WO2022082136A1 - Processes for making 3-d objects from blends of polyethylene and semi-amorphous polymers - Google Patents

Abstract

This invention relates to a process for making a three-dimensional object using an additive manufacturing process. A blend can be prepared that can include polyethylene and a semi-amorphous polymer having at least 60 wt% propylene-derived units and from 5 to 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g. The blend can be extruded to make a filament. The filament can be inserted into an additive manufacturing apparatus that can have a nozzle. The filament can be heated. A fluid bead of the filament can be dispensed out of the nozzle to manufacture a three-dimensional object.

Description

Processes for Making 3-D Objects from Blends of Polyethylene and Semi- Amorphous

Polymers

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application 63/090876 filed October 13, 2020, entitled “Processes for Making 3-D Objects from Blends of Polyethylene and Semi-Amorphous Polymers,” the entirety of which is incorporated by reference herein.

FIELD

[0002] This invention relates to additive manufacturing. More particularly, this invention relates to using an additive manufacturing process such as fused filament fabrication to make 3-D objects from blends of polyethylene and semi-amorphous polymers.

BACKGROUND

[0002] Traditional manufacturing processes, known as “subtractive manufacturing”, use material that are carved or shaped into a desired product by parts of the material being removed in a variety of ways. Additive manufacturing, also known as 3-D printing, was created to do the opposite. In additive manufacturing, a 3-D object is made by successively adding material layer-by-layer to produce a product having a predetermined geometry. The design of the 3-D object is typically made and controlled by a computer. A computer-aided design (CAD) software program is typically used to relay messages to a 3-D printer so that it “prints” in the desired shape.

[0003] The benefits of this more modem technology are that new products can be made with massive customization, improved material utilization, and a greater range of designs. Designs that cannot be manufactured in one entire piece with traditional means can easily be achieved using additive manufacturing. For example, shapes with a scooped out or hollow center can be produced as a single piece, without the need to weld or attach individual components together. Due to such benefits, additive manufacturing has found application in, for example, the plastics, construction, and automotive industries.

[0004] Because of its relative simplicity, the additive manufacturing process known as fused filament fabrication (FFF) is widely used for the production of plastics. In FFF, filaments of a thermoplastic are melted or extruded through a hot end of a nozzle and deposited as layers that harden and build up to form the desired 3-D object. Currently, two commercially available thermoplastics (i.e., acrylonitrile-butadiene-styrene (ABS) and polylactic acid (PLA)) and three engineering thermoplastics (i.e., polycarbonate (PC), poly(ether imide) (PEI), and polyether ether ketone (PEEK)) are primarily used for FFF due to their availability and ability to form products with adequate mechanical properties and dimensional accuracy. One drawback for using such specialty polymers is their high cost.

[0005] Ideally, low cost commodity thermoplastics could be used in additive manufacturing via FFF. However, there are challenges that arise from the nature of the FFF process with using commodity thermoplastics, particularly polyolefins. For example, degradation of mechanical properties of the final product can occur as a result of internal interfaces between the layers of deposited polymer. Also, the final product can experience warpage due to crystallization induced stresses caused by thermal expansion.

[0006] A need therefore exists for a thermoplastic that is suitable for use in additive manufacturing, particularly FFF, and can be used to produce products having adequate mechanical properties and less warpage.

[0007] Additional references of interest may include: CN103980395B, CN103980396A, JP2018035461A, JP2019203228A, WO 2002/034795, W02007/018871, WO2013/083285, W02013/078018, and WO2019/197582.

SUMMARY OF INVENTION

[0008] A process for making an obj ect using an additive manufacturing process is provided herein. In some examples, a blend can be prepared that can include polyethylene and a semi- amorphous polymer having at least 60 wt% propylene-derived units and from 5 to 25 wt% ethylene-derived units, based on a total weight of the semi -amorphous polymer, and having a heat of fusion of less than about 80 J/g. The blend can be extruded to make a filament. The filament can be inserted into an additive manufacturing apparatus that can have a nozzle. The filament can be heated. A fluid bead of the filament can be dispensed out of the nozzle to manufacture a three-dimensional object.

[0009] A process for making a filament is also provided herein. In some examples, a blend can be prepared that can include polyethylene and a semi-amorphous polymer having at least 60 wt% propylene-derived units and from 5 to 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g. The blend can be extruded to make a filament where the filament has a diameter from 0.01 mm to 1 m. The filament can be collected on a spool.

[0010] A filament is also provided herein. The filament can include a blend of polyethylene and a semi-amorphous polymer having at least 60 wt% propylene-derived units and from 5 to 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g. The filament can have a diameter from about 1 mm to about 3 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figures 1a and 1b depict AFM images at different resolutions (as indicated by the legends therein) showing heterogeneous morphology of the 3D printed part. The AFM of Figures 1a and 1b was conducted on cross section (TD).

[0012] Figures 2a and 2b likewise depict AFM images at differing resolutions as indicated by the legends therein, each conducted on an internal surface parallel to the layering of 3D printing (MD).

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0013] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, and/or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the Figures. Moreover, the exemplary embodiments presented below can be combined in any combination of ways, i.e., any element from one exemplary embodiment can be used in any other exemplary embodiment, without departing from the scope of the disclosure.

[0014] For purposes of this invention and the claims thereto, a “catalyst system” is a combination of at least one catalyst compound, an activator, and a support material. The catalyst systems may further comprise one or more additional catalyst compounds. The terms “mixed catalyst system”, “dual catalyst system”, “mixed catalyst” are used to indicate two or more catalyst compounds in the catalyst system. The term “supported catalyst system” may be used interchangeably herein with “catalyst system.” For the purposes of this invention and the claims thereto, when catalyst systems are described as comprising neutral stable forms of the components, it is well understood by one of ordinary skill in the art, that the ionic form of the component is the form that reacts with the monomers to produce polymers.

[0015] The term “complex” is used to describe molecules in which an ancillary ligand is coordinated to a central transition metal atom. The ligand is bulky and stably bonded to the transition metal so as to maintain its influence during use of the catalyst, such as polymerization. The ligand may be coordinated to the transition metal by covalent bond and/or electron donation coordination or intermediate bonds. The transition metal complexes are generally subjected to activation to perform their polymerization function using an activator which is believed to create a cation as a result of the removal of an anionic group, often referred to as a leaving group, from the transition metal. "Complex," as used herein, is also often referred to as "catalyst precursor", "pre-catalyst", "catalyst", "catalyst compound", "metal compound", "transition metal compound", or "transition metal complex". These words are used interchangeably. “Activator” and “cocatalyst” are also used interchangeably.

[0016] The terms "hydrocarbyl radical," "hydrocarbyl" and "hydrocarbyl group" are used interchangeably throughout this document. Likewise the terms "group", "radical", and "substituent" are also used interchangeably in this document. For purposes of this invention, "hydrocarbyl radical" is defined to be C₁-C₁₀₀ radicals, that may be linear, branched, or cyclic, and when cyclic, aromatic or non-aromatic.

[0017] For purposes of this invention and claims thereto, unless otherwise indicated (e.g., the definition of "substituted hydrocarbyl" etc.), the term “substituted” means that a hydrogen group has been replaced with at least one non-hydrogen group, such as a hydrocarbyl group, a heteroatom, or a heteroatom containing group. For example, substituted hydrocarbyl radicals can be radicals in which at least one hydrogen atom of the hydrocarbyl radical has been substituted with at least one functional group, such as halogen (such as Br, Cl, F or I) or at least one functional group such as -NR*₂, -OR*, -SeR*, -TeR*, -PR*₂, -AsR*₂, -SbR*₂,-SR*, -

BR*₂, -SiR*₃, -GeR*₃, -SnR*₃, -PbR*₃, -(CH₂)q-SiR*₃, and the like, where q is 1 to 10 and each R* is independently hydrogen, a hydrocarbyl or halocarbyl radical, and two or more R* may join together to form a substituted or unsubstituted completely saturated, partially unsaturated, or aromatic cyclic or polycyclic ring structure), or where at least one heteroatom has been inserted within a hydrocarbyl ring.

[0018] The term "substituted hydrocarbyl" means a hydrocarbyl radical in which at least one hydrogen atom of the hydrocarbyl radical has been substituted with at least one heteroatom (such as halogen, e.g., Br, Cl, F or I) or heteroatom-containing group (such as a functional group, e.g., -NR*₂, -OR*, -SeR*, -TeR*, -PR*₂, -AsR*₂, -SbR*₂, -SR*, -BR*₂, -SiR*₃, -

GeR*₃, -SnR*₃, -PbR*₃, -(CH₂)q-SiR*₃, and the like, where q is 1 to 10 and each R* is independently hydrogen, a hydrocarbyl or halocarbyl radical, and two or more R* may join together to form a substituted or unsubstituted completely saturated, partially unsaturated, or aromatic cyclic or polycyclic ring structure), or where at least one heteroatom has been inserted within a hydrocarbyl ring.

[0019] The term "ring atom" means an atom that is part of a cyclic ring structure. By this definition, a benzyl group has six ring atoms and tetrahydrofuran has 5 ring atoms.

[0020] A "ring carbon atom" is a carbon atom that is part of a cyclic ring structure. By this definition, a benzyl group has six ring carbon atoms and para-methylstyrene also has six ring carbon atoms.

[0021] The term "aryl" or "aryl group" means a six carbon aromatic ring, including but not limited to, phenyl, 2-methyl-phenyl, xylyl, 4-bromo-xylyl. Likewise, heteroaryl means an aryl group where a ring carbon atom (or two or three ring carbon atoms) has been replaced with a heteroatom, preferably, N, O, or S. A substituted aryl group is an aryl group having 1 or more hydrogen groups replaced by a hydrocarbyl, substituted hydrocarbyl, heteroatom or heteroatom containing group.

[0022] A "heterocyclic ring" is a ring having a heteroatom in the ring structure as opposed to a heteroatom substituted ring where a hydrogen on a ring atom is replaced with a heteroatom. For example, tetrahydrofuran is a heterocyclic ring and 4-N,N-dimethylamino-phenyl is a heteroatom substituted ring.

[0023] As used herein the term "aromatic" also refers to pseudoaromatic heterocycles which are heterocyclic substituents that have similar properties and structures (nearly planar) to aromatic heterocyclic ligands, but are not by definition aromatic. The term "substituted aromatic," means an aromatic group having 1 or more hydrogen groups replaced by a hydrocarbyl, substituted hydrocarbyl, heteroatom or heteroatom containing group.

[0024] The term "continuous" means a system that operates without interruption or cessation. For example, a continuous process to produce a polymer would be one where the reactants are continually introduced into one or more reactors and polymer product is continually withdrawn.

[0025] As used herein, the numbering scheme for the Periodic Table groups is the new notation as set out in Chemical and Engineering News, v.63(5), pg.27, (1985).

