the volatile gases is collected as a value-added pyrolysis product.

[00127] When one or more gases are released from the NC-enhanced 3D-printed composite material in an inert atmosphere, the NC-enhanced composite material is transformed into a carbonized NC-enhanced 3D-printed composite material. Without being bound by theory, carbonized NC-enhanced 3D-printed composite materials are or include a rigid carbon matrix formed by a rigid crosslinked microstructure (i.e., a carbon foam) that form as the value-added pyrolysis products, such as VOCs and pyrolysis liquids, are removed from the NC-enhanced 3D- printed composite material. In one such embodiment, the removal of value-added pyrolysis products from the NC-enhanced 3D-printed composite material results in a carbonized NC- enhanced 3D-printed composite material having a volume larger than the NC-enhanced 3D- printed composite material. In one such embodiment, the carbonized NC-enhanced 3D-printed composite material has a volume greater than or equal to 20% larger than the NC-enhanced 3D- printed composite material, alternatively greater than or equal to 30% larger than the NC- enhanced 3D-printed composite material, alternatively greater than or equal to 45% larger than the NC-enhanced 3D-printed composite material, or alternatively greater than or equal to 60% larger than the NC-enhanced 3D-printed composite material. In one embodiment, the carbonized NC-enhanced 3D-printed composite material has a volume between 20% and 60% larger than the NC-enhanced 3D-printed composite material, or alternatively between 30% and 45% larger than the NC-enhanced 3D-printed composite material.

[00128] The NC-enhanced composite material formed by the system and method 100 may comprise between 50-90% natural carbon by weight, alternatively between 60-90% natural carbon by weight, alternatively between 70-90% natural carbon by weight, or alternatively between 80-90% natural carbon by weight. The NC-enhanced composite material formed by the system and method 100 may comprise between 5-50% thermoplastic by weight, alternatively between 5-40% thermoplastic by weight, alternatively between 5-30% thermoplastic by weight, alternatively between 5-20% thermoplastic by weight, or alternatively between 5-10% thermoplastic by weight. In one embodiment, a portion of the thermoplastic material included in the NC-enhanced composite material formulation is removed during the carbonization process. [00129] With reference to FIG. 3, a system and method 300 for producing an NC- enhanced composite material is provided. Unless otherwise stated, description for the system and method 100 applies to the system and method 300. The system and method 300 includes a mixer 302 which is configured to receive the natural carbon and a thermoset resin. The mixer 302 may be implemented using a mechanical mixing device selected from the list consisting of a helix mixer, a centrifugal mixer, magnetic stir plate and stir rod, or any other type of mechanical mixer that can achieve a good dispersion of a slurry. In one embodiment, the mixer 302 is configured to produce an NC-enhanced composite material slurry.

[00130] The thermoset resin may be selected from the group consisting of an epoxy resin, polyester, a phenolic resin, a bismaleimide resin, some other suitable thermoset resin, or a combination thereof. In one embodiment, the mixture of the natural carbon and the thermoset resin form the NC-enhanced composite material formulation for the system and method 300. In another embodiment where one or more optional additive is included, the mixture of the natural carbon, the thermoset resin, and the one or more additive form the NC-enhanced composite material formulation for the system and method 300.

[00131] One or more optional additives may be added to the natural carbon material to improve the manufacturing of at least one of the NC-enhanced composite material and/or to improve the performance of the NC-enhanced composite material. With regard to improving the manufacturing of the NC-enhanced composite material, the one or more additives may include, for example, a process aid, a binder, a chemical foaming agent, an anti-foaming agent, a lubricant, another suitable additive for improving the manufacturing of an NC-enhanced composite material, or a combination thereof. With regard to improving the performance of the NC-enhanced composite material, the one or more additives may include, for example, a fiber, an additional filler, a crosslinking agent, a metal, inorganic material, other suitable additives for improving performance of the NC-enhanced composite material, or a combination thereof.

[00132] In one embodiment, the one or more additives include a process aid such as, for example, a binder (discussed further below), a fiber, a particle (e.g., a carbon black particle), a metal, or a combination thereof. In one such embodiment, the carbon black particles act as a shear thinning agent. In a further embodiment thereof, the binder may include, for example, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid, methyl acrylate, and combinations thereof, poly vinylidene chloride latex, styrene-butadiene latex, carboxylated acrylonitrile butadiene rubber, carboxylated butadiene copolymer rubber, styrene- acrylic emulsion polymers including resin supported emulsions, vinyl-acetate based polymers such as vinyl acetate ethylene copolymers and vinyl acrylic latex, nitrile latex elastomers, nitrilebutadiene elastomers, polybutadiene elastomers produced from 1,3-butadiene elastomers, dicyclopentadiene-based elastomers, ethylene propylene dicyclopentadiene-based elastomers, neoprene binder, natural rubber binder, water-based polyurethane elastomers, starch/dextrin- based binders, protein/casein-based binders, silicone-based binders, other suitable binders, and combinations thereof. In one embodiment, the one or more additives includes an additional filler such as, for example, saw dust or other similar organic particulate matter. In one embodiment, the one or more additives includes a chemical foaming agent such as, for example, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, azodicarbonamide, hydrazocarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylene tetramine, toluenesulfonyl hydrazide, p,p’-oxybis(benzenesulfonylhydrazide), azobisisobutyronitrile, barium azodicarboxylate, other suitable chemical foaming agents, or a combination thereof. In one embodiment, the additive includes an antifoaming agent such as, for example, an oil-based anti-foaming agent (e.g., a mineral oil, a vegetable oil, or another oil that is insoluble in the carbon foam), a silicon-based antifoaming agent (e.g., a polymer with a silicon backbone, a hydrophobic silica, silicone glycol), an alkyl polyacrylate, some other suitable additive that reduces or inhibits foaming, or a combination thereof. In one embodiment, the one or more additive includes a lubricant such as, for example, a solid lubricant (e.g., a lamellar solids such as graphite, PTFE, etc.), oil-based lubricants, water-based lubricants, silicone based lubricants, other suitable lubricants, or a combination thereof. In one embodiment, the additive includes a fiber such as, for example, a carbon fiber, a carbon nanotube, a metal fiber, an inorganic fiber, some other suitable fibrous material, or a combination thereof to improve performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a crosslinking agent such as, for example, dialdehydes (e.g., glutaraldehyde (GA), phthalaldyhyde (OPA)), hydrazides, alkoxyamines, isocyanates, carbodiamides, some other suitable crosslinking agent, or a combination thereof. In one embodiment, the one or more additives includes a metal or metal fiber made of, for example, steel, iron, aluminum, chromium, titanium, cobalt, lead, nickel, manganese, molybdenum, copper, gold, silver, beryllium, magnesium, rhodium, tungsten, zinc, an alloy including one or more of the aforementioned metals, or a combination thereof. [00133] One or more of these additives may be added to the natural carbon material and thermoset resin to define a NC-enhanced composite material formulation. In exemplary embodiments, the one or more additives collectively are included in an amount less than or equal to 20% by weight of the composite material formulation, or alternatively in an amount less than or equal to 10% by weight of the composite material formulation, or yet alternatively in an amount less than or equal to 5% by weight of the composite material formulation, or still alternatively in an amount less than or equal to 1% by weight of the composite material formulation. In one embodiment, the one or more additives includes a process aid in an amount between 0-7 % by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In one such embodiment, the process aid includes carbon black particles. In an alternate embodiment, the one or more additives includes a process aid in an amount between 0.05-3% by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In one such embodiment, the process aid includes carbon black particles. In yet another alternate embodiment, the one or more additives includes a process aid in an amount between 0.05-1.0% by weight of the composite material formulation to improve the manufacturing of the NC-enhanced composite material. In one such embodiment, the process aid includes carbon black particles. In one embodiment, the one or more additives includes a chemical foaming agent to improve the manufacturing of the NC-enhanced composite material. In one embodiment, the one or more additives includes a lubricant in an amount between 1-5% by weight of the composite material to improve the manufacturing of the NC-enhanced composite. In an alternate embodiment, the one or more additives includes a lubricant in an amount between 1-1.5% by weight of the composite material to improve the manufacturing of the NC-enhanced composite. In one embodiment, the one or more additives includes a fiber in an amount between 0-7% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In an alternate embodiment, the one or more additives includes a fiber in an amount between 0.05-2% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In yet another alternate embodiment, the one or more additives includes a fiber in an amount between 0.05-1.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a thermoset resin in an amount between 1 - 10% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes a crosslinking agent in an amount between 0.5-5.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material. In one embodiment, the one or more additives includes at least one of a metal or a metal fiber in an amount between 0.5-5.0% by weight of the composite material formulation to improve the performance of the NC-enhanced composite material.

[00134] One or more of these additives may be added to the natural carbon material to impart or enhance a property of the resulting NC-enhanced composite material such as, for example, the strength, the electrical conductivity, the thermal conductivity, stiffness, resilience, modulus of elasticity, density, impact resistance, or a combination thereof. In one embodiment, the one or more additives includes a metal or metal fiber such as, for example, steel, iron, aluminum, chromium, titanium, cobalt, lead, nickel, manganese, molybdenum, copper, an alloy including one or more of the aforementioned metals, or a combination thereof that enhances the strength of the NC-enhanced composite material. In one embodiment, the one or more additives includes a metal or metal fiber such as, for example, copper, gold, aluminum, silver, an alloy including one or more of the aforementioned metals, or a combination thereof that imparts or enhances electrical conductivity of the NC-enhanced composite material. In one embodiment, the one or more additive includes a metal or metal such as, for example, copper, gold, aluminum, silver, beryllium, iron, magnesium, molybdenum, nickel, rhodium, tungsten, zinc, an alloy including one or more of the aforementioned metals, or a combination thereof to impart or enhance thermal conductivity of the NC-enhanced composite material. Metal fibers may be used in addition to or instead of ordinary metals (e.g., metal particles) to increase the strength of the resulting NC-enhanced composite material over a comparable embodiment only using a metal.

[00135] The NC-enhanced composite material formulation may comprise between 50-

90% natural carbon by weight, alternatively between 60-90% natural carbon by weight, altematively between 70-90% natural carbon by weight, or alternatively between 80-90% natural carbon by weight. The NC-enhanced composite material formulation may comprise between 5- 50% thermoset polymer by weight, alternatively between 5-40% thermoset polymer by weight, alternatively between 5-30% thermoset polymer by weight, or alternatively between 5-20% thermoset polymer by weight.

[001361 In one embodiment, the mixer 302 is configured to degas the NC-enhanced composite material formulation. In another embodiment, the NC-enhanced material formulation is transferred from the mixer 302 to the optional degasser 304 to degas the NC-enhanced material formulation. In embodiments including the degasser 304, the degasser may comprise, for example, a pressure degasser (e.g., a vacuum degasser), a membrane degasser, a chemical degasser, a thermal degasser, some other suitable type of degassing device or method, or a combination thereof. The NC-enhanced material formulation may be degassed until greater than or equal to 90% of the dissolved gas is removed, alternatively until greater than or equal to 95% of the dissolved gas is removed, or alternatively until greater than or equal to 99% of the dissolved gas is removed.

[00137] Following the mixer 302 or, in embodiments including the optional degasser 304, the optional degasser 304, the degassed NC-enhanced composite material formulation is received by the 3D printer 306. In one embodiment, the 3D printer 306 is configured to implement an additive manufacturing method selected from the group consisting of a direct ink writing (DIW) additive manufacturing or some other type of additive manufacturing configured to use a liquid/slurry input for additive manufacturing. In one embodiment, the NC-enhanced DIW- printed composite material formed by the 3D printer 306 is the end product. In another embodiment, the NC-enhanced DIW-printed composite material formed by the 3D printer 306 is further processed to manufacture the end product.

[00138] In one embodiment, the DIW additive manufacturing method comprises using a heated print head to configured to manufacture crosslinked NC-enhanced DIW-printed composite material. In one such embodiment, the heated print head is kept at a temperature between 100-180°C. In one embodiment, the crosslinked NC-enhanced DIW-printed composite material formed by the 3D printer 306 is the end product. In another embodiment, the crosslinked NC-enhanced DIW-printed composite material formed by the 3D printer 306 is further processed to manufacture the end product.

[00139] Optionally following the 3D printer 306 in embodiments not including a heated print head, an optional furnace 308 may be used to heat the NC-enhanced DIW-printed composite material. In one such embodiment, the optional furnace 308 is used to crosslink the NC-enhanced DIW-printed composite material, forming the crosslinked NC-enhanced DIW- printed composite material. In a further embodiment, the optional furnace 308 is kept at a temperature between 100-180°C to crosslink the NC-enhanced DIW-printed composite material. The time needed to crosslink the NC-enhanced DIW-printed composite material depends on the temperature applied to the NC-enhanced DIW-printed composite material and may range from between 1-2 hours, or alternatively between 1-24 hours.

