WO2017113180A1

WO2017113180A1 - Methods and systems for improving the heat resistance of 3d-printed objects

Info

Publication number: WO2017113180A1
Application number: PCT/CN2015/099846
Authority: WO
Inventors: Xiaofan Luo; Junheng ZHAO
Original assignee: Jf Polymers (Suzhou) Co. Ltd.
Priority date: 2015-12-30
Filing date: 2015-12-30
Publication date: 2017-07-06
Also published as: CN108472889B; CN108472889A

Abstract

Disclosed herein are methods and systems for making an object using additive manufacturing, including processing the object to improve its heat resistance, such as processing the object to allow the material of the object to crystalize in a reversible gelation medium. The reversible gelation medium may serve as a temporary mold for the object to reduce, minimize, or eliminate deformation of the object during processing. Such processing of the object may increase the softening temperature of the material of the object, and thus may improve the heat resistance of the object comparing to that of the object prior to processing.

Description

METHODS AND SYSTEMS FOR IMPROVING THE HEAT RESISTANCE OF 3D-PRINTED OBJECTS

Technical Field

The present disclosure relates to additive manufacturing in general, and more specifically, methods and systems for processing objects created using additive manufacturing processes.

Background

Additive manufacturing is any of various manufacturing technologies that build objects in an additive, typically layer-by-layer, fashion. Additive manufacturing is commonly referred to by the general public as "3D printing" . One type of the additive manufacturing technologies is based on extrusion deposition, such as fused deposition modeling (FDM) or fused filament fabrication (FFF) . Over the last few years FDM or FFF has become a commonly used technology for modeling, prototyping, and production applications.

FDM or FFF, generally involves feeding a thermoplastic polymer in the form of a continuous filament to a heated extrusion nozzle. The thermoplastic polymer in the extrusion nozzle may be heated to a temperature above its glass transition temperature, at which the thermoplastic filament may become a viscous melt and therefore be extruded. The extrusion nozzle may be moved in three-dimensional motion and precisely controlled by step motors and computer aided manufacturing (CAM) software so that an object may be built from the bottom up, one layer at a time. The first layer of the object may be deposited on a substrate and additional layers may be sequentially deposited and fused (or partially fused) to the previous layer by solidification due to a drop in temperature. The process may continue until the three-dimensional object is fully constructed. This technology was disclosed in, for example, U.S. Patent No. 5,121,329.

Thermoplastic polymers are typically used as the constructing material in the additive manufacturing technologies based on extrusion deposition. For example, poly (lactic acid) (PLA) has traditionally been regarded as a material that may allow for easy and trouble-free 3D printing. A major drawback of the 3D-printed objects using such materials is their limited resistance to high temperatures due to the low softening temperatures and/or glass transition temperatures of these thermoplastic polymers. For example, a 3D-printed object using PLA may soften, deform, or even start to flow at temperatures above the glass transition temperature (T_g) of PLA, which ranges from about 55℃ to about 60℃. The limited heat resistance of 3D-printed objects may prevent them from being used in applications that require good heat resistance or thermal stability. For example, 3D-printed objects using PLA will not be suitable to beused as machine parts to be used in high-temperature environment, or to be used as medical devices because they may not be sterilized by autoclaving, which is typically conducted at about 100℃ or above.

Methods for improving the heat resistance of a 3D-printed object may include, for example, inducing crystallization in the thermoplastic polymer of the 3D-printed object in a post-processing procedure. This may increase the crystallinity and/or a melting temperature of the thermoplastic polymer, which may result in an increase of the softening temperature of the material, and thus may improve the heat resistance of the 3D-printed object. For example, in PCT/CN2014/077119, a method to induce crystallization in 3D printing filaments made of PLA involving a post-processing step is disclosed. However, the PLA parts made by 3D printing still remain substantially amorphous, due to the rapid cooling during the 3D printing process (i.e. not enough time for PLA to crystalize) . Therefore, the softening temperature of the 3D-printed parts made from PLA is still quite low after the post-processing step, e.g., less than or at about 60℃, limiting the use of many thermoplastic polymers, such as PLA, as a 3D printing material.

Thus, a need exists to develop methods and systems to improve the heat resistance of objects constructed using additive manufacturing technologies.

Summary of the Disclosure

Disclosed herein are methods and systems for making an object. In one embodiment, the method comprises: forming the object using a 3D printer, and processing the object in at least one reversible gelation medium. In one embodiment of the present disclosure, the method further comprises annealing the object in the at least one reversible gelation medium to allow the material of the object to crystallize. In one embodiment, the method comprises increasing a softening temperature and/or heat resistance of the object by allowing the material of the object to crystallize.

In one embodiment of the present disclosure, the method comprises increasing a temperature of the at least one reversible gelation medium to an annealing temperature of the material of the object, wherein the annealing temperature may be above a glass transition temperature and below a melting temperature of the material of the object. In one embodiment, the reversible gelation medium may be a temperature-responsive gelation medium configured to have a transition temperature. In one embodiment, the method comprises increasing the temperature of the temperature-responsive gelation medium from a temperature below the transition temperature to a temperature above the transition temperature, during which the temperature-responsive gelation medium may transition from a liquid to a solid gel. In one embodiment, the annealing temperature may be above the transition temperature and the temperature-responsive gelation medium may be configured to be a solid gel during annealing. The solid gel may serve as a temporary mold to the object during annealing. In one embodiment, the method comprises minimizing or eliminating deformation of the object during annealing with the temporary mold.

In one embodiment, the method comprises decreasing the temperature of the temperature-responsive gelation medium from a temperature above the transition temperature to a temperature below the transition temperature after annealing, during which the temperature-responsive gelation medium transitions from a solid gel to a liquid. In one embodiment, the object may be partially or wholly submerged in the liquid and/or partially or wholly retrieved from the liquid.

In one embodiment of the present disclosure, the system for making an object comprises: a 3D printer configured to form the object； and at least one reversible gelation medium configured for processing the object. In one embodiment, the system further includes an annealing unit including at least one reversible gelation medium to anneal the object to allow the material of the object to crystallize. In one embodiment, a softening temperature and/or heat resistance of the object may be increased by allowing the material of the object to crystallize.

In one embodiment, the system includes a temperature control unit configured to increase a temperature of the at least one reversible gelation medium to an annealing temperature of the material of the object, wherein the annealing temperature may be above a glass transition temperature and below a melting temperature of the material of the object. In one embodiment, the reversible gelation medium may be a temperature-responsive gelation medium configured to have a transition temperature. In one embodiment, the temperature control unit may increase the temperature of the temperature-responsive gelation medium from a temperature below the transition temperature to a temperature above the transition temperature, during which the temperature-responsive gelation medium may transition from a liquid to a solid gel. In one embodiment, the annealing temperature may be above the transition temperature and the temperature-responsive gelation medium may be configured to be a solid gel during annealing. The solid gel may serve as a temporary mold to the object during annealing. In one embodiment, deformation of the object during annealing with the temporary mold may be minimized or eliminated.

In one embodiment, the temperature control unit may decrease the temperature of the temperature-responsive gelation medium from a temperature above the transition temperature to a temperature below the transition temperature after annealing, during which the temperature-responsive gelation medium may transition from a solid gel to a liquid.

In one embodiment, the material of the object may remain amorphous after being extruded from an extrusion nozzle of the 3D printer. In one embodiment, the material of the object after annealing may be less elastic and more rigid or stiffer than that before annealing.

The details of one or more variations of the subject matter disclosed herein are set forth below and the accompanying drawings. Other features and advantages of the subject matter disclosed herein will be apparent from the detailed description below and drawings, and from the claims.