[0026] An "olefin", is a linear, branched, or cyclic compound of carbon and hydrogen having at least one double bond. For purposes of this specification and the claims appended thereto, when a polymer or copolymer is referred to as comprising an olefin, the olefin present in such polymer or copolymer is the polymerized form of the olefin. For example, when a copolymer is said to have an "ethylene" content of 35 wt% to 55 wt%, it is understood that the mer unit in the copolymer is derived from ethylene in the polymerization reaction and said derived units are present at 35 wt% to 55 wt%, based upon the weight of the copolymer. A “polymer” has two or more of the same or different mer units. A “homopolymer” is a polymer having mer units that are the same. A “copolymer” is a polymer having two or more mer units that are different from each other. “Different” as used to refer to mer units indicates that the mer units differ from each other by at least one atom or are different isomerically. Accordingly, the definition of copolymer, as used herein, includes terpolymers and the like. An "ethylene polymer" or "ethylene copolymer" is a polymer or copolymer comprising at least 50 mol% ethylene derived units, a "propylene polymer" or "propylene copolymer" is a polymer or copolymer comprising at least 50 mol% propylene derived units, and so on.

[0027] A “random copolymer” is a polymer having individual repeating units of one of the monomers present in a random or statistical distribution in the polymer chain. A “propylene random copolymer” is a propylene polymer having repeating units of the ethylene monomer(s) present in a random or statistical distribution in the polymer chain.

[0028] As used herein, M_n is number average molecular weight, M_w is weight average molecular weight, and M_z is z average molecular weight, wt% is weight percent, and mol% is mole percent. Molecular weight distribution (MWD), also referred to as polydispersity index (PDI), is defined to be M_w divided by M_n. Unless otherwise noted, all molecular weights (e.g., M_w, M_n, M_z) are reported in units of g/mol.

[0029] As used herein, the term "polypropylene", "propylene polymer," or "PP" refers to homopolymers, copolymers, terpolymers, and interpolymers, typically comprising from 50 to 100 mol% propylene. Alternately the polypropylene comprises 50 to 100 weight % of propylene.

[0030] As used herein a "semi-amorphous polymer" is defined to be an olefin polymer having a heat of fusion of 80 J/g or less (as determined by DSC, described in test methods below). Preferably, the semi-amorphous polymer is a propylene copolymer having a heat of fusion of less than 80 J/g.

[0031] This invention relates to a novel 3D printing material which can include a blend of a polyethylene having a density of 0.94 g/cm³ or less and a semi-amorphous polymers that can include at least about 60 wt% propylene-derived units and from about 5 to about 25 wt% ethylene-derived units, based on total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g. [0032] It has been surprising and unexpectedly discovered that using an additive manufacturing process such as fused filament fabrication to make 3-D objects from blends of polyethylene, and in particular linear low density polyethylene (LLDPE) or low density polyethylene (LDPE), having a density of less than 0.94 g/cm³, and semi-amorphous polymers can have reduced shrinkage, reduced warpage, and are capable of forming a uniform diameter printing filament.

[0033] Typically, the polyethylene(s) are present in the blends or other compositions of the present invention at from 40 wt% to 99.9 wt% (based upon the weight of the polyethylene and the semi-amorphous polymer) in one embodiment, and from 50 wt% to 99 wt% in another embodiment, and in various other embodiments from a low of any of 60 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 90 wt% to a high of any of 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%, or 99.9 wt%, wherein a desirable range may be any combination of any upper wt% limit with any lower wt% limit described herein; and further noting that the wt% values reported herein are on the basis of polyethylene plus semi-amorphous polymer in the blend.

[0034] Thus, in some embodiments, the semi-amorphous polymer is present in the blend from a low of any of 0.1, 1, 2, 3, 4, or 5 wt%, to a high of any one of 10, 15, 20, 25, 30, or 40 wt%, wherein a desirable range may be any combination of any upper wt% limit with any lower wt% limit described herein (e.g., 0.1 wt% to 15 wt%, such as 1 wt% to 10 wt%, or 2 wt% to 15 wt%).

[0035] In one embodiment, the Mw of the semi-amorphous polymer is different from the Mw of the polyethylene. The blend used in the additive manufacturing process can have a bimodal molecular weight distribution. In one embodiment, the Mw of the semi-amorphous polymer is lower than the Mw of the polyethylene. Alternatively, the Mw of the semi- amorphous polymer is higher than the Mw of the polyethylene. A blend with bimodal molecular weight distribution can enhance shear thinning and thus improve the printing process and other characteristics. In one embodiment, the MWD of the blend is 4 or more, preferably 5 or more, more preferably 10 or more.

Semi-Amorphous Polymer

[0036] Described herein are compositions comprising semi-amorphous polymers that are suitable for the additive manufacturing process. The semi-amorphous polymers preferably have from 1 to 25 mole% (alternately from 2 to 20 mole%, alternately from 3 to 20 mole%, preferably from 3 to 20 mole%) of one or more of ethylene and/or C₄ to C₂₀ olefin comonomer (preferably ethylene and/or C₄ to C₁₂ alpha-olefin, more preferably ethylene, butene, hexene, octene, decene, dodecene, even more preferably ethylene, butene, hexene, octene), or are copolymers of propylene preferably having from 2 to 35 wt% (alternately from 5 to 32 wt%, alternately from 7 to 25 wt%) of one or more of C₂ or C₄ to C₂₀ olefin comonomer (preferably ethylene or C₄ to C₁₂ alpha-olefin, more preferably ethylene, butene, hexene, octene, decene, dodecene, even more preferably ethylene, butene, hexene, octene). Useful semi-amorphous polymers comprise one or more comonomers in addition to propylene and can be a random copolymer, a statistical copolymer, a block copolymer, and/or blends thereof. In particular, the semi-amorphous polymer described herein may be physical blends or in situ blends of more than one type of propylene copolymer. The method of making the semi-amorphous polymer is not critical, as it can be made by gas phase, slurry, and solution or other suitable processes, and by using catalyst systems appropriate for the polymerization of semi-amorphous polymers, such as Ziegler-Natta-type catalysts, metallocene-type catalysts, post metallocene and other appropriate catalyst systems or combinations thereof.

[0037] Preferably, the semi-amorphous polymers are copolymers of propylene having 5 to 35 wt% (alternately from 10 to 32 wt%, alternately from 11 to 25 wt%) of one, two, three, four, or more of ethylene, butene, hexene, octene, decene, dodecene, more preferably ethylene, butene, hexene, and octene.

[0038] In one or more embodiments, the semi-amorphous polymer has a weight average molecular weight (Mw) of 50,000 g/mol or more, or about 100,000 g/mol or more, or about 150,000 g/mol or more, or about 200,000 g/mol or more; a number average molecular weight (Mn) of 25,000 g/mol or more, 50,000 g/mole or more, 75,000 g/mole or more, 100,000 g/mole or more; an MWD (or PDI) in a range of 1.5 to 15, or 2.0 to 10, or 2.5 to 10. Molecular weight and its moments are determined using GPC-4D.

[0039] In one or more embodiments, the semi-amorphous polymer has a melt flow rate (MFR) of 800 g/10 min or less, or 600 g/10 min or less, or 400 g/10 min or less, or 200 g/10 min or less, or 100 g/10 min or less, or 80 g/10 min or less, or 60 g/10 min or less, or 30 g/10 min or less, or 10 g/10 min or less, or 5 g/10 min or less, or 3 g/10 min or less, or 1 g/10 min or less.

[0040] In one or more embodiments, the semi-amorphous polymer has a Brookfield viscosity of 500 mPa.sec or more, or 1000 mPa.sec or more, or 5000 mPa.sec or more, or 10000 mPa.sec or more, or 100000 mPa.sec or more. Brookfield viscosity is determined according to the procedure of ASTM D2983 at a temperature of 190 °C. [0041] In one or more embodiments, the semi -amorphous polymer has a melting temperature of 155 °C or less, 140 °C or less, 130 °C or less. In other embodiments, semi- amorphous polymer can have a melting point of at least 10°C, or at least 20°C, or at least 30°C, or at least 50°C, or at least 60°C. For example, the semi-amorphous polymer can have a melting point from at least 10°C to about 130°C. Alternatively, the semi-amorphous polymer has a melting temperature of 10°C or less, preferably 5°C or less. In alternative embodiments, the semi-amorphous polymer is amorphous without measurable melting temperature in DSC.

[0042] In one or more embodiments, the semi-amorphous polymer has a crystallization temperature of 130 °C or less, 120 °C or less, 110 °C or less. In other embodiments, the polymer produced herein can have a crystallization point of at least 0°C, or at least 10°C, or at least 15 °C, or at least 20°C, or at least 30°C. For example, the polymer can have a crystallization point from at least 0°C to about 130°C. In additional embodiments, the semi- amorphous polymer is amorphous without measurable crystallization temperature in DSC.

[0043] In alternative embodiments, the semi-amorphous polymer has a glass transition temperature of 5 °C or less, 0 °C or less, -5 °C or less.

[0044] In one or more embodiments, the semi-amorphous polymer has a heat of fusion of 80 J/g or less, 70 J/g or less, 60 J/g or less. In other embodiments, the polymer produced herein can have a heat of fusion of at least 5 J/g, or at least 10 J/g, or at least 15 J/g, or at least 20 J/g. For example, the polymer can have a heat of fusion from at least about 5 J/g to about 70 J/g. In alternative embodiments, the semi-amorphous polymer is amorphous without measurable crystallization peak and melting peaks in DSC.

[0045] In one or more embodiments, the semi-amorphous polymer has long chain branched architecture. The degree of long chain branched is measured by a branching index measured using GPC-4D. Preferably the branching index, g’_vis is 0.95 or less, or 0.90 or less.

[0046] In one or more embodiments, the semi-amorphous polymer has a propylene-derived crystallinity that is isotactic, syndiotactic, or a combination thereof. In a preferred embodiment, the semi-amorphous polymer has isotactic sequences. The presence of isotactic sequences can be determined by NMR measurements showing two or more adjacent propylene derived units arranged isotactically. Such isotactic sequences can, in some cases be interrupted by propylene units that are not isotactically arranged or by insertion of other monomers that otherwise disturb the crystallinity derived from the isotactic sequences. In addition to differences in tacticity, the semi-amorphous polymer can also have defect structures that are regio-specific. [0047] In some embodiments, the semi-amorphous polymer is a propylene-ethylene copolymer that has at least four, or at least five, or at least six, or at least seven, or at least eight, or all nine of the following properties (i) from about 8 to about 25 wt%, or from about 12 to about 20 wt%, or from about 14 wt% to about 18 wt% ethylene-derived units, based on the weight of the semi-amorphous polymer; (ii) a Tm of from 30 to about 110°C, or from about 40 to about 100°C, or from about 50 to about 90°C; (iii) aHf of less than about 80 J/g, or less than 70 J/g, or less than 40 J/g, or from about 1.0 to about 15 J/g or from about 3.0 to about 10 J/g; (iv) a melt index of from about 0.5 to about 10 g/10 min or from about 0.75 to about 8.0 g/10 min; (v) a MFR of from about 0.5 to about 100 g/10 min, or from 0.75 to about 80 g/10 min, or from about 0.75 to about 50 g/10 min; (vi) a Mw of from about 100,000 to about 300,000 g/mol, or from about 120,000 to about 250,000 g/mol, or from about 150,000 to about 250,000 g/mol, or from about 150,000 to about 240,000 g/mol; (vii) a Mn of from about 50,000 to about 200,000 g/mol, or from about 60,000 to about 150,000 g/mol, or from about 80,000 to about 120,000 g/mol; (viii) a MWD of from about 1.0 to about 5, or from about 1.5 to about 4, or from about 1.8 to about 3; and/or (ix) a Shore D hardness of less than 30, or less than 25, or less than 20.