[00140] Optionally following the optional furnace 308, the crosslinked NC-enhanced DIW-printed composite material may be subjected to an optional pyrolysis kiln 310 (having the same parameters and embodiments as described above for the optional pyrolysis kiln 112). In one such embodiment, the optional pyrolysis kiln 310 is configured to produce a carbonized NC- enhanced DIW printed composite. [00141] Embodiments of the invention are described in the following non-limiting examples.

[00142] Example 1

[00143] An NC-enhanced composite materials in accordance with principles of the present invention, specifically NC-enhanced filaments, were prepared and tested and compared. Specifically, NC-enhanced filaments comprising natural carbon and one of four thermoplastic resins were prepared in accordance with the descriptions of the system and method 100 corresponding to producing an NC-enhanced 3D-printed composite material, specifically using a FDM additive manufacturing method.

[00144] Materials

[00145] Materials tested in the NC-enhanced filaments include natural carbon, specifically bituminous Pittsburgh No.8 (P8) coal, and a thermoplastic resin, specifically (A) PLA; (B) PETG; (C) HDPE; and (D) PA12. With respect to PLA NC-enhanced composite materials, tested compositions included 0 wt.% coal, 30 wt.% coal, and 40 wt.% coal. With respect to PETG NC-enhanced composite materials, tested compositions included 0 wt.% coal, 30 wt.% coal, and 40 wt.% coal. With respect to the HDPE NC-enhanced composite materials, tested compositions included 0 wt.% coal, 40 wt.% coal, and 50 wt.% coal, 60 wt. % coal, and 70 wt.% coal. Additionally, HDPE composites included 1 wt.% of a lubricant, specifically Struktol TPW 104, as a processing additive for embodiments having greater than or equal to 55 wt.% coal. With respect to the PAI 2 NC-enhanced composite materials, tested compositions included 0 wt.% coal, 20 wt.% coal, and 30 wt.% coal. For all NC-enhanced composite materials described above, the remainder of the composition was the corresponding thermoplastic resin.

[00146] Methods [00147] Where indicated, the testing procedure was performed to substantially conform with the processes outlined by the American Society for Testing and Materials (ASTM). For example, the process used may have a designation of ASTM D1894-14. In this case, the designated test 1894 was either originally adopted or most recently revised in 2014.

Additionally, the most recent year the test was reapproved is indicated by subsequently including the year in parenthesis, for example, ASTM D5264-98 (2019).

[00148] Tensile Strength: Tensile strength was determined using the “Standard Test

Method for Tensile Properties of Plastics” procedure set forth in ASTM D638-14, which is hereby incorporated by reference.

[00149] Modulus of Elasticity: Modulus of elasticity was determined using the “Standard Test Method for Tensile Properties of Plastics” procedure set forth in ASTM D638-14.

[00150] Flexural Strength: Flexural strength was determined using the “Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical

Insulating Materials” procedure set forth in ASTM D790-17, which is hereby incorporated by reference.

[00151] Flexural Modulus: Flexural modulus was determined using the “Standard Test

Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials” procedure set forth in ASTM D790-17.

[00152] Coefficient of Thermal Expansion: The coefficient of thermal expansion (CTE) of all NC-enhanced composite materials were experimentally determined using an Instron 3119-606 environmental testing chamber and an Instron 2630-115 extensometer with a one-inch gauge length. The extensometer was mounted flat wise to the face of CM rectangular samples (63 mm x 12.7 mm x 3.5 mm) and a Type K thermocouple was used to record sample temperature. After equilibrating the sample and testing chamber at room temperature (23°C), the environmental chamber was ramped to 100°C at 20°C/minute. The sample temperature data was correlated with the measured sample strain throughout the heating segment and plotted. Linear regression with an R² greater than or equal to 0.98 was then used to estimate the CTE of the materials. Materials were tested in sample sets of three and average values are reported in FIG. 6.

[001531 Heat Deflection Temperature Testing: Heat deflection temperatures (HDTs) were determined using the “Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position” procedure set forth in ASTM D648-18, which is hereby incorporated by reference.

[00154] Discussion

[00155] With reference to FIGS. 4A-D, graphs comparing tensile strengths (MPa) and the elastic moduli (GPa) for each type of NC-enhanced composite material were compared at the various inclusion rates of natural carbon (P8 bituminous coal) described above. Generally speaking, as the amount of coal increased, the tensile strength of the NC-enhanced composite material would decrease. There were two exceptions to this general trend. First, the tensile strength of the HDPE NC-enhanced composite material increased when increasing the coal amount from 60 wt.% to 70 wt.% (+0.8 MPa). Second, the tensile strength of the PA-12 NC- enhanced composite material increased when increasing the coal amount from 0 wt.% to 20 wt.% (+14.5 MPa). Moreover, while the tensile strength of the PA- 12 NC-enhanced composite material decreased from 20 wt.% to 30 wt.% (-6.9 MPa), there was still an increased tensile strength when comparing 0 wt.% coal to 30 wt.% coal (+7.6 MPa).

[00156] With continued reference to FIGS. 4A-4D, the modulus of elasticity increased for all tested NC-enhanced composite materials as the amount of coal increased. [00157] With reference to FIGS. A-D, graphs comparing the flexural strengths (MPa) and flexural moduli (GPa) for each type of NC-enhanced composite material were compared at the various inclusion rates of natural carbon (P8 bituminous coal) described above. Generally speaking, as the amount of coal increased, the flexural strength of the NC-enhanced composite material would decrease. There were two exceptions to this general trend. First, the flexural strength of the HDPE NC-enhanced composite material increased when increasing the coal amount from 40 wt.% to 50 wt.% (+0.8 MPa). Second, the tensile strength of the PA-12 NC- enhanced composite material increased when increasing the coal amount from 0 wt.% to 20 wt.% (+2.7 MPa).

[00158] With continued reference to FIGS. 5A-D, the flexural modulus increased for all tested NC-enhanced composite materials as the amount of coal increased.

[00159] With reference to FIG. 6, the CTE for all tested NC-enhanced composite materials decreased as the amount of coal increased.

[00160] With reference to FIG. 7, the HDT for the tested NC-enhanced composite materials generally remained constant or close to constant (A = + 1°C) without a clear trend as coal content increased. The exception to this general trend was the HDPE NC-enhanced composite material, which demonstrated significant increases in HDT as coal content increased. [00161] Any embodiment of the present invention may include any of the optional or preferred features of the other embodiments of the present invention. The exemplary embodiments herein disclosed are not intended to be exhaustive or to unnecessarily limit the scope of the invention. The exemplary embodiments were chosen and described in order to explain some of the principles of the present invention so that others skilled in the art may practice the invention. Having shown and described exemplary embodiments of the present invention, those skilled in the art will realize that many variations and modifications may be made to the described invention. Many of those variations and modifications will provide the same result and fall within the spirit of the claimed invention.

[00162] The primary objective of this research was to characterize key thermophysical properties of newly developed 3D printable CPC materials. Novel PLA-, PETG-, HDPE-, and PA12-coal composite filaments were formulated at maximum achievable filler contents (20-70 wt. %). Understanding the thermophysical properties of CPCs is essential for technology maturation in the AM space because 1) material coefficient of thermal expansion (CTE) directly impacts the warping and shrinkage of printed parts, 2) quantification of the glass transition and melt temperatures provides insight into the printing temperatures and the material processing window, 3) understanding the thermal stability of the material provides insight into the temperature limits for processing the composites, 4) for large scale printing, heat transfer into the filament and heat dissipation from printed structures is governed by the material’s specific heat capacity (Cp) and thermal conductivity, and 5) C_p indicates energy requirements for processing the composites which elucidates to future manufacturing costs. Experimental quantification of the thermophysical properties of the CPC materials establishes a benchmark for future technology scaling and designing for end-use applications.

[00163] 2. METHODOLOGY

[00164] 2.1 Materials

[00165] Virgin plastic pellets and bituminous coal filler were used to make CPC filaments.

PLA (PPLA110000, 1.24 g/cm³) and PETG (PPTG110000, 1.24 g/cm³) pellets were purchased from 3DXTECH, and Paxon EA55-003 HDPE pellets (1.24 g/cm³) were supplied by

ExxonMobil. PA12 pellets (044, 1.02 g/cm³) were acquired from Scientific Polymer Products Inc.. Lubricant (Struktol TPW 104) was added to the HDPE composites to aid in processing. CONSOL Energy supplied the bituminous Pittsburgh No. 8 (P8) coal.

[00166] 2.2 Material Synthesis

[00167] Pulverized P8 coal was sieved below a 38 pm particle size. To decrease the moisture content to less than 1 wt. %, the coal powder was dried in a convection oven at 110 °C for 24 h. Dried coal (20-70 wt. %) and balance matrix resins were melt-mixed for 5 min at 100 rpm using a Rheomix 600 batch mixer. Lubricant (i.e., 1 wt. % Struktol TPW 104) was added to the HDPE composites during this step. Composite formulations were compounded and tested up to the maximum filler content of each matrix resin at which 1.75 mm FDM filament was successfully extruded and 3D printed following the procedures outlined in Section 2.3. CPC materials were melt-mixed at temperatures ranging from 180°C to 210°C based on the matrix resin, and the compounded CPC materials were ground using a Retsch SM 100 cutting mill.

Composite pellets were stored in a desiccator for further processing.

Table 1: Printing parameters used to 3D print CPC parts.

[00168] 2.3 Filament extrusion and FDM Printing

[00169] Single-screw filament extruders (3devo Composer 450 or Filabot Ex2) were used to extrude 1.75 mm diameter composite filaments. The materials were processed at barrel temperatures ranging from 175°C to 230°C, and resulting filaments were air-cooled.

[00170] A FlashForge Creator Pro FDM printer was used to process the CPC filaments. Composite samples were 3D printed in the horizontal orientation shown in FIG. 8. Composite filaments were 3D printed using the same processing parameters as the respective neat plastics. The 3D printing parameters are provided in Table 1.

[00171] 2.4 Compression molding

[00172] CPC pellets were compression molded (CM) to produce samples for thermophysical testing. A Model 3912 Carver Press was used to compression mold 200 mm x 200 mm x 3.5 mm sheets from aluminum molds coated with Frekote 770-NC mold release agent. Composite materials were heated at 180-195°C for 20 min prior to pressing to 8 metric tons for 5 min. The sheets were allowed to air cool in the mold.

[00173] CTE and heat deflection temperature (HDT) samples were cut from the composite sheets using a ProtoMAX water-jet cutter. Thermal conductivity samples were cut from the CM sheets using a 12.7 mm diameter hole saw. [00174] Differential scanning calorimetry (DSC) samples were CM with the Carver press. Annular shims at the desired sample thickness were placed between two 1/16th inch thick polytetrafluoroethylene (PTFE) sheets. CPC pellets were placed inside the annular shim and heated in the mold for 5 min at 180-195°C before being pressed to 5 metric tons for 5 min. The composite disks were air cooled in the mold before being removed and trimmed. Solid circular DSC samples (6.5 mm diameter x 0.25 mm thick) were cut from the disks using a steel punch. [00175] 2.5 Coefficient of thermal expansion testing

[00176] The CTE values of all CPC materials were experimentally determined using an Instron 3119-606 environmental testing chamber and an Instron 2630-115 extensometer with a one-inch gauge length. The extensometer was mounted flatwise to the face of CM rectangular samples (63 mm x 12.7 mmx3.5 mm), and a Type K thermocouple was used to record sample temperature. After equilibrating the sample and testing chamber at room temperature (23 °C), the environmental chamber was ramped to 100°C at 20°C/min. The sample temperature data was correlated with the measured sample strain throughout the heating segment and plotted. Linear regression with an R² > 0.98 was then used to estimate the CTE of the materials. Materials were tested in sample sets of three, and average values were reported.

