Polyester GELS and aerogels

Abstract

Polyester gels aerogels. In particular, a method of making polyester gels and aerogels using environmentally benign solvents for gel formation. The polyester gels and aerogels may specifically be sourced from poly(ethylene terephthalate).

Description

POLYESTER GELS AND AEROGELSField

[0001] The present invention is directed to polyester gels and aerogels. In particular, a method of making polyester gels and aerogels using environmentally benign solvents for gel formation. The polyester gels and aerogels may specifically be sourced from poly(ethylene terephthalate).Background

[0002] Polymeric gels are known to contain a polymeric network that is said to exhibit solid-like behavior while physically retaining liquids or gases within their three-dimensional macromolecular framework. The gel network can be held together with covalent chemical bonds, as in the case of crosslinked gels, or by physical interactions, in the case of physical gels. The physical interactions that compose a physical gel network can include hydrogen bonding, helix formation, phase separation, polymer entanglements, ionic aggregation, n-n interactions, and polymer crystallites. Physical gels are also described as thermoreversible, as their physical interactions are thermally labile.

[0003] Thermoreversible gelation has been reported for poly(vinyl chloride), polyethylene, isotatic polypropylene, sydiotactic polystyrene, poly(L-lactic acid), polyoxymethylene, polyamide-6, poly(vinylidene fluoride), poly(ethylene terephthalate), poly(phenylene oxide), syndiotactic poly (methyl methacrylate) and poly (phenylene sulfide). The choice of solvent reportedly leads to differences in gel morphology and properties.

[0004] When the solvent in a gel network is replaced with a gas (e.g. air), it is understood to be an aerogel. Evaporative drying, freeze-drying, and supercritical fluid extraction are reportedly utilized for removing the solvent from a gel. Aerogels so produced reportedly have relatively low density, relatively high porosity, relatively high surface area, and relatively low thermal conductivity.

[0005] Accordingly, one object herein is to provide a method of making polyester gels and polyester aerogels with, e.g., improved thermal conductivity and mechanical properties and a method of making polyester aerogels, based upon the use of what can be described as an environmentally benign solvent, such as 1,3 -diphenylacetone (DPA).Summary

[0006] A method of forming a polyester aerogel comprising supplying a crystallizable polyester,

[0007] supplying 1 ,3-diphenylacetone solvent and combining the crystallizable polyester and 1 ,3- diphcnylacctonc solvent. This is then followed by heating to a dissolution temperature to form a solution of the crystallizable polyester in 1,3-dipheny lacetone solvent. The solution is then cooled with formation of a polyester gel. The polyester gel so formed in 1,3-diphenylacetone can then undergo solvent exchange with replacement of the 1 ,3-diphenylacetone with an aliphatic alcohol solvent or acetone. This is then followed by replacement of the aliphatic alcohol or acetone solvent with water and then the gel can be lyophilized to remove water, resulting in the polyester aerogel. In addition, the polyester gel containing aliphatic alcohol solvent may undergo supercritical CO2 extraction to form the aerogel. The crystallizable polymer may preferably be selected from poly(ethylene terephthalate).

[0008] A method of 3D printing a polyester aerogel comprising supplying a crystallizable polyester, supplying a solvent for said crystallizable polyester that has a boiling point of at or greater than 300 °C, and combining the crystallizable polyester and solvent and heating to a dissolution temperature to form a solution of the crystallizable polyester in the solvent. This is followed by cooling the solution and forming a solvated polyester gel in the presence of the solvent and forming pellets of the solvated polyester gel. The pellets of the solvated polyester gel and then fed into an extruder followed by extruding one or more layers of the solvated polyester gel. One can then replace the solvent in the solvated polyester gel with an aliphatic alcohol or acetone solvent followed by: (1) replacement of the aliphatic alcohol or acetone solvent with water and forming a polyester hydrogel where the polyester hydrogel is lyophilized to remove water; or (2) removal of the aliphatic alcohol or acetone solvent via supercritical CO2 extraction with formation of the polyester aerogel.Brief Description of the Drawings

[0009] FIG. 1 is a scanning electron micrograph (SEM) of a 15.0 % wt. PET aerogel gelled in 1,3- diphenylacetone showing axialitic morphology.

[0010] FIG. 2 is a scanning electron micrograph (SEM) of a 15.0 % wt. PET aerogel gelled in 1,3- diphenylacetone showing spherulite morphology.

