Composition for depolymerizing resins and methods of accomplishing the same

Abstract

Disclosed herein is a method of solubilizing a polymeric resin comprising treating the polymeric resin or a composite comprising the polymeric resin with a first mixture of fluids for one or more pressure cycles; where the first mixture comprises a first superheated fluid and a first supercritical fluid; where each pressure cycle comprises a pressurization step, a pressure retention step and a depressurization step; and treating the polymeric resin or the composite comprising the polymeric resin to one or more pressure cycles with a second mixture of fluids; where the second mixture of fluids comprises superheated water, a second superheated or supercritical fluid and a third supercritical fluid; where the first superheated fluid and the second superheated or supercritical fluid comprise a solvent has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2.

Description

COMPOSITION FOR DEPOLYMERIZING RESINS AND METHODS OFACCOMPLISHING THE SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application 63 / 541,047 filed on September 28, 2023, the entire contents of which is incorporated herein in its entirety.BACKGROUND

[0002] This disclosure relates to a composition for depolymerizing resins and a method of accomplishing the same. More specifically, this disclosure relates to a composition for separating fillers from resins in which they are embedded in addition to depolymerizing the resins in which the fibers are embedded.

[0003] Polymeric resins are used to manufacture a wide variety of commercial products. For example, they are used in food packaging, exterior body panels of automobiles and computers, marine watercraft and boat hulls, fiberglass line pipe and down hole tubulars, exterior skins for radar evading aircraft, textiles, helmets, automobile tires, composites that are used in sports equipment and wind turbine airfoils, and the like. When these commercial products are discarded, they are transported to a landfill, where they remain for a large number of years because depolymerization under ambient conditions occurs very slowly. Polymeric resins are a large contributor to landfills, where they remain for large periods of time. In addition, commercial products that include polymeric resins often contaminate bodies of water such as oceans and lakes, where it difficult to collect and recycle them.

[0004] The recycling of polymeric resins first requires the various items found in a landfill to be segregated according to the type of resin used and then subjected to decomposition or depolymerization. Both of these processes are labor intensive and are expensive.

[0005] One manner of decomposing discarded polymeric resins is via thermal degradation. This involves heating the polymeric resin above its thermal decomposition temperature in an oxygen containing atmosphere to form carbon dioxide and a variety of other carbon containing byproducts. The carbon dioxide obtained from such a process has to be either released to the atmosphere, which is undesirable, or alternatively, be captured and sequestered, which is expensive and adds to the cost of such a recycling program. There are not very many available commercial products that can use the carbon dioxide generated fromthe artificial decomposing of polymers to make the recycling of resins be a successful commercial venture.

[0006] One particularly large class of resins, and their composites, are thermoset based where their crosslinking prevents them from melting. Thus, their only option for recycling would involve cutting, shredding, or grinding the material and incorporate it as a filler. Another option is to decompose and pyrolyze the resin to retrieve the reinforcement, other inorganics or metallics for recycle, but this process is energy intensive and often detrimentally affects quality of the remining reinforcement, inorganic, or metallic materials.

[0007] It is therefore desirable to develop solutions for recycling polymeric resins that reduces environmental pollution, can be broadly applied to a variety of different resins at one time, and that facilitates the reuse of the recycled products.SUMMARY

[0008] Disclosed herein is a method of solubilizing a polymeric resin comprising treating the polymeric resin or a composite comprising the polymeric resin with a first mixture of fluids for one or more pressure cycles; where the first mixture comprises a first superheated fluid and a first supercritical fluid; where each pressure cycle comprises a pressurization step, a pressure retention step and a depressurization step; and treating the polymeric resin or the composite comprising the polymeric resin to one or more pressure cycles with a second mixture of fluids; where the second mixture of fluids comprises superheated water, a second superheated or supercritical fluid and a third supercritical fluid; where the first superheated fluid and the second superheated or supercritical fluid comprise a solvent has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2.BRIEF DESCRIPTION OF THE FIGURES

[0009] FIG. 1 depicts an illustration of the pressure cycle process whereby pressurizing step and depressurizing step are separated by a pressure retention step where pressure is maintained;

[0010] FIG. 2 depicts a detail of a typical pressure cycle that illustrates the pressurization step, the pressure retention step, and the depressurization step that can be slow or rapid.

[0011] FIG. 3 illustrates an amine cured epoxy cylinder before and after being subjected to a single pressure cycle where fragmentation of the network has occurred.

[0012] FIG. 4 depicts the reaction between bisphenol A diglycidyl ether and a polyetheramine (Jeffamine D230); and

[0013] FIG. 5 is a schematic depiction of potential species that are generated upon liquification of an amine-crosslinked epoxy network.

[0014] FIG. 6A is a depiction of the nomenclature used to define the different experimental samples; it also shows the different fluid compositions that are used to liquify polymers;

[0015] FIGS. 6B-1 and 6B-2 are depictions of two different NMR spectra that show different aromatic and aliphatic species obtained from the decomposition of an epoxy polymer used in a composite;

[0016] FIG. 7 includes Table 5 that shows the molar ratios of aromatic to aliphatic species using NMR spectroscopy;

[0017] FIG. 8 is another depiction of the nomenclature used to define the different experimental samples; it also shows the different fluid compositions that are used to liquify polymers; superheated ethylene glycol or superheated glycerol may be used in addition to supercritical carbon dioxide and superheated water to facilitate liquification of an epoxy polymer in a composite; and