[00177] 2.6 Heat deflection temperature testing

[00178] HDTs were tested in accordance with ASTM D648 Method A. CM samples (127 mm x 12.7 mm x 3.5 mm) were prepared and cut with the waterjet following the procedure outlined in Section 2.4. Sample sets of three were sent for testing at Applied Testing and Geosciences, LLC. Samples were tested in a mineral oil temperature bath, and a noncontact laser distance sensor was used to measure sample deflection. Samples were loaded to a 1.82 MPa fiber stress, and the data was reported as average HDT. [00179] 2.7 Glass transition temperature, melt temperature, and crystallinity testing

[00180] Glass transition and melt temperatures were determined in accordance with

ASTM E794. CM DSC samples were seated in 40 pL aluminum crucibles. The materials were tested in sample sets of two (10 mg each) using a Mettler Toledo HP DSC 2 + high pressure DSC. Tests were conducted under nitrogen. Samples were subjected to an isothermal segment at 30°C for five minutes to equilibrate the equipment before a dynamic heating segment at 10°C/min to 220°C. Transition onset temperatures were determined using Mettler Toledo STARe evaluation software. From the DSC heat flow data, the crystallinity of the polymer fraction of the composites was then estimated.

[00181] 2.8 Specific heat capacity testing

[00182] The C_p of the composites was evaluated via the direct DSC method. DSC samples were tested in sample sets of two (10 mg each) using a Mettler Toledo HP DSC 2 + high pressure DSC. Solid samples were placed in 40 pL aluminum crucibles and were subjected to an isothermal segment at 30°C for five minutes to equilibrate. Subsequently, the temperature was ramped at a heating rate of 10°C/min for ten minutes. All samples were tested under nitrogen.

The direct method was then used to calculate the C_p of the sample after the transient period using Eq. (1).

Where C_p = specific heat capacity of the sample.

HF = blank corrected sample heat flow. m = sample mass.

P - heating rate of the sample. [00183] 2.9 Thermal conductivity testing

[00184] Thermal conductivity of the composite samples was measured using flash thermal diffusivity testing. Laser flash thermal diffusivity tests were performed on disk samples (12.7 mm diameter x 3.5 mm thick). Tests were conducted by Dynalene Labs. The composite thermal conductivities were estimated using Eq. (2). k = apC_p (2)

Where k = thermal conductivity. a = thermal diffusivity. p = density.

C_p = specific heat capacity.

[00185] 2.10 Thermogravimetric analysis

[00186] Thermogravimetric analysis (TGA) was used to evaluate the impact of coal on the thermal stability of the CPC materials. CPC pellets and coal were tested using a TA Q500 TGA. Sample sets of two (10 mg each) were tested under air. After being equilibrated at room temperature, samples underwent a linear, dynamic heating segment to 800°C. PLA-, PETG-, and HDPE-based composites were tested at a rate of 20°C/min, but PA 12 composite samples exhibited rapid decomposition rates that led to testing inaccuracies at that heating rate. Similar intense thermal degradation of polyamides has been reported in literature. To correct for this testing inaccuracy, PA12 samples were tested at a heating rate of 5°C/min. Central difference was used to generate the derivative TGA (DTG) curves of the composites. Decomposition onset temperatures of the materials were identified at 5 % (Ts %) and 50 % (Tso %) weight loss.

[00187] 3. RESULTS AND DISCUSSION

[00188] 3.1 Coefficient of thermal expansion [00189] Coefficient of thermal expansion (CTE) values for the CPC materials are shown in FIG. 6. All four polymer composites demonstrated decreasing CTE with increasing coal content. Several studies reported similar trends where the CTE of polymers decreased in fiber and particle filled composites. Decreases in CTE for the HDPE composites could also be attributed to the increase in crystallinity with the introduction of coal (Section 3.3.). PLA-based composites demonstrated a 53.1 % decrease in CTE from 59.7 pm m^{- 1} °C^{- 1} to 28.0 pm m^{- 1} °C- ¹ at 40 wt. % coal, and PETG-based composites showed a 24.2 % decrease from 55.4 pm m^{- 1} °C" ¹ to 42.0 pm m" ¹ °C" ¹ at 40 wt. % coal. The neat HDPE had a CTE of 109.2 pm nT ¹ °C" ¹ . At 40 wt. % coal, the CTE decreased 15.5 % to 92.3 pm m^{- 1} °C- and at 70 wt. % coal, the CTE decreased 44.8 % to 60.3 pm m^{- 1} °C^{- 1} . The PA12 composite exhibited a 16.7 % decrease from 148.3 pm m“ ¹ °C" ¹ to 123.6 pm m^{- 1} °C^{- 1} at 30 wt. % coal. Both HDPE and PA12 can be challenging to 3D print in comparison to PLA and PETG due to their high CTEs. However, increasing the coal content to 70 wt. % reduced the CTE of HDPE making it comparable to neat PLA and PETG. Such positive impact was limited for the PA 12-based composite due to the lower coal content that could be achieved.

[00190] Reduction in CTE improved the 3D printing of the materials twofold. First, the reduction in CTE improved the dimensional accuracy of final printed parts. As the thermoplastic materials are extruded from the FDM nozzle in a molten state, they cool, solidify, and shrink. The printed composite materials, with lower CTEs, therefore shrunk less during the cooling process compared to the neat plastics. This allowed for parts to be designed and printed with tighter tolerances. Second, the reduction in CTE reduced the warping of PA 12 and HDPE prints, resulting in consistent printing of HDPE materials. FIG. 9 shows the impact of CTE reduction on

3D printed HDPE samples. The HDPE samples with 50 wt. % coal exhibited less curling at the comers and less warping across the length of the sample. The reduced warping led to less delamination from the print bed and from print layers which translated to more reliable printing. The decrease in CTE allowed for the fabrication of dimensionally accurate HDPE-based prints outside of a heated chamber which suggests lower energy usage during printing compared to producing comparable parts from neat HDPE.

[001911 Materials utilized in current state-of-the-art technologies face costs and performance challenges which might slow the development and commercial adoption of AM in high-volume and structural applications such as composite tooling and home construction.

Existing AM materials used in these applications include WPCs, UV curable thermosetting resins, and cementitious slurries. While manufacturing with WPCs is more sustainable and economically viable than with neat plastics, WPCs face serious challenges including low thermal stability of the wood filler, high moisture absorption of wood filler, low filler-matrix ratio (e.g., 50 wt. %), and low dimensional stability and durability of the plastics and composites. AM using HDPE-based CPC materials is projected to substantially reduce manufacturing and material costs, reduce waste, minimize secondary operations (curing and post-curing for thermoset based AM, and space heating for thermoplastic -based AM), increase dimensional stability (expansioncontraction due to changes in environment), increase service life, lower embodied energy and emissions, and reduce construction lead time. In addition, these state-of-the-art technologies use expensive and less widely available plastics (compared to HDPE), which might be an issue for the projected future demands for high-volume applications. Furthermore, AM of existing biocomposites face processing challenges that, unliked CPCs, might require modifications to commercially available AM equipment. Hence, slower technology development and deployment could result. [00192] 3.2 Heal deflection temperature

[00193] FIG. 7 shows the impact of coal on the heat deflection temperatures (HDTs) of PLA, PETG, HDPE, and PA12. At all filler contents, the PLA, PETG, and PA12 composites showed less than ± 0.5 % change in HDT, but the HDPE-based composites exhibit a drastic change in HDT with the introduction of coal. The neat HDPE had an HDT of 49.1 °C. At 40 wt. % coal, the HDT of the HDPE composite increased 30.4 % to 64.0°C. At 70 wt. % coal, the HDPE composite demonstrated a 102.2 % increase in HDT to 99.2°C. Previous work also found that the introduction of particle fillers increased the HDT of PE materials, and CPC materials showed similar or greater HDT enhancements compared to existing PE -based WPCs. Increases in HDT with the introduction of coal are attributed to increased moduli of the filled polymers and restricted polymer chain mobility. The PLA, PETG, and PA12 polymers started with a stiffness greater than the neat HDPE material. Thus, the increases in HDPE stiffness with the introduction of coal lead to greater enhancements of the HDT. Additionally, increases in the polymer crystallinity have shown to enhance HDT. The increase in HDT for the HDPE composites corresponds to the significant increase in polymer crystallinity (discussed in Section 3.3) due to the introduction of coal. Similarly, the lesser changes in crystallinity of the PLA, PETG, and PA12 polymers resulted in HDTs less affected by the introduction of coal. For potential composite tooling applications, increased HDT is beneficial for maintaining accurate mold dimensions at elevated temperatures. Higher HDTs translate to greater distortion resistance which permits molds to be heated for polymer processing and ensures that the mold geometry is maintained during exothermic thermoset curing.

[00194] 3.3 Glass transition temperature, melt temperature, and crystallinity [00195] The glass transition and melt temperatures of the composite materials provide insight into the temperature ratings for different applications and the processing window for AM. The glass transition and melt temperatures of the CPC materials are shown in FIG. 10A-D. Both the glass transition and melt temperatures exhibited relatively no change with filler content as compared to the respective neat PLA and neat PETG. Similarly, the melt transition temperature of the HDPE composites remains comparable, ranging from 123.8°C at 0 wt. % coal to 122.4°C at 70 wt. % coal. Previous research showed the introduction of fillers caused minimal changes to the glass transition and melt temperatures of polymer composites. The glass transition temperature of the HDPE materials is reported in literature below - 100°C and was therefore below the testing capabilities of the DSC utilized in the current study.

[00196] The PA12 composites showed a slightly different trend. The introduction of coal resulted in a slight increase in both the glass transition and melt temperatures. The neat plastic exhibited a glass transition temperature of 44.9°C and a melt temperature of 170.7°C. At 20 wt. % coal, the glass transition temperature increased to 48.1 °C and a melt transition temperature increased to 172.5°C. Studies have shown that the presence of hydrogen bonding raised the glass transition temperature of polymer-based composites. The chemical structures of the PA12 and the P8 coal suggest that hydrogen bonding could potentially form between the PA 12 amide group and hydroxyl groups located in the coal phenol structures.

[00197] With the melt temperature of all CPCs being comparable to the respective matrix polymer, the CPCs can be readily processed and 3D printed with commercially available equipment. The ability to 3D print CPC filaments without the need for equipment modifications promotes more rapid potential adoption of the technology in industrial and commercial settings.

Table 2: The crystallinity of the polymer fraction of the CPC composites.

[00198] The crystallinity of the polymer fractions of the CPC materials are shown in Table 2. The introduction of coal particles resulted in minimal changes in the crystallinity of the PLA and PETG polymer fractions. At 20 wt. % coal, the PA12 composite showed a 68.1 % increase in crystallinity, but the HDPE showed the most significant increases in crystallinity. The HDPE materials exhibit a 95 % increase in crystallinity from 29.7 % for the neat plastic to 57.9 % for the composite with 60 wt. % coal. The coal particles potentially provides nucleation sites for polymer crystal growth which most predominantly impacted the crystallinity of the HDPE composites.

[00199] 3.4 Specific heat capacity

[00200] The specific heat capacity (C_p) values of the CPC materials provide insight into the energy requirements needed during material processing. The C_p values of the PLA, PETG, HDPE, and PA 12 composites are shown from 50°C to 90°C in FIG. 11A-D. All four polymer types demonstrated increasing C_p values with temperature. For all polymers, the introduction of coal resulted in a decrease in C_p. At 40 wt. % coal, the PLA showed a 23.8 % decrease in C_p from 1.74 Jg^{- 1} °C^{- 1} to 1.32 Jg^{- l o}C“ ¹ at 50°C. The C_p of the PETG composites was less impacted by the introduction of coal. At 50°C, the PETG composites exhibited a 9.5 % reduction in C_p from 1.41 Jg^{- 1} °C^{- 1} to 1.28 Jg^{- l o}C" ¹ with 40 wt. % coal. The HDPE composites with 40 wt. % and 70 wt. % coal showed a 20.5 % decrease and a 26.7 % decrease from 2.24 Jg^{- lo}C" ¹ to 1.78 Jg^{- 1} °C^{- 1} and 1.64 Jg^{- 1} °C^{- 1} , respectively, at 50°C. Increasing filler from 40 wt. % to 70 wt. % coal had minimal effect in further decreasing the C_P of the material. The PA 12 composites with 30 wt. % coal demonstrated an 18.7 % decrease in C_p from 2.55 Jg^{- 1} °C^{- 1} to 2.07 Jg^{- 1} °C^{- 1} at 50°C.

[00201] The decrease in composite C_p can be attributed to the introduction of the bituminous coal filler which has a lower C_p. At 50°C, bituminous coal has a C_p of approximately 1.16 Jg“ ¹ °C“ Following the rule of mixtures, as more coal was introduced, the C_p of the composite decreased from the C_P of the neat polymer materials. Coal’s minimal effect on the C_P of the PETG composites can be attributed to the initial neat- PETG C_p being only 21.6 % greater than that of the coal, whereas the starting HDPE and PA12 neat-plastic C_p values were 93.5 % and 119.6 % greater, respectively. Reduced material C_p suggests lower energy requirements are needed for heating the material during 3D printing. Lower energy requirements translate to reduced costs for future large-scale applications such as additive home construction and composite tooling manufacturing.