[0011] FIG. 3 is a plot of compression modulus versus gelation temperature for PET aerogels formed from a 15.0 % (wt.) solution of PET / DPA.

[0012] FIG. 4A is a SEM micrograph a PET aerogel formed herein at the indicated magnification.

[0013] FIG. 4B is a SEM micrograph of a PET aerogel formed herein at the indicated magnification.

[0014] FIG. 5A is a cross polarized light micrograph of a thin section PET gel in DPA prepared at 210 °C and relatively rapid cooling producing a featureless (dark) PLM image.

[0015] FIG. 5B is a cross polarized small-angle laser light scattering image of a thin section PET gel in DPA prepared at 210 °C and relatively rapid cooling producing a featureless (dark) SALLS image..

[0016] FIG. 5C shows a cross polarized light micrograph of a thin section PET gel in DPA prepared at 230 °C and relatively rapid cooling producing a PLM image of birefringent PET spherulites.

[0017] FIG. 5D shows a cross polarized small-angle laser light scattering image of a thin section PET gel in DPA prepared at 230 °C and relatively rapid cooling producing a four-lobe SALLS image characteristic of birefringent spherulites.

[0018] FIG. 5E shows a SEM image of a 15.0 wt. % PET aerogel processed at a dissolution temperature of 230 °C revealing a globular morphology with relatively large disconnected structures characteristic of spherulites.Detailed Description

[0019] The polyester polymers that are suitable here for the preparation of a polyester aerogel are contemplated to preferably include crystallizable polyesters. A crystallizable polyester is reference to a polyester polymer where chain alignment can take place, which may include folding of the chains into ordered crystalline regions. Crystallizable polyesters may therefore be initially identified upon cooling from the molten state along with the formation of ordered regions that include lamellae which may compose relatively larger regions identified as spherulites. Preferably, the crystallizable polyesters herein that are suitable for aerogel formation are those that can indicate a degree of crystallinity with appropriate cooling form the melt state of at least 10.0%, more preferably at least 25.0%, and most preferably, at least 50.0%.

[0020] Polyester polymers herein therefore preferably include polyalkylene terephthalates which are generally understood as polymers containing a repeat unit composed of an ester group, an aromatic group, and an aliphatic methylene group [e.g., -(CEh - or -(CH2)4-]. Such polyesters are sometimes more generally referred to as aliphatic-aromatic polyesters. Particularly preferred polyester polymers herein suitable for preparation of the polyester aerogel herein are contemplatedto include poly(ethylene terephthalate) or PET, poly(propylene terephthalate), poly(butylene terephthalate) or PBT, poly(hcxamcthylcnctcrcphthalatc), and poly(cthylcnc naphthalatc) or PEN. The molecular weight of selected and preferred crystallizable polyesters below are such that the value of n in the repeating unit provides a number average molecular weight (Mn) in the range of 10,000 to 100,000.

[0021] The PET itself may include virgin PET and / or recycled PET. Recycled PET is reference to PET that is recovered from PET manufacture (e.g. PET regrind) and / or PET recovered from a given consumer or commercial application. Recycled PET that is suitable for use herein to form a polyester aerogel from a benign environmental solvent may therefore include PET recovered from bottles or containers, food packaging, films, and / or textile products. In addition, it is contemplated that the crystallizable polyester polymers suitable for aerogel formation herein include segmented polyester block copolymers (virgin or recycled). One preferred example of a segmented polyester block copolymer includes poly(butylene terephthalate) segments in combination with what is termed a soft segment that is preferably composed of a polyalkylene ether [e.g., poly(butylene oxide)] or an aliphatic type polyester.

[0022] The crystallizable polyester polymers herein are initially combined with an environmentally benign solvent which upon heating forms a solution of the polyester polymer, followed by cooling and gelation, a solvent exchange step, and ultimately removal of solvent and formation of the PET aerogel. The solution so formed at elevated temperature is preferably ahomogenous solution. The environmentally benign solvent is selected from 1 ,3-diphenylacetone (DPA) which has a melting point of 34 °C, a boiling point of 330 °C, and which is identified as an FDA-approved food grade additive. The structure of DPA is set out below:

[0023] As alluded to above, the initial step is to provide the crystallizable polyester polymer and mix with the solvent DPA. By way of preferred example in the case of PET as the exemplary crystallizable polyester polymer, one prepares a PET / DPA solution at a preferred polymer concentration in the range of 5.0 % (wt.) to 50.0 % (wt.), including all individual values and increments therein. For polyester aerogel formation, an even more preferred range is 5.0 % (wt.) to 25.0 % (wt.). In one further and more particularly preferred embodiment, the PET / DPA solution is prepared at a polymer concentration in the range of 10.0 % (wt.) to 20.0 wt. %. In addition, such PET / DPA solution is preferably prepared by heating the mixture of PET and DPA to a dissolution temperature of at least 205 °C, more preferably 205 ° to a temperature of less than or equal to 230 °C, including all values and increments therein. More preferably, the dissolution temperature is in the range of 205 ° C to less than 230 °, such as in the range of 205 °C to 225 °C or 205 °C to 220 °C. It is worth noting that during the preparation of the PET / DPA solution, it has been found preferable to ensure that one mechanically agitates or stirs the PET / DPA mixture upon heating and from the point that the DPA melts up to the selected dissolution temperature. Such stirring upon heating has been observed to provide a relatively more homogenous solution and relatively more homogenous aerogel with relatively uniform mechanical properties.

[0024] In one embodiment, the PET / DPA mixture is dissolved at a preferred temperature that is limited to a temperature below the point at which the last PET crystals melt as determined by differential scanning calorimetry (DSC). . It should be appreciated that semicrystalline polymers typically melt over a broad range of temperatures due to a wide range of crystallite thicknesses. It should also be appreciated that relatively thin crystals melt at relatively lower temperatures, while the relatively thicker crystals melt at higher temperatures. It should also be appreciated that solvents that dissolve a given polymer can typically lower the range of melting, known as melting point depression.

[0025] Accordingly, in the preferred embodiment, the dissolution temperature of the crystallizable polyester such as PET in DPA can be preferably limited to a temperature below the point where the last crystal melts as determined by DSC. It is also contemplated that under these preferred conditions, the resulting solution or dispersion will retain a relatively small portion of un-melted PET crystallites in solution (self nuclei), known as melt-memory. Without being bound by theory, upon cooling, these un-melted PET crystallites in solution can then provide a relatively high nucleation density to facilitate the formation of a preferably nanofibrillar gel morphology. Accordingly, the level of spherulites can be made to be less than or equal to 10.0 % by volume, or less than or equal to 5.0 % by volume, or even less than or equal to 2.5% by volume. Such can be readily determined from SEM micrographs.

[0026] In contrast, if the dissolution temperature is at or above the point that the last PET crystal melts as determined by DSC, all the crystallites are contemplated to melt, resulting in a relatively low or non-existent self-nucleation density upon cooling. With a relatively low or non-existent self-nucleation density, crystal growth is spatially uninhibited allowing for the undesirable development of a significant amount of large spherulites in the resulting gel.

[0027] The PET / DPA solution so prepared is then subject to cooling to induce gelation. The gel so formed may be understood as a solvated gel, containing phase separated polymer in the DPA solvent. Cooling is preferably achieved by taking the heated PET / DPA solution and pouring into open-ended cylindrical glass tubes, which are preferably held in a well heater, and set to a desired cooling temperature. Preferably, the crystallizable polyester polymer in the DPA solvent at a level of 10.0 wt. % to 20.0 wt. % is heated to a temperature in the range of 205 °C to 215 °C to dissolve, or more preferably, to incompletely dissolve as discussed above, the crystallizable polyester followed by cooling at a temperature in the range of 135 °C to 145 °C. The cylindrical glass tubes preferably have a nominal inner diameter of 9.0 mm and a length of 100 mm. Gelation was observed to occur after a period of about 5.0 minutes, and the total cooling time may fall in the range of up to 24 hours. It is also worth noting that the PET / DPA appears to follow what may be termed a solid-liquid (S-L) phase separation, meaning that upon cooling, the PET crystallizes from the solution and organizes into crystalline lamellae, and given sufficient room to grow (i.e. low nucleating density), the lamellae can convert into relatively large spherulites. A spherulite is understood as a spherical crystalline object emanating from a common center. Alternatively, and preferably, when the nucleation density is relatively high, it was observed that the lateral growthof the lamellae was more limited, resulting in a relatively dense collection of axialites (an immature spherulite at a relatively early development stage). An axialitc may therefore be understood as stacked lamellar crystals growing out from a common edge, commonly referred to as immature spherulites.