[0018] FIG. 9 is bar graph that shows the percentage of soluble species obtained when ethylene glycol or glycerol are respectively used in addition to supercritical carbon dioxide and superheated water to facilitate liquification of an epoxy polymer in a composite.DETAILED DESCRIPTIONDefinitions

[0019] The polymeric resins defined herein are described as being either in pure form or in composite form. Polymeric resins in their pure form generally contain the polymer in amounts of greater than 93 weight percent (wt%), preferably greater than 96 wt%, based on total weight of a commercial product. They may contain small amounts of additives such as antioxidants, antiozonants, mold release agents, thermal stabilizers, dyes and colorants, impact modifiers, gelling agents, fibers, or the like, or a combination thereof. The additives are generally uniformly dispersed throughout the volume of the polymer (i.e., the polymer in its pure form may be considered to be homogeneous) and the properties are isotropic. Examples of a polymeric resin in its pure form include Ziploc® bags, Saran wrap, soft drinkcontainers, milk containers, automotive outer body panels, plastic furniture, computer housing(s), or the like.

[0020] The polymeric resins in composite form generally contain fillers in amounts of 7 to 90 wt%, based on a total weight of the polymeric composite. The fillers may be in particulate form or in fibrous form. Fillers in particulate form include glass beads, graphite particles, graphene oxide particles, carbon black, fumed silica or titania, or the like. Fillers in their fibrous form can include polymeric fibers or inorganic fibers. The inorganic fibers may include glass fibers, carbon fibers, ceramic fibers, carbon nanotubes, or the like. Examples of polymeric resins in composite form include wind turbine airfoils, tennis rackets, automotive frames, or the like. The fibers may be chopped fibers or continuous fibers. Polymeric resins in their composite form may generally be heterogeneous and their properties may or may not be isotropic.

[0021] Another class of polymers includes polymer alloys and blends where two or more chemically distinct polymers are blended to create miscible blends or immiscible blends to produce polymeric materials with distinct properties.

[0022] It is to be noted, that there may be some overlap in the definitions of pure polymers and polymers contained in composites. There may be some overlap between the amounts of polymers contained in the pure polymer form and the polymers present in composite form.

[0023] Disclosed herein is a fluid composition for depolymerizing polymeric resins into their constituent building blocks (e.g., the lower molecular weight species that may possibly undergo polymerization to produce the polymeric resin) without subjecting the polymeric resin to thermal degradation, to mechanical abrasion, or a combination thereof. The fluid composition comprises first mixture that comprises a first superheated fluid and a first supercritical fluid. The first superheated fluid and the first supercritical fluid have different chemical compositions from each other. The first superheated fluid may be superheated water or a first superheated solvent, where the first superheated solvent has a Hildebrand solubility parameter of 15 to 38 MPa1 / 2at room temperature. In an embodiment, the first mixture may also contain at least one of a fluid, preferably a liquid (at room temperature) that does not reach its superheated state or its supercritical state when the first mixture is pressurized. In an embodiment, the first mixture may also contain initiators and / or crosslinking agents that promote crosslinking in thermoplastic or crosslinked resins (sometimes referred to herein as thermosetting agents) that are being depolymerized.

[0024] Disclosed herein too is a method of treating a polymeric resin (either in its pure form or as part of a polymeric composite) with the first mixture to depolymerize the polymeric resin into a plurality of lower molecular weight species (oligomers) that may be reused to form the polymeric resin. When a composite is treated with the first mixture, the polymeric resin (either in polymeric form or in the form of a lower molecular weight species) is also separated from the fillers. The method comprises subjecting a polymeric resin (either in its pure form, polymer alloy or blend, or as part of a polymeric composite) to one or more pressure cycles in the presence of the first mixture of fluids, where the first mixture of fluids comprises the first superheated fluid and the first supercritical fluid prior to exposing it to a second mixture of a superheated water, a second superheated solvent or supercritical solvent and a third supercritical gas. A key embodiment of this process is that the depressurization rate in one or more pressure cycles is rapid relative to the pressurization rate so as to cause a rapid phase change in one or more of the combined liquids the polymeric material is subjected to.

[0025] In an embodiment, the fluid composition may contain at least one or more fluids that are not in their supercritical state or superheated states, while other fluids in the composition are in their respective supercritical or superheated states. For example, the first mixture or the second mixture may comprise a fluid that is not in its supercritical state or its superheated state, while the other fluids in the first mixture or the second mixture are in their respective supercritical or superheated states. This additional fluid may be used to facilitate compatibilization of the superheated and / or supercritical fluids with the polymer being depolymerized. It may also be used to distribute initiators and / or crosslinking agents uniformly through the volume of the first mixture and the polymer being depolymerized. It is to be noted that the initiator and / or crosslinking agent may also be used to facilitate additional crosslinking in polymers that are already lightly crosslinked prior to being subjected to the first mixture.

[0026] In an embodiment, the first superheated fluid and the second superheated or supercritical fluid comprise a solvent that has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2. In an embodiment, the first superheated fluid (used in the first mixture) and the second superheated fluid or supercritical fluid (used in the second mixture) comprise the same solvent. In an embodiment, the first supercritical fluid and the third supercritical fluid are the same fluid. In an embodiment, the first supercritical fluid and the third supercritical fluid are carbon dioxide.