[00202] 3.5 Thermal conductivity

[00203] The thermal conductivities of the CPC materials are shown in FIG. 12A-D. PLA,

HDPE, and PA 12 composites demonstrated decreasing thermal conductivity with increasing coal content. Most notably, the neat HDPE exhibited a thermal conductivity of 0.61 Wm" ¹ K” ¹ , and the HDPE with 70 wt. % coal demonstrated a 37.2 % decrease in thermal conductivity to 0.38 Wm^{- 1} K“ ¹. The thermal conductivity of the PETG composites remained relatively constant at 0.26 Wm" ¹ K^{- 1} to 0.27 Wm" ¹ K^{- 1} at all coal loadings. P8 coal has a reported thermal conductivity between 0.196 Wm^{- 1} K^{- 1} to 0.27 Wm^{- 1} K“ ¹. The introduction of the coal filler with lower or comparable thermal conductivity than the matrix resins resulted in the respective decreasing or constant trends. With thermal conductivities in the range of 0.23 Wm^{- 1} KT ¹ to 0.61 Wm^{- 1} K“ CPC materials used for additive housing applications could provide comparable or improved thermal insulation compared to houses additively manufactured using cementitious materials which have exhibited thermal conductivities ranging from 0.47 Wm^{- 1} K^{- 1} to 1.24 Win’ ¹ K^{- 1}.

[00204] 3.6 Thermogravimetric analysis

[00205] The thermogravimetric (TGA) and derivative TGA (DTG) curves of the PLA, PETG, HDPE, and PA12 composites are shown in FIG. 13A-D. The decomposition onset temperatures at 5 % weight loss (Ts %), the decomposition temperatures at 50 % weight loss (Tso %), and the maximum decomposition rates of the composites are summarized in FIG. 14. Neat PLA (FIG. 13A) showed a single-stage degradation of the polymer. When coal is added at 30 wt. % and 40 wt. %, the composite experienced a two-stage decomposition mechanism, consisting of polymer matrix degradation followed by the coal filler. Similarly, the PETG, HDPE, and PA12 CPCs demonstrated multi-stage decompositions. Previous research showed similar two stage decompositions in HDPE-based WPCs.

[00206] The thermal stability of the PLA -based composite was improved by the addition of coal. T5 % of the PLA increased from 347°C to 359°C at 40 wt. % coal, and the T50 % increased from 38O°C to 390°C when loaded with 40 wt. % coal. Additionally, the decomposition rate of the PLA decreased from 52.3 %/min to 45.8 %/min at 30 wt. % coal.

[00207] PETG composites demonstrated a slightly different behavior. The PETG composites exhibited comparable Ts % to the neat plastic. The neat PETG experienced T5 % at 402°C, and the PETG composite with 40 wt. % coal experienced T5 % at 400°C. The PETG composite demonstrated a 5.3 % increase in T50 % from 443°C to 467°C at 40 wt. % coal. Similar to the PLA composites, the PETG composites showed slower peak decomposition rates. The neat PETG degraded at a peak rate of 36.9 %/min, but the PETG with 40 wt. % coal experienced a two-stage decomposition which resulted in a peak rate of 20.9 %/min, 43.4 % lower than the neat plastic decomposition rate.

[00208] The HDPE composites exhibited the most notable improvements in thermal stability. The neat HDPE exhibited T5 % and Tso% of 312°C and 406°C, respectively, and the P8 coal exhibited Ts % and Tso % of 384°C and 484°C, respectively. The HDPE composites demonstrated thermal stability greater than the individual components. The HDPE with 50 wt. % coal demonstrated a T5 % of 417°C, 33.5 % greater than the neat plastic. The HDPE composite with 70 wt. % coal showed a T50 % of 525°C which was 52.6 % greater than the neat HDPE T50 % of 406°C and 8.5 % greater than the P8 coal T50 % of 484°C. Additionally, when loaded at 60 wt. %, P8 coal was able to reduce the maximum decomposition rate of the HDPE by 55.2 % from 45.2 %/min to 20.3 %/min. Previous work suggested coal was able to provide similar enhancements to the thermal stability of HDPE composites by trapping free radicals and acting as a primary and secondary antioxidant.

[00209] Similar to the behavior of the HDPE materials, the PA12 composites exhibited thermal stabilities greater than the individual constituents. Tested at the slower 5°C/min heating rate, the neat PA 12 showed a T5 % of 401 °C, and the P8 coal showed a Ts % of 359°C. The PA 12 composite with 20 wt. % coal, however, demonstrated a T5 % of 409°C. The PA12 composites loaded with 30 wt. % coal exhibited a maximum decomposition rate of 9.2 %/min which was 26.4 % less than the 12.5 %/min decomposition rate of the neat PA12. The decomposition of PA12 can be initiated by multiple mechanisms including homolytic scission of the N-alkylamide bonds or scission of the CH2-CH2 bonds in the P-position. Similar to the role in HDPE-based composites, the coal acts as an antioxidant by trapping free radicals and mitigating propagation of the decomposition reactions.

[00210] In this work, P8 coal was incorporated as a particulate filler in thermoplasticbased composites to develop 1.75 mm diameter filaments for utilization in FDM 3D printing. The composites were developed from PLA, PETG, HDPE, and PA 12 resins with coal loaded from 20 wt. % to 70 wt. %. The introduction of coal substantially reduced CTE of the materials by up to 53.1 %. Reductions in CTE led to reduced warping and shrinkage in 3D printed parts, a current obstacle with the FDM of HDPE-based materials. The reduced warping led to the ability to reliably 3D print dimensionally accurate HDPE-based materials without the need for a heated chamber. HDPE CPCs demonstrated increased heat deflection temperature with coal introduction implying that the CPC is a dimensionally stable material for heated mold or exothermic thermoset mold applications. Coal had little effect on the glass transition and melt temperatures of the composites which allowed the materials to be readily printed with commercial extruders. The composites demonstrated reduced Cp values which implies reduced energy consumptions for heating and extruding the materials. The introduction of coal reduced the thermal conductivity of the composite materials, making it more insulating than additively manufactured concrete. Coal improved thermal stability and decreased the maximum rate of decomposition for all polymer composites. The thermophysical enhancements induced hy the coal filler lends CPCs as a viable, sustainable feedstock for extrusion-based AM for future industrial and construction applications.

[00211] Example 2

[00212] The objective of this research was to develop 3D printable CPC materials and investigate the composites’ behavior. CPC FDM filaments were developed to maximize the coal filler content, and the respective printing parameters were identified. CPC materials made with PLA, PETG, HDPE, and PA 12 resins were characterized. A foundational understanding of the mechanical response of the CPC materials is critical for the development of the technology for future industrial applications, such as additive housing construction or large-scale composite tooling manufacturing. The tensile and flexural strength and moduli are fundamental for design in structural applications, and impact resistance provides insights into the materials’ energy dissipation. The hardness of the materials characterizes the CPCs for wearing environments. Furthermore, the interactions between coal and plastics were studied via molecular dynamics simulations involving atomistic models of P8 coal, plastics, and composites. Avogadro and ChemDraw were utilized to build the atomistic models, and various simulation techniques such as plane-wave basis density functional theory (DFT), reactive force field (REAXFF), and molecular mechanics force fields (MM3) were employed. Quantification of the composites’ mechanical properties, processing parameters, and molecular interactions is essential for future technology development and adoption.

[00213] 2. METHODOLOGY

[00214] 2.1 Experimental Section.

[00215] 2.1.1 Materials. [00216] CPC filaments were derived from virgin plastic pellets and a bituminous coal filler. PLA (PPLA110000, p - 1.24 g/cm³) and PETG (PPTG110000, p = 1.24 g/cm³) pellets were sourced from 3DXTECH. Paxon EA55-003 HDPE pellets (p = 1.24 g/cm³) were supplied by ExxonMobil, and PA12 pellets (044, p = 1.02 g/cm³) were obtained from Scientific Polymer Products Inc. Struktol TPW 104 processing additive was used as a lubricant for processing HDPE filaments. Bituminous P8 coal was supplied by CONSOL Energy.

[00217] 2.1.2 Material Synthesis.

[00218] Composite formulations containing 20-70 wt. % coal were developed based on successful filament extrusion trials from the different matrix resins. P8 coal was pulverized and sieved below a particle size of 38 pm. The coal powder was dried in a convection oven at 110 °C for 24 h to decrease the moisture content to less than 1 wt. %. Dried coal (20-70 wt. %) and balance matrix resins were melt- mixed for 5 min at 100 rpm using a Rheomix 600 batch mixer. Processing additives (i.e., 1 wt. % Struktol TPW 104 for HDPE composites) were introduced during this step. Based on the resin type, CPC materials were compounded at temperatures ranging from 180 to 210 °C. The compounded CPC materials were ground using a Retsch SM 100 cutting mill and were stored in a desiccator for further processing.

[00219] 2.7.3 Filament Extrusion and FDM Printing.

[00220] CPC pellets were extruded into filaments using a 3devo Composer 450 and a Filabot Ex2 single- screw filament extruder. The materials were processed at barrel temperatures ranging from 175 to 230 °C. The filaments were drawn to a 1 .75 mm diameter before being aircooled.

[00221] Subsequently, CPC filaments were 3D printed (3DP) by using a FlashForge

Creator Pro FDM printer. Mechanical test samples were printed in the horizontal orientation with 0-90° linear infill to promote isotropic behavior for comparison to traditionally manufactured samples. The print orientation is shown in FIG. 8. The printing parameters, the print temperatures, and the bed adhesion methods for each matrix resin are provided in Tables 3 and 4.

Table 3: Print Parameters used to 3D print CPC test specimens

Table 4: Printing temperatures and bed adhesion used to 3D print CPC test specimens.

[00222] 2.1.4 Compression Molding.

[00223] For characterization of the intrinsic filament composite material and for comparison to the as-printed state, CPC pellets were compression-molded (CM) to produce samples for mechanical testing. A model 3912 Carver Press was used to compression mold 200 mm x 200 mm x 3.5 mm sheets from aluminum molds coated with a Frekote 770-NC mold release agent. The materials were heated at 180 to 195 °C for 20 min prior to pressing to 8 metric tons for 5 min. The sheets were allowed to cool in air in the mold. Type IV tensile, flexural, and Izod impact resistance samples were cut from the composite sheets by using a ProtoMAX waterjet cutter.

[00224] 2.1.5 Mechanical Testing.

[00225] Tensile and flexural tests were performed using an Instron 5966 load frame.

Tensile tests were conducted according to ASTM D638. Type IV tensile samples were tested at a displacement rate of 5 mm/min, and a one-inch clip-on extensometer was used to measure the sample strain. Three-point flexural testing was performed in accordance with ASTM D790 procedure B using a span-to-thickness ratio of 16. All stresses are reported as engineering stresses, and the tensile and flexural moduli values were estimated by using linear regression.

[00226] Izod impact resistance tests were performed using an Instron CEAST 9050 pendulum impact machine. Izod impact samples were notched using an Instron notching fixture, and notched Izod tests were performed according to ASTM D256 Test Method A.

[00227] Composite hardness was determined using a Gain Express 560- 10D Shore D hand-held durometer. For all mechanical tests, a minimum of six samples were tested.

[00228] 2.1.6 Microscopy.

[00229] Optical microscopy was performed using a Keyence VHX-7000 digital microscope to investigate the coal dispersion and the composite microstructure. A JEOL JSM- 6390LV scanning electron microscope was used to investigate the matrix-filler interface. As- fractured flexural samples were sputter coated with gold at 20 mA for 180 s. Images at lOOOx magnification were captured using an accelerating voltage of 15 kV. Scanning electron microscopy (SEM) images were used to identify mechanical failure mechanisms present in the composite.

[00230] 2.1.7 Fourier-Transform Infrared Spectroscopy.

[00231] Attenuated total reflection Fourier-transform infrared spectroscopy (FTIR) was conducted using a Thermo Scientific Nicolet 6700. Composite disc samples were CM by using stainless steel ring molds and polytetrafluoroethylene platen sheets. Thin composite sheets (0.25 mm thick) were tested by using a diamond ZnSe crystal.

[00232] 2.2 Simulation of P8 Coal, Plastics, and CPC Models.