[0028] After the preferred gelation time of at least 20.0 minutes, the PET / DPA gels are removed from the tubes and then subjected to solvent exchange. Preferably, this is achieved by placing the PET / DPA solvated gels in an ethanol bath to exchange the DPA solvent with an aliphatic alcohol, such as ethanol. After about 24 hours, the ethanol is then preferably exchanged with fresh ethanol, to facilitate further removal of the DPA. After a further time of about 24 hours in the ethanol bath, the gels were transferred to a Soxhlet extractor to further replace any residual DPA with ethanol. Soxhlet extraction was earned out for a preferred period of up to or about 4 days. The ethanol- soaked gels are then exchanged with deionized water for about 4 days in a water bath. The water is preferably replaced with fresh deionized water on a daily basis. The hydrogels so obtained are then preferably frozen overnight and then preferably lyophilized (sublimation of the residual water) over about 24 hours to yield a freeze-dried PET aerogel. It is also worth noting that via this procedure, the level of residual DPA can be reduced to less than 5.0 ng / pL, or even less than 2.5 ng / pL, or even less than 1.5 ng / pL. It is also worth noting that one can take the ethanol or acetone- soaked gels noted above and utilize supercritical CO2 extraction procedures to remove the ethanol or acetone to again provide the polyester aerogel.

[0029] FIG. 1 is a scanning electron micrograph (SEM) of a 15.0 % wt. PET aerogel gelled in DPA. More specifically, the PET was dissolved in DPA at a temperature of about 210 °C and gelled at about 140 °C, which then underwent the solvent exchange to form a hydrogel and then the freeze-drying protocol noted herein. As shown in FIG. 1, the aerogel is characterized as having an axialitic morphology and a density of 0.1594 g / cc. FIG. 2 is a scanning electron micrograph (SEM) of a 15.0% wt. PET aerogel also gelled in DPA. Here, the PET was dissolved at a temperature of about 220 °C and gelled at about 140 °C. As shown in FIG. 2, the aerogel is characterized as having a mixed axialitic / spherulite morphology and a density of 0.1763 g / cc. If the PET is dissolved at temperatures above 230 °C or above, melt memory as noted herein is significantly compromised and ultimately totally lost, and the resulting low nucleation density allows for the formation of discrete and poorly interconnected spherulites In the broad context ofthe present invention, the PET aerogels are contemplated to have a density in the range of 0.09 g / cc to 0.25 g / cc, including all values and increments therein.

[0030] The polyester aerogels herein were then evaluated for their thermal conductivity characteristics. Specifically, steady-state thermal conductivity measurements were performed using a Calibrated Hot Plate Thermal Conductivity Analyzer developed by Aerogel Technologies Inc. (Boston, MA), following ASTM Standard El 225

[2009] . In this setup, the aerogel sample (of unknown thermal conductivity) and a National Institute of Standards and Technology (NIST) reference material with known thermal conductivity (expanded polystyrene board, NIST SRM 1453 are placed in series between a hot plate (set at 37.5 °C) and a cold plate (set at 0 °C). See, Zarr, R. and Pintar, A. (2012), Standard Reference Materials: SRM 1453, Expanded Polystyrene Board, for Thermal Conductivity from 281 K to 313 K, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD, [online], https: / / doi.org / 10.6028 / NIST.SP.260-175 (Accessed July 9, 2025). Assuming one-dimensional heat transfer under steady-state conditions, the thermal conductivity of the aerogel (kaerogei') is calculated using the following equation:

[0031] where, kN,STis the thermal conductivity of the reference material (NIST SRM 1453, with a bulk density of 0.048 g / cm3and a room temperature thermal conductivity of 35.6 mW / mK), and TNIST, ^aerogel - ^NIST- and taerogeltemperature differences and the thicknesses of the NIST standard sample and the aerogel specimen, respectively. See, S. A. Steiner, et al. (2023). Recipes and Designs for Aerogels. In: Aegerter, M.A., Leventis, N., Koebel, M., Steiner III, S.A. (eds) Springer Handbook of Aerogels. Springer Handbooks. Springer, Cham. https: / / doi.org / 10.1007 / 978-3-030-27322-4_65.