[0027] The first mixture is used to treat a polymeric resin (in either its pure form or as part of a polymeric composite) to one or more pressure cycles to facilitate delamination of the polymer from fillers (when it is in composite form) and to depolymerize it to form a plurality of lower molecular weight species. In an embodiment, when the polymeric resin (in either its pure form or as part of a polymeric composite) is being treated with the first mixture, it may be subjected to crosslinking while simultaneously being expanded. In other words, the first mixture that contains the first superheated fluid and the first supercritical fluid may also contain initiators and crosslinking agent that may be used to facilitate crosslinking of thermoplastic resins that are being depolymerized. In another embodiment, the first mixture may contain an additional fluid (preferably one that is a liquid at room temperature) apart from the first superheated fluid and the first supercritical fluid that is never transformed into its superheated or supercritical state when it contacts the polymer in a pressurized vessel (also know as a reactor).

[0028] Thermoplastic resins in contrast to thermosetting resins tend to expand upon removal of the pressurized first mixture to form foams. The formation of a foam reduces the probability of decomposition of the polymer upon depressurization. It is therefore desirable to subject thermoplastic resins to crosslinking during the first pressurization step so that it can be converted into a thermoset and therefore more easily depolymerized.

[0029] The treatment of the polymeric resin with the second mixture facilitates liquification of the lower molecular weight species. This liquification enables further washing, purification and segregation of the various lower molecular weight species (obtained from the depolymerization) so that they can be recycled.

[0030] Exposing the polymeric resin (either in its pure form or as part of a composite) to a first mixture of the first superheated fluid and the first supercritical fluid (and the optional additional fluid that is not in a superheated or supercritical state) (where the first superheated fluid is not the same as the first supercritical fluid) to one or more pressure cycles where the depressurization rate is rapid promotes fragmentation of the polymeric materials thereby dramatically increasing the surface area for subsequent depolymerization of the polymeric resin. In the case of a composite that contains a crosslinked polymer (e.g., a crosslinked polyepoxide), this exposure to a one or more pressure cycles facilitates the fragmentation of the organic phase of the composites and also enhances hygrothermal stresses at interfaces between the fillers and or reinforcement to promote delamination. This increased surface area arising from the rapid depressurization of one of more pressure cyclesresults in increased efficiency in the depolymerization into a mixture of low molecular weight species (herein after “oligomers”) that is not achieved with slow depressurization rates or by pressurizing the polymeric materials for a short period of time (e.g., less than 30 minutes).

[0031] It also facilitates delamination of the polymer matrix from the fillers contained in a composite due to increased hygrothermal expansion of the organic polymer as well as the selective rapid expansion of the organic polymer leaving the filler / reinforcement intact for further recycle into new products. After the pressure cycle(s) is / are completed, these oligomers can optionally be treated with an additional second mixture that comprises a set of fluids that has a different composition from the first mixture of fluids. The second mixture of fluids comprises a superheated water, a second superheated solvent or second supercritical solvent and supercritical carbon dioxide to facilitate further depolymerization of the oligomers and liquification of the oligomers. This additional depolymerization increases solubilization of the oligomers in regularly used room temperature solvents such as tetrahydrofuran, alcohols (methanol, ethanol, propanol, butanol, or the like) ketones (acetone, benzophenone, acetophenone, or the like), toluene, methyl acetate, pentane, hexane, benzene, or the like, or a combination thereof. These room temperature solvents can be used to wash the oligomers and to segregate them from one another for further use.

[0032] The second mixture may also contain an optional fluid that is not in its superheated or supercritical state during pressurization in the reactor. The optional fluid may be any of the solvents listed in the Table 1 below. In general, a fluid from Table 1 is selected that requires a different pressure or temperature to reach its superheated or supercritical point when compared with the other fluids that are in their superheated or supercritical states. This additional fluid may be used to facilitate compatibilization of the superheated and / or supercritical fluids with the polymer being depolymerized. It is generally desirable for the second mixture to be free of initiators and crosslinking agents. The second mixture may preferably however, contain catalysts that facilitate depolymerization of the polymer.

[0033] During the pressurization and soak step of the pressure cycle(s), the mixture of the superheated fluid and the supercritical fluid impregnates the polymeric resin (either in its pure form or as part of a polymeric composite) while under pressure. At the depressurization step, the rate of depressurization is selected to be rapid to promote expansion and fragmentation of the organic polymer. A retention pressure (also referred to soak pressure) is depicted in the FIGS. 1 and 2. FIG. 1 is a graphical representation (not to scale) of multiple pressure cycles that the polymeric resin may be subjected to with the first mixture, while theFIG. 2 is an expanded view of section ABCD from the FIG. 1. FIG. 2 is an expanded view of a graphical representation for the first pressure cycle of the FIG. 1.

[0034] With reference now to FIGS. 1 and 2, during the pressurization step, the first mixture comprising the first superheated fluid, the first supercritical fluid and the optional additional fluid (that does not reach its superheated or supercritical state) impregnates the polymeric resin causing it to swell. Additional initiators or crosslinking agents may be added to the first mixture if desired. The polymeric resin may be placed in a reactor (not shown) for this step. The pressure is raised to the desired value and retained at this constant value for a time period. This is called the pressurization and soak step and it is followed by a rapid depressurization step. When depressurization occurs, the polymeric resin undergoes expansion resulting in an increase in surface area as the superheated water and the supercritical fluid dissolved in the polymeric resin undergo a phase change from their respective liquid states at high pressure to gasses and vapor at lower pressures. Crosslinking of the polymer chains may also occur at this stage if a crosslinking agent is contained in the first mixture. Initiators and crosslinking agents may be added if the polymeric resin is a thermoplastic or lightly crosslinked thermoset. This increase in surface area permits a greater contact with the first superheated water and the first supercritical fluid during the next pressure cycle (see FIG. 3), which promotes accelerated depolymerization and results in a greater amount of swelling of the polymeric resin when compared with amount of swelling during the preceding pressurize cycle (the first pressure cycle).