[00233] Representative models for the matrix materials (PEA, PETG, HDPE, and PA 12), filler (P8 coal), and their composite models were constructed using ChemDraw and Avogadro. To ensure the accuracy and reliability of the simulations, an extensive ensemble of structural models was analyzed, involving statistically meaningful sampling of the configuration space of the material of interest. For this purpose, 20 coal models (C166H138O15N2S2) were manually built based on the 2D structure for Pittsburgh bituminous coal proposed by Solomon (see the representative model in FIG. 15A). At first, the aliphatic and aromatic structures in each P8 coal model were constructed in a 3D box. Subsequently, the MM3 force field, as implemented in ChemDraw and Avogadro, was used for the conformation optimization and energy minimization of the constructed models. Supercell models containing 20 units of P8 coal were generated using the PACKMOE software package (see the representative 3D coal model in FIG. 16B). The final models were subsequently validated using DFT and REAXFF potentials via a conjugate gradient relaxation. DFT calculations were implemented within the Vienna Ab initio Simulation Package

(VASP) with the projector augmented wave (PAW) method and the Perdew- Burke-Ernzerhof (PBE) exchange-correlation functional. The REAXFF calculations were performed using the large-scale atomic/molecular massively parallel simulator (LAMMPS). In all of the models (coal and plastics), hydrogen, carbon, nitrogen, oxygen, and sulfur atoms were colored white, gray, blue, red, and yellow, respectively.

[00234] The plastics were constructed from scratch using ChemDraw, with monomers repeated 100 times. FIGS. 16A-D depicts atomic structure representations of the different plastics investigated in this study. The PACKMOL algorithm was used to construct the CPC models, ensuring a minimum pairwise distance of about 3 A between atoms from different molecules to prevent disruptive van der Waals repulsive interactions and atom overlap in the initial configurations. To simulate the laboratory process of melt-mixing the plastic and coal, the composite models were heated in a canonical ensemble that was controlled by a Nose-Hoover thermostat at a temperature of 200 °C. Subsequently, the models were optimized to reach an energy minimal configuration using the conjugate gradient implementation. The REAXFF interatomic potential was employed in the simulated melt-mixing protocol with a time step of 0.25 fs to account for the high-frequency dynamics of the hydrogen atoms in the models.

[00235] 3. RESULTS AND DISCUSSION

[00236] 3.1 Experimental Results.

[00237] 3.1.1 CPC Filament Processing.

[00238] CPC filaments were extruded from PLA, PETG, HDPE, and PA 12 resins to achieve the maximum levels of coal filler content. PLA and PETG filaments were created with up to 40 wt % coal, and successful HDPE composite filaments were extruded containing up to 70 wt % coal. The PA12 composite filament was produced at 20 wt % coal for comparison to the processability of CPCs at commercial chopped carbon fiber loadings, and PAI 2 filaments were successfully produced with up to 30 wt % coal.

[00239] FIGS. 17-20 show representative strands of the CPC filaments. The CPC filaments were extruded using the same extrusion parameters as those for the respective neat plastics. All CPC filaments exhibited smooth surface finishes comparable to those of the neat plastic filaments and were extruded within the acceptable tolerances for commercially available printers. HDPE-based filaments required the addition of a 1 wt % TPW-104 lubricant to achieve a smooth surface finish and consistent filament diameter. Additionally, the composites did not show macroscale porosity or agglomeration throughout the microstructure (Section 3.1.2).

[00240] The CPC filaments were 3D printed into mechanical test samples. Examples of 3D printed CPC samples are provided in FIGS. 21-24. The CPC filaments were processed using the same printing parameters as the respective unfilled plastics, demonstrating compatibility with existing AM techniques, which might lead to fast commercial adoption of the technology. In addition, CPC materials were processed using the same nozzle size and printing speeds utilized for common AM plastics, indicating similar manufacturing times for any given object and affinity with established AM processes.

[00241] The printability of the HDPE-based composites was impacted the most by the introduction of coal. FIG. 25 shows images of additively manufactured virgin HDPE and HDPE- based composites with 50 wt % P8 coal. The neat HDPE flexural samples exhibited an average deflection from warping of 0. 12 mm/mm along the axial length of the sample. When printed with 50 wt % coal, the average deflection of the HDPE composite reduced by 59.5% to 0.05 mm/mm along the axial length of the sample. The reduced deflection from warping resulted in greater dimensional accuracy of the printed parts. Increasing P8 content significantly reduced the warping of the HDPE prints and helped to overcome one of the key challenges limiting the utilization of HDPE in AM applications. Resolving the warping issues associated with the AM of HDPE allows for the utilization of more widely available and inexpensive plastics compared to the plastics readily used in current commercial technologies (i.e., PLA and PETG). In addition, reduced warping allowed for additive fabrication outside of a heated chamber, suggesting lower energy usage and higher dimensional stability of the HDPE-based composites in comparison to neat HDPE.

[00242] It was successfully demonstrated that CPC materials including formulations with a high filler content (up to 70 wt % P8 coal) could be integrated with several types of commercially available 3D printers without processing issues or the need for equipment modifications. The utilization of HDPE-based CPC materials in targeted applications such as additive housing construction and composite tooling is projected to substantially reduce manufacturing and material costs, reduce waste, minimize secondary operations during printing (curing and postcuring for thermoset-based AM and space heating for thermoplastic -based AM), increase dimensional stability, increase service life, lower embodied energy and emissions, and reduce manufacturing lead time.

[00243] 3.1.2 Composite Micro structure.

[00244] Optical microscopy was used to evaluate the microstructure of the CPC filaments. FIG. 26 shows a representative example of CPC filament microstructures. The HDPE filament with 60 wt % P8 coal shows no porosity throughout the filament cross-section at l 50 magnification. Furthermore, the composite filaments exhibited even dispersion of the coal particles throughout the matrix with minimal regions of agglomeration. Images of all CPC filament microstructures are shown in FIGS. 27-30. [00245] FIG. 31 shows representative tensile stress-strain curves of the four different CM polymer composites. As-fractured tensile and flexural samples were investigated by using SEM to evaluate particle-matrix interfaces and failure mechanisms in the composites. CPCs at different filler contents demonstrated comparable microstructures and failure mechanisms that were well represented by the SEM images shown in FIG. 31. FIG. 31 shows the SEM images for the PLA, PETG, and HDPE composites loaded at 40 wt % coal for direct comparison. The image and stress-strain curve for the PA12 composite is shown for the 30 wt % coal material because 30 wt % was the maximum coal loading achieved for the PA12 matrix which is most comparable to the other composites presented. While the matrix polymer had the greatest effect on the local microstructure, all four polymer materials showed minimal instances of porosity at the particle-matrix interface as the coal particles were well encased by the plastic. The fractured surfaces of these composites demonstrate two primary failure mechanisms

[00246] CM samples showed instances of both particle pull-out (circle) and particle fracture (arrow), as shown in FIG. 31 Particle pull-out was the primary failure mechanism in the PLA, PETG, and HDPE composites, and pull-out locations were readily visible throughout all four polymer composites. Additionally, instances of coal particle fracture indicated that the load was efficiently transferred from the matrix material to the particle filler. Alternatively, coal particle fractures could have been induced during material processing. While particle fractures were present in all four composites, the PA 12 composites demonstrated a greater abundance of particle fracture locations. The particle fracture sites further indicate a beneficial interaction between PA12 and the reinforcing coal particle (Section 3.2.3.), below.

[00247] The stress-strain curves of the PLA and PETG composites demonstrated a linear elastic response followed by a brittle fracture. The SEM images showed smooth, glossy fracture surfaces, confirming the brittle failure of the composites. Originally, the neat PLA and PETG materials exhibited ductile failures, with regions of plastic deformation after a yield point. The neat plastics possessed greater strain to failure than the respective CPCs. The HDPE and PA12 composites exhibited a yield point and possessed a small region of ductile plastic deformation prior to failure. In the SEM images (FIG. 31), the polymer portions of the HDPE and PA12 composites show fibrillated strands of the polymer matrix which have undergone ductile deformation during testing. The yielding of the plastic around the coal particles results in a more ductile response seen in the stress-strain curves. In comparison, the neat HDPE material demonstrated a similar mechanical response but had a greater strain to failure and, thus, a larger region of plastic deformation than the composite. The neat PA12 and PA12 composites exhibited comparable stress-strain relations and strains to failure.

[00248] 3.1.3 Tensile Properties.

[00249] Tensile properties, shown in FIG. 32, of the 3D printed (3DP) composite materials were determined and compared with those of the CM composites. Comparing the mechanical response of the 3DP composites to the performance of the traditionally manufactured (i.e., CM) composites provides insights into the effects of the AM process. Furthermore, investigating CM CPCs establishes a benchmark of the isotropic performance of the intrinsic filament material prior to use in the 3D printing process which could introduce anisotropic responses due to layer orientations and print raster angles. The 3DP and CM samples exhibited analogous trends in tensile performance with respect to coal loading. As expected, the ultimate tensile strength (UTS) of the PLA, PETG, and HDPE composites decreased with an increase in coal content. The 3DP PLA composites exhibited a 38.6% decrease in UTS from 53.6 to 32.9

MPa at 40 wt % coal loading, and the 3DP PETG composites showed a 42.4% decrease in UTS from 52.9 to 30.5 MPa at 40 wt % coal loading. The UTS of the HDPE composites was impacted to a lesser extent by the introduction of coal. At 40 wt % coal, the UTS of the 3DP HDPE composite decreased 24.3% from 17.0 to 12.9 MPa. At 70 wt % coal, the UTS of the 3DP HDPE decreased to 9.5 MPa or 44.4% of the neat plastic strength. The reduction of UTS at high coal loadings could be attributed to particle agglomeration and weak coal-plastic interfacial bonding. Additionally, simulation results (Section 3.2.2., below) showed little chemical interaction between the PLA, PETG, and HDPE and the P8 coal, making the composite analogous to a physical mixture. Weak interfacial bonding led to an increased number of stress concentration sites throughout the polymer matrix which provoked particle pull-out into being the most frequent failure mechanism in these composites (Section 3.1.2., above). Akin to previous work, the strength of the composite exhibited a decreasing trend as more filler was introduced.

[00250] The PA12 composites exhibit remarkably different behavior. The 3DP PA12 samples with 20 wt % coal loading demonstrated an increase in UTS from 28.9 to 30.4 MPa. The UTS of CM PA12 had the greatest response to coal introduction. The neat CM PA12 demonstrated an UTS of 32.1 MPa. However, when loaded with 20 wt % P8 coal, the CM PA12 composite exhibited a 45.2% increase in UTS, reaching a peak tensile strength of 46.6 MPa. These results are in agreement with previously published literature regarding the reinforcing effect of carbon and coal fillers in polyamide-based composite materials. Enhanced UTS for the PA 12-based composites could be attributed to improved interfacial bonding between coal and PAI 2, leading to an efficient load transfer from the polymer to the coal particle. Molecular simulations (Section 3.2.3.) and FTIR results (Section 3.2.3) further discuss the chemical bonding between the PA 12 and the coal particles. [00251] EM of all CPC materials showed increasing trends with increasing coal contents for both the 3DP and CM materials. Most notably, the 3DP HDPE composites exhibited a 340.6% increase in EM from 0.5 to 2.2 GPa from the neat plastic to 70 wt % coal. The stiffness of the PLA composites was the least impacted as the 3DP material only showed a 12.9% increase in the EM at 30 wt % coal. The 3DP PETG composites showed a 20.7% increase in EM at 40 wt % coal, and the 3DP PA12 composites showed a 42.5% increase in EM at 30 wt % coal. The increases in EM can be attributed to two primary factors: (1) the coal particles are stiffer than the matrix polymer, increasing the stiffness of the resulting composite, and (2) the increase in filler content reduced polymer chain mobility throughout the composite material. Similar trends have been reported for particulate-filled polymer composites.

[00252] 3.1.4 Flexural Properties.

[00253] Flexural properties of the 3DP and CM CPCs are shown in FIG. 33. The flexural properties of the composite materials reflect analogous trends to the tensile properties with respect to coal content. Flexural strength (FS) of both the CM and 3DP materials showed inverse proportionality with coal content for the PLA-, PETG-, and HDPE-based composites. The 3DP PLA composites demonstrated a 50.5% decrease in FS from 77.2 to 38.2 MPa at 40 wt % coal, and the 3DP PETG composites demonstrated a 36.9% decrease in FS from 75.5 to 47.7 MPa at 40 wt % coal. As observed with the UTS, the 3DP HDPE composite strengths were less sensitive to the introduction of coal, and at 40 wt % coal, the 3DP HDPE composite showed only an 8.3% decrease in FS from 20.9 to 19.1 MPa. At 70 wt % coal loading, the CM HDPE composite displayed a 28.1% decrease in FS. Previous research showed similar FS trends with the introduction of particulate fillers in polymer matrices. The reduction of the FS values was primarily due to agglomeration and weak interfacial bonding. [00254] Similar to the tensile properties, the PA 12 composites demonstrated a FS increase with the introduction of coal. 3DP PA12 composites exhibited a 16.9% increase in FS from 30.2 MPa to a peak FS of 35.3 MPa at 20 wt % coal loading. This increase was attributed to improved interfacial bonding between the coal and PA12 (Section 3.2.3.), below.