[0048] In some embodiments, such a semi -amorphous polymer is a reactor-blended semi- amorphous polymer. In one embodiment, the semi-amorphous polymer is a blend of a propylene copolymer having an ethylene content of from about 10 wt% to 18 wt% and an MFR of from 1 to 5 g/10min and a propylene copolymer having ethylene content of from about 2 wt% to 8 wt% and an MFR of from 5 to 15 g/10min. Both propylene copolymers can be produced in a solution process with two reactors in parallel configuration.

[0049] Preferred semi-amorphous polymers can be produced in a solution process using a single-site catalyst. In any embodiment, a single-site catalyst useful in the process includes metallocene catalysts, salen catalysts, pyridyl diamide catalysts, and other single-site catalysts. Some of the catalysts are also referred as to non-metallocene catalysts. The term “non- metallocene catalyst,” also known as “post-metallocene catalyst” describe transition metal complexes that do not feature any pi-coordinated cyclopentadienyl anion donors (or the like) and are useful the polymerization of olefins when combined with common activators. The term catalyst and catalyst precursor are used interchangeably herein unless otherwise noted.

[0050] In a preferred embodiment, a continuous solution polymerization process is used to produce copolymers of propylene utilizing a metallocene catalyst, namely, dimethylsilylbis(indenyl)hafnium dimethyl in combination with dimethylaniliniumtetrakis(pentafluorophenyl) borate. Preferably the solution polymerization is conducted in a single, or optionally in two, continuous stirred tank reactors connected in series or parallel with isohexane used as the solvent. All feed can transferred to the first reactor or split between two reactors at a reaction temperature between about 50° C to about 220° C. Hydrogen gas may also be added to the reactors as a further molecular weight regulator.

[0051] Preferred semi-amorphous polymers may also be produced by the continuous solution polymerization process described in W02002/034795, which is incorporated by reference herein in its entirety.

[0052] Preferred semi-amorphous polymers include Vistamaxx™ 3000, Vistamaxx™ 3020/3020FL, Vistamaxx™ 3588, and Vistamaxx ™ 3980, and Vistamaxx™ 6102/6102FL, Vistamaxx™ 6502, all of which are commercially available from ExxonMobil Chemical Company in Houston, Texas.

Polyethylene

[0053] In some examples, the polyethylene can include ethylene homopolymers and ethylene copolymers. The polyethylene may comprise from 100 to about 80.0 wt%, 99.0 to 85.0 wt%, 99.0 to 87.5 wt%, 99.0 to 90.0 wt%, 99.0 to 92.5 wt%, 99.0 to 95.0 wt%, or 99.0 to 97.0 wt%, of polymer units derived from ethylene, 0 to about 20.0 wt%, 0.1 to about 20.0 wt% 1.0 to 15.0 wt%, 0.5 to 12.5 wt%, 1.0 to 10.0 wt%, 1.0 to 7.5 wt%, 1.0 to 5.0 wt%, or 1.0 to 3.0 wt% of polymer units derived from one or more C₃ to C₂₀ α-olefin comonomers, preferably C₃ to C₁₀ α-olefins, and more preferably C₄ to C₈ α-olefins, such as hexene and octene. The α-olefin comonomer may be linear or branched, and two or more comonomers may be used, if desired.

[0054] Examples of suitable comonomers include propylene, butene, 1 -pentene; 1 -pentene with one or more methyl, ethyl, or propyl substituents; 1 -hexene; 1 -hexene with one or more methyl, ethyl, or propyl substituents; 1 -heptene; 1 -heptene with one or more methyl, ethyl, or propyl substituents; 1 -octene; 1 -octene with one or more methyl, ethyl, or propyl substituents; 1 -nonene; 1 -nonene with one or more methyl, ethyl, or propyl substituents; ethyl, methyl, or dimethyl-substituted 1 -decene; 1 -dodecene; and styrene. Particularly suitable comonomers include 1 -butene, 1 -hexene, and 1 -octene, 1 -hexene, and mixtures thereof.

[0055] The polyethylene may have a melt index, I_2.16, according to the test method listed below, of ≥ about 0.10 g/10 min, e.g., ≥ about 0.15 g/10 min, ≥ about 0.18 g/10 min, ≥ about 0.20 g/10 min, ≥ about 0.22 g/10 min, ≥ about 0.25 g/10 min, ≥ about 0.28 g/10 min, or ≥ about 0.30 g/10 min and, also, a melt index ( I_2.16) ≤ about 3.00 g/10 min, e.g., ≤ about 2.00 g/10 min, ≤ about 1.00 g/10 min, ≤ about 0.70 g/10 min, ≤ about 0.50 g/10 min, ≤ about 0.40 g/10 min, or ≤ about 0.30 g/10 min. Ranges expressly disclosed include, but are not limited to, ranges formed by combinations any of the above-enumerated values, e.g., about 0.10 to about 0.30, about 0.15 to about 0.25, about 0.18 to about 0.22 g/10 min, etc. In another embodiment, the melt index could be about 0.1 g/10 min to about 30 g/10 min, such as about 20 g/10 min to about 30 g/10 min.

[0056] The polyethylene may have a high load melt index (HLMI) ( I_21.6) in accordance with the test method listed below of from 1 to 60 g/10 min, 5 to 40 g/10 min, 5 to 50 g/10 min, 15 to 50 g/10 min, or 20 to 50 g/10 min.

[0057] The polyethylene may have a melt index ratio (MIR), from 10 to 90, from 20 to 45, from 25 to 60, alternatively, from 30 to 55, alternatively, from 35 to 55, and alternatively, from 35 to 50 or 35 to 45. MIR is defined as I_21.6/ I_2.16.

[0058] The polyethylene may have a density of about 0.920 g/cm³, about 0.918 g/cm³ , or ≥ about 0.910 g/cm³, e.g., ≥ about 0.912 g/cm³, ≥ about 0.919 g/cm³, ≥ about 0.919 g/cm³ ≥ about 0.919 g/cm³, ≥ about 0.92 g/cm³, ≥ about 0.930 g/cm³, ≥ about 0.932 g/cm³. Additionally, the polyethylene may have a density ≤ about 0.950 g/cm³, e.g., ≤ about 0.945 g/cm³, ≤ about 0.940 g/cm³, ≤ about 0.937 g/cm³, ≤ about 0.935 g/cm³, ≤ about 0.933 g/cm³, or ≤ about 0.930 g/cm³. Ranges expressly disclosed include, but are not limited to, ranges formed by combinations any of the above-enumerated values, e.g., about 0.919 to about 0.945 g/cm³, 0.920 to 0.930 g/cm³, 0.925 to 0.935 g/cm³, 0.920 to 0.940 g/cm³, etc. Density is determined in accordance with the test method listed below.

[0059] The polyethylene may have a molecular weight distribution (MWD, defined as M_w/M_n) of about 1 to about 12, about 5 to about 10.5 or 11, about 2.5 to about 5.5.

[0060] More generally, the polyethylene can have one or more of the following properties: a) a density of from 0.890 g/cm³ to 0.950 g/cm³, such as from 0.910 to 0.945 or 0.940 g/cm³; b) MI of from 0.1 g/10 min to 30 g/10 min, such as 0.2 to 10, or 0.5 to 4 g/10 min; c) MIR of from 10 to 90; d) Mw of from 50,000 to 500,000 g/mol; such as from 60,000 to 200,000 g/mol; e) Mn of from 10,000 to 150,000 g/mol; such as from 15,000 to 100,000 g/mol; f) Mz of from 100,000 to 1,500,000 g/mol, such as from 125,000 to 750,000 or 1,000,000 g/mol; g) an M_w/M_n of from 2 to 12; h) an M_z/M_w of from 2.0 to 4.0 or 5.0; i) an M_z/M_n of from 10 to 40; and j) a g’(_vis) of at least 0.900, alternatively, at least 0.930, alternatively, at least 0.940, alternatively, at least 0.950, and alternatively, at least 0.994.

[0061] In various embodiments, the polyethylene has a unimodal or multimodal molecular weight distribution as determined by Gel Permeation Chromatography (GPC). By "unimodal" is meant that the GPC chromatograph has one peak or inflection point. By "multimodal" is meant that the GPC chromatograph has at least two peaks or inflection points. An inflection point is that point where the second derivative of the curve changes in sign (e.g., from negative to positive or vice versus).

[0062] In yet other embodiments, the polyethylene may have properties in accordance with (a) - (j) above, but have long chain branch architecture, with the level of branching is measured by the branching index (g’_vis) using GPC-4D. Thus, a lower value for g’_vis indicates higher level of branching. The value for g’_vis in such embodiments is preferably less than 0.98 or 0.95 or 0.92 or 0.90, or within a range of from 0.80 or 0.85 to 0.90 or 0.95 or 0.97. A polyethylene is “linear” when the ethylene polymer has no long chain branches, typically having a g'_vis of 0.98 or above.

[0063] The polyethylene preferably has a complex viscosity at a frequency of 0.1 rad/sec and a temperature of 190°C within the range of from 1,000 or 5,000 or 10,000 or 20,000, or 30,000 or 50,000 Pa.s to 60,000 or 80,000 or 100,000 or 200,000 or 1,000,000 Pa.s. The polyethylene preferably has a complex viscosity at a frequency of 100 rad/sec and a temperature of 190 °C within the range of from 50 or 100 or 200 or 500 Pa.s to 1,000 or 5,000 or 10,000 or 15,000 Pa.s.

[0064] In one or more embodiments, the polyethylene has significant shear induced viscosity thinning. Shear thinning is characterized by the decrease of the complex viscosity with increasing shear rate. One way to quantify the shear thinning is to use a ratio of complex viscosity at a frequency of 0.1 rad/s to the complex viscosity at a frequency of 100 rad/s. Preferably, the complex viscosity ratio of the ethylene polymer is 5 or more, more preferably 10 or more, even more preferably 15 or more when the complex viscosity is measured at 190°C using a small amplitude oscillatory shear (SAOS) using the procedure described in the Test methods section.