[0035] When depressurization occurs for a second time, the polymeric resin displays an even greater increase in surface area than compared with the increase in surface area that occurs after the preceding depressurization cycle. Thus, with each pressure cycle, larger portions of the polymeric resin come into contact with the first mixture (the first superheated fluid and the first supercritical fluid) to promote an even greater increase in surface area through a mechanochemical process. This continual increase in surface area with each pressure cycle promotes greater solubilization of the polymeric resin in the first mixture. In an embodiment, almost all of the polymeric resin may be fragmented and depolymerized to produce solubilized oligomers in the liquid phase during the pressure cycles. As noted above, if the polymeric resin is a thermoplastic resin or a lightly crosslinked resin, then the expansion may simultaneously occur with crosslinking during treatment with the first mixture. The crosslinking increases the elastic modulus of the thermoplastic resin to thepoint that when further expansion and depressurization occur in the reaction vessel, the hitherto thermoplastic resin begins to undergo fragmentation.

[0036] The temperature at which the pressure cycle is conducted is typically above the boiling point of water (100°C) but below its critical temperature (374°C), preferably between 200 and 350°C, and more preferably between 240 and 300°C. In an embodiment, the successive pressurization cycles may be conducted at a single temperature with the time intervals (for the pressure retention step) between pressurization and depressurization in each pressure cycle being constant. In another embodiment, the successive pressurization cycles may be conducted at a single temperature with the time intervals between pressurization and depressurization in each pressure cycle being varied. In yet another embodiment, each successive pressurization cycle may be conducted at a different temperature with time intervals between pressurization and depressurization in each pressure cycle being constant or being varied. In yet another embodiment, each successive pressurization cycle may be conducted at a greater temperature than a temperature of the preceding pressure cycle with the time intervals between pressurization and depressurization in each pressure cycle being constant or being varied. It is generally desirable for the time interval between pressurization and depressurization in each successive pressure cycle to be constant.

[0037] In an embodiment, if an initiator and a crosslinking agent are added to the first mixture, the thermoplastic polymer or the lightly crosslinked polymer undergoes additional crosslinking with each pressurization cycle until it can no longer undergo further crosslinking at which point it begins to undergo fragmentation during the depressurization cycles. In an embodiment, portions of the polymer can undergo fragmentation while other portions that are not as crosslinked undergo expansion. Both expansion of the polymeric resin as well as fragmentation can occur simultaneously.

[0038] During the rapid depressurization, a condenser can be added to the reactor to also capture lower molecular weight oligomers and monomers volatilized at the temperature upon depressurization. These constituents like the liquid products obtained from complete liquification of the organic polymer can be further reused in other materials.

[0039] In an embodiment, the pressure retention step of each pressure cycle may be conducted at a pressure of 3,000 pounds per square inch (psi) to 25,000 psi, preferably 4,000 to 22,000 psi, preferably 4,500 to 21,000 psi, preferably 5000 to 20,000 psi. The rate of pressurization (to the point of pressure retention or pressure soaking) during each pressure cycle can range between 1 psi / minute to 10,000 psi / minute.

[0040] The pressure retention or pressure soak step of each pressure cycle may be maintained for a time interval of 30 minutes to 5 days, preferably 1 hour to 3 days, and preferably 2 hours to 2 days. The time interval begins at the point where the pressure in the reactor (where the pressure cycle is being conducted) has reached a desirable selected value which will be maintained until depressurization. As noted above the time interval for successive pressure cycles may be a constant value or may be varied.

[0041] With reference now to the FIG. 2, it may be seen that the depressurization may be conducted rapidly or slowly. A slow depressurization will cause no appreciable increase in the surface area of the polymeric resin, while a rapid depressurization typically leads to fragmentation of the polymeric resin.

[0042] The depressurization step begins with a release in pressure from the reactor and may be conducted rapidly at a rate of 5000 psi per second (psi / second) to 50,000 psi / second, 10,000 to 40,000 psi / minute, 20,000 to 35,000 psi / minute till ambient conditions are reached. Alternatively, the depressurization may be conducted slowly at a rate of 100 psi / second to less than 5000 psi / second, 200 psi / second to 3000 psi / second, 300 to 1000 psi / second till ambient conditions are reached. A combination of rapid and slow depressurization rates may be used during a single depressurization. In an embodiment, some of the depressurization steps in the pressure cycle may be conducted slowly, while others may be conducted rapidly. For example, the depressurization in the second and fourth pressure cycle may be conducted slowly, while the depressurization in the third cycle may be conducted rapidly or vice versa.

[0043] The depressurization rate depends on the overall minimum size dimension of the material being depolymerized and liquified. The minimum size dimension refers to the smallest dimension of the polymer being treated. For example, in a rectangular prism, it could be either the width, the height or the length. In order for fragmentation to occur, the rate of depressurization should exceed the rate of diffusion of the fluid composition being used for depolymerization. Under these conditions, the fluid composition cannot escape the material, and the material is then subjected to excessive hydrostatic tension that will cause the material to fragment thereby dramatically enhancing the surface area for faster depolymerization of the material upon further treatment of the fluid composition.

[0044] For materials with minimum dimensions of 0.125 inches thick, minimum depressurization rates of 1000 psi / second are useful with rates of 5000 psi / second to 50000 psi / second being more effective. Higher depressurization rates will always produce finerfragments until a saturation point is obtained for a particular material to be depolymerized and fluid composition being used. For materials with minimum thickness greater than 0.125 inches and on the order of 1 inch thick, slower depressurizations rates can be used and a minimum range of 100 psi / second but a preferred range of 1000 psi / second to 5000 psi / second may be sufficient. For materials with material thicknesses greater than 1 inch, minimum depressurization rates in the range of 10 psi / second may be sufficient for fragmentation.