[0032] More specifically, PET, as an exemplary polyester herein, was dissolved at 15.0 % (wt.) in DPA at the preferred temperature of 210 °C to yield an axialitic morphology, followed by gelation at a temperature of 140 °C, solvent exchange and freeze-drying. The polyester aerogel so producedindicated a thermal conductivity of 28.9 ± 0.9 milliwatts per meter Kelvin (mW / mK). It is contemplated herein that the polyester aerogels herein may therefore indicate a thermal conductivity in the range of 15.0 mW / mK to 30.0 mW / mK, including all values and increments therein. In particularly preferred embodiments, the thermal conductivity is contemplated to fall in the range of 20.0 mW / mK to 30.0 mW / mK, including all values and increments therein.

[0033] The polyester aerogels herein were also evaluated for their mechanical properties. FIG. 3 provides a plot of the compression modulus observed versus gelation temperature for PET aerogels formed from a 15.0 % (wt.) solution of PET / DPA, with the preferred dissolution temperature of 210 °C. As can be observed, the compression modulus of the polyester aerogels indicated a compression modulus in the range of 7.0 MPa to 18.0 MPa, including all values and increments therein. Preferably, the polyester aerogels herein indicate a compression modulus in the range of 14.0 MPa to 18.0 MPa, including all values and increments therein. In contrast to the surprisingly high modulus of these PET aerogels, gels produced from high dissolution temperatures, such as above 230 °C, produced spherulitic morphologies that disintegrated into powders upon solvent extraction and were thus incapable of mechanical testing.

[0034] SEM micrographs of a 15.0 wt. % PET aerogel processed at a dissolution temperature of 210 °C revealed a morphology composed of isotropically oriented and relatively highly interconnected nano fibrils. See FIGS. 4A and 4B. Accordingly, the PET aerogels herein may be understood to preferably comprise, consist essentially of, or consist of, nanofibril morphology. Nanofibril morphology may be understood as fibrils having diameters in the range of 1.0 nanometers to 100.0 nanometers.

[0035] PET / DPA solutions were next examined by cross-polarized light microscopy (PLM) and small-angle laser light scattering (HV SALLS). For the PET / DPA solution prepared at 210 °C, and relatively rapid cooling to Tgel < 140 °C produced a featureless (dark) PLM image and negligible Hv SALLS scattering, indicating no evidence of birefringence (FIGS. 5A and 5B). In contrast, the PET / DPA solution cooled from 230 °C, yielded the classic Maltese cross extinction patterns in PLM (FIG. 5C) and a distinct four-lobe pattern in Hv SALLS (FIG. 5D), characteristic of birefringent polymer spherulites with radially oriented lamella. The average size of the spherulites as measured by PLM (10.9 ± 0.4 pm) agrees well with the size of the globular features observed by SEM (FIG. 5E), now confirmed as spherulites. Given that the PET component in both the spherulitic and fibrillar gels is semi-crystalline with comparable degrees of crystallinity (Xc = 42.8± 3.5% and 43.7±5.4%, respectively), the lack of birefringence in the fibrillar gel suggests that the inherently ordered crystalline lamella are aligned along the major axis of the fibrils. Since the fibrils are isotropically oriented in the gel, there are no preferential optical axes, and thus no birefringence in the bulk. It is also observed that the fibrillar morphology achieved with the PET aerogels herein provides a surface area in the range of 100 m2 / g to 200 m2 / g, including all values and increments therein.

[0036] A relatively high degree of porosity, n, for the PET aerogels was calculated from the bulk and skeletal densities (i.e., the density of the solid component of the aerogel, dependent on the degree of crystallinity, %Ac) using the following relationship:

[0037] where pb is the bulk density, ps is skeletal density, calculated as:

[0038] where Xc is the degree of crystallinity, %, determined by DSC, pc is the crystalline density of PET (1.46 g / cm3), and pa is the amorphous density of PET (1.35 g / cm3). The 15.0 wt. % fibrillar PET aerogels were found to have a bulk density of pb = 0.152 g / cm3and a skeletal density of ps= 1.40 g / cm3, leading to a porosity of II = 89.1%. Accordingly, in the broad context of the present disclosure, porosity levels of 80.0% or greater are contemplated, or greater than 85.0%, or in the preferred range of 80.0% to 95.0% or 85.0% to 95.0%. In comparison, the 15.0 wt. % spherulitic PET aerogels were found to have a bulk density of pb = 0.222 g / cm3, yielding a porosity of II = 77.8%.