Further modifications and alternative embodiments will be apparent to those of ordinary skill in the art in view of the disclosure herein. For example, the systems and the methods may include additional components or steps that are omitted from the diagrams and description for clarity of operation. Accordingly, the detailed description below is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the present disclosures. It is to be understood that the various embodiments disclosed herein are to be taken as exemplary. Elements and materials, and arrangements of those elements and materials, may be substituted for those illustrated and disclosed herein, objects and processes may be reversed, and certain features of the present teachings may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of the disclosure herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary system, in accordance with the present disclosure.

FIG. 2 is a flow chart of exemplary methods of making an object, in accordance with the present disclosure.

FIG. 3 is a flow chart of exemplary methods of processing an object, in accordance with the present disclosure.

FIG. 4 is a graph of an exemplary data set of penetration depth vs. temperature of the objects, in accordance with the present disclosure.

FIG. 5 is a graph comparing exemplary differential scanning calorimetry thermographs of materials of as-printed object and of object processed by exemplary methods in accordance with the present disclosure.

DETAILED DESCRIPTION

This description and the accompanying drawings that illustrate exemplary embodiments should not be taken as limiting. Various mechanical, compositional, structural, chemical, electrical, and operational changes may be made without departing from the scope of this description and the claims, including equivalents. In some instances, well-known structures and techniques have not been shown or described in detail so as not to obscure the disclosure. Similar reference numbers in two or more figures represent the same or similar elements. Furthermore, elements and their associated features that are disclosed in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment.

For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages, or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about, ” to the extent they are not already so modified. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

It is noted that, as used in this specification and the appended claims, the singular forms “a, ” “an, ” and “the, ” and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, embodiments, and substitution of equivalents that all fall with the scope of the present disclosure.

Disclosed herein are methods for making an object using additive manufacturing, including processing the object to improve its heat resistance. Exemplary methods in accordance with the present disclosure may include processing the object to allow the material of the object to crystalize in a reversible gelation medium. As disclosed herein, gelation may refer to a transition in which a system changes from a liquid or a viscous liquid to a solid or an elastic solid. During processing, the reversible gelation medium may serve as a temporary mold for the object to minimize or eliminate deformation of the object. Such processing of the object may convert the material of the object, for example, a thermoplastic polymer, from being amorphous to being semi-crystalline, and thus may increase the softening temperature of the material of the object, and thus may improve the heat resistance of the object comparing to that of the object prior to processing.

As disclosed herein, heat resistance may be characterized using a softening temperature, which may be referred to as the temperature at which a material starts to soften. The softening temperature may be used to describe materials that may not melt rapidly into a liquid as the temperature rises, but instead may gradually get softer, e.g., over a predetermined amount of time or temperature range. Different tests or methods may be used to determine the softening temperature, which may vary depending on the material or the intended use. In some embodiments, the softening temperature of a material may be the temperature at which the material softens beyond some arbitrary softness. The softening temperature may be determined, for example, by the Vicat softening point test, whose standard procedure is described in, for example, ASTM D1525 and ISO 306. In some embodiments, the softening temperature of the material may be affected by the melting temperature of the material. For example, increasing the melting temperature of the material may increase its softening temperature.

FIG. 1 is a schematic diagram of an exemplary system in accordance with the present disclosure. System 100 includes a 3D printer 110 and a reversible gelation medium 130. 3D printer 110 may be configured to construct an object 120 using any of the additive manufacturing technologies. In some embodiments, reversible gelation medium 130 may be, for example, a temperature-responsive gelation medium, and system 100 may further include a temperature control unit 140 configured to be operatively connected to reversible gelation medium 130 and regulate the temperature of reversible gelation medium 130. For example, temperature control unit 140 includes a heating element, a cooling element, a sensor, and/or a processor to detect, increase, decrease, regulate, control, and/or maintain the temperature of reversible gelation medium 130. In some embodiments, object 120 may be manually or automatically removed from 3D printer 110 after being constructed and may be then submerged partially or wholly in reversible gelation medium 130 for processing. In other embodiments, reversible gelation medium 130 may be a component of 3D printer 110, and object 120 after being constructed may be manually or automatically submerged partially or wholly in reversible gelation medium 130 for processing. In some embodiments, object 120 may be manually or automatically removed from reversible gelation medium 130 after being processed.

For the purpose of illustration, the following embodiment is used: 3D printer 110 constructs object 120 using an additive manufacturing technology based on extrusion deposition, such as fused deposition modeling (FDM) or fused filament fabrication (FFF) . Additive manufacturing technologies other than FDM and FFF may also be used with the present disclosure, which may include, for example, binder jetting, material jetting, sheet lamination, and powder bed fusion based technologies. The additive manufacturing technology may, for example, be at least one method selected from selective laser melting (SLM) , direct metal laser sintering (DMLS) , selective laser sintering (SLS) , selective heat sintering (SHS) , robocasting, stereolithography (SLA) , laminated object manufacturing (LOM) , digital light processing (DLP) , plaster-based 3D printing (PP) , electron-beam melting (EBM) , electron beam freeform fabrication (EBF) , photopolymerization, binding of granular materials, and lamination.

For FDM or FFF, a thermoplastic polymer may, for example, be used as the material to build object 120. For the purpose of illustration, the following embodiment is used: 3D printer 110 constructs object 120 using poly (lactic acid) (PLA) as the material. In some embodiments, object 120 may, for example, be made of at least one thermoplastic polymer selected from thermoplastic polyurethanes (TPUs) , polyoxymethylen (POM) , poly (ethylene terephthalate) (PET) , PET copolymers, vinyl acetal polymers, acrylonitrile-butadiene-styrene (ABS) , polycarbonate (PC) , polystyrene (PS) , high impact polystyrene (HIPS) , polycaprolactone (PCL) , polyphenylsulfone (PPSF) , Ultem 9085, polyamide, polyamide copolymers, cellulose based polymers, acrylic or acrylate based polymers, nylon, polybenzimidazole, polyether sulfone (PES) , polyether ether ketone (PEEK) , polyethene (PE) , polyphenylene oxide (PPO) , polyphenylene sulfide (PPS) , polypropylene (PP) , polyvinyl chloride (PVC) , and polytetrafluoroethylene (PTFE) .

Thermoplastic polymers used for 3D printing may, for example, be chosen from semi-crystalline polymers. Generally speaking, polymers may be divided into two categories: amorphous polymers and semi-crystalline polymers. Amorphous polymers are those whose polymer chains exist in a random coil-like fashion with no or limited ordered structures, i.e., crystalline structures. Semi-crystalline polymers are those that include crystalline domains whose polymer chains exist in ordered structures in addition to amorphous domains. The term “semi-crystalline” is used because no polymer can be 100％ crystalline and crystalline domains typically coexist with amorphous domains. For example, the degree of crystallinity of a semi-crystalline polymer may be above 5％.

For semi-crystalline polymers, the crystalline domain may melt when the polymer chains of the crystalline domain fall out of their ordered structures upon being heated to and/or above a melting temperature (T_m) . The crystalline domain may crystallize and the polymer chains may resume their ordered structures upon cooling from a melted state. The amorphous domain of a semi-crystalline polymer may undergo a glass-liquid transition, a glass-rubber transition, or a glass transition from a hard and relatively stiff or rigid state into a molten or rubber-like state when the polymer chains obtain more mobility upon being heated to and/or above a glass transition temperature (T_g) . The stiffness or mechanical strength of a semi-crystalline polymer material may change when the temperature of the material changes and may correlate with the melting temperature (T_m) of the material. For example, when the temperature of a semi-crystalline polymer material becomes above the glass transition temperature (T_g) of the amorphous domain, the crystalline domain may still provide some or substantial mechanical strength. But when temperature of the semi-crystalline polymer material becomes above the melting temperature (T_m) of the crystalline domain, the material may start to soften or get softer. The softening temperature of the semi- crystalline polymer material may be correlated with the melting temperature (T_m) of the material. The melting temperature (T_m) of the crystalline domain may typically be higher than the glass transition temperature (T_g) of the amorphous domain of semi-crystalline polymers.