[0045] The number of pressure cycles conducted on a polymeric resin may be dependent upon a number of different factors such as the molecular weight between crosslinks, the amount of filler in a composite, the size of the specimens, the amount of soluble material desired for a given sample, and so on. The number of pressure cycles “n” may be greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 5 and greater than or equal to 10.

[0046] As noted above, during depressurization the surface area of the polymeric resin is increased. Depending upon the rate of depressurization, portions of the polymeric resin may undergo fragmentation and liquification in the first mixture. It is desirable to conduct the pressure cycles till almost all of the polymeric resin (either in its pure form or as part of a composite) is soluble in the first mixture (that comprises the superheated water and the supercritical fluid).

[0047] The first mixture which comprises the first superheated fluid and the first supercritical fluid for use in the pressure cycles will now be described.

[0048] A superheated fluid is a liquid that is heated to a temperature higher than its boiling point as measured at atmospheric pressure (14.7 psi). The first superheated fluid is superheated water or a first superheated solvent that has a Hildebrandt solubility parameter in SI units of 15 to 40 (MPa)1 / 2. Combinations of superheated water with a superheated solvent (where the superheated solvent has a Hildebrandt solubility parameter in SI units of 15 to 40 (MPa)1 / 2may be used as the first superheated fluid.

[0049] The superheated water is preferably distilled water having a purity of 99 mole percent (mole%) or greater. Superheated water (SI1H2O) is liquid water under pressure at a temperature higher than its usual boiling point (100°C) but lower than its critical point (374°C). A critical point (or critical state) is the end point of a phase equilibrium curve. One example is the liquid-vapor critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist. At highertemperatures, the gas cannot be liquefied by pressure alone. At the critical point, defined by a critical temperature Tcand a critical pressure Pc, phase boundaries between the liquid state and gaseous state vanish.

[0050] The properties of superheated water are highly temperature dependent due to their hydrogen bonds. Hydrogen bonding of water is broken under high temperature causing the decreasing of polarity and increasing solubility of organic materials. Additionally, selfionization of water increases with temperature. The concentration of H3CE and OH" in superheated water can be much higher than room temperature water. The significantly increased acidity and basicity of superheated water make various chemistries including cleavage of bonds happen without adding other chemical reagents.

[0051] A superheated solvent may be used in place of the superheated water or in combination with the superheated water in the first mixture. The term “solvent” as applied to the first mixture excludes water and is typically one that has a Hildebrand solubility parameter in SI units of 15 to 40 (MPa)1 / 2, preferably 18 to 30 (MPa)1 / 2and more preferably 22 to 28 (MPa)1 / 2. The superheated solvent is typically a liquid at room temperature and room pressure. The Hildebrand solubility parameter is defined as the square root of the cohesive energy density given by the following equation:5 = (E / V)1 / 2, where E is the energy of vaporization, V = Volume and 5 is the Hildebrand solubility parameter. This value is generally reported in MPa1 / 2. Some examples of solvents that may be used in superheated form in the first mixture (or in supercritical form in the second mixture) are listed in the non-limiting Table 1 below. Combinations of solvents from the Table 1 may be used. Combinations of water with solvents from Table 1 may also be used in the first mixture.Table 1Water has a Hildebrand solubility parameter of 48 (MPa)1 / 2.

[0052] The organic solvents used in the first mixture as the first superheated fluid or in the second mixture as the second supercritical fluid (some of these are listed in the Table 1) may be classified as polar aprotic solvents, polar protic solvents, non-polar solvents, or combinations thereof. Examples of liquid polar aprotic solvents such as, propylene carbonate, ethylene carbonate, butyrolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, or the like, or a combination thereof. Polar protic solvents include alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, or the like, or combinations thereof), diols (e.g., ethylene glycol, 1,4-butanediol, propylene- 1,3-diol, beta propylene glycol, or the like, or a combination thereof), triols (e.g., glycerol), acetic acid, formic acid, or a combination thereof. Non-polar solvents include benzene, toluene, methylene chloride, carbon tetrachloride, hexane, diethyl ether, tetrahydrofuran, or the like, or a combination thereof. Co- solvents comprising a polar solvent with a non-polar solvent may also be utilized to modify the solvating power (the ability to penetrate and solubilize the polymeric composition) of the first mixture and the second mixture.

[0053] It is generally desirable to use polar solvents to treat polar polymers and nonpolar solvents to treat non-polar polymers, though combinations of these fluids may be used to treat either polar or non-polar polymers. Conversely, a polar fluid may be used to treat a non-polar polymer that contains a polar dispersed polymeric phase or alternatively, a nonpolar fluid may be used to treat a polar polymer that has dispersed in it a non-polar dispersed polymeric phase.

[0054] Exemplary superheated fluids for use in the first mixture (which is used for the pressure cycling) include water, ethanol, or a combination thereof.

[0055] As noted above, the first mixture also contains a first supercritical fluid in addition to the first superheated fluid. The first supercritical fluid can include a supercritical gas or a supercritical solvent. The first superheated fluid and the first supercritical fluidpresent in the first mixture cannot be the same material. The first supercritical fluid always has a different chemical composition from the first superheated fluid in the first mixture. For example, the first superheated fluid in the first mixture and the first supercritical fluid in the first mixture cannot both be ethanol.