[0039] It is also contemplated herein that the polyester aerogels may be prepared via additive manufacturing and 3D printed via a selective extrusion of a polyester solution preferably through a heated direct ink write (DIW) system. A DIW system is reference to an extrusion-based 3D printing technique in which a liquid feedstock of selected viscosity is dispensed through nozzles under a selected pressure and flow rate. Initially, to prepare the feedstock for printing via a DIW system, crystallizable polyester, as described herein, is dissolved in a relatively high boiling solvent. A relatively high boiling solvent herein is a solvent that indicates a boiling point of at orgreater than 300 °C. Accordingly, DPA may be preferably utilized since it indicates a boiling point of 330 °C, and as noted above, it is listed as an FDA food grade additive.

[0040] Therefore, as disclosed herein, the crystallizable polyester is combined into the relatively high boiling solvent followed by heating to form a solution of the crystallizable polyester in the relatively high boiling solvent, of which DPA is preferred. Preferably, the concentration of the crystallizable polymer in the DPA is at the relatively high end of the concentration range disclosed herein, e.g., in the preferred range of 40.0 % (wt.) to 50.0 % (wt.). The solution is again cooled with formation of the solvated polyester aerogel (polyester gel phase separated in the relatively high boiling solvent). This solvated polyester gel can now be broken into pellet size pieces that are contemplated to serve as a gel feedstock. The pellet size pieces, which preferably have a longest cross-sectional dimension in the range of 3.0 mm to 5.0 mm, may then be loaded into a heated extruder where the temperature is raised to form a liquid feedstock suitable for printing. With application of pneumatic pressure, the liquid may be extruded through one or a plurality of nozzles and deposited on a print substrate. The extrudate will then cool at which point it reverts back to form the solvated polyester gel. The extrudate so cooled is contemplated to have sufficient viscosity to maintain its printed shape including the capability of supporting additional printed layers as a selected part geometry is then built on a selected substrate. After printing, the part can undergo solvent exchange with replacement of the relatively high boiling solvent with an aliphatic alcohol solvent, followed by replacement of the aliphatic alcohol solvent with water and then the printed part can be lyophilized to remove water to provide the 3D printed polyester aerogel. In addition, it is contemplated that the aliphatic alcohol solvent in the 3D printed polyester may be removed by supercritical CO2 extraction.

Claims

Claims:

1. A method of forming a polyester gel comprising: a. supplying a crystallizable polyester; b. supplying 1,3-diphenylacetone solvent; c. combining said crystallizablc polyester and 1,3-diphcnylacctonc solvent and heating to dissolution temperature to form a solution of said crystallizable polyester in said 1,3- diphenylacetone solvent; d. cooling the solution and forming a solvated polyester gel in the presence of said 1,3-diphenylacetone solvent.

2. The method of claim 1, wherein the dissolution temperature is at a temperature below the point at which the last crystallizable polyester crystal melts as determined by differential scanning calorimetry.

3. The method of claim 1, wherein upon cooling there is formation of a nanofibrillar gel morphology wherein the level of spherulites is at or below 10.0 % by volume.

4. The method of claim 1, wherein said solvated polyester gel undergoes solvent exchange and replacement of said 1,3-diphenylacetone with an aliphatic alcohol or acetone solvent.

5. The method of claim 4, wherein said aliphatic alcohol or acetone solvent is replaced with water and providing a polyester hydrogel.

6. The method of claim 5, wherein said polyester hydrogel is lyophilized to remove water to provide a polyester aerogel.

7. The method of claim 4, wherein said aliphatic alcohol or acetone solvent is removed by supercritical CO2 extraction to form a polyester aerogel.

8. The method of claim 1, wherein said crystallizable polyester comprises a poly alkylene terephthalate.

9. The method of claim 1, wherein said crystallizablc polyester is combined with said 1,3- diphenylacetone at a level in the range of 5.0 % (wt.) to 50.0 % (wt.).

10. The method of claim 8, wherein said polyalkylene terephthalate comprises poly(ethylene terephthalate), polypropylene terephthalate), poly(butylene terephthalate), or poly(hexamethyleneterephthalate).

11. The method of claim 1, wherein said crystallizable polyester comprises poly(ethylene naphthalate).

12. The method of claim 1, wherein the crystallizable polyester comprises poly(ethylene terephthalate) and heating in step (c) comprises heating to a dissolution temperature in the range of 205 °C to a temperature of less than or equal to 230 °C.