[0065] The polyethylene can be produced by polymerizing ethylene and the optional olefin comonomer in the presence of a transition metal catalyst such as a Ziegler-Natta catalyst (i.e. , an organometallic catalyst), a “Philips” type of catalyst (i. e. , a supported chromium/chromium oxide catalyst), a metallocene catalyst containing a tetraval ent transition metal, or combinations thereof. Other suitable catalysts are known in the art. The polymerization process can be performed in solution phase (e.g., when octene is the comonomer), slurry phase or in a gas phase reactor (e.g., when butene or hexene is the comonomer). The polymerization temperature and other process variables can be effective to affect the amount of long chain branching. In some examples, the polyethylene is a linear low-density polyethylene (LLDPE). An exemplary method of producing the LLDPE copolymer can be found in US Patent Application No. 2019/0144575, which is incorporated by reference herein in its entirety.

[0066] An example of a suitable polyethylene is Exceed™ XP 8656ML, an LLDPE commercially available from ExxonMobil Chemical Company in Houston, Texas. Other suitable examples include those sold under the EXCEED™ or ENABLE™ trade names, also available from ExxonMobil Chemical Company.

[0067] Other suitable polyethylenes may include LDPEs (low density polyethylenes), such as those made by a high pressure polymerization process employing free radical polymerization using initiators. Such LDPE and/or processes for making them are descried, e.g., in W02007/018871, WO2013/083285, and W02013/078018.

Additives

[0068] Additives may be included in the polyethylene, the semi-amorphous polymer, or the blends of the polyethylene, the semi-amorphous polymer of this invention. Such additives and their use are generally well known in the art. These include those commonly employed with plastics such as heat stabilizers or antioxidants, plasticizers, neutralizers, slip agents, antiblock agents, pigments, metal deactivators, stearates, antifogging agents, antistatic agents, clarifiers, nucleating agents, ultraviolet absorbers or light stabilizers, fillers and other additives in conventional amounts. Effective levels are known in the art and depend on the details of the base polymers, the fabrication mode and the end application. In some examples, fillers are present in the blend in an amount of up 50 wt%, up to 40 wt%, up to 30 wt%, up to 20 wt% based on a combined weight of the additives, the polyethylene, and the semi-amorphous polymer. In some examples, fillers are present in the blend in an amount from about 1 wt% to about up 50 wt%, from about 5 wt% to about up 50 wt%, from about 10 wt% to about up 50 wt%, from about 20 wt% to about up 50 wt%, from about 1 wt% to about up 40 wt%, from about 5 wt% to about up 40 wt%, from about 10 wt% to about up 40 wt%, or from about 20 wt% to about up 40 wt% based on a combined weight of the additives, the polyethylene, and the semi-amorphous polymer. In some examples, the filler can be calcium carbonate, magnesium carbonate, carbon black, silica, carbon-silica dual-phase filler, clay (layered silicates), lignin, carbon-nano-tubes, amorphous fillers, such as glass particle based fillers, starch based fillers, or combinations thereof.

[0069] The additives can also include enforcing agents including fibers. For FFF processing, polymer pellets and fibers can be mixed in a blender first and then delivered to an extruder to be fabricated into filaments. Short fibers including glass fibers and carbon fibers are commonly used to improve the mechanical properties of 3D printed objects. Nanomaterials such as carbon nanotube, graphene, graphite, ceramic, and metal nanoparticle often exhibit unique mechanical, electrical, and thermal properties. Thus, the addition of nanomaterials into polymers can enable creation of high performance 3D objects with specific functionality. Homogenous dispersion of nanoparticles into polymers is essential for manufacturing a composite with desired performances by 3D printing technique. Surface treatment of nanoparticles prior to printing processes can be adopted to avoid the agglomeration of nanoparticles and ensure a good interfacial bonding between nanoparticles and polymers.

Foaming Agents

[0070] Foaming agents or additives may generally be divided into two classes: physical foaming agents and chemical foaming agents.

[0071] Physical foaming or blowing agents are generally gases such as carbon dioxide or nitrogen. Hydrocarbon gases, such as butane or pentane and fluorocarbon gases, such as trichlorofluromethane and dichlorodifluromethane can be effective as physical blowing agents producing good quality foams. Because hydrocarbon and flurocarbon gases are viewed as presenting certain health and environmental concerns, the use of these gases is generally not the most desirable. More desirable physical blowing agents are carbon dioxide, nitrogen and argon. Physical blowing agents are utilized when low foam densities (

0.5 g/cm³) are required. [0072] Chemical blowing agents allow the production of foamed produces having a density of generally greater than 0.5 g/cm³. Examples of chemical blowing agents include bicarbonate of soda (used typically in combination with citric acid), azodicarbonamide, sulfonyl hydrazide, sulfonyl semicarbazide. Bicarbonate of soda (endothermic agent) and azodicarbonamide (exothermic agent) are perhaps the most widely used chemical blowing agents.

[0073] When used at low levels, generally less than 1 wt%, and desirably around 0.25 wt% based on the weight of the polymer being foamed, chemical blowing agents may function as bubble nucleating agents and facilitate the formation of more uniformly sized bubble. This function is often utilized even when the primary foaming medium is a physical blowing agent, such as carbon dioxide gas. Talc can also be utilized for bubble nucleation.

Sterilization

[0074] In some examples, the polyethylene can be sterilized by radiation sterilization. Radiation sterilization can use gamma, X-ray or electron radiation, which can deactivate microorganisms such as bacteria, fungi, viruses and spores. In some examples, the polyethylene can be sterilized by ultraviolet (UV) light. Short wavelength UV light can deactivate microorganisms such as bacteria, fungi, viruses and spores. Radiation sterilization or UV sterilization can occur to one or more of the polyethylene, the semi -amorphous polymer, the filament, and the 3D printed article.

Blends

[0075] In one or more embodiments, the blends described herein comprise the semi- amorphous polymer, the polyethylene, optionally additives, and optionally foaming agents and can be formed using any suitable means and are typically blended to yield an intimately mixed composition or a uniform mixture. The blends described herein can be formed using conventional equipment and methods, such as by dry blend using a tumbler, double-cone blender, ribbon blender, or other suitable blender and subsequently subjected to melt mixing in a mixer, or by mixing the components together directly in a mixer, such as, for example, a Banbury mixer, a Haake mixer, a Brabender internal mixer, or a single or twin-screw extruder, which may include a compounding extruder and a side-arm extruder. In other embodiments, the polyethylene and semi-amorphous polymer are blended by a combination of approaches, for example a tumbler followed by an extruder. Additionally, additives and/or foaming agents can be included in the blend, in one or more components of the blend, and/or in a product formed from the blend, such as a filament, as desired.

[0076] In yet more embodiments, the semi-amorphous polymer and the polyethylene can be blended using a “master batch” approach. The mixing step can take place as part of an additive manufacturing process to fabricate 3D articles, such as in the melting chamber on a 3D printing machine.

[0077] In yet further embodiments, a heterogeneous blend of polyethylene and semi- amorphous polymer that constitutes the continuous phase and particles of polyethylene different from, and more crystalline than, the semi-amorphous polymer dispersed within the continuous phase. The dispersed particles typically have an average size of less than 50 or 40 or 30 microns, for example in the range of about 50 nanometers to less than 50 microns. Preferably, the dispersed particles have an average size of less than 30 microns, such as less than 20 microns, for example less than or equal to 10 microns, for example between about 100 nanometers and about 10 microns.

[0078] In alternative embodiments, the 3D objects are printed from a heterogeneous blend of polyethylene and semi-amorphous polymer that constitutes discrete packets in the dispersed phase and particles of semi-amorphous polymer different from, and more crystalline than, the polyethylene in the continuous matrix phase. The dispersed particles typically have an average size of less than 50 or 40 or 30 microns, for example in the range of about 50 nanometers to less than 50 microns. Preferably, the dispersed particles have an average size of less than 30 microns, such as less than 20 microns, for example less than or equal to 10 microns, for example between about 100 nanometers and about 10 microns.

[0079] A blend according to either of the just-noted embodiments involving heterogeneous blends may be characterized as a blend having heterogeneous morphology in the solid state, as such heterogeneous nature will be exhibited when the blend is in solid state.

[0080] In a preferred aspect of the invention, the semi-amorphous polymer and the polyethylene along with optional additives and/or foaming agents (if present) are “melt blended” in an apparatus such as an extruder (single or twin screw) or batch mixer. Preferably, the screw of the melt extruder has multiple sections along the length of the barrel including the feed, the compression, and the metering sections. The raw material can be fed from the hopper directly into the feed section. The polymers are mainly melted in the compression zone. The polymers exist in a molten state when entering the metering section, which has the main function of reducing the pulsating flow to ensure a uniform delivery rate through the die. Preferably the temperatures of all of the barrels can be independent and can be accurately controlled in a range from 30°C to 250°C. The extruder die is used to shape the molten strand as it leaves the extruder into filament. In one preferred embodiment, the temperature can be increased from about 150°C in the feed section to about 210°C in the metering section of the barrel. In this manner, filaments can be formed from the blend that can have a diameter of about 2.40 mm to about 3.00 mm, preferably about 2.65 mm to about 3.00 mm, and more preferably about 2.75 mm to about 3.00 mm. A preferred method of blending is to include the final stage of blending as part of the filament fabrication step, such as in the extruder used to melt and convey the composition to a printing nozzle (or a die).

[0081] In another aspect of the invention, the polymer components can be blended in solution by any suitable means, by using a solvent that dissolves both components to a significant extent. The blending may occur at any temperature or pressure where the polymers remain in solution. Preferred conditions include blending at high temperatures, such as 20°C or more, preferably 30°C or more over the peak melting point of the polyethylene. Such solution blending could be particularly useful in processes where the polymer components are made by solution process and the mixing step is part of the finishing train, rather than added to the dry polymer in another blending step altogether. Such solution blending could also be particularly useful in processes where the polyethylene is made in a bulk or high pressure process where the both the polymers are soluble in the monomer.

[0082] Rheological properties of the blend can play a key role in controlling and improving the coalescence of the deposited beads on the obj ect being printed. The molten viscosity should be high enough to provide structural support and low enough to enable extrusion. The blend preferably has a complex viscosity at a frequency of 0.1 rad/sec and a temperature of 190°C within the range of from 1,000 or 3,000 or 5,000 or 8,000, or 10,000 or 15,000 Pa.s to 20,000 or 50,000 or 100,000 or 500,000 or 1,000,000 Pa.s. The blend preferably has a complex viscosity at a frequency of 100 rad/sec and a temperature of 190°C within the range of from 50 or 100 or 200 or 500 Pa.s to 5,000 or 8,000 or 10,000 or 15,000 Pa.s.