[0056] An optional fluid not in its superheated or supercritical state may also be fed to the reactor as part of the first mixture. This fluid is chosen to have its boiling point be greater than the temperature of the reactor during the operation. It therefore does not reach the superheated or supercritical state during the pressurization or depressurization of the reactor. This introduction of the optional fluid not in its supercritical or superheated state may be done either prior to the introduction of the other superheated or supercritical fluids into the reactor, simultaneously with the introduction of the other superheated or supercritical fluids, or after the introduction of the other superheated or supercritical fluids into the reactor. In an embodiment, it is preferably conducted prior to the introduction of the other superheated or supercritical fluids into the reactor. The introduction of an additional fluid that does not reach its supercritical or superheated state may be done as part of the first mixture or as part of the second mixture.

[0057] This additional fluid that does not reach its superheated or supercritical state may be conducted to facilitate penetration of the superheated or supercritical fluids into the polymer (i.e., it serves as a compatibilizer). It may also serve as a carrier for any initiators and / or crosslinking agents that may be introduced into the reactor to facilitate crosslinking of thermoplastic polymers or lightly crosslinked polymers.

[0058] The first supercritical fluid used in the first mixture may be a gas at room temperature or an organic solvent that is a liquid at room temperature. A supercritical fluid (SCF) is a material that can be either liquid or gas, used in a state above the critical temperature and critical pressure where gases and liquids can coexist. The supercritical fluid has no surface tension as there is no liquid / gas phase boundary. The “gas” that is used as the supercritical fluid in the first mixture (that is used for the pressure cycles) is typically in gaseous form at room temperature and pressure. Examples of such gases include oxygen, nitrogen, carbon dioxide, gaseous hydrocarbons, nitrous oxide, nitric oxide, nitrogen dioxide, ammonia, sulfur dioxide, ozone, halogens, dichlorodifluoromethane, or the like, or a combination thereof. Examples of gaseous hydrocarbons are methane, ethane, propane, butane, methylene, ethylene, propylene, butylene, or the like, or a combination thereof. Examples of halogens are fluorine, chlorine, bromine, or a combination thereof.

[0059] The organic solvents for use as a supercritical fluid in the first mixture are those having a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2. These are discussed above and will not be detailed again here in the interests of brevity.

[0060] An exemplary supercritical fluid for use in the first mixture is supercritical carbon dioxide or supercritical ethanol. It is to be noted that the supercritical gas or the supercritical solvent used as the supercritical fluid in the first mixture may be varied in type or quantity in order to change the solvating power of the first mixture.

[0061] In a preferred embodiment, the first supercritical fluid used in the first mixture comprises supercritical carbon dioxide or supercritical ethanol.

[0062] The first superheated fluid used in the first mixture may be present in an amount of 5 to 95 volume percent, preferably 25 to 75 volume percent, and more preferably 40 to 60 volume percent, while the first supercritical fluid used in the first mixture may be present in an amount of 5 to 95 volume percent, preferably 25 to 75 volume percent, and more preferably 40 to 60 volume percent, based on a total volume of the first mixture. In an embodiment, the first mixture comprises superheated water and supercritical carbon dioxide in a volume ratio of 44:55 to 55:45.

[0063] As noted above, the solubilized polymer obtained after the desired number of pressure cycles may optionally be subjected to additional solubilization using a second mixture of fluids comprising superheated water, a superheated organic solvent (also referred to herein as a second superheated fluid) or supercritical organic solvent (also referred to herein as a second supercritical fluid) and a supercritical gas (a gas in its supercritical state) (also referred to herein as a third supercritical fluid). The polymeric resin (in pure form or as part of a composite) may be treated with the second mixture of fluids for one or more pressure cycles. In an embodiment, the treatment with the second mixture can be conducted for two or more pressure cycles, three or more pressure cycles, five or more pressure cycles. The pressure cycles conducted with the second mixture can be the same as those conducted with the first mixture.

[0064] The superheated water, the organic solvents (used as either a second superheated fluid or a second supercritical fluid) and the gas (used as a third supercritical fluid) present in the second mixture are already detailed above and will not be described in detail here in the interests or brevity. The second mixture therefore comprises three fluids in either superheated or supercritical state, while the first mixture generally comprises two fluids one of which is in a superheated while the other is in a supercritical state. In the secondmixture, two fluids can be superheated fluids while the other can be a supercritical fluid, or alternatively, two fluids can be supercritical fluids, while the other fluid can be a superheated fluid. In an embodiment, the second mixture used to fragment, liquify and depolymerize the polymeric resins may comprise two or more superheated fluids and one or more supercritical fluids. In another embodiment, the second mixture used to fragment, liquify and depolymerize the polymeric resins may comprise two or more supercritical fluids and one or more superheated fluids.

[0065] The treatment with the second mixture is conducted to facilitate fragmentation and liquification of the oligomers so that they can be purified and segregated for reuse to manufacture the same or other polymers. Even if the polymeric resin is already fragmented during the pressure cycling, the treatment with the second mixture can be used to further fragment the polymeric resin. The presence of the supercritical gas in addition to the superheated water and the superheated or supercritical organic solvent increases the solubility of the polymeric resin in the second mixture.

[0066] In an embodiment, each ingredient (the gas, water and the organic solvent) may be present in the second mixture in an amount of 5 to 90 volume percent, preferably 20 to 70 volume percent and preferably 25 to 40 volume percent, based on a total volume of the second mixture. It is to be noted that while the volume of the water and the organic solvent are measured at room temperature, the volume of the gas is determined under supercritical conditions (i.e., when it is in both a liquid and gaseous state) or alternatively, when it is in liquid form.