13. The method of claim 1, wherein the crystallizable polyester comprises poly(ethylene terephthalate) and is present in step (c) at a level of 10.0 wt. % to 20.0 wt. % in said 1,3- dipheny lacetone solvent and is heated to a dissolution temperature in the range of 205 °C to 215 °C followed by cooling at a temperature in the range of 135 °C to 145 °C.

14. The method of claim 7, wherein said polyester aerogel has a density in the range of 0.09 g / cc to 0.25 g / cc.

15. The method of claim 7, wherein said polyester aerogel indicates a thermal conductivity in the range of 15.0 mW / mK to 30.0 mW / mK.

16. The method of claim 6, wherein said polyester aerogel comprises nanofibril morphology.

17. The method of claim 6, wherein said polyester aerogel indicates a porosity of 80.0% or greater.

18. The method of claim 6, wherein said polyester aerogel indicates a compression modulus in the range of 7.0 MPa to 18.0 MPa.

19. A method of forming a poly (ethylene terephthalate) gel comprising: a. supplying poly(ethylene terephthalate); b. supplying 1,3-diphenylacetone solvent; c. combining said poly(ethylene terephthalate) and 1,3-diphenylacetone solvent and heating to a dissolution temperature to form a solution of said poly(ethylene terephthalate) in said 1,3-diphenylacetone solvent; and d. cooling the solution and forming a solvated poly(ethylene terephthalate) gel in the presence of said 1,3-diphenylacetone solvent.

20. The method of claim 19, wherein said solvated poly(ethylene terephthalate) gel undergoes solvent exchange and replacement of said 1,3-diphenylacetone with an aliphatic alcohol or acetone solvent.

21. The method of claim 20, wherein said aliphatic alcohol or acetone solvent is replaced with water and providing a poly(ethylene terephthalate) hydrogel.

22. The method of claim 21, wherein said poly(ethylene terephthalate) hydrogel is lyophilized to remove water and providing a polyester aerogel.

23. The method of claim 20, wherein said aliphatic alcohol or acetone solvent is removed by supercritical CO2 extraction to form a polyester aerogel.

24. The method of claim 19, wherein said poly(ethylene terephthalate) comprises recycled poly (ethylene terephthalate).

25. The method of claim 19, wherein said poly(ethylene terephthalate) is combined with said 1,3-diphenylacetone at a level in the range of 5.0 % (wt.) to 50.0 % (wt.).

26. The method of claim 19, wherein heating in step (c) comprises heating to a dissolution temperature in the range of 130 °C to 220 °C.

27. The method of claim 19, wherein the poly (ethylene terephthalate) is present in step (c) at a level of 10.0 wt. % to 20.0 wt. % in said 1,3-dipheny lacetone solvent, is heated to a dissolution temperature in the range of 205 °C to 215 °C, followed by cooling at a temperature in the range of 135 °C to 145 °C.

28. The method of claim 22, wherein said poly(ethylene terephthalate) aerogel has a density in the range of 0.09 g / cc to 0.25 g / cc.

29. The method of claim 22, wherein said poly(ethylene terephthalate) aerogel indicates a thermal conductivity in the range of 15.0 mW / mK to 30.0 mW / mK.

30. The method of claim 22, wherein said poly(ethylene terephthalate) aerogel indicates a compression modulus in the range of 7.0 MPa to 18.0 MPa.

31. A polyester aerogel comprising a crystallizablc polyester having a thermal conductivity in the range of 15.0 mW / mK to 30.0 mW / mK.

32. A method of 3D printing a polyester aerogel comprising: a. supplying a crystallizable polyester; b. supplying a solvent for said crystallizable polyester that has a boiling point of at or greater than 300 °C; c. combining said crystallizable polyester and solvent and heating to a dissolution temperature to form a solution of said crystallizablc polyester in said solvent; d. cooling the solution and forming a solvated polyester gel in the presence of said solvent; e. forming pellets of said solvated polyester gel f. feeding said pellets of said solvated polyester gel into an extruder and extruding one or more layers of said solvated polyester gel;g. replacing said solvent in said solvated polyester gel with an aliphatic alcohol or acetone solvent followed by: (1) replacement of said aliphatic alcohol or acetone solvent with water and forming a polyester hydrogel where said polyester hydrogel is lyophilized to remove water; or (2) removal of said aliphatic alcohol or acetone solvent via supercritical CO2 extraction with formation of the polyester aerogel.

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