[0083] In one embodiment, the blend has significant shear induced viscosity thinning. Shear thinning is characterized by the decrease of the complex viscosity with increasing shear rate. One way to quantify the shear thinning is to use a ratio of complex viscosity at a frequency of 0.1 rad/s to the complex viscosity at a frequency of 100 rad/s. Preferably, the complex viscosity ratio of the blend is 5 or more, more preferably 10 or more, even more preferably 15 or more when the complex viscosity is measured at 190°C using a small amplitude oscillatory shear (SAGS).

[0084] In at least one embodiment, the melt strength of the blend may be from about 1 cN to about 540 cN, about 1 cN to about 50 cN, about 1 cN to about 25 cN, about 3 cN to about 15 cN, about 4 cN to about 12 cN, about 5 cN to about 10 cN, or about 5 cN to about 15 cN, when measured at 190°C. In some embodiments, the blend has a melt strength of at least about 5 cN, at least about 10 cN, or at least about 15 cN, or at least about 20 cN, when measured at 190°C. The melt strength of a blend at a particular temperature may be determined with a Gottfert Rheotens Melt Strength Apparatus. To determine the melt strength, a composition (e.g., of a film) melt strand extruded from the capillary die is gripped between two counter- rotating wheels on the apparatus. The take-up speed is increased at a constant acceleration of about 12 mm/s². The maximum pulling force (in the unit of cN) achieved before the strand breaks or starts to show draw-resonance is determined as the melt strength. The temperature of the rheometer is set at 190°C. The capillary die has a length of about 30 mm and a diameter of about 2 mm. The film melt is extruded from the die at a speed of about 10 mm/s. The distance between the die exit and the wheel contact point should be about 122 mm.

[0085] The polymers suitable for use in the present invention can be in any physical form when used for filament fabrication. In one embodiment, reactor granules, defined as the granules of polymer that are isolated from the polymerization reactor prior to any processing procedures, are used to make blends of the invention. The reactor granules typically have an average diameter of from 50 pm to 10 mm in one embodiment, and from 10 pm to 5 mm in another embodiment. In another embodiment, the polymer is in the form of pellets, such as, for example, having an average diameter of from 1 mm to 10 mm that are formed from melt extrusion of the reactor granules.

[0086] It has been unexpectedly discovered that specific process conditions in an additive manufacturing process can result in the formation of an object having superior properties, such as elasticity, stiffness, tensile properties, and/or resistance to warpage properties. For instance, prior to performing the additive manufacturing process, the blend made from the polyethylene and the semi-amorphous polymer can be extruded into filaments, or otherwise extruded in a manner suitable for additive manufacturing processes. Those filaments or other extrudate containing the blend can then be introduced to an additive manufacturing process, e.g., in which they are extruded through a nozzle to form one or more layers. The layers can be allowed to build up to form a desired object. The object can be or can include any part of a three- dimensional (3-D) or two-dimensional (2-D) solid material. Suitable additive-manufacturing processes using the above-described blend of polyethylene and semi-amorphous polymer are described in more detail below.

Additive Manufacturing Processes and Devices

[0087] In an additive-manufacturing process, a model of the component that is being produced can be defined in any suitable manner. In some examples, the model can be designed with computer aided design software. The model can include 3D numeric coordinates of the entire configuration of the component including both external and internal surfaces. The model can include a number of successive 2D cross-sectional slices that together form the 3D component.

[0088] As such, additive manufacturing systems can be used to print or otherwise build three-dimensional ("3D") parts from digital representations of the 3D parts using one or more additive manufacturing techniques, such as fused filament fabrication (FFF). Although FFF is a preferred additive manufacturing method in accordance with various embodiments of the present disclosure, any other 3D printing techniques, particularly extrusion-based 3D printing techniques, are also suitable.

[0089] When the filaments or other extrudate are deposited on a substrate or the object being printed, the filaments/ extrudates coalesce and bond to the substrate or the object in order to form the layers and the parts. This physical phenomenon is called “coalescence”. Coalescence is important in bond formation and control of the void growth in the plastic parts. Obviously, poor coalescence between the layers and deposited beads leads to weak filaments bonding, high porosity rate, and poor mechanical properties of the parts. Solidification is another important step in 3D object fabrication processes. The molten polymer must be self- supporting to maintain a desired shape when it emerges from the printer nozzle and deposits on the 3D object until the polymer is cooled below its solidification temperature. For a semi- amorphous polymer, solidification is mainly realized through crystallization. An ideal 3D printing requires good balance between coalescence and solidification since coalescence and crystallization take place concurrently. The extruded molten polymer needs to have enough time to allow itself to arrange itself to form filament bonding before crystallization. This bonding must occur faster than the crystallization. If the crystallization is faster, the filaments will solidify rapidly and they will not bond together well. On the other hand, slow crystallization allows cross-interfacial crystallization. Some of the polymer chains across two adjacent filament layers are linked into a single crystalline structure.

[0090] It is believed that the coalescence is mainly governed by the viscosity and the surface tension of polymers. Low viscosity or low plateau module of the molten polymer enhances coalescence. The molten viscosity should be high enough to provide structural support and low enough to enable extrusion. Thus, as noted previously, rheology of the blend can be important in this aspect of 3D printing or other additive-manufacturing processes. Thus, as previously noted, the blend according to some embodiments may have complex viscosity at a frequency of 0.1 rad/sec and/or at 100 rad/sec, and at 190°C, as described above (e.g., within the range of from 1,000 to 1,000,000 Pa.s at 0.1 rad/sec, or any other range as previously noted; and/or within the range from 50 to 15,000 Pa.s at 100 rad/sec, or any other range as previously noted).

[0091] Controlling the crystallization can be very helpful in optimizing the properties of the parts printed with semi-amorphase polymers. Furthermore, controlling the kinetics of crystallization and the parameters influencing the crystallization kinetics can help improve FFF or other additive-manufacturing processes. In turn, in addition to the properties of material used and geometric shape of the object, cooling rate can strongly influence crystallization. The cooling rate highly depends on the printing conditions such as printing temperature (temperature at the nozzle), environment temperature, and inlet velocity of the polymer filaments. On the other hand, the cooling rate directly influences the crystallization kinetics, viscosity increase with decreasing temperature, bonding rate, and porosity ratio of the final product. In one embodiment, the temperature at die nozzle is in a range from 25 °C to 450 °C. The temperature of the build plate or other object or surface on which rests the substrate or object to which filaments are deposited is in a range of -20 to 250 °C. The environment temperature can be adjusted to optimize the crystallization rate and thus the mechanical properties of a 3D object.

[0092] It is preferable to select the processing temperature in the melting chamber well above the melting temperature of the blend to ensure that the polymer is fully melted. The temperature is also used as means for viscosity control. In one embodiment, the temperature in the heating chamber is 150 °C or higher, preferably 170 °C or higher, even more preferably 190 °C or higher. The temperature in the melting chamber can be adjusted to optimize the mechanical properties. In one embodiment, the temperature in the melting chamber is set in a range from 250 to 350 °C and the temperature at the platform is set at up to 280 °C.

[0093] High temperature at the printer nozzle and low cooling rate of the 3D object being printed can also prevent the void formation and residual stress and part warpage. The temperature of the blend being passed to tire nozzle can range from about 0 to about 250°C.

[0094] The nozzle can have an extrusion temperature of about 150 to about 400°C, a diameter of about 0.001 to about 1,000.000 mm, and a minimum nozzle throughput area of about 10^-7 to about 10⁶ mm². The blend can be extruded through the nozzle at a speed of about 0.001 to about 1,000.000 mm/s. The thickness of each layer of the object that is formed can range from about 0.001 to about 1,000.000 mm Also, the object that is formed can have an infill density of about 0.01 to about 100.00 %. The specific values of these process conditions can vary depending on, for example, the molecular weights, melt indices, and melt flow rates of the particular ethylene polymer and the particular semi-amorphous polymer used in the blend.

[0095] In addition to the properties of material used, many process variables affect the surface roughness of the printed part, such as the cross-section of the deposited beads. The cross-section of the beads mainly depends on the diameter of the nozzle and the height of the deposited beads. In one embodiment, the layer thickness must not exceed 0.4 mm. Although a small nozzle diameter (e.g.. less than 0.2 mm) can increase the accuracy and surface roughness of the printed parts, it can also reduce the mechanical properties of the printed part and lower the production rate.

[0096] fa alternative embodiments, filament is not required in the additive manufacture process. The polymers along with other additives (if present) are “melt blended” in an apparatus such as an extruder, and then the molten material is directly fed to the 3D printing nozzle for deposition or layering on a 3D object being fabricated. The filament fabrication step is eliminated.

[0097] With the above principles of temperature, cooling, and crystallization kinetics in mind, an example process of 3D printing is now described, starting with the digital representation of the previously-noted model or 3D part for reproduction. At an initial stage, the digital representation of the 3D part is sliced into multiple horizontal layers. For each sliced layer, a path is then generated, which provides instructions for the additive manufacturing system to print the given layer.

[0098] Conventional fused filament fabrication printer designs and methods of operation can be found in US Pat. No. 7,604,470. In some examples, fused filament fabrication printers can be provided with one or more than one printing nozzle.

[0099] The 3D printing filament used in the process can include a blend comprising polyethylene and a semi -amorphous polymer as described above. The polyethylene, the semi- amorphous polymer, and optional additives can be blended before being extruded into a filament or they can be blended as they are extruded into a filament. Any suitable processes to make 3D filaments can be used, such as the process described in the examples below.

[00100] A three-dimensional structure can be formed through consecutive deposition of a filament using the extrusion nozzle. Examples of devices suitable for performing additive manufacturing processes include any commercially available device for such purpose. The three-dimensional structure can be built in layers, the depth of each layer typically being controllable by selectively adjusting the output from each extrusion nozzle.

[00101] The devices can utilize a computing system which implements design tools and/or topology optimization according to desired design aspects. The system can include a memory. The memory can store data. The memory can store executable instructions used to implement the topology optimization according to the desired design. [00102] The specification can be transferred to an additive manufacturing device which performs the additive manufacturing techniques according to the specification in order to create the 3D structure. While not required in all aspects, the additive manufacturing device can include processors that interpret the specification, and control other elements which apply the materials using robots, nozzles, lasers or the like to add the materials as layers or coatings to produce the 3D structure.

[00103] The machine controller can control the operation of the extrusion nozzle along the "X," "Y," and "Z" axes via a plurality of drive motors. Each of these motors can be operating separately, or one or more of them may be operating simultaneously, depending upon the shape of the structure to be formed. Circular patterns for each layer can be generated by controlled movement along the "X" and "Y" axes of the build platform.

[00104] The extrusion nozzle can be initially positioned a predetermined height above the build platform to form the first layer of the three-dimensional structure. The height of each subsequent layer can be then closely controlled. In some examples, thinner layers result in an overall smoother surface.