[00255] The flexural modulus (FM) of all CPC materials increased with the increase in coal content. At 40 wt % coal, the CM PLA composites showed a slight 7.3% increase in FM from 3.8 to 4.1 GPa analogous to the PLA EM behavior. The 3DP PETG composites exhibited a 23.0% increase in FM from 2.0 to 2.5 GPa at 40 wt % coal, and the 3DP PA12 composites demonstrated a 39.3% increase in FM from 0.7 to 1.0 GPa at 30 wt % coal. HDPE composite stiffness had the most significant response to coal introduction. The 3DP HDPE composites at 70 wt % coal showed a 105.6% increase in FM to 1.2 GPa, and the CM HDPE composites at 70 wt % showed a 176.6% increase in FM to 3.2 GPa. Similar’ trends have been reported in the literature where the higher stiffness values were attributed to stiffer particles and limited polymer chain mobility.

[00256] 3.1.5 Impact Resistance.

[00257] Notched Izod impact resistance was determined for the 3DP and CM CPC materials. FIG. 34 shows the impact resistances of the composite materials at different coal contents. For all matrix polymers, the impact resistance of the composite decreased with filler content for the 3DP and CM materials. The 3DP PA12 composites exhibited a 40.1% decrease in impact resistance from 33.4 to 20.0 J m^-1 at 30 wt % coal. Similarly, the 3DP PLA and PETG composites exhibited a 58.7 and 44.6% decrease, respectively, in impact resistance at 40 wt % coal. The HDPE composites exhibited the greatest decrease in impact resistance with the introduction of coal. The 3DP HDPE composites exhibited an 82.0% decrease in impact resistance from 94.2 to 16.9 J m^-1 at 40 wt % coal, and the 3DP impact resistance continued to decrease to 3.4 J m^-1 at 70 wt % coal. Previous work with particulate-filled polymer composites showed similar impact resistance trends. Increased particle loading resulted in a greater coal- polymer interface surface area, therefore enhancing crack initiation and propagation.

[00258] 3.1.6 Hardness.

[00259] FIG. 35 shows that the CPC materials demonstrated increasing Shore D hardness with coal content due to the introduction of a filler material harder than the matrix. Previous studies have shown that polymer composites with harder particulate filler materials exhibited comparable tendencies. Most notably, the HDPE composites demonstrated a 19.3% increase from a neat plastic hardness of 59.0 to a hardness of 70.4 at 70 wt % coal loading. The increased hardness of the composites improved the FDM of the HDPE filaments. Due to the neat HDPE’s low hardness, the FDM printer’s extruder wheel caused significant filament abrasion, resulting in underextruded material and failed prints. Conversely, the harder composite filament resisted abrasion and improved the printing reliability. The PLA and PETG composites showed a respective increase in hardness of 4.6 to 84.4% and 9.0 to 79.8% at 40 wt % coal. Similarly, the PA12 composites exhibited a 4.6% increase in hardness from 72.5 to 75.8 at 30 wt % coal.

[00260] 3.2 Simulation Results.

[00261] 3.2.1 P8 Coal Chemical Structure Validation.

[00262] To analyze the local conformation of the coal model, an ab initio multiplescattering calculation of the extended X-ray absorption fine structure (EXAFS) was performed using the real-space Green’s function code FEFF10.53 The K-edge of sulfur was studied, and the extracted postedge oscillations [%(E)] were Fourier transformed (FT) into real space using the

Kaiser windowing function with P = 2.54 The resulting spectrum provides the radial distribution function (RDF). The peaks of the normalized Fourier amplitude obtained for the coal model were compared with experimental data from Huffman and co-workers. The peak positions from this study were found to be in close agreement with the FTIR experimental values. The positions of the first, second, and third peaks from this work (ref. 55) were 1.74 A (1.75 A), 3.04 A (2.84 A), and 3.99 A (4.02 A), respectively. This confirms that the coal models used in this study reasonably predict the structure of the bituminous coal. The EXAFS spectra for the P8 coal model are provided in FIG. 36.

[00263] 3.2.2 Coal-Plastic Interfacial Phenomena.

[00264] Molecular simulations of the coal models at the experimental processing temperature were performed to gain insights into possible bond-breaking and bond-forming sites in the coal. The interactions in the models were investigated by calculating the bond order per atom and chemical species at specific intervals during the simulation. At the beginning of each simulation, the number of coal and plastic molecules was known, and the bond order and available chemical species provided information on intra- and intermolecular interactions.

[00265] FIG. 37 provides an illustration of the bond-breaking sites in the P8 coal model. The coal macromolecules are generally seen to break down into three subunits, represented by green, teal, and magenta clusters. The bond-breaking sites, highlighted in black circles in FIG. 37, were identified as the self-associated OH hydrogen bonds between two phenol-hydroxides (ph-OH) in the P8 coal. The chemical formulas of the coal subunits, along with their associated colors in FIG. 37, are C105H88O10N2S2 (green), C42H34O4 (teal), and C19H16O (magenta). Interestingly, CH3 and H2 were released in about 14% of the simulation realizations at an early stage of heating. The CH3 fragments result from the breaking of the ethylene bridges during the thermal process, which is also observed experimentally during P8 coal pyrolysis. [00266] The interfacial phenomena between coal and PLA, PETG, and HDPE in the composites were investigated, and the results are illustrated in FIGS. 38-40. After 5 ns of heating, the configuration of the system revealed that the molecules tend to aggregate and form clusters without observable evidence of chemical bonding. This suggests that the equilibrium state of the heterogeneous matrix involves purely physical mixing without intermolecular bonding. This simulation data supports the experimental observation of the negative impact of coal on the UTS and FS for the composites made using PLA, PETG, and HDPE polymers. However, it is worth noting that PA 12 showed different behavior in the simulation, indicating that it may have beneficial interfacial phenomena (i.e., chemical bonding) with coal, leading to improved mechanical properties.

[00267] 3.2.3 Hydrogen Bonding in PA12-Based Composites.

[00268] Both the widely accepted structural models of coal, namely, the host-guest model and the associated model, have extensively investigated the impact of noncovalent bonds, such as van der Waals forces, hydrogen bonding, ionic linkages, and it-it interactions, on the chemical structure of coal. Studies by Larsen and co-workers estimated that noncovalent bonds surpass the number of covalent cross-links by a factor of 4 in coal, and specifically for P8 coal, it was suggested that approximately 0.3 cross-linking hydrogen bonds are present per 100 carbon atoms. Additionally, Brenner demonstrated that hydrogen bonding likely contributes to the high glass transition temperature and glassy properties observed in bituminous coal. Molecular simulations of the interaction between PA 12 and P8 coal revealed prevalent forms of hydrogen bonding between the hydroxide (OH) in the phenolic group of coal (ph-OH) and the amide group

(- NH-C=O-) in PA 12. [00269] FIGS. 41 A-C provides visual representations of hydrogen bond formation in the PA12 composite material. FIG. 41A displays snapshots of the local environment before and after the formation of hydrogen bonding between the strong proton donor ph-OH in coal and the strong proton acceptor oxygen in the amide group. In some instances, double hydrogen bonds were observed, as shown in FIG. 41B. The hydrogen bond lengths ranged from 1.61 to 1.86 A. A proposed mechanism for the hydrogen bonding observed in the PA12-coal composite is that it results from the high polarity of the amide linkages along the polyamide chain, as depicted in FIG. 42.

[00270] The rigidity and planarity of the amide linkage induce a positive and negative charge on the nitrogen and oxygen atoms, respectively, facilitating K-bond cooperativity, also known as resonance-assisted hydrogen bonding (RAHB). In RAHB, the polarization occurs by charge flow through the n bonds. The N-H in the amide group becomes a stronger donor if the amide O atom accepts a hydrogen bond (i.e., Ph-OH- • O=C-N-H), as portrayed in FIG. 41B, resulting in a stabilized zwitterionic resonance. Except for HDPE, which is nonpolar, both PLA and PETG, like PA12, possess polar functional groups (COOH in PLA and OH in PETG) capable of forming H-bonds. However, the closely packed nonpolar carbon backbone in these polymers (i.e., the methyl group in the PLA monomers and the cyclohexanes and benzene aromatic structures in PETG monomers) induces steric congestion, which can significantly reduce the reactivity (H-bonding) of the polar functional groups in these materials. In contrast, PA 12 features a longer linear backbone with 12 carbon atoms, leading to less steric hindrance. Consequently, PA12 exhibits higher conformational flexibility, enabling its molecules to adopt desired spatial rearrangements. [00271] The presence of hydrogen bonding between PA 12 and P8 coal in the composite was validated experimentally through FTIR analysis. The FTIR spectra obtained for the PA12 composites (FIG. 41C) were normalized to the C-H peak, assuming that the C-H bonds along the PA12 molecule remained constant during the composite compounding process. The spectra for the composite materials with 0, 20, and 30% coal are shown in black, green, and orange, respectively. No new peak formations or disappearances were observed with the introduction of coal, suggesting that no covalent bonds exist between PA 12 and coal.

[00272] However, a notable decrease in the N-H in-plane bending peak at — 1557 cm ¹ was observed with the addition of coal, as shown in the inset in FIG. 41C, yet the N-H stretching peak at -3284 cm^-1 remained unchanged. The absence of a new peak for covalent bonding, combined with the results obtained from the simulations, suggests that the reduction in the N-H in-plane bending peak could be attributed to the formation of hydrogen bonding, which constrains the mobility of the initially free N-H bond. The presence of hydrogen bonding throughout the composite allows the coal particles to act as reinforcing fillers, as demonstrated by the experimental tensile and flexural results. The formation of hydrogen bonds between PA 12 and coal particles enhances the interfacial adhesion and overall mechanical performance of the composite.

[00273] In this work, bituminous P8 coal was incorporated as a particulate filler in thermoplastic -based composites to develop 1.75 mm diameter filaments for utilization in FDM printing. The composites, composed of PLA, PETG, HDPE, and PAI 2 resins with coal loadings of 20 to 70 wt %, were evaluated for their tensile properties, flexural properties, and Izod impact resistance in both 3DP and CM states. CPC filaments were extruded and 3D printed by using the same processing parameters as the respective neat plastics. The introduction of coal significantly reduced warping in HDPE-based prints, thus addressing a serious problem and providing a viable avenue to additively manufacture HDPE parts. The resulting CPCs exhibited increased moduli and improved tensile and flexural strength in the PA12 composite, but all materials demonstrated a decreasing impact resistance with a coal content. Analysis of failure mechanisms revealed particle pull-out and particle fracture as the dominant failure modes, and the composite hardness increased with coal content. Atomistic models of the polymers and P8 coal were created to simulate their interactions. PA 12 CPC simulations revealed hydrogen bonding between the polymer and the coal molecules. The hydrogen bonding between PA 12 and P8 coal formed between the hydroxide (OH) in the phenolic group of P8 coal (ph-OH) and the amide group (-NH-C=O-) in PA12. The formation of hydrogen bonds in PA12 CPC materials was supported by FTIR spectra and provided a possible basis for the enhanced mechanical performance of the composite. These findings, along with the development of CPC filaments and supporting molecular simulations, demonstrate a viable avenue for FDM printing of CPC components and structures.

[00274] Example

[00275] Materials

[00276] ExxonMobil EA55-003 high-density polyethylene (HDPE) was used as the polymer matrix for all lab-scale composite formulations. The natural carbon fillers included Bituminous coal (Keystone 325), semi-anthracite coal (Keystone 121 ), and two types of coal- derived carbon dust: CFoam Green (foamed at 550 °C) and CFoam Calcined (heat-treated at 1050 °C). For comparison, commercial filler materials — milled carbon fiber (average diameter -7 pm, length 80-100 pm) and wood flour (average particle size -150 pm) — were also investigated. To improve extrudability and surface finish during compounding, TPW 104 lubricant from Struktol was added to the HDPE-based blends. Prior to melt-mixing, all natural carbon fillers (coal and coal-derived carbons) were dried in a convection oven at 150 °C for 24 hours to reduce moisture content to <1 wt%.