[0067] In a preferred embodiment, when the polymeric resin (present in pure form or in composite form) is a polar polymer (e.g., a poly epoxide, a polyamide, a polycarbonate, or the like) the second mixture generally comprises carbon dioxide in supercritical fluid form in an amount of 25 to 40 volume percent, preferably 28 to 35 volume percent; superheated water in an amount of 25 to 40 volume percent, preferably 27 to 35 volume percent; and an alcohol in either its superheated state or supercritical fluid state in an amount of 25 to 40 volume percent, preferably 27 to 35 volume percent, based on a total volume of the second mixture.

[0068] In an embodiment, treatment of the polymeric resin with the second mixture is conducted with the superheated water and the superheated or supercritical alcohol being present in a volume ratio of 45:55 to 55:45 (in the reactor where the impregnation of the polymeric resin takes place). The remaining portion of the second mixture comprises the supercritical carbon dioxide.

[0069] In an embodiment, the first mixture and / or the second mixture may contain a variety of different additives. These additives include additives that facilitate impregnation of the polymeric resin by the components present in the second mixture such as surfactants and salts. Other additives can include catalysts that facilitate depolymerization of the polymeric resin.

[0070] The additions of salts may be advantageous. The salts may be inorganic salts or salts that include organic and inorganic ions. Common salt-forming cations include ammonium (NH4+), calcium (Ca2+), iron (Fe2+and Fe3+), magnesium (Mg2+), potassium (K+), pyridinium (CsH5NH+), quaternary ammonium (NR4+), and sodium (Na+). The anions may be inorganic or organic. Common salt- forming anions (parent acids in parentheses where available) include carbonates (CO32‘) (carbonic acid), chlorides (Cl-) (hydrochloric acid), cyanides (CN-) (hydrocyanic acid), fluorides (F-) (hydrofluoric acid), nitrates (NO3 ") (nitric acid), nitrites (NO2 ") (nitrous acid), phosphates (PO4a”) (phosphoric acid), sulfates (SO42”) (sulfuric acid), all anions of carboxylic acid (including formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid and andarachidic acid) such as, for example, acetates (CFFCOO-) (acetic acid), citrates (HOC(COO-)(CH2COO“)2) (citric acid), oxalates, and stearates. Combinations of salts may be used.

[0071] In an embodiment, the catalyst is formed from a metal selected from the group consisting of zirconium, titanium, hafnium, vanadium, niobium, tantalum, scandium, yttrium, iron, cobalt, nickel, chromium, molybdenum, manganese, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. The ligands for the selected metal catalysts can comprise, halides, alkoxides, acetates or other carboxylates, Inflates, tosylates, or a combination thereof. Alternatively, the metal catalysts may be multi-metallic clusters have oxo ligands and combinations of halides, alkoxides, acetates or other carboxylates, triflates, tosylates, or a combination thereof.

[0072] As noted above, when thermoplastic resins or lightly crosslinked resins are to be depolymerized, it may be desirable to crosslink them to improve the efficiency of the depolymerization. This crosslinking may be brought about during the contact with the first mixture and even during contact with the first mixture. In a preferred embodiment, it is desirable to facilitate crosslinking during contact with the first mixture. This crosslinkingmay be brought about by using an initiator and a crosslinking agent in the first mixture. The initiators typically generate radicals upon activation by thermal energy, radiation, or a combination thereof.

[0073] Suitable examples of initiators include thermal initiators, photoinitiators, or a combination thereof. Examples of these initiators include peroxides (e.g., dicumyl peroxide, benzoyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (commercially available as Luperox 101)), azo compounds (e.g., azobisisobutyronitrile (AIBN)), photoinitiators (e.g., compounds that generate radicals when exposed to UV light, or gamma radiation commonly used in light-curing processes for polyolefins), sulfur-based initiators (e.g., sulfur-containing compounds (e.g., particularly in vulcanization of rubber materials), sulfur monochloride, or the like), or a combination thereof.

[0074] Crosslinking agents may also be added to the reaction vessel along with the initiator to facilitate crosslinking. Common crosslinking agents include silane compounds, anhydrides, hydrazine derivatives, or the like, or a combination thereof.

[0075] In an embodiment, unsaturated small molecules can be added to the first mixture that can then initiate crosslinking in the thermoplastic or lightly crosslinked resin. Examples of the unsaturated groups that can be added to the first mixture to induce crosslinking in the hitherto uncrossed or lightly crosslinked polymer include ethylenically unsaturated groups such as vinyl, allyl, allenyl, norbornyl, ethynyl, acrylates, methacrylates, itaconates, maleimides, maleic anhydride and maleic anhydride derivatives, acrylamides, styrenic, vinyl carboxylates, acrylonitriles, or the like, or a combination thereof.

[0076] Other functional linkages that facilitate crosslinking may be added to the first mixture when it contacts the polymeric resin that is to be depolymerized. These may include functional linkages or functional groups, such as ethers, esters, amides, sulfonates, hydroxy, thiols, cyano, amines, aldehydes, carboxyls, alkyl halides, ketones, allyls, allenyls, norbornyls, ethynyls, acrylates, methacrylates, itaconates, maleimides, maleic anhydrides, or the like, or a combination thereof.