Since amorphous polymers have no or limited crystalline structures, amorphous polymers do not have a melting temperature (T_m) , but have a glass transition temperature (T_g) . The softening temperature of an amorphous polymeric material may be correlated with the glass transition temperature (T_g) of the material. For example, when the temperature of an amorphous polymeric material increases above its glass transition temperature (T_g) , the material may become softer.

Semi-crystalline polymers may crystalize or have increased crystallinity, transition from an amorphous state to a semi-crystalline state, and/or solidify upon cooling from a molten state, mechanical stretching, and/or solvent evaporation. Semi-crystalline polymers, therefore, may be softened by heat and solidify on cooling and thus be reshaped by heating and cooling. The degree of crystallinity of semi-crystalline polymers may be characterized, for example, by a percentage of the volume of the material that is crystalline and may range, for example, from about 5％ to about 80％. Methods of evaluating the degree of crystallinity of semi-crystalline polymers may include, for example, density measurement, softness or toughness measurement, differential scanning calorimetry (DSC) , and X-ray diffraction (XRD) . The measured degree of crystallinity may depend, for example, on the method used, typically quoted together with the degree of crystallinity measured. A higher degree of crystallinity of a semi-crystalline polymer may result in a more rigid or stiffer, but also harder and more thermally stable material.

In some embodiments, object 120 may be constructed by 3D printer 110 using a material including at least one semi-crystalline polymer. In some embodiments, introducing crystallization and/or increasing crystallinity of the material of object 120 may increase, for example, a melting temperature and/or a softening temperature of the material, and thus may improve the heat resistance or thermal stability of object 120. In other embodiments, introducing crystallization and/or increasing crystallinity of the material of object 120 may improve the mechanical properties, such as stiffness, hardness, rigidness, and/or strength of object 120.

Some materials used for making object 120 may have fast crystallization kinetics or rate, and may, for example, crystallize immediately after being extruded from a molten state, such as in an FDM or FFF process. Such fast crystallization may, for example, induce a large and/or rapid volumetric shrinkage of the material, which may result in layer delamination, deformation, and/or warping of object 120. Thus, the materials including at least one semi-crystalline polymer that have fast crystallization kinetics may not be suitable for making object 120. In some embodiments, the materials including at least one semi-crystalline polymer that have slow crystallization kinetics may be suitable for making object 120. As disclosed herein, materials having fast crystallization kinetics may substantially crystalize or may develop a substantial degree of crystallinity, for example, of about 5％ or more, when cooled at a rate, for example, from about 50℃/s to about 100℃/s, from the molten or amorphous state. Materials having slow crystallization kinetics may not substantially crystalize, may not develop a substantial degree of crystallinity, and/or may remain substantially amorphous when cooled at a rate, for example, from about 50℃/sto about 100℃/s, from the molten or amorphous state.

In some embodiments, the material of object 120 may include at least one semi-crystalline polymer with slow crystallization kinetics. In some embodiments, the material of object 120 may remain substantially amorphous after being extruded from the molten state, all the way through the entire constructing process. For example, the material of object 120 may, remain at an amorphous state or a molten state during and/or throughout an FDM or FFF process. In some embodiments, the material of object 120 may transition from the amorphous state to a semi-crystalline state upon appropriate processing, such as annealing and/or cooling.

In some embodiments, as disclosed herein, inducing crystallization, introducing crystallization, annealing, developing crystallinity, and/or increasing the degree of crystallinity of object 120 or the material of object 120 may refer to holding the material or object isothermal at a predetermined temperature or an annealing temperature (T_a) , at which crystallization may take place, or may refer to slowly heating object 120 at a constant rate or varying heating rates, ranging, for example, from about 0.1℃/min to about 50℃/min, such as from about 0.1℃/min to about 10℃/min, from about 10℃/min to about 20℃/min, from about 20℃/min to about 30℃/min, from about 30℃/min to about 40℃/min, or from about 40℃/min to about 50℃/min, at temperatures ranging from the glass transition temperature (T_g) to the melting temperature (T_m) .

In some embodiments, annealing of object 120 may be temperature dependent and may be carried out at an annealing temperature (T_a) . For example, the annealing temperature (T_a) may be higher than an ambient temperature, i.e., room temperature. Further, for example, the annealing temperature (T_a) may range from the glass transition temperature (T_g) to the melting temperature (T_m) of the material. In some embodiments, the material of object 120 may have a crystallization temperature (T_c) . The crystallization temperature (T_c) may be the temperature at which the material of object 120 has a maximum or substantial crystal growth rate. The crystallization temperature (T_c) may be higher than the glass transition temperature (T_g) and lower than the melting temperature (T_m) of the material. In some embodiments, crystallization kinetics or rate of the material of object 120 may depend on the difference between the annealing temperature (T_a) and the crystallization temperature (T_c) . For example, to increase the crystallization rate of the material of object 120 during annealing, an annealing temperature (T_a) closer to crystallization temperature (T_c) may be selected. In some embodiments, the annealing temperature (T_a) may be substantially close to or the same as the crystallization temperature (T_c) .

In some embodiments, annealing may allow the material of object 120 to crystalize under a slow and/or regulated rate to allow a substantial degree of crystallinity (e.g. 5％ or more) to develop within predetermined time frames, ranging from several minutes to hours, for example, and may change the crystal structure, the degree of crystallinity, the morphology, and/or the orientation of the polymer chains of the material. For example, annealing may allow the material of object 120 to crystallize for a substantial degree of crystallinity, for example, from about 5％to about 10％, from about 10％ to about 20％, from about 20％ to about 30％, from about 30％ to about 40％, from about 5％ to about 20％, from about 10％ to about 30％, from about 25％ to about 40％, from about 5％ to about 30％, from about 10％ to about 40％, from about 5％ to about 20％, from about 20％ to about 40％, or from about 5％ to about 40％ crystallinity. Further, in some embodiments, annealing may increase the melting temperature and/or the softening temperature of the material of object 120, and thus may improve the heat resistance or thermal stability of object 120.

One technical problem with directly annealing the material of object 120 is that the material may soften substantially when the temperature of the material becomes close to the annealing temperature (T_a) and/or higher than the glass transition temperature (T_g) . Softening or melting of the material of object 120 during annealing may lead to deformation, collapse, and/or warping of object 120 before sufficient crystallinity can be achieved. To overcome this problem, object 120 can be constrained or supported during annealing to limit, minimize, or eliminate the delamination, deformation, collapse, and/or warping of object 120 that may take place during annealing. For example, in some injection molding processes, an injected object may be annealed for an extended period of time while it is still in the mold under pressure, and may be de-molded when a desired crystallinity is achieved. This may not, however, be applicable to object 120 made by additive manufacturing or 3D printing, which is a “moldless” process and constructs object 120 in a layer-by-layer fashion without using any mold. Thus, in some embodiments, a temporary mold is advantageously used to substantially constrain or support object 120 constructed by 3D printer 110 during the crystallization or annealing of object 120 by using reversible gelation medium 130.

In some embodiments, reversible gelation medium 130 may be capable to reversibly change phases and/or its physical states, for example, from a liquid to a solid gel or from a solid gel to a liquid. The liquid may be a viscous liquid. The solid gel may be an elastic solid. As disclosed herein, a gel may refer to any chemical system that forms a cross-linked network structure via covalent crosslinks and/or physical crosslinks, or both, and may behave in a solid-like fashion.

In some embodiments, object 120 constructed by 3D printer 110 may be processed or annealed in reversible gelation medium 130. For example, object 120 may be put into and partially or wholly submerged in reversible gelation medium 130 at a liquid phase. During the annealing of object 120, reversible gelation medium 130 may change from a liquid to a solid gel, and therefore may serve as a temporary mold to object 120. Deformation, collapse, and/or warping of object 120 during annealing may thus be minimized or eliminated with the temporary mold formed by reversible gelation medium 130 at a solid phase. In some embodiments, reversible gelation medium 130 may change from a solid gel to a liquid after annealing and object 120 may be retrieved from reversible gelation medium 130 at a liquid phase. In other embodiments, reversible gelation medium 130 may change from a solid gel to a liquid after the material of object 120 achieves a sufficient or substantial degree of crystallization or the softening temperature of the material of object 120 is substantially increased, and object 120 may be retrieved from reversible gelation medium 130 at the liquid phase.