[00277] Particle Size Analysis

[00278] Keystone 325 (bituminous coal) and Keystone 121 (semi-anthracite coal) coal were used as received, whereas the coal-derived carbon powders were pulverized and sieved through a 325-mesh sieve. The average particle size of natural carbon fillers used in this study is shown in Table 1, below. Size distribution is commonly represented by three specific values: d(0.9), d(0.5), and d(0.1). The d(0.9) value represents the size below which 90% of particles fall, and similarly, d(0.5) and d(0.1) denote the sizes for 50 % and 10 % of particles, respectively.

[00279] Table 1: Average particle size of the natural carbon fillers.

[00280] Compounding and Filament Extrusion

[00281] A Haake Rheocord batch mixer was utlized to melt-mix the composite formulations. In this method, HDPE was melt-mixed with the natural carbons at 100 rpm for 5 min at 195 °C. Subsequently, the resulting composites were ground using a Retsch SM 100 cutting mill. Composites produced from the batch process were used to create filament for FDM lab-scale 3D-printing experimentation. The pelletized composite formulations were extruded into 1 .75 mm and 2.85 mm filaments using a Filabot EX2 single screw extruder and a 3devo extruder.

[00282] Printing Trails

[00283] Bench- scale Flashforge Creator Pro FDM printer was used to 3D-print the test specimens for all composite formulations. Test specimens included tensile, compression, flexural, and impact samples following ASTM D638, D695, D790, D256, respectively. All test specimens were 3D-printed using the printing parameters summarized in Table 2.

[00284] Table 2: 3D-printing parameters for NCPC, CFC, and WPC formulations.

[00285] Tensile Testing

[00286] 3D-printed type IV tensile samples were tested as per ASTM D638. Testing was conducted using an Instron 5966 at a crosshead speed of 5 mm/min. Strain values were recorded using a clip-on 1-inch extensometer, and the load was applied until the point of fracture was reached. A minimum of six samples were tested, and average tensile strength and tensile moduli were reported.

[00287] Compression Testing

[00288] 3D-printed compression samples were tested as per ASTM D695. The dimensions of the compression samples were 12.7 x 12.7 x 50.8 mm rectangular prisms. The testing was conducted using an Instron 5966 at a crosshead speed of 1.3 mm/min. A minimum of six samples were tested, and average compression yield strength and modulus values were reported. [00289] Flexural Testing

[00290] 3D-printed flexural samples were tested in accordance with ASTM D790. The dimensions for the flexural samples were 100 mm in length, 12.7 mm in width, and 3.2 mm thick. Three-point bending tests were conducted using Instron 5966.

[00291] Impact Testing

[00292] Izod impact resistance tests were conducted as per ASTM D256. The dimensions of impact samples were 63.5 mm in length, 12.7 mm in width, and 3.2 mm thick. Testing was conducted using Instron CEAST 9050 impact tester. Samples were notched using an Instron CEAST 9000 manual notching machine to have a width of 10.16 mm. A minimum of six samples were tested, and average impact resistance values were reported.

[00293] Tensile Properties of NCPC Materials

[00294] Tensile properties including ultimate tensile strength (UTS) and modulus of elasticity (MOE) of the NCPC formulations, WPC formulations, and unfilled HDPE are shown in FIG. 43. Results indicated that all NCPC formulations possessed lower UTS compared to the unfilled HDPE, except for the NCPC formulations with 15 wt. % Keystone 325, 15 wt.% Keystone 121, 60 wt.% CFoam Green, and 15 wt.% CFoam Calcined. Contrary to expectations, at the higher filler content (i.e., 40-60 wt. %), the UTS values were not significantly different for some of the NCPC formulations. This behavior could be primarily attributed to porosity and weak inter-layer bonds dominating the failure mechanism. MOE values for the NCPC formulations were higher than the unfilled HDPE. However, the change in MOE varied, often resulting in minimal increases or changes that were not statistically significant, except for the 60 and 70 wt. % formulations. In comparison to WPC, NCPC formulations exhibited higher UTS except at 15 wt.% CFoam Green. Furthermore, the MOE values for the WPC formulations were higher than the NCPC formulations at the respective weight loading expect for the CFoam Calcined formulations and all 60 wt.% NCPC formations. At the lower carbon content (i.e., 15 wt. %), the NCPC formulations exhibited higher or comparable UTS and MOE values than the CFC. However, at higher filler content, CFC materials demonstrated superior tensile performance. Furthermore, NCPC formulations filled with CFoam Calcined possessed higher UTS and MOE compared to unfilled HDPE and NCPC formulations filled with Keystone 325, Keystone 121, and CFoam Green expect for the UTS at 60 wt.% Keystone 121 and CFoam Green. The 70 wt.% NCPC formulations decreased in UTS and increased in MOE compared to the 60 wt.% formulations expect for the MOE for the CFoam Green formulations where there was a slight decrease of 1.2 GPa to 1.0 GPa. That can be due to the inclusion of stiffer particles in the polymer matrix making the 70 wt.% formulations stiffer. The decrease in tensile strength can be attributed to weak interfacial bonding between the coal and HDPE, weak inter-layer bonds between the 3D-printed layers, or porosity from the 3D-printing process.

[00295] The rise in MOE with increasing filler content is attributed to the incorporation of stiffer coal particles and limited polymer chain mobility. The reduction in UTS with increased filler content may be primarily due to weak interfacial bonding between the composite constituents, filler agglomeration, and porosity. While all these factors are present in the material, it is believed that the porosity introduced by the printing process and the poor adhesion between the printing layers was the predominant factor influencing this reduction. Although the composite formulations typically followed the trend with the incorporation and inclusion of additives, there are still some formulations that are discrepancies in those trends. For example, the increase in UTS from 50 to 60 wt.% Keystone 121. These deviations may result from process-related variations during 3D printing, such as fluctuations in extrusion stability, temperature gradients, or cooling rates, which can influence layer bonding and internal defect formation.

[00296] Compression Properties of NCPC Materials

[00297] The compression data for the NCPC, WPC, and CFC formulations compared to unfilled HDPE is shown in FIG. 44. The Keystone 325 formulations had varying results for the compressive properties as the coal content increased. For the 40-50 wt.% formulations, both strength and modulus decreased; however, from 50 to 60 wt.%, they increased before declining again at 70 wt.% loading. For NCPC formulations containing 15 to 70 wt.% Keystone 121, the modulus increased, as expected, due to the incorporation of stiff filler particles that enhance the overall rigidity of the polymer matrix. The compressive yield strength for the Keystone 121 formulations decreased from 15 to 50 wt.% but increased to 14.2 MPa at 60 wt.% and 19.2 MPa at 70 wt.%. NCPC formulations with Keystone 325 coal had higher compressive yield strength and compressive modulus values compared to the Keystone 121 formulations at 40-60 wt.% filler. NCPC formulations filled with CFoam Green exhibited a similar trend to the Keystone 325 formulations, with yield strength initially increasing and then decreasing as filler content increased. However, the Keystone 325 formulations consistently demonstrated superior strength values across the 15-60 wt.% range. NCPC formulations with CFoam Calcined filler had superior compressive modulus values compared to the other NCPC formulation, except for 70 wt.% Keystone 121. The WPC formulations had the lowest compressive properties compared to the NCPC formulations, except for modulus for the NCPC formulations with 15 wt.% Keystone 325 and CFoam Green filler. The carbon fiber composite with 15 wt.% filler had the highest compressive properties compared to all the other formulations tested, but the 40 wt.% properties were comparable to the 40 wt.% NCPC properties. Discrepancies in the data can be attributed to variations in porosity levels within the formulations and insufficient adhesion between the 3D- printed layers. Variability in compressive properties upon incorporation of reinforcements into the polymer matrix has been observed in comparing neat PETG with PETG-based composites reinforced with carbon fiber and Kevlar fiber. Additionally, decreasing trends in compressive properties with increasing filler loading have been reported in other material systems, such as PLA-based particulate-filled composites and polymer/cement composite slurries, where higher filler contents tend to promote agglomeration and weaken the matrix-filler interface. The results for the 10% carbon fiber volume fraction yielded a proportional limit stress of 30.0-40.5 MPa and compressive stress of 1.0-1.7 GPa depending on the 3D-printing orientation. The highest compressive results gave a proportional limit stress of 53.3 MPa and a compressive modulus of 2.1 GPa by having a 24.4% carbon fiber volume fraction and an equidistant concentric printing orientation. The graphite reinforced PLA gave superior results compared to neat PLA and had a compressive strength value of 38.6 MPa. Overall, the compressive yield strength of the NCPC materials was higher than their tensile strength. This behavior can be attributed to the closure of interlayer porosity within the 3D-printed structure under compressive loading, which densifies the material and enables it to withstand higher loads.

[00298] One of the targeted applications for this research is additive housing construction. To assess the suitability of the NCPC materials for such applications, it is essential to compare their mechanical performance to that of conventional construction materials, such as concrete. According to ASTM C387, which specifies requirements for packaged, dry, combined materials for concrete and high-strength mortar, the compressive strength of concrete typically ranges from 17.0 to 35.0 MPa, depending on the concrete type and curing time. Similarly, EN 206:2013,

Concrete — Specification, Performance, Production and Conformity, states that normal- to heavy-weight concrete should exhibit compressive strengths between 8 and 115 MPa, while lightweight concrete typically ranges from 8 to 88 MPa, depending on the concrete class. In addition, ASTM C62, which specifies requirements for building brick, establishes a minimum average compressive strength of 17.2 MPa. Some of the NCPC formulations do fall within those requirements by having compressive yield strengths ranging from 11.6-21.4 MPa depending on the weight loading and filler type.

[00299] Flexural Properties of NCPC Materials

[00300] Flexural properties including flexural strength (FS) and flexural modulus (FM) for the NCPC materials, unfilled HDPE, CFC, and WPC formulations are shown in FIGS. 47, 48, and 49. FS for the NCPC/Keystone 325 formulations initially increased with filler content up to 40 wt. % and then decreased at the higher coal loadings (50-60 wt. %) but did increase at 70 wt.% formulation. Unlike the NCPC/Keystone 325 formulations, NCPC/Keystone 121 formulations possessed FS values lower than unfilled HDPE. FM for the NCPC/Keystone 325 formulations exhibited direct proportionality with coal content, while possessing higher FM compared to NCPC/Keystone 121. Additionally, the FM for both 70 wt.% Keystone 325 and Keystone 121 formulations increased compared to the 60 wt.% formulations due to stiffer coal particles being incorporated in the polymer matrix. The flexural strength also increased from 60 wt.% to 70 wt.% for both Keystone 325 and Keystone 121 NCPC formulations. These results suggest that the NCPC/Keystone 325 formulations outperformed the NCPC/Keystone 121 under flexural loading. The superior performance of the NCPC/Keystone 325 formulations under flexural loading can be attributed to the smaller coal particles of Keystone 325 compared to Keystone 121. Smaller particles in the polymer matrix require higher stress to debond and pull out, enhancing the composite material's overall strength and durability. The CFoam Calcined formulations had superior FS compared to the CFoam Green formulations at 15 and 70 wt.% filler and had overall higher FM values. The CFoam Calcined formulations also had superior FS compared to the Keystone 325 formulations except at 40 wt.% and had overall superior FM values compared to Keystone 325. In comparison to WPC formulations, Keystone 325, CFoam Green, and CFoam Calcined formulations demonstrated superior FS and FM values. At the lower carbon content (i.e., 15-40 wt. %), the NCPC formulations exhibited lower FS and FM values in comparison to CFCs. However, at 50 wt. % carbon content, FS values were comparable, but the FM of the CFC was significantly higher. The reduction in FS was attributed to the weak interfacial bonds between the polymer matrix and the coal particles. Since one of the targeted applications for this research is additive manufacturing for housing and construction, it is important to evaluate the performance of the NCPC materials relative to conventional materials used in these applications, such as concrete. According to ASTM C1782, the standard specification for segmental concrete paving slabs, the required modulus of rupture (i.e., flexural strength) is 5.0 MPa. All NCPC formulations developed in this study, across the full range of weight loadings (15-70 wt.%), exceeded this threshold.