[00105] Thicker layers can increase the speed at which the structure is built. Layers as thin as 0.0001 mm can be formed. The layers can be formed horizontally, vertically, or in any other orientation. Depositing of the resin can take place along any of the three axes. The dispensing of the resin can take place along only the "X" - "Y" plane (i.e., horizontal plane), until it is advantageous to deposit in the "X" "Z" plane or the "Z" "Y" plane. In some examples, the extrusion nozzle can be mounted along generally perpendicular to the build platform, and thus perpendicular to the "X" - "Y" plane of build platform. The first layer can take any shape dictated by the computer program. A second and each subsequent layer can take slightly different shapes, as dictated by the particular cross section for each layer from the computer program and layering software. In the pattern situation for each layer wherein each layer is formed only in a horizontal "X" - "Y" plane. A motor supporting the extrusion nozzle can be selectively actuated after each layer is formed to raise the nozzle incrementally along the "Z" axis in a closely controlled manner.

[00106] The multiple layers can be of uniform thickness, or the layers can vary in thickness, as necessary and appropriate for the forming of a particular structure. Also, the layers may each vary in thickness across the height of each layer.

[00107] Additive manufacturing systems build the solid part one layer at a time. Typical layer thicknesses range from about 0.001 to about 1,000,000 mm, from about 0.001 to about 1,000 mm, from about 0.001 to about 100 mm. Depending on the design, the layer can be thicker or thinner as practicable. The thickness can be adjusted depending on the process parameters, including the total number of layers that make up the structure, and the speed in which the structure is being built.

[00108] The device may operate generally according to a method comprising the following steps: inserting the filament into an additive manufacturing apparatus having a nozzle; heating the filament; and dispensing a fluid bead out of the filament out of the nozzle to manufacture a three-dimensional object.

[00109] When 3D printing thermoplastic polymers using additive manufacturing, the adhesion between the first printed layer and the printing bed can be crucial, since it provides the foundation to the subsequent layers. Inadequate adhesion can result in poor printing quality or destroyed bed surfaces. The optimal adhesion of the printed sample to the printing bed can be achieved by heating the printing bed at temperatures above glass transition temperature (Tg) or melting temperature (Tm) of the filament material. Increasing the temperature above the filament’s Tg or Tm leads to a reduction of the surface tension between the printing bed and the printing material and to a larger contact area that ultimately causes better adhesion between the bed and the filament. For 3D printing polyolefins, the build plate temperature range can be any temperature above Tg, and below degradation temperature (whatever is lower) of the printing filament. In some examples, the extrusion temperature is from 100 to 250°C, preferred from 120-240°C, more preferred from 155 to 230°C. The Extruder screw rotation speed can be from 30 to 50 RPM, preferred from 35 to 45 RPM, more preferred from 38 to 40 RPM.

[00110] The 3D printer nozzle temperature can be above the melting temperature and below the degradation temperature of the printing filament.

[00111] To prevent warping, 3D printed parts can have good adhesion to the build plate. Physical adjustments to ensure good adhesion between 3D printed parts and build plate can include one or more of the following:

(1) Using a heated build plate. When printing polymers, the build plate temperature can be around 25 °C.

(2) Applying an adhesive to the build plate. The commonly used adhesives for polyolefin include commercially available printing adhesive solution, or polyolefin based tapes.

(3) Ensure the build plate is leveled correctly. It can be important that the first print layer of a print is pressed firmly onto the glass plate, to allow it to bond properly. If the distance between the nozzle and build plate is too wide, the material can easily become loose. (4) Ensure build plate surface is smooth and clean.

(5) Materials that require a high build plate temperature requires an isothermal printing environment. Cooler airflows from the environment can cause adhesion problems, and in extreme cases, may cause the print to separate from the build plate.

[00112] Software adjustments to help improve adhesion can include:

1) Use a “brim”. Placing a single-layer-thick flat area around the object can creating a larger adhesion surface. Print warping can be minimized by this. After printing, the brim can be removed easily.

2) Use a raft. For some materials or models, a brim might not be enough to prevent warping. In these instances, using a raft can be advisable. A raft can add a thick grid between the model and the build plate, ensuring that the heat is distributed equally. It is particularly useful when the bottom of a model is not completely flat, or when printing with industrial materials.

3) Two important settings (relating to the first layer) that influence adhesion are the initial layer height and initial layer speed. In some cases, a thicker initial layer can make adhesion easier, as build plate calibration is not as critical. It is important not to set the initial layer speed too high, as the material may attach to the nozzle and get dragged around with it, instead of remaining fixed to the build plate. Adjusting initial layer settings to use a low initial layer speed can ensure that the material has enough time to properly adhere to the build plate. For polyolefins, first layer printing speed can be around 6 mm/s.

4) Cooling can be one of the main causes of warping. Material contracts when cooling, and can cause the material to pull on itself. Materials can be cooled properly before the next layer is added, but excessive cooling should be avoided to ensure a smooth, warp-free print. For polyolefins, the recommended cooling can vary material by material.

Properties of Printed Objects

[00113] In some examples, the 3-D component can contain from 2 to an unlimited number of engineered layers; from 2 to about 10,000 layers; from 2 to about 5,000 layers; from 2 to about 1,000 layers; from 2 to about 500 layers; from 2 to about 250 layers; from 2 to about 100 layers; from 10 to about 500 layers; from 50 to about 500 layers; from 100 to about 500 layers; or from 250 to about 500 layers. Each layer can have the same or different dimensions. Components having almost any shape can be prepared by additive manufacturing. In some examples, the 3D printed component can be personal protective devices, medical facemasks, masks, mask components, tubing, goggles, shoes, hats or ventilator components. [00114] Surprisingly, objects formed via additive manufacturing in accordance with the aforementioned process conditions and/or using the above-described blends can have the following properties: a flex modulus of about 152.86 to about 160.88 MPa; a 1% Secant modulus of about 222.52 to about 231.26 MPa; a Young’s modulus of about 224.21 to about 227.45 MPa; a tensile stress of about 8.26 to about 8.54 MPa; a tensile stress at break of about 20.15 to about 22.71 MPa; a strain at break of about 506.86 to about 524.52 %. All of the foregoing properties are measured on the specimen prepared according to ISO 37 Type 3.

[00115] In some embodiments, the blend has an Izod impact strength of from about 40 J/m to about 55 J/m, or about 44 J/m to about 50 J/m, at room temperature according to ASTM D256A. In some embodiments, the blend has an Izod impact strength of from about 10 J/m to about 30 J/m, such as from about 17 J/m to about 25 J/m, at -18°C according to ASTM D256A. In some embodiments, the blend has a flexural modulus of from about 1000 MPa to about 1136 MPa to about 1704 MPa, according to ASTM D790A. The specific test method employed for each property described herein are provided in Table 1 below.

Table 1: Test Methods for Additive-Manufactured Objects

[00116] The additive-manufactured objects or 3D objects made using the inventive process has many desirable properties. In one or more embodiments, the melting temperature of the 3D objects is within a range from 110 or 135 °C and the crystallization temperature is with a range from 30 °C to 130 °C. The 3D objects can have a heat of fusion within the range from 10 or 20 or 25 J/g to 50 or 100 or 150 or 200 or 250 or 300 J/g. Both the melting temperature and crystallization temperature are determined using DSC according to the procedure of ASTM D3418.

[00117] In one or more embodiments, the 3D objects have a 100% Modulus of greater than 200 or 250 or 300 or 350 or 400 or 500 or 600 psi, or within the range from 200 or 250 or 300 psi to 2000 or 2100 or 2300 or 2500 psi. The 3D objects can have an Ultimate Elongation within the range from 80 or 100 or 120 to 200 or 300 or 400%. The 3D objects can have an ultimate tension strength within the range from 400 or 500 to 2300 or 2400 or 2500 or 2600 psi.

[00118] In one or more embodiments, the 3D obj ects described herein have a Shore hardness of 2A to 90 D, preferably 10 A to 50 D, as measured by ASTM D 2240.

[00119] Infill density or packing density is a measure of porosity or volumetric percent of the material used in a 3D object relative to the whole volume of the 3D object and is measured in percent. 0% is generally equivalent to no infill (hollow object) and 100% is equivalent to a solid print. The ideal value of the infill percentage depends on the end application of the 3D objects. A higher infill density improves the mechanical properties of the printed parts by reducing their porosity. In one embodiment, the infill density is in a range of 0.01 % to 100%, preferably 20% or more. Alternatively, the 3D object has an infill density of 80% or more, preferably 90% or more.

[00120] In one or more embodiments, particularly those in which the blend is a heterogeneous blend as described above, the 3D objects prepared using the inventive additive manufacturing process has a heterogeneous morphology. As used herein, the term “heterogeneous blend” means a composition having two or more morphological phases in the same state. For example, a blend of two polymers where one polymer forms discrete packets dispersed in a matrix or “continuous phase” of another polymer is said to be heterogeneous in the solid state. Also, a heterogeneous blend is defined to include co-continuous blends where the blend components are separately visible, but it is unclear which is the “continuous phase” and which is the discontinuous phase. Such morphology is determined using atomic force microscopy (AFM). In contrast, a “homogeneous blend” is a composition having substantially one morphological phase in the same state. For example, a blend of two polymers where one polymer is miscible with another polymer is said to be homogeneous in the solid state. By miscible is meant that that the blend of two or more polymers exhibits single-phase behaviour for the glass transition temperature, e.g. the Tg would exist as a single sharp transition temperature on a dynamic mechanical thermal analyzer (DMTA) trace of tan δ (i.e., the ratio of the loss modulus to the storage modulus) versus temperature. By contrast, two separate transition temperatures would be observed for an immiscible blend, typically corresponding to the temperatures for each of the individual components of the blend. Thus, a polymer blend is miscible when there is one Tg indicated on the DMTA trace. A miscible blend is homogeneous, while an immiscible blend is heterogeneous.

EXAMPLES

Test Methods

Dynamic Mechanical Analysis (DMA)

[00121] The glass transition temperature (T_g) was measured using dynamic mechanical analysis. This test provides information about the small-strain mechanical response of a sample as a function of temperature over a temperature range that includes the glass transition region and the visco-elastic region prior to melting. Specimens were tested using a commercially available DMA instrument (e.g., TA Instruments DMA 2980 or Rheometrics RSA) equipped with a dual cantilever test fixture. Each specimen was cooled to -130°C and then heated to 60°C at a heating rate of 2°C/min while subjecting to an oscillatory deformation at 0.1% strain and a frequency of 1 rad/sec. The output of these DMA experiments was the storage modulus (E’) and loss modulus (E”). The storage modulus measures the elastic response or the ability of the material to store energy, and the loss modulus measures the viscous response or the ability of the material to dissipate energy. The ratio of E"/E', called Tan-delta, gives a measure of the damping ability of the material; peaks in Tan-delta are associated with relaxation modes for the material. T_g is defined to be the peak temperature associated with the α-relaxation mode, which typically occurs in a temperature range of -80 to +20°C for polyolefins. In a hetero- phase blend, separate a-relaxation modes for each blend component may cause more than one T_g to be detected for the blend; assignment of the T_g for each component are preferably based on the T_g observed when the individual components are similarly analyzed by DMA (although slight temperature shifts are possible). For the claims herein, the Tg measured using DMTA was used.