Different environmental factors can trigger phase and/or physical state changes of reversible gelation medium 130. For example, exposure of reversible gelation medium 130 to a stimuli may cause reversible gelation medium 130 to change phases from a liquid to a solid gel, or vice versa. Such environmental stimuli may, for example, be selected from temperature, pH, light, mechanical force/pressure, radiation, electrical and/or magnetic fields, and electrical current. The type of stimuli required to change reversible gelation medium 130 from one phase or physical state to another may affect the applications for which reversible gelation medium 130 is used. For example, reversible gelation medium 130 may include one or more temperature-responsive medium, such as a polymer solution or a hydrogel, and may change between a solid phase and a liquid phase upon changing of its temperature.

In some embodiments, reversible gelation medium 130 may, for example, may have a sol-gel transition temperature (T_t) . As disclosed herein, the sol-gel transition temperature (T_t) , may generally be defined as the temperature at which a temperature-responsive gelation medium changes from a liquid to a solid gel and/or changes from a solid gel to a liquid. The sol-gel transition temperature (T_t) , may be measured using rheological or optical methods. For example, one may measure a viscosity and/or shear modulus of reversible gelation medium 130 at increasing temperatures, and the temperature at which a substantial increase in the viscosity or shear modulus occurs may be defined as the sol-gel transition temperature (T_t) . For another example, one may measure a viscosity and/or shear modulus of reversible gelation medium 130 at decreasing temperatures, and the temperature at which a substantial decrease in the viscosity or shear modulus occurs may be defined as the sol-gel transition temperature (T_t) .

In some embodiments, when the temperature (T) of reversible gelation medium 130 is lower than the sol-gel transition temperature (T_t) , i.e., T < T_t, reversible gelation medium 130 may exist as a liquid. When the temperature of reversible gelation medium 130 is higher than the sol-gel transition temperature (T_t) , i.e., T > T_t, reversible gelation medium 130 may exist as a solid gel. In some embodiments, when reversible gelation medium 130 is heated from a temperature below the sol-gel transition temperature (T_t) to a temperature above the sol-gel transition temperature (T_t) , reversible gelation medium 130 may change from a liquid to a solid gel. When reversible gelation medium 130 is cooled from a temperature above the sol-gel transition temperature (T_t) to a temperature below the sol-gel transition temperature (T_t) , reversible gelation medium 130 may change from a solid gel to a liquid.

In some embodiments, the sol-gel transition temperature (T_t) may be a lower critical solution temperature (LCST) of reversible gelation medium 130. For example, when reversible gelation medium 130 is a solution including at least one polymer and water, a LCST may be used to describe the sol-gel transition temperature (T_t) . The sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) may vary for different reversible gelation media 130. In some embodiments, the sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) of reversible gelation medium 130 may be controlled or regulated in a wide temperature range by adjusting the composition, the molecular weight, water content, ionic strength, and/or other physical or chemical properties of the reversible gelation medium.

In some embodiments, the phase transition from a liquid to a solid gel and/or from a solid gel to a liquid of reversible gelation medium 130 may be gradual and may occur over a range of temperatures around the sol-gel transition temperature (T_t) . For example, the phase transition of reversible gelation medium 130 may occur over a temperature range from about 25℃ to about 35℃, from about 35℃ to about 45℃, from about 45℃ to about 55℃, from about 55℃ to about 65℃, from about 30℃ to about 40℃, from about 40℃ to about 50℃, from about 50℃ to about 60℃, from about 30℃ to about 50℃, or from about 40℃ to about 60℃. In other embodiments, the phase transition of reversible gelation medium 130 may occur more abruptly as a given temperature threshold or a sol-gel transition temperature (T_t) is crossed.

In some embodiments, a sol-gel transition temperature (T_t) from a liquid to a solid gel phase may be different from a sol-gel transition temperature (T_t) of a solid gel to a liquid phase. In some embodiments, the abruptness or the range of temperatures around the sol-gel transition temperature (T_t) of the phase transition of reversible gelation medium 130 may vary depending on the direction of the phase transition. The gradual or abrupt nature of the phase transition may be affected, at least in part, by the polymer, solvent, and/or chemical components used in reversible gelation medium 130, or by environmental conditions, such as the surrounding temperature or humidity, or the method of heating and cooling. In some embodiments, the phase transition of reversible gelation medium 130 from a liquid to a solid gel or vice versa may take less than a minute； while in some embodiments, the phase transition may take several minutes or longer. For example, the phase transition may take approximately 30 seconds, from about 1 to about 2 minutes, from about 5 to about 30 minutes, or up to about two hours or longer.

As disclosed herein, any suitable polymer or combination of polymers may be used to form reversible gelation medium 130. For example, reversible gelation medium 130 may include at least one polymer selected from poly (N- isopropylacrylamide) (PNIPAAm) , poly (N, N-diethylacrylamide) (PDEAAm) , poly (N-vinlycaprolactam) (PVCL) , poly [2- (dimethylamino) ethyl methacrylate] (PDMAEMA) poly (ethylene glycol) (PEG) , poly (ethylene oxide) (PEO) , PEG methacrylate polymers (PEGMA) , polyoxypropylene (PPO) , polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO-PPO-PEO) , ethyl (hydroxyethyl) cellulose (EHEC) , Pluronics, and Poloxamers.

Additionally or alternatively, a suitable reversible gelation medium may undergo the phase transition from a liquid to a solid gel or from a solid gel to a liquid responsive to one or more stimuli applied to the reversible gelation medium, such as temperature, pH, light, mechanical force and/or pressure, radiation, electrical and/or magnetic fields, electrical current, or a combination thereof. . Examples of suitable stimuli-responsive materials that may be used as the reversible gelation medium include, but are not limited to, pH sensitive reversible materials, such as poly (acrylic acid) , poly (acetoacetoxyethyl methacrylate) , poly (glutamic acid) , poly (sodium acrylate) , poly (sodium-4-vinylbenzoate) , poly (N-vinylimidazole) , and copolymers and polymer blends containing the above polymers or chain segments； and light sensitive reversible materials, such as polymers or oligomers comprising at least one entity chosen, for example, from azobenzene groups, stilbenes moieties, anthracene derivatives, spiropyran groups, sulfide bonds, and suitable light sensitive material.

In some embodiments, the sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) of reversible gelation medium 130 may range from about 20℃ to about 30℃, from about 30℃ to about 40℃, from about 40℃ to about 50℃, from about 50℃ to about 60℃, from about 60℃ to about 70℃, from about 70℃ to about 80℃, from about 80℃ to about 90℃, from about 20℃ to about 40℃, from about 20℃ to about 50℃, from about 20℃ to about 60℃, from about 20℃ to about 70℃, from about 20℃ to about 80℃, from about 20℃ to about 90℃, from about 30℃ to about 40℃, from about 30℃ to about 50℃, from about 30℃ to about 60℃, from about 30℃ to about 70℃, from about 30℃ to about 80℃, from about 30℃ to about 90℃, from about 40℃ to about 60℃, from about 40℃ to about 70℃, from about 40℃ to about 80℃, from about 40℃ to about 90℃, from about 50℃ to about 70℃, from about 50℃ to about 80℃, from about 50℃ to about 90℃, from about 60℃ to about 80℃, from about 60℃ to about 90℃, or from about 70℃ to about 90℃.