[00301] Impact Testing

[00302] Izod impact resistance values for the NCPC formulations, unfilled HDPE, CFC, and WPC are shown in FIG. 46. Increasing the filler content has been shown to decrease impact resistance. At the lower coal content (i.e., 15 wt. % & 40 wt. %), NCPC/Keystone 325 formulations possessed higher impact resistance compared to NCPC/Keystone 121 . However, at higher filler content (50, 60, and 70 wt. %), the NCPC/Keystone 121 exhibited higher impact resistance values. This behavior could be attributed to particle size differences; with increased filler content, the finer particles in NCPC/Keystone 325 composites become harder to disperse/wet out, resulting in the formation of pathways for crack propagation. This adversely affects the composite's impact resistance. Out of the NCPC formulations, the CFoam Calcined filler exhibited the highest impact resistance. Compared to the WPC formulations, NCPC materials with Keystone 325 and Keystone 121 coals demonstrated lower impact resistance. This was attributed to the wood fillers possessing a higher aspect ratio, which contributes to a more effective stress distribution upon impact, thereby improving the material's ability to absorb and dissipate energy more efficiently than the smaller and less elongated coal particles. The CFC formulations possessed the highest impact resistance values compared to the other composite formulations.

[00303] Example

[00304] Large-scale AM Trials

[00305] Two NCPC formulations were successfully printed using the large-scale FGF printer. The first formulation was the HDPE-based formulation with 70 wt.% Keystone 325 coal. Representative results from the printing trials are shown in FIGS. 47 A, 47B, 48 A, 48B, and 49, and the corresponding printing parameters are provided in Table 1, below. Following the successful printing trials, a wind turbine blade tooling prototype was fabricated using the NCPC formulation containing 70 wt.% coal (FIG. 50).

[00306] Table 1: Successful HDPE-based parameters for large-scale FGF 3D-printing. [00307] The second formulation that was investigated using FGF technology was a PETG- based formulation with 55 wt.% Keystone 325 coal. The optimized printing parameters can be found in Table 2 (below) and the printing trials can be found in FIGS. , 51 A, 5 IB, 52A, 52B, and 53 for the formulation.

[00308] Table 1: Successful PETG-based parameters for large-scale FGF 3D-printing.

[00309] Due to the success, a 1-m tall wind turbine blade tooling and wall design were successfully 3D-printed from the NCPC formulation. Those parts are shown in FIGS. 54 and 55. [00310] FIGS. 52A and 52B arc photographs showing a positive overhang test and a negative overhang test, respectively, for the 55 wt.% Keyston 325 - PETG formulation. FIG. 53 is a bridge test for the 55 wt.% Keyston 325 - PETG formulation. FIGS. 54 and 55 are photos of a wind turbine tooling and a wall design, respectively for the 55 wt.% Keyston 325 - PETG formulation.

[00311] Example

[00312] Material flow (i.e., HDPE-based with 70 wt.% coal, 1.5 wt.% lubricant) from a 4 mm nozzle is shown in FIG. 56. The material flow was according to the following table.

[00313] Table: Material flow rate from a 4.0 mm nozzle.

[00314] Additional photos of material tests are shown in FIGS.57, 58, 59, 60, 61, 62A, 62B, 63A, 63B, 64A, 64B, and 65. A hexagonal test print with 8 inch square sides is shown in FIG. 57. A negative overhang test with a 2 mm nozzle is shown in FIG. 58. A positive overhang test with a 2 mm nozzle is shown in FIG. 59. A negative overhang test with a 4 mm nozzle is shown in FIG. 60. A positive overhang test with a 4 mm nozzle is shown in Fig. 61. A bridge test for a 2 mm nozzle is shown in Figs. 62A and 62B. The bridged gap and sag are found in the table below.

[00315] Table: bridged gap and sag for 2 mm nozzle

[00316] A bridge test for a 4 mm nozzle is shown in Figs. 63A and 63B. The bridged gap and sag are found in the table below.

[00317] Table: bridged gap and sag for 4 mm nozzle

[00318] A negative overhang test with a 6 mm nozzle is shown in FIG. 64A. A positive overhang test with a 6 mm nozzle is shown in FIG. 64B. A bridge test for a 6 mm nozzle is shown in Fig. 65. The bridged gap and sag are found in the table below.

[00319] Table: bridged gap and sag for 6 mm nozzle

[00320] A summary of printing parameters for each of the 2.0, 4.0, and 6.0 mm nozzles is tabulated below.

[00321] While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in some detail, it is not the intention of the inventors to restrict or in any way limit the scope of the appended claims to such detail. Thus, additional advantages and modifications will readily appear to those of ordinary skill in the art. The various features of the invention may be used alone or in any combination depending on the needs and preferences of the user.

[00322] WHAT IS CLAIMED IS :

Claims

1. An natural carbon (NC)-enhanced composite material comprising: a natural carbon, wherein the natural carbon comprises between 50 wt.% to 90 wt.% by weight of the NC-enhanced composite material; and a thermoplastic resin, wherein the thermoplastic resin comprises between 10 wt.% to 50 wt. % of the NC-enhanced composite material, wherein the NC-enhanced composite material comprises a material selected from the group consisting of an NC-enhanced filament, an NC-enhanced pellet, an NC-enhanced 3D- printed composite material, and a carbonized NC-enhanced 3D-printed material.

2. The NC-enhanced composite material of claim 1, wherein the natural carbon comprises between 55 wt.% to 90 wt.% by weight of the NC-enhanced composite material, the NC- enhanced composite material further comprising: a lubricant, wherein the lubricant comprises between 1 wt.% by 5 wt.% by weight of the NC-enhanced composite material.

3. The NC-enhanced composite material of claim 2, wherein the lubricant comprises between 1 wt.% and between 1.5 wt.% by weight of the NC-enhanced composite material.

4. The NC-enhanced composite material of any preceding claim, further comprising: an additive, wherein the additive comprises between 1% and between 20 wt.% by weight of the NC-enhanced composite material.

5. The NC-enhanced composite material of claim 4, wherein the additive comprises a material selected from the group consisting of a process aid, a binder, a chemical foaming agent, an anti-foaming agent, and a combination thereof.

6. The NC-enhanced composite material of claim 4 or claim 5, wherein the additive comprises a material selected from the group consisting of a fiber, an additional filler, a coupling agent, a thermoset resin, a crosslinking agent, a metal, inorganic material, and a combination thereof.

7. The NC-enhanced composite material of any preceding claim, wherein the natural carbon comprises a material selected from the group consisting of coal, reclaimed coal waste, coal- derived carbons, and a combination thereof.

8. The NC-enhanced composite material of any preceding claim, wherein the thermoplastic material comprises a material selected from the group consisting of PLA, PETG, HDPE, PA 12, and a combination thereof.

9. The NC-enhanced composite material of claim 8, wherein the thermoplastic material comprises HDPE.

10. The NC-enhanced composite material of claim 9, wherein the natural carbon comprises between 80 wt.% and 90 wt.% by weight of the NC-enhanced composite material.

11 . The NC-enhanced composite material of any preceding claim, wherein the NC-enhanced material is an NC-enhanced filament or NC-enhanced pellets.

12. The NC-enhanced composite material of any preceding claim, wherein the NC-enhanced material is an NC-enhanced 3D-printed composite material.

13. The NC-enhanced composite material of any preceding claim, wherein the NC-enhanced material is a carbonized NC-enhanced 3D-printed composite material.

14. A natural carbon (NC)-enhanced composite material comprising: a natural carbon, wherein the natural carbon comprises between 50 wt.% to 90 wt.% by weight of the NC-enhanced composite material; and a thermoset resin, wherein the thermoset resin comprises between 10 wt.% to 50 wt. % of the NC-enhanced composite material, wherein the NC-enhanced composite material comprises a material selected from the group consisting of an NC-enhanced composite slurry, an NC-enhanced printed composite material, a crosslinked NC-enhanced printed composite material, and a carbonized NC-enhanced printed composite material.

15. The NC-enhanced composite material of claim 14 further comprising: an additive, wherein the additive comprises between 1% and between 20 wt.% by weight of the NC-enhanced composite material.

16. The NC-enhanced composite material of claim 15, wherein the additive comprises a material selected from the group consisting of a process aid, a binder, a chemical foaming agent, an anti-foaming agent, and a combination thereof.

17. The NC-enhanced composite material of claim 14 or claim 15, wherein the additive comprises a material selected from the group consisting of a fiber, an additional filler, a coupling agent, a thermoplastic resin, a crosslinking agent, a shear-thickening agent, a shear-thinning agent, shear, a metal, inorganic material, and a combination thereof.

18. The NC-enhanced composite material of any of claims 14-17, wherein the natural carbon comprises a material selected from the group consisting of coal, reclaimed coal waste, coal- derived carbons, and a combination thereof.

19. The NC-enhanced composite material of any of claims 14-18, wherein the thermoset resins comprises a material selected from the group consisting of epoxy resin, polyester, a phenolic resin, a bismaleimide resin, and a combination thereof.

20. The NC-enhanced composite material of any of claims 14-19, wherein the natural carbon comprises between 80 wt.% and 90 wt.% by weight of the NC-enhanced composite material.

21. The NC-enhanced composite material of any of claims 14-20, wherein the NC-enhanced material is an NC-enhanced composite slurry.

22. The NC-enhanced composite material of any of claims 14-20, wherein the NC-enhanced material is an NC-enhanced 3D-printed composite material.

23. The NC-enhanced composite material of any of claims 14-20, wherein the NC-enhanced material is a crosslinked NC-enhanced 3D-printed composite material.

24. The NC-enhanced composite material of any of claims 14-20, wherein the NC-enhanced material is a carbonized NC-enhanced 3D-printed composite material.

25. A method of manufacturing an natural carbon (NC)-enhanced composite material selected from the list consisting of an NC-enhanced filament, an NC-enhanced pellet, an NC- enhanced 3D-printed composite material, and a carbonized NC-enhanced 3D-printed material, the method comprising: melt mixing an NC material and a thermoplastic resin to form an NC-enhanced composite material formulation; and extruding the NC-enhanced material formulation as a material selected from the group consisting of an NC-enhanced filament and an NC-enhanced pellet.

26. The method of claim 25, further comprising cooling the NC-enhanced filament or the NC-enhanced pellet.

27. The method of claim 25 or claim 26, wherein extruding the NC-enhanced material formulation comprises extruding an NC enhanced pellet, the method further comprising: additively manufacturing an NC-enhanced 3D-printed composite material using the NC- enhanced pellet as an input.

28. The method of claim 27, wherein additively manufacturing the NC-enhanced 3D-printed composite material comprises FGF additive manufacturing.

29. The method of any of claims 25-28, further comprising: carbonizing the NC-enhanced 3D-printed composite material in an inert atmosphere to produce a carbonized NC-enhanced 3D-printed composite material.

30. The method of any of claims 25-29, wherein extruding the NC-enhanced material formulation comprises extruding an NC enhanced filament, the method further comprising: spooling the NC-enhanced filament.

31. The method of any of claims 25-28, wherein extruding the NC-enhanced material formulation comprises extruding an NC enhanced filament, the method further comprising: additively manufacturing an NC-enhanced 3D-printed composite material using the NC- enhanced filament as an input.

32. The method of claim 31 , wherein additively manufacturing the NC-enhanced 3D-printed composite material comprises FDM additive manufacturing.

33. The method of claim 32, further comprising: carbonizing the NC-enhanced 3D-printed composite material in an inert atmosphere to produce a carbonized NC-enhanced 3D-printed composite material.

34. The method of any of claims 25-33, further comprising: adding at least one additive to the NC-enhanced composite material formulation prior to melt mixing.

35. A method of manufacturing a natural carbon (NC)-enhanced composite material selected from the list consisting of an NC-enhanced composite slurry, an NC-enhanced 3D-printed composite material, a crosslinked NC-enhanced 3D-printed composite material, and a carbonized NC-enhanced 3D-printed composite material, the method comprising: mixing an NC material and a thermoset resin to form an NC-enhanced composite slurry; and degassing the NC-enhanced composite slurry.

36. The method of claim 35, further comprising: adding at least one additive to the NC material or the thermoset resin prior to mixing.

37. The method of claim 35 or claim 36, further comprising: additively manufacturing an NC-enhanced 3D-printed composite material using the NC- enhanced slurry as an input.

38. The method of any one of claims 35-37, further comprising: crosslinking the NC-enhanced 3D-printed composite material using the NC-enhanced 3D-printed composite material as an input and an external heat source.

39. The method of claim 35 or claim 36, further comprising: additively manufacturing a crosslinked NC-enhanced 3D-printed composite material using the NC-enhanced slurry as an input, wherein additively manufacturing comprises using a heated print head to crosslink the NC-enhanced composite slurry during the additively manufacturing step.