Gel Permeation Chromatography (GPC)

[00122] Unless otherwise indicated, the distribution and the moments of molecular weight (Mw, Mn, Mz, Mw/Mn, etc.), the comonomer content, and the branching index (g^' _vis) were determined by using a high temperature Gel Permeation Chromatography (Polymer Char GPC- IR) equipped with a multiple-channel band-filter based Infrared detector IR5 with a multiple- channel band filter based infrared detector ensemble IR5 with band region covering from about 2,700 cm^-1 to about 3,000 cm^-1 (representing saturated C-H stretching vibration), an 18-angle light scattering detector and a viscometer. Three Agilent PLgel 10-μm Mixed-B LS columns were used to provide polymer separation. Reagent grade 1, 2, 4-trichlorobenzene (TCB) (from Sigma- Aldrich) comprising -300 ppm antioxidant butylated hydroxytoluene (BHT) was used as the mobile phase at a nominal flow rate of -1.0 mL/min and a nominal injection volume of -200 μL. The whole system including transfer lines, columns, and detectors was contained in an oven maintained at ~145°C. A given amount of sample was weighed and sealed in a standard vial with -10 μL flow marker (heptane) added thereto. After loading the vial in the auto-sampler, the oligomer or polymer was dissolved in the instrument with -8 mL added TCB solvent at ~160°C with continuous shaking. The sample solution concentration was from ~0.2 to ~2.0 mg/ml, with lower concentrations used for higher molecular weight samples. The concentration, c, at each point in the chromatogram could be calculated from the baseline subtracted IR5 broadband signal, I, using the equation: c=αl, where α is the mass constant determined with polyethylene or polypropylene standards. The mass recovery could be calculated from the ratio of the integrated area of the concentration chromatography over elution volume and the injection mass which is equal to the pre-determined concentration multiplied by injection loop volume. The conventional molecular weight (IR MW) was determined by combining universal calibration relationship with the column calibration which is performed with a series of monodispersed polystyrene (PS) standards ranging from 700 to 10M gm/mole. The MW at each elution volume was calculated with following equation:

where the variables with subscript “PS” stand for polystyrene while those without a subscript are for the test samples. In this method, α_PS = 0.67 and K_PS = 0.000175, α and K for other materials were as calculated in the published in literature (Sun, T. et al. Macromolecules 2001, v.34, pg. 6812), except that for purposes of this invention and claims thereto, α = 0.695+(0.01*(wt. fraction propylene)) and K = 0.000579-(0.0003502*(wt. fraction propylene)) for ethylene-propylene copolymers, α = 0.695 and K = 0.000579 for other linear ethylene polymers, α = 0.705 and K = 0.0002288 for linear propylene polymers. Concentrations were expressed in g/cm³, molecular weight was expressed in g/mole, and intrinsic viscosity (hence K in the Mark-Houwink equation) was expressed in dL/g unless otherwise noted.

[00123] The comonomer composition was determined by the ratio of the IR5 detector intensity corresponding to CH₂ and CH₃ channel calibrated with a series of PE and PP homo/copolymer standards whose nominal was are predetermined by NMR or FTIR. In particular, this provides the methyls per 1,000 total carbons (CH₃/1000TC) as a function of molecular weight. The short-chain branch (SCB) content per 1,000TC (SCB/1000TC) was then computed as a function of molecular weight by applying a chain-end correction to theCH₃/IOOOTC function, assuming each chain to be linear and terminated by a methyl group at each end. The weight % comonomer was then obtained from the following expression in which f is 0.3, 0.4, 0.6, 0.8, and so on for C₃, C₄, C₆, C₈, and so on co-monomers, respectively: w2 = f * SCB/1000TC

[00124] The bulk composition of the polymer from the GPC-IR and GPC-4D analyses was obtained by considering the entire signals of the CH₃ and CH₂ channels between the integration limits of the concentration chromatogram. First, the following ratio was obtained

[00125] Then the same calibration of the CH₃ and CH₂ signal ratio, as mentioned previously in obtaining the CH3/1000TC as a function of molecular weight, was applied to obtain the bulk CH3/1000TC. A bulk methyl chain ends per 1000TC (bulk CH3end/1000TC) was obtained by weight-averaging the chain-end correction over the molecular-weight range. Then w2b = f * bulk CH3/1000TC;

and bulk SCB/1000TC is converted to bulk w2 in the same manner as described above.

[00126] The LS detector used was an 18-angle Wyatt Technology High Temperature DAWN HELEOSII. The LS molecular weight (M) at each point in the chromatogram was determined by analyzing the LS output using the Zimm model for static light scattering (Light Scattering from Polymer Solutions,' Huglin, M. B., Ed.; Academic Press, 1972.):

Here, ΔR(θ) is the measured excess Rayleigh scattering intensity at scattering angle θ, c is the polymer concentration determined from the IR5 analysis, A₂ is the second virial coefficient, P(θ) is the form factor for a monodisperse random coil, and K_o is the optical constant for the system:

where N_A is Avogadro’s number, and (dn/dc) is the refractive index increment for the system. The refractive index, n = 1.500 for TCB at 145 C and λ = 665 nm. For analyzing polyethylene homopolymers, ethyl ene-hexene copolymers, and ethylene-octene copolymers, dn/dc = 0.1048 ml/mg and A₂ = 0.0015; for analyzing ethylene-butene copolymers, dn/dc = 0.1048*(l-0.00126*w2) ml/mg and A₂ = 0.0015 where w2 is weight percent butene comonomer.

[00127] A high temperature Agilent (or Viscotek Corporation) viscometer, which has four capillaries arranged in a Wheatstone bridge configuration with two pressure transducers, was used to determine specific viscosity. One transducer measured the total pressure drop across the detector, and the other, positioned between the two sides of the bridge, measured a differential pressure. The specific viscosity, ƞ _s, for the solution flowing through the viscometer was calculated from their outputs. The intrinsic viscosity, [ ƞ], at each point in the chromatogram was calculated from the equation [ ƞ]= ƞ_S/c, where c is concentration and is determined from the IR5 broadband channel output. The viscosity MW at each point was calculated as , where α_ps is 0.67 and K_ps is 0.000175.

[00128] The branching index (g'_vis) was calculated using the output of the GPC-IR5-LS-

VIS method as follows. The average intrinsic viscosity, [ ƞ]_avg, of the sample was calculated by:

where the summations are over the chromatographic slices, i, between the integration limits.

The branching index g'_vis is defined as where M_v is the viscosity-average

molecular weight based on molecular weights determined by LS analysis and the K and α are for the reference linear polymer, which are, for purposes of this invention and claims thereto, α = 0.695+(0.01*(wt. fraction propylene)) and K = 0.000579-(0.0003502*(wt. fraction propylene) for ethylene-propylene copolymers, α = 0.695 and K = 0.000579 for other linear ethylene polymers, α = 0.705 and K = 0.0002288 for linear propylene polymers. Concentrations were expressed in g/cm³, molecular weight was expressed in g/mole, and intrinsic viscosity (hence K in the Mark-Houwink equation) was expressed in dL/g unless otherwise noted. Calculation of the w2b values is as discussed above.

Differential Scanning Calorimetry (DSC)

[00129] The procedure for DSC determinations is as follows. Peak melting point, Tm, (also referred to as melting point), peak crystallization temperature, Tc, (also referred to as crystallization temperature), glass transition temperature (Tg), heat of fusion (ΔHf or Hf) of the polymer were measured using DSC using commercially available equipment such as a TA Instruments Q200 or DSC2500 according to the procedure of ASTM D3418. Samples weighing approximately 5-10 mg were sealed in an aluminum hermetic sample pan. The DSC data was recorded by first gradually heating the sample to 200°C at a rate of 10°C/minute. The sample was kept at 200°C for 2 minutes, then cooled to -90°C at a rate of 10°C/minute, followed by an isothermal for 2 minutes and heating to 200°C at 10°C/minute. Both the first and second cycle thermal events were recorded. Areas under the endothermic peaks were measured and used to determine the heat of fusion and the percent of crystallinity. The percent crystallinity was calculated using the formula, [area under the melting peak (Joules/gram) / B (Joules/gram)] * 100, where B is the heat of fusion for the 100% crystalline homopolymer of the major monomer component. These values for B were obtained from the Polymer Handbook, Fourth Edition, published by John Wiley and Sons, New York 1999, provided; however, that a value of 207 J/g (B) was used as the heat of fusion for 100% crystalline polypropylene, a value of 290 J/g was used for the heat of fusion for 100% crystalline polyethylene. The melting and crystallization temperatures reported here were obtained during the second heating/cooling cycle unless otherwise noted. Unless otherwise noted all melting points (T_m) are DSC second melt.

[00130] For polymers displaying multiple endothermic and exothermic peaks, all the peak crystallization temperatures and peak melting temperatures were reported. The heat of fusion for each endothermic peak was calculated individually. The percent crystallinity was calculated using the sum of heat of fusions from all endothermic peaks. Some of the polymer blends produced showed a secondary melting/cooling peak overlapping with the principal peak, which peaks were considered together as a single melting/cooling peak. The highest of these peaks was considered the peak melting temperature/crystallization point. For the amorphous polymers, having comparatively low levels of crystallinity, the melting temperature was typically measured and reported during the first heating cycle. Prior to the DSC measurement, the sample was aged (typically by holding it at ambient temperature for a period of 2 days) or annealed to maximize the level of crystallinity.

Other Test methods

[00131] Melt flow rate (MFR) was determined according to ASTM D 1238-13 (230°C/2.16 kg).

[00132] Melt index (MI) was determined according to ASTM D 1238-13 (190°C/2.16kg).

[00133] Environmental stress cracking resistance (ESCR) was determined according to ASTM D 1693-15.

Example 1. LLDPE/Semi -Amorphous Propylene

Blend Formation Process

[00134] A blend containing 90 wt% ethylene polymer and 10 wt% semi-amorphous polymer (Example 1) was prepared and compared to the ethylene polymer alone (Comparative Example 1). The ethylene polymer was Exceed™ XP 8656ML, and the semi-amorphous polymer was Vistamaxx™ 6102FL. Both the Exceed™ XP 8656ML and Vistamaxx™ 6102FL were obtained from ExxonMobil. Table 3 below reports various properties of Exceed™ XP 8656ML and Vistamaxx™ 6102FL along with the crystallization temperature (Tc) and melting temperature (Tm). The Tc and Tm were measured using Differential Scanning Calorimetry (DSC). The melt index of Exceed™ XP 8656ML was determined using ASTM D1238-13, and the melt flow rate of Vistamaxx™ 6102FL was determined using ASTM D1238. The density of Exceed™ XP 8656ML was determined according to ASTM D1505-18 using column density, where samples were molded under ASTM D4703-10a, Procedure C and then conditioned under ASTM D618-08 for 40 hours before testing.