In some embodiments, the annealing of object 120 in reversible gelation medium 130 may increase the softening temperate of object 120 by about 10℃ to about 50℃, about 10℃ to about 80℃, about 10℃ to about 100℃, from about 50℃ to about 80℃, from about 50℃ to about 100℃, from about 50℃ to about 150℃, from about 80℃ to about 100℃, from about 80℃ to about 150℃, or from about 100℃ to about 150℃.

In some embodiments, the annealing of object 120 may include heating reversible gelation medium 130, where object 120 may be partially or wholly submerged, to a predetermined temperature or an annealing temperature (T_a) , keeping the reversible gelation medium 130 at the predetermined temperature or the annealing temperature (T_a) for a period of time, and then cooling the reversible gelation medium 130 to a temperature, for example, room temperature. In some embodiments, the temperature of reversible gelation medium 130 may be controlled or regulated by temperature control unit 140. In some embodiments, the annealing temperature (T_a) may be higher than the sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) of reversible gelation medium 130. In some embodiments, the annealing temperature (T_a) may be higher than the glass transition temperature (T_g) of the material of object 120. For example, the annealing temperature (T_a) may be higher than the glass transition temperature (T_g) by about 10℃ to about 100℃. In other embodiments, the annealing temperature (T_a) may be lower than the melting temperature (T_m) of the material of object 120. For example, the annealing temperature (T_a) may be lower than the melting temperature (T_m) by about 10℃ to about 100℃. In some embodiments, the annealing temperature (T_a) may be determined such that the reversible gelation medium 130 is stable at the annealing temperature (T_a) . For example, the annealing temperature (T_a) may be set at a value at which reversible gelation medium 130 has limited, minimized, or no degree of degradation or boiling. In some embodiments, the annealing temperature (T_a) may range from about 60℃ to about 120℃, from about 60℃ to about 100℃, from about 60℃ to about 80℃, from about 80℃ to about 100℃, or from about 100℃ to about 120℃.

In some embodiments, the annealing temperature (T_a) may be selected at a value at which the material of object 120 may develop a sufficient or substantial degree of crystallinity during annealing. For example, the material of object 120 may develop, for example, a degree of crystallinity ranging from about 5％ to about 10％, from about 10％ to about 20％, from about 20％ to about 30％, from about 30％ to about 40％, from about 5％ to about 20％, from about 10％ to about 30％, from about 25％ to about 40％, from about 5％ to about 30％, from about 10％ to about 40％, from about 5％ to about 20％, from about 20％ to about 40％, or from about 5％ to about 40％ crystallinity. The material of object 120 may also develop, for example, about 40％ or higher crystallinity. In some embodiments, the annealing temperature (T_a) may vary for different materials of object 120 and/or reversible gelation medium 130, and may vary under different environmental conditions, such as temperature, pH, light, pressure, tension, radiation, and electrical current. In some embodiments, the annealing temperature (T_a) of the material of object 120 may be controlled or regulated in a wide temperature range by adjusting the composition, the molecular weight, water content, ionic strength, and/or other physical or chemical properties of the material. In other embodiments, the annealing temperature (T_a) may be determined from a combination of conditions discussed above.

In some embodiments, the annealing temperature (T_a) and/or the glass transition temperature (T_g) of the material of object 120 may be higher than the sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) of reversible gelation medium 130. For example, the sol-gel transition temperature (T_t) or the lower critical solution temperature (LCST) may be selected or controlled to be less than the glass transition temperature (T_g) such that object 120 may not become soft or deform when reversible gelation medium 130 exists as a liquid.

In some embodiments, the annealing of object 120 may be time dependent. An annealing time may be determined to allow the material develop a sufficient or substantial degree of crystallinity, for example, about 5％, about 8％, about 10％, about 15％, or about 20％ crystallinity. In some embodiments, the time for annealing may be determined to allow the material of object 120 to have a higher softening temperate, and thus to have improved heat resistance or thermal stability. In some embodiments, the annealing time may vary depending on the annealing temperature (T_a) . In some embodiments, an annealing temperature (T_a) may be set to reduce or minimize the annealing time. In some embodiments, the annealing time may vary depending on the size and/or material of object 120, the size and/or material of reversible gelation medium 130, environmental temperature, performance of temperature control unit 140, and/or additional operational procedures. In some embodiments, the annealing time may be less than about a minute, while in other embodiments, may be about several minutes up to several hours. For example, the annealing time may take approximately 30 seconds, from about 1 to about 2 minutes, from about 5 to about 10 minutes, or up to about two hours or a few hours.

In some embodiments, object 120 may be made with PLA. PLA is a polyester with high molecular weight and is synthesized by the polymerization of lactide monomers, which is a cyclic dimer of lactic acid, or 2-hydroxypropionic acid. Lactic acid is a chiral molecule with two enantiomeric forms, L-lactic acid and D-lactic acid. In some embodiments, the PLA of object 120 may include both L-lactic acid and D-lactic acid. The composition of L-lactic acid and D-lactic acid in PLA may, for example, affect the crystallization behavior of PLA, including the degree of crystallinity and crystallization kinetics. Most commercially available PLAs have higher L-lactic acid content than D-lactic acid content. When D-lactic acid content increases, the degree of crystallinity, melting temperature, and/or crystallization rate may decrease. For example, PLA may show little tendency to crystallize when the content of D-lactic acid exceeds about 15％ by weight. Further, for example, the crystallization kinetics or rate of PLA may be controlled or regulated by adjusting the relative content of D-lactic acid and L-lactic acid. In some embodiments, object 120 constructed using PLA in accordance with the present disclosure may have an L-lactic acid content in the range from about 85％ to about 100％ by weight. Examples of such PLA materials include 2500HP, 4032D, 2003D, 4043D, and 7001 D from NatureWorks LLC.

FIG. 2 shows a flow chart of exemplary methods of making object 120 in accordance with the present disclosure. In one embodiment, the method includes

steps

210, 220, 230, and 240. Step 210 may include constructing object 120 using 3D printer 110. For example, object 120 may be constructed using PLA extruded from a heated extrusion nozzle of 3D printer 110. Step 220 may include placing object 120 in reversible gelation medium 130. For example, object 120 may be manually or automatically placed and partially or wholly submerged in reversible gelation medium 130 at a liquid phase and undergo crystallization or annealing while being partially or wholly submerged in reversible gelation medium 130. In some embodiments, step 220 may include preparing reversible gelation medium 130 at a liquid phase to allow object 120 to be partially or wholly submerged. Step 230 may include processing object 120 in reversible gelation medium 130. For example, step 230 may include annealing object 120 in reversible gelation medium 130, allowing the material of object 120 to undergo crystallization. In some embodiments,

steps

220, 230, and 240 may be iterated for as many or as few times as necessary, for example, about 2 to 5 times, until object 120 develops a sufficient or substantial degree of crystallinity, has a desirable softening temperature, and/or has a certain degree of toughness or softness. For example, after step 240, object 120 may have a softening temperate increased by from about 50℃ to about 150℃, and/or have a degree of crystallinity a degree of crystallinity ranging from about 5％ to about 10％, from about 10％ to about 20％, from about 20％ to about 30％, from about 30％ to about 40％, from about 5％ to about 20％, from about 10％ to about 30％, from about 25％ to about 40％, from about 5％ to about 30％, from about 10％ to about 40％, from about 5％ to about 20％, from about 20％ to about 40％, or from about 5％ to about 40％ crystallinity, or higher.

FIG. 3 shows a flow chart of exemplary methods for processing 3D-printed object 120 at step 230 in accordance with the present disclosure. In one embodiment, step 230 may include

steps

231, 232, and 233. Step 231 may include heating reversible gelation medium 130 from a first temperature, for example, room temperature, to a second temperature, for example, the annealing temperature (T_a) of the material of object 120. In some embodiments, step 231 may include detecting and/or increasing the temperature of reversible gelation medium 130 by temperature control unit 140 until the second temperature is reached. In some embodiments, step 231 may include, continuously or intermittently, increasing the temperature of reversible gelation medium 130 at a rate controlled by temperature control unit 140 to the second temperature and/or over a range of temperatures. In some embodiments, the second temperature and/or the annealing temperature (T_a) are higher than the sol-gel transition temperature (T_t) of reversible gelation medium 130 such that the temperature of reversible gelation medium 130 passes the sol-gel transition temperature (T_t) , allowing reversible gelation medium 130 to change from a liquid to a solid gel.

Step 232 may include annealing object 120 in reversible gelation medium 130 at the second temperature, such as the annealing temperature (T_a) . In some embodiments, step 232 may include annealing object 120 in reversible gelation medium 130 at more than one temperatures, such as a ranges of temperatures around the annealing temperature (T_a) . In some embodiments, step 232 may include detecting and/or maintaining the temperature of reversible gelation medium 130 at the second temperature by temperature control unit 140. In some embodiments, the second temperature and/or the annealing temperature (T_a) may be higher than the glass transition temperature (T_g) of the material of object 120 such that the material of object 120 may undergo crystallization and/or be at a molten or amorphous state during annealing. For example, object 120 constructed with PLA may have a glass transition temperature of about 60℃ and the annealing temperature may, for example, be in the range from about 70℃ to about 120 ℃. In some embodiments, step 232 may last for a certain period of time until the material of object 120 develops a sufficient or substantial degree of crystallinity, has a desirable softening temperature, and/or has a certain degree of toughness or softness. In some embodiments, at step 232, reversible gelation medium 130 while at a solid phase may serve as a temporary mold to object 120 during annealing, and thus may minimize or eliminate deformation of object 120 during annealing.

Step 233 may include cooling reversible gelation medium 130. In some embodiments, step 233 may include detecting and/or decreasing the temperature of reversible gelation medium 130 by temperature control unit 140 until the first temperature, for example, room temperature, is reached. In some embodiments, the temperature of reversible gelation medium 130 may pass the sol-gel transition temperature (T_t) during cooling such that reversible gelation medium 130 changes from a solid gel to a liquid. In other embodiments, step 234 may include detecting and/or decreasing the temperature of reversible gelation medium 130 by temperature control unit 140 until reversible gelation medium 130 changes from a solid gel to a liquid. In some situations,

steps

231, 232, and 233 may be iterated for as many or as few times as necessary until object 120 develops a sufficient degree of crystallinity, has a desirable softening temperature, and/or has a certain degree of toughness or softness. For example, steps 231, 232, and 233 may be iterated for 2 to 5 times until object 120 constructed with PLA has a softening temperature increased by about 10℃ to about 100℃. In some embodiments,

steps

231, 232, and 233 may be repeated using a second reversible gelation medium having the same or different chemical components.

In some embodiments, step 230 may include

steps

231, 234, 235, and 233. In some embodiments, step 231 may include heating reversible gelation medium 130 from a first temperature, for example, room temperature, to a second temperature, such as the sol-gel transition temperature (T_t) of reversible gelation medium 130 or a temporary temperature (t) above the sol-gel transition temperature (T_t) . In some embodiments, step 231 may include detecting and/or increasing the temperature of reversible gelation medium 130 by temperature control unit 140 until the second temperature is reached. In some embodiments, step 231 may include holding reversible gelation medium 130 at about the second temperature for a period of time. In some embodiments, the second temperature may be higher than the sol-gel transition temperature (T_t) but lower than the annealing temperature (T_a) and/or the glass transition temperature (T_g) of the material of object 120 such that as reversible gelation medium 130 changes from a liquid to a solid gel, object 120 may not become soft or deform during the transition.

Step 234 may include heating reversible gelation medium 130 from the second temperature, for example, the sol-gel transition temperature (T_t) of reversible gelation medium 130 or a temporary temperature (t) above the sol-gel transition temperature (T_t) to a third temperature, for example, the annealing temperature (T_a) . In some embodiments, step 234 may include detecting and/or increasing the temperature of reversible gelation medium 130 by temperature control unit 140 until the third temperature is reached. In some embodiments, as the temperature of reversible gelation medium 130 is increased from the second temperature to the third temperature, reversible gelation medium 130 may remain at a solid gel phase and may serve as a temporary mold.

Step 235 may include annealing object 120 in reversible gelation medium 130 at the third temperature, for example, the annealing temperature (T_a) , for a period of time. In some embodiments, step 235 may include detecting and/or maintaining the temperature of reversible gelation medium 130 at the third temperature or the annealing temperature (T_a) by temperature control unit 140. In some embodiments, the third temperature or the annealing temperature (T_a) may be higher than the glass transition temperature (T_g) and/or may be about the same as the crystallization temperature (T_c) of the material of object 120 such that the material of object 120 may undergo crystallization and/or be at a molten state during annealing. For example, object 120 constructed with PLA may have a glass transition temperature of about 60℃ and the annealing temperature may range from about 70℃ to about 120℃. In some embodiments, step 235 may last for a certain period of time until the material of object 120 develops a sufficient degree of crystallinity, has a desirable softening temperature, and/or has a certain degree of toughness or softness. In some embodiments, at step 235, reversible gelation medium 130 at a solid gel phase may serve as a temporary mold to object 120 during annealing, and thus may minimize or eliminate deformation of object 120 during annealing.

In some embodiments, step 233 after step 235 may include cooling reversible gelation medium 130 from the third temperature to the second temperature. For example, step 233 may include detecting and/or decreasing the temperature of reversible gelation medium 130 by temperature control unit 140 until the second temperature, for example, the sol-gel transition temperature (T_t) or a temporary temperature (t) above the sol-gel transition temperature (T_t) , is reached. In some embodiments, reversible gelation medium 130 may or may not change from a solid gel to a liquid at the second temperature. In some embodiments, step 233 may include cooling reversible gelation medium 130 from the third temperature to the first temperature or even a lower temperature than the first temperature. In some embodiments, the temperature of reversible gelation medium 130 may pass the transition temperature (T_t) during cooling such that reversible gelation medium 130 changes from a solid gel to a liquid.

In some embodiments, step 233 may include detecting and/or decreasing the temperature of reversible gelation medium 130 by temperature control unit 140 until reversible gelation medium 130 changes from a solid gel to a liquid. In some situations,

steps

231, 234, 235, and 233 may be iterated for as many or as few times as necessary until object 120 develops a sufficient degree of crystallinity, has a desirable softening temperature, and/or has a certain degree of toughness or softness. For example, steps 231, 234, 235, and 233 may be performed or iterated for 2 to 5 times until object 120 constructed with PLA may have a softening temperature increased by about 50℃ to about 100℃.

Examples of making object 120 with improved heat resistance

A 40 wt-％ aqueous solution of PEO-PPO-PEO triblock copolymer was prepared as the reversible gelation medium by dissolving 12 g of Pluronic F68 (produced by BASF, PPO Mw ＝ 1800 g/mol, PEO wt-％＝ 80％) in water. Sample objects (20 mm x 20 mm x 4 mm) were constructed using the FFF process on a desktop 3D printer (MakerBot Replicator 2) . The material for constructing the sample objects was PLA (4043D from NatureWorks) . The PLA used for this experiment had a softening temperature of about 60℃. The 3D printer was set with the following parameters: layer height ＝ 0.2 mm； infill ＝ 100％； number of shells ＝ 2； printing temperature ＝ 200℃； printing speed ＝ 90 mm/s.

One sample object was placed in the reversible gelation medium at room temperature (approximately 18℃) for processing. The sample object was fully submerged in the reversible gelation medium. The reversible gelation medium was then sealed to prevent water evaporation, heated to a temperature in the range from about 40℃ to about 50℃, and kept isothermal for about 30 min to allow the solution to change to a solid gel. The temperature was then further increased to about 90℃ and maintained at about 90℃ for about 4 hours to anneal the sample object. After annealing, the reversible gelation medium was allowed to cool to room temperature and to change from a solid gel to a solution. The sample object was then taken out from the reversible gelation medium, rinsed, and dried.