Table 2: Blend Properties.

Filament Fabrication Process

[00135] Filaments of all examples were prepared using ThermoFisher Process 11 Parallel Twin-Screw Extruder, and spooler. The extrusion and spooler conditions used are tabulated in Table 2. Extrusion is a process used to create objects of a fixed cross-sectional profile. In a typical extrusion process, a material is pushed through a die of the desired cross-section. For each filament, 200 gm weight of the example resins in pellet form were fed into the extruder hopper, and then extruded out from a circular die with 3 mm diameter. By controlling the take- off speed of the spooler, the diameter of the filament is adjusted to be 2.85 mm ± 0.1 mm measured by Neiko 01407A Electronic Digital Caliper.

Preparation of FDM Printed Parts and 3D Printing Process

[00136] All Fused Filament Fabrication (FFF) specimens were fabricated with an Airwolf3D® Axiom Single Head 3-D Printer. The geometry for the specimens investigated in this patent were ISO 37 Type 3 tensile bars. Dassault Systems SolidWorks software, which is a computer-aided design (CAD) package, was first used to create 3D printable model with the dimension of ISO 37 Type 3 tensile bar. Then, the CAD model is tessellated and exported in STL format. The STL file was then sliced using Repetier Host software from Hot-World GmbH & Co. KG to convert the STL file into G-code, which is the standard language for 3D printers. G-code is a numerically controlled programming language that contains commands to move parts within the printer.

[00137] After filament was loaded to the 3D printer, and 3D printer set up following printing conditions tabulated in Table 3, the FFF specimens were able to be produced. This was repeated for each example. The FFF involved extruding the filaments through a nozzle to form layers. The layers were allowed to build up in the shape of the desired object. The process conditions include: the temperature of the filament bed before the filaments were introduced to the 3-D printer; the diameter, speed, temperature, and minimum nozzle throughput area of the nozzle used for the extrusion; the speed at which the filaments were extruded through the nozzle; the thickness of each layer that was formed; and the infill density of the tensile bar and the Notch Impact object that were formed.

[00138] Figures la and lb depict AFM images at different resolutions (as indicated by the legends therein) showing heterogeneous morphology of the 3D printed part. The AFM of Figures la and lb was conducted on cross section (TD). Figures 2a and 2b likewise depict AFM images at differing resolutions as indicated by the legends therein, each conducted on an internal surface parallel to the layering of 3D printing (MD). Table 3: Process Conditions of Filament Fabrication and 3D Printing

Injection Molding Process

[00139] In order to measure the reference strength and behavior of the filament materials for comparison with FFF, additional specimens containing the compositions from Ex.1 and C.Ex.l were fabricated by injection molding (IM). Mold cavity dimensions were the same as those described for the FFF specimens, which is the ISO 37 Type 3 tensile bar. All molded specimens were fabricated from the same FFF example resin pellets. The pellets were then fed into the hopper of a BOY XS injection molding machine. Molding parameters were set to the recommended values for example resins. The injection molding machine was set to an injection speed of 50 to 1000 rpm, preferably 100 to 500 rpm, more preferably 100 to 300 rpm. The barrel temperature of the injection molding machine was set at 100°C to 300°C, preferably 120°C to 250°C, more preferably 150°C to 230°C. Five replicate specimens were molded for each of five tests. Tensile and flexural tests were performed on an Instron Autox750 Automatic Contacting Extensometer with 0.001 N force accuracy. The machine has a 10kN load force capacity. Instron Bluehill software was used to record the data. All materials are injection molded or 3D printed into ISO37 Type 3 bar dimensions (that is, ISO37 is followed, except that the dumb-bell specimen was 3D printed where indicated by “FFF” or injection molded where indicated by “IM”). The average values from five specimens with ISO 37 bars were reported. The testing rate was 50.8mm/min. Flexural modulus tests of all specimens were conducted using to the 3 point flexure (Bend) test, according to ASTM D 790 (A, 1.0 mm/min). The testing rate was 1.0mm/min. The measured properties of the FFF specimens are provided in Tables 4 and 5 below.

Table 4: Measured Properties of Specimens Formed by the Indicated Process

Table 5: Flex Modulus of Specimens Formed by the Indicated Process

[00140] The FFF processed blend of Ex.1 surprisingly exhibited superior properties compared to the injection molded Ethylene polymer of C.Ex.1 and the injection molded blend of C.Ex.2. The high flexural modulus of the FFF processed blend of Ex. 1 was particularly unexpected considering the relatively low flexural modulus of Vistamaxx™ 6102FL semi- amorphous polymer, which is exhibited by its softness. FFF processing also advantageously consumed less polymer than injection molding.

[00141] Compared to the injection molded blend of C.Ex.2, the FFF processed blend of Ex. 1 had an estimated 86% enhancement in 1% Secant modulus, an estimated 117% enhancement in Young’s modulus, an estimated 48% enhancement in tensile stress at break, an estimated 70% enhancement in strain at break, and an estimated 48% enhancement in flexural modulus. [00142] Compared to the injection molded Ethylene polymer of C.Ex.l, the FFF processed blend of Ex. 1 had an estimated 9% enhancement in 1% Secant Modulus, an estimated 24% enhancement in Young’s modulus, an estimated 48% enhancement in tensile stress at break, and an estimated 93% enhancement in strain at break.

[00143] Based on these result, it was surprisingly discovered that FFF processing of a blend of Ethylene polymer and semi-amorphous polymer produces improved elasticity, stiffness, stress, strain, and resistance to warpage properties compared to injection molding of that same blend or of Ethylene polymer. It was particularly unexpected that the blend exhibited a high resistance to warpage.

Claims

CLAIMS: What is claimed is:

1. A process for making a three-dimensional object using an additive-manufacturing process, comprising: preparing a blend comprising a polyethylene having a density within the range from 0.890 g/cm³ to 0.940 g/cm³ and a semi-amorphous polymer comprising at least about 60 wt% propylene-derived units and from about 5 to about 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g.; providing the blend to an additive-manufacturing apparatus having a nozzle; and using the blend to form the three-dimensional object.

2. The process of claim 1 , wherein the blend is a filament formed by extrusion; and further wherein using the blend to form the three-dimensional object comprises inserting the filament into the additive-manufacturing apparatus, heating the filament, and dispensing a fluid bead of the filament out of the nozzle to manufacture the three-dimensional object.

3. The process of claim 2, wherein the fluid bead of the filament is dispensed out of the nozzle onto a heated build plate.

4. The process of claim 3, wherein the heated build plate has an adhesive applied to a surface of the heated build plate.

5. The process of claim 1 or any one of claims 2-4, wherein the polyethylene has one or more of the following properties:

MI from 0.1 g/10 min to 30 g/10 min;

MIR from 10 to 90;

Mw from 60,000 to 200,000 g/mol

M_w/M_n from 2 to 12; and

M_z/M_w from 2.0 to 5.0.

6. The process of claim 1 or any one of claims 2-5, wherein the blend further comprises a foaming agent.

7. The process of claim 1 or any one of claims 2-6, wherein the blend comprises from about 50 wt% to about 99 wt% of the polyethylene and from 1 wt% to 50 wt% of the semi- amorphous polymer based on a total weight of the polyethylene and the semi-amorphous polymer.

8. The process of claim 1 or any one of claims 2-7, wherein the blend has heterogeneous morphology in the solid state.

9. The process of claim 1 or any one of claims 2-8, wherein the nozzle has a diameter of about 0.001 mm to about 1,000.000 mm, and a throughput area of at least 10^-7 mm², and furthermore wherein the nozzle is maintained at a temperature of about 150°C to about 400°C during the forming of the three-dimensional object.

10. The process of claim 1 or any one of claims 2-9, wherein using the blend to form the three-dimensional object comprises introducing the blend to the nozzle at a temperature of about 0°C to about 250°C, and wherein the blend is extruded through the nozzle at a speed of about 0.001 mm/s to about 1,000.000 mm/s.

11. A blend comprising:

(1) a polyethylene having a density within the range from 0.890 g/cm³ to 0.940 g/cm³ and furthermore having all of the following properties:

MI from 0.1 g/10 min to 30 g/10 min;

MIR from 10 to 90;

Mw from 60,000 to 200,000 g/mol

M_w/M_n from 2 to 12; and

M_z/M_w from 2.0 to 5.0; and

(2) a semi-amorphous polymer comprising at least about 60 wt% propylene-derived units and from about 5 to about 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g.; further wherein the blend has the following properties: bimodal molecular weight distribution; complex viscosity (at 0.1 rad/sec, 190°C) within the range from 15,000 Pa.s to 50,000 Pa.s; complex viscosity (at 100 rad/sec, 190°C) within the range from 500 Pa.s to 8,000 Pa.s; and complex viscosity ratio (ratio of complex viscosity at 0.1 rad/sec to complex viscosity at 100 rad/sec, 190°C) of 15 or more.

12. The blend of claim 11, further having melt strength within the range from 5 cN to 15 cN at 190°C.

13. The blend of claim 11 or claim 12, wherein the polyethylene is present in the blend within the range from 85 to 99.9 wt%, on the basis of total weight of polyethylene and semi- amorphous polymer.

14. An obj ect made by an additive-manufacturing process, wherein the obj ect is made from a blend comprising a polyethylene having a density within the range from 0.890 g/cm³ to 0.940 g/cm³ and a semi-amorphous polymer comprising at least about 60 wt% propylene-derived units and from about 5 to about 25 wt% ethylene-derived units, based on a total weight of the semi-amorphous polymer, and having a heat of fusion of less than about 80 J/g.; and further wherein the object has one or more of the following properties as measured according to ISO 37 Type 3 (except that the dumb-bell specimen is 3-D printed):

(a) a flexural modulus of 90 MPa to 180 MPa;

(b) a 1% Secant modulus of 100 MPa to 350 MPa;

(c) a Young’s modulus 100 MPa to 350 MPa;

(d) a tensile stress at yield of 5.0 MPa to 15.0 MPa;

(e) a tensile stress at break of 10.0 MPa to 30 MPa; and

(f) a strain at break of 250.0 % to 800.0 %.

15. The object of claim 14, having all of the properties (a) through (f).

16. The process of claim 1 or any one of claims 5-10, wherein the polymer blend is directly fed to the 3D printing nozzle for deposition or layering on a 3D object being fabricated without the fabrication of filament.