Vicat softening test was performed to compare the softening behavior of the processed sample object and an as-printed sample object. The test was carried out under the following conditions: force ＝ 1 N； heating rate ＝ 120℃/h. Vicat softening curves showing penetration depths vs. temperatures of the processed sample object 401 and of the as-printed object 402 are shown in FIG. 4. It can be seen from FIG. 4 that the penetration depth of the processed sample object remain to be around zero until the temperature was increased to about 140℃. On the other hand, the penetration depth of the as-printed sample object started to increase when the temperature was increased to about 50℃. This result shows that the processed sample object had substantially improved heat resistance than the as-printed sample object, showing a softening temperature higher than about 140℃. In contrast, the as-printed sample object showed substantial softening or a softening temperature at about 60℃.

Differential scanning calorimetry (DSC) was performed to characterize the degrees of crystallinity of the processed sample object and the as-printed sample object. DSC (TA Instruments, Q2000) is a standard tool for characterizing degrees of crystallinity of polymers. The samples for DSC measurements were prepared by encapsulating several milligrams of the materials of the processed sample object and the as-printed sample object in DSC pans. The samples were first equilibrated at 20℃, and then heated to 200℃ at a rate of 20℃/min. FIG. 5 graphically compares the DSC thermograph 501 of the materials of the processed sample object and the DSC thermograph 502 of the materials of the as-printed sample object, showing heat flow in the y axis and temperature in the x axis. The degree of crystallinity of the materials was calculated by:

wherein: ΔH_m, ΔH_c, and ΔH_f are the heat of melting, heat of cold crystallization, and heat of fusion, respectively. ΔH_m and ΔH_c can be determined by integrating the endothermic melting peak and the exothermic cold crystallization peak, respectively, on the DSC curve. ΔH_f is taken from literature as 146 kJ/mol (Polymer Data Handbook, Oxford University Press, Inc., 1999) .

As shown in FIG. 5, thermograph 502 of the as-printed sample object showed a substantial cold crystallization peak (an exothermic peak) in the temperature range from 100℃ to 140℃, indicating a lack of crystallinity of the sample, followed by a melting peak (an endothermic peak) centered around 150℃. In contrast, as shown in FIG. 5, thermograph 501 of the processed sample object showed only a substantial melting peak, centered around 156℃, with no observable cold-crystallization peak. Thermograph 501 of the processed sample object indicated substantial crystallization developed in the material of the object.

Calculated according to the above equation, the degree of crystallinity of the as-printed sample object was less than 1％, whereas the degree of crystallinity of the processed sample object was 25.9％. This result showed that the processed sample object had a higher degree of crystallinity, which corresponds to a higher softening temperature, and thus an improved heat resistance compared to the as-printed sample object.

Embodiments of the present disclosure may provide several benefits over currently available methods for making objects using additive manufacturing. For example, embodiments of the disclosure may provide a method for making an object that has improved heat resistance and limited or no undesirable deformation for different applications. Exemplary uses may include machine parts, medical devices, drug delivery scaffolds, and culinary tools. Furthermore, the degree of crystallinity or heat resistance may be controlled by adjusting the annealing time or the annealing temperature to be suitable for various applications. Reversible gelation medium 130 may be reusable and recyclable. In addition, methods in accordance with present disclosure may be used to adjust the mechanical properties, for example, softness, stiffness, rigidness, and/or brittleness of 3D-printed objects.

In some embodiments, the material used for constructing object 120 may further include, for example, at least one additive selected from dyes and/or pigments that may add color to the object, and pharmaceutical agents when the object is used as medical devices or drug delivery scaffolds. For example, such pharmaceutical agents may include anesthetics, anti-inflammatories, antiseptics, or medications that facilitate tissue regeneration, prevent infection (e.g., antibiotics) , or treat diseases (e.g., cancer) . Other additives may include, for example, chemicals, ceramics, and biomaterials, such as growth factor, cytokines, fibrinogen, platelet-rich plasma, cells, tissue, or other suitable materials or combination of materials. In some embodiments, reversible gelation medium 130 for processing 3D-printed object 120 may further include at least one additional material selected from, for example, a solvent, a buffer, and any other chemical that may be used to control or adjust the phase transition from a solid gel to a liquid, and vice versa.

It is to be understood that the particular examples and embodiments set forth herein are non-limiting, and modifications to structure, dimensions, materials, and methodologies may be made without departing from the scope of the present teachings. It will be evident that various modifications and changes may be made without departing from the broader spirit and scope of the disclosure as set forth in the claims that follow. The specification and drawings are accordingly to be regarded as illustrative rather than restrictive.

Claims

A method of processing an object, comprising:

annealing the object in at least one reversible gelation medium, and

increasing a degree of crystallinity of a material of the object .
The method of claim 1, further comprising forming the object using a 3D printer.
The method of claim 1, further comprising increasing the degree of crystallinity of the material of the object by 5％ to 40％.
The method of claim 1, further comprising increasing a softening temperature and/or heat resistance of the object by increasing the degree of crystallinity of the material of the object.
The method of claim 4, further comprising increasing the softening temperature of the object by 50℃ to 150℃ measured by a Vicat softening point test.
The method of claim 1, wherein the reversible gelation medium can undergo a phase transition from a liquid to a solid gel and/or from a solid gel to a liquid, in response to at least one stimuli selected from temperature, pH, light, mechanical force and/or pressure, radiation, electrical and/or magnetic fields, and electrical current.
The method of claim 1, wherein the reversible gelation medium is a temperature-responsive gelation medium configured to have a transition temperature.
The method of claim 7, further comprising increasing a temperature of the reversible gelation medium from a first temperature to a second temperature.
The method of claim 8, wherein the first temperature is a temperature below the transition temperature of the reversible gelation medium.
The method of claim 9, wherein the second temperature is around or higher than an annealing temperature of the material of the object, wherein the annealing temperature is above a glass transition temperature and below a melting temperature of the material of the object.
The method of claim 9, wherein the second temperature is around or close to the crystallization temperature of the material of the object.
The method of claim 9, wherein the second temperature is a temperature above the transition temperature of the reversible gelation medium such that the reversible gelation medium transitions from a liquid to a solid gel during the increase of the temperature of the reversible gelation medium.
The method of claim 12, wherein the second temperature is lower than a glass transition temperature of the material of the object.
The method of claim 13, further comprising increasing the temperature of the reversible gelation medium from the second temperature to a third temperature.
The method of claim 14, wherein the third temperature is around or higher than the annealing temperature of the material of the object, wherein the annealing temperature is above a glass transition temperature and below a melting temperature of the material of the object.
The method of claim 12, further comprising providing a temporary mold to the object with the solid gel during annealing.
The method of claim 16, further comprising reducing, minimizing, or eliminating deformation of the object during annealing with the temporary mold.
The method of claim 12, further comprising decreasing the temperature of the reversible gelation medium from the second temperature to the first temperature during which the reversible gelation medium transitions from a solid gel to a liquid.
The method of claim 12, wherein the object is partially or wholly submerged in the liquid.
The method of claim 18, wherein the object can be partially or wholly retrieved from the liquid.
The method of claim 2, wherein the material of the object remains amorphous after being extruded from an extrusion nozzle of the 3D printer.
The method of claim 1, wherein the material of the object after annealing is less elastic and/or more rigid or stiffer than that before annealing.
The method of claim 1, wherein the material of the object comprises at least one crystallizable polymer.
The method of claim 23, wherein the material of the object comprises at least one polymer selected from poly (lactic acid) (PLA) , poly (ethylene terephthalate) (PET) , PET copolymers, polyamide, polyamide copolymers, and nylon.
The method of claim 1, wherein the material of the object comprises at least one polymer selected from thermoplastic polyurethanes (TPUs) , polyoxymethylen (POM) , poly (lactic acid) (PLA) , thermoplastic polyurethanes, poly (ethylene terephthalate) (PET) , PET copolymers, vinyl acetal polymers, acrylonitrile-butadiene-styrene (ABS) , polycarbonate (PC) , polystyrene (PS) , high impact polystyrene (HIPS) , polycaprolactone (PCL) , polyphenylsulfone (PPSF) , Ultem 9085, polyamide, polyamide copolymers, cellulose based polymers, acrylic or acrylate based polymers, nylon, polybenzimidazole, polyether sulfone (PES) , polyether ether ketone (PEEK) , polyethene (PE) , polyphenylene oxide (PPO) , polyphenylene sulfide (PPS) , polypropylene (PP) , polyvinyl chloride (PVC) , and polytetrafluoroethylene (PTFE) .
The method of claim 2, wherein the 3D printer performs an additive manufacturing technology to form the object, using at least one method selected from selective laser melting (SLM) , direct metal laser sintering (DMLS) , selective laser sintering (SLS) , selective heat sintering (SHS) , fused deposition modeling (FDM) , fused filament fabrication (FFF) , robocasting, stereolithography (SLA) , laminated object manufacturing (LOM) , digital light processing (DLP) , plaster-based 3D printing (PP) , electron-beam melting (EBM) , electron beam freeform fabrication (EBF) , photopolymerization, binding of granular materials, extrusion deposition, and lamination.
The method of claim 2, wherein the 3D printer performs an additive manufacturing technology to form the object, using at least one method selected from fused deposition modeling (FDM) , fused filament fabrication (FFF) , and extrusion deposition.
The method of claim 7, wherein the temperature-responsive gelation medium comprises at least one polymer selected from poly (N-isopropylacrylamide) (PNIPAAm) , poly (N, N-diethylacrylamide) (PDEAAm) , poly (N-vinlycaprolactam) (PVCL) , poly [2-(dimethylamino) ethyl methacrylate] (PDMAEMA) poly (ethylene glycol) (PEG) , poly (ethylene oxide) (PEO) , PEG methacrylate polymers (PEGMA) , polyoxypropylene (PPO) , polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO-PPO-PEO) , ethyl (hydroxyethyl) cellulose (EHEC) , Pluronics, and Poloxamers.
A system for processing an object, comprising:

an annealing apparatus comprising at least one reversible gelation medium configured to anneal the object and to increase a degree of crystallinity of a material of the object.
The system of claim 29, further comprising a 3D printer configured to form the object.
The system of claim 29, wherein the degree of crystallinity of the material of the object is increased by 5％ to 40％.
The system of claim 29, wherein a softening temperature and/or heat resistance of the object is increased by increasing the degree of crystallinity of the material of the object.
The system of claim 32, wherein the softening temperature of the object is increased by 50℃ to 150℃ measured by a Vicat softening point test.
The system of claim 29, wherein the reversible gelation medium can undergo a phase transition from a liquid to a solid gel and/or from a solid gel to a liquid, in response to at least one stimuli selected from temperature, pH, light, mechanical force and/or pressure, radiation, electrical and/or magnetic fields, and electrical current.
The system of claim 29, wherein the reversible gelation medium is a temperature-responsive gelation medium configured to have a transition temperature.
The system of claim 35, further comprising a temperature control unit configured to increase a temperature of the reversible gelation medium from a first temperature to a second temperature.
The system of claim 36, wherein the first temperature is a temperature below the transition temperature of the reversible gelation medium.
The system of claim 37, wherein the second temperature is around or higher than an annealing temperature of the material of the object, wherein the annealing temperature is above a glass transition temperature and below a melting temperature of the material of the object.
The system of claim 37, wherein the second temperature is around of close to the crystallization temperature of the material of the object.
The system of claim 37, wherein the second temperature is a temperature above the transition temperature of the reversible gelation medium such that the reversible gelation medium transitions from a liquid to a solid gel during the increase of the temperature of the reversible gelation medium.
The system of claim 40, wherein the second temperature is lower than a glass transition temperature of the material of the object.
The system of claim 41, further comprising increasing the temperature of the reversible gelation medium from the second temperature to a third temperature.
The system of claim 42, wherein the third temperature is around or higher than the annealing temperature of the material of the object, wherein the annealing temperature is above a glass transition temperature and below a melting temperature of the material of the object.
The system of claim 40, wherein the solid gel serves as a temporary mold to the object during annealing.
The system of claim 44, wherein deformation of the object during annealing with the temporary mold is reduced, minimized, or eliminated.
The system of claim 40, wherein the temperature control unit is configured to decrease the temperature of the reversible gelation medium from the second temperature to the first temperature during which the reversible gelation medium transitions from a solid gel to a liquid.
The system of claim 40, wherein the object is partially or wholly submerged in the liquid.
The system of claim 46, wherein the object can be partially or wholly retrieved from the liquid.
The system of claim 30, wherein the material of the object remains amorphous after being extruded from an extrusion nozzle of the 3D printer.
The system of claim 29, wherein the material of the object after annealing is less elastic and/or more rigid or stiffer than that before annealing.
The system of claim 29, wherein the object comprises at least one crystallizable polymer.
The system of claim 51, wherein the material of the object comprises at least one polymer selected from poly (lactic acid) (PLA) , poly (ethylene terephthalate) (PET) , PET copolymers, polyamide, polyamide copolymers, and nylon.
The system of claim 29, wherein the material of the object comprises at least one polymer selected from thermoplastic polyurethanes (TPUs) , polyoxymethylen (POM) , poly (lactic acid) (PLA) , thermoplastic polyurethanes, poly (ethylene terephthalate) (PET) , PET copolymers, vinyl acetal polymers, acrylonitrile-butadiene-styrene (ABS) , polycarbonate (PC) , polystyrene (PS) , high impact polystyrene (HIPS) , polycaprolactone (PCL) , polyphenylsulfone (PPSF) , Ultem 9085, polyamide, polyamide copolymers, cellulose based polymers, acrylic or acrylate based polymers, nylon, polybenzimidazole, polyether sulfone (PES) , polyether ether ketone (PEEK) , polyethene (PE) , polyphenylene oxide (PPO) , polyphenylene sulfide (PPS) , polypropylene (PP) , polyvinyl chloride (PVC) , and polytetrafluoroethylene (PTFE) .
The system of claim 30, wherein the 3D printer performs an additive manufacturing technology to construct the object, using at least one method selected from selective laser melting (SLM) , direct metal laser sintering (DMLS) , selective laser sintering (SLS) , selective heat sintering (SHS) , fused deposition modeling (FDM) , fused filament fabrication (FFF) , robocasting, stereolithography (SLA) , laminated object manufacturing (LOM) , digital light processing (DLP) , plaster-based 3D printing (PP) , electron-beam melting (EBM) , electron beam freeform fabrication (EBF) , photopolymerization, binding of granular materials, extrusion deposition, and lamination.
The system of claim 30, wherein the 3D printer performs an additive manufacturing technology to form the object, using at least one method selected from: fused deposition modeling (FDM) , fused filament fabrication (FFF) or extrusion deposition.
The system of claim 35, wherein the temperature-responsive gelation medium comprises at least one polymer selected from poly (N-isopropylacrylamide) (PNIPAAm) , poly (N, N-diethylacrylamide) (PDEAAm) , poly (N-vinlycaprolactam) (PVCL) , poly [2-(dimethylamino) ethyl methacrylate] (PDMAEMA) poly (ethylene glycol) (PEG) , poly (ethylene oxide) (PEO) , PEG methacrylate polymers (PEGMA) , polyoxypropylene (PPO) , polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO-PPO-PEO) , ethyl (hydroxyethyl) cellulose (EHEC) , Pluronics, and Poloxamers.