[0077] Polymeric resins (in pure form or in composite form) that can be treated with the first and second mixtures include thermoplastic polymers, thermosetting polymers (crosslinked polymers), blends of thermoplastic polymers, blends of thermosetting polymers, and blends of thermoplastic polymers with thermosetting polymers. The polymeric resin can be a homopolymer, a copolymer, a block copolymer, an alternating copolymer, a random copolymer, a random block copolymer, a graft copolymer, a star block copolymer, anionomer, a dendrimer, or a combination thereof. The polymer may be a biodegradable polymer, an electrolyte, or a combination thereof.

[0078] Examples of thermoplastic polymers that can be used in the polymeric material include polyacetals, polyacrylics, polycarbonates, polyalkyds, polystyrenes, polyolefins, polyesters, polyamides, polyaramides, polyamideimides, polyarylates, polyurethanes, epoxy polymers, phenolics, silicones, polyarylsulfones, polyethersulfones, polyphenylene sulfides, polysulfones, polyimides, polyetherimides, polytetrafluoroethylenes, poly etherketones, polyether ether ketones, polyether ketone ketones, polybenzoxazoles, polyoxadiazoles, polybenzothiazinophenothiazines, polybenzothiazoles, polypyrazinoquinoxalines, polypyromellitimides, polyguinoxalines, polybenzimidazoles, polyoxindoles, polyoxoisoindolines, polydioxoisoindolines, polytriazines, polypyridazines, polypiperazines, polypyridines, polypiperidines, polytriazoles, polypyrazoles, polycarboranes, polyoxabicyclononanes, poly dibenzofurans, polyphthalides, poly anhydrides, polyvinyl ethers, polyvinyl thioethers, polyvinyl alcohols, polyvinyl ketones, polyvinyl halides, polyvinyl nitriles, polyvinyl esters, polysulfonates, polysulfides, poly thioesters, polysulfones, polysulfonamides, polyureas, polyphosphazenes, polysilazanes, polypropylenes, polyethylenes, polyethylene terephthalates, polyvinylidene fluorides, polysiloxanes, or the like, or a combination thereof.

[0079] Examples of thermosetting polymers include epoxy polymers, unsaturated polyester polymers, polyimide polymers, bismaleimide polymers, bismaleimide triazine polymers, cyanate ester polymers, vinyl polymers, benzoxazine polymers, benzocyclobutene polymers, acrylics, alkyds, phenol-formaldehyde polymers, novolacs, resoles, melamineformaldehyde polymers, urea-formaldehyde polymers, hydroxymethylfurans, isocyanates, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, unsaturated polyesterimides, or the like, or a combination thereof.

[0080] Examples of blends of thermoplastic polymers include acrylonitrile-butadiene- styrene / polyamide blends, polycarbonate / acrylonitrile-butadiene-styrene blends, acrylonitrile butadiene styrene / polyvinyl chloride blends, polyphenylene ether / polystyrene blends, polyphenylene ether / polyamide blends, polysulfone / acrylonitrile-butadiene-styrene blends, polycarbonate / thermoplastic urethane blends, polycarbonate / polyethylene terephthalate blends, polycarbonate / polybutylene terephthalate blends, thermoplastic elastomer alloys, polyamide elastomers, polyester elastomers, polyethylene terephthalate / polybutylene terephthalate blends, polyacetal elastomers, styrene-maleic anhydride / acrylonitrile-butadiene-styrene, poly ether ether ketone / poly ethersulfone blends, poly ether ether ketone / poly etherimide poly ethylene / poly amide blends, poly ethylene / poly acetal blends, or the like.

[0081] Examples of biodegradable polymers include polylactic acid (PLA) polyglycolic acid (PGA), polylactic-co-glycolic acid (PLGA), poly-caprolactone (PCL), copolymers of poly lactic -glycolic acid and poly-caprolactone (PCL-PLGA copolymer), polyhydroxy alkanoates, polyhydroxy-butyrate-valerate (PHBV), polyorthoester (POE), polyethylene oxide-butylene terephthalate (PEO-PBTP), poly-D,L-lactic acid-p-dioxanonc- poly ethylene glycol block copolymer (PLA-DX-PEG), or the like, or a combination thereof.

[0082] Examples of polyelectrolytes are polystyrene sulfonic acid, polyacrylic acid, pectin, carrageenan, alginates, carboxymethylcellulose, polyvinylpyrrolidone, or the like, or a combination thereof.

[0083] In an embodiment, the polymeric resin that is treated with the second mixture is preferably a thermosetting polymer. An exemplary polymeric resin that is treated with the second mixture to delaminate it from the filler is a polyepoxide.

[0084] Polymeric composites contain particulate or fibrous fillers. The fibrous fillers may be glass fibers, carbon fibers, ceramic fibers, metal fibers, or a combination thereof. The fibers may be continuous or chopped. The fibrous fillers may be present in the composite in the form of woven and non-woven plies. The fibrous fillers may be present in amounts of greater than 40 wt%, preferably greater than 50 wt%, based on a total weight of the polymeric composite.

[0085] In an embodiment, in one method of using the second mixture, the swollen or fragmented polymer obtained after treatment with the first mixture is treated with one or more superheated and / or supercritical fluid(s) (superheated water and the second superheated fluid and / or the second supercritical fluid (e.g., where the second fluid is an organic solvent such as, for example ethanol) in a reactor that is capable being effectively pressurized and heated to a desired temperature. This is followed by adding a third supercritical fluid (e.g., carbon dioxide) to the reactor. The combination of a) the first superheated fluid (e.g., water) b) the second superheated fluid or second supercritical fluid (e.g., ethanol) and c) the third supercritical fluid (e.g., carbon dioxide) to the reactor forms the second mixture in the reactor. The superheated fluid(s) or the combination of the superheated fluid with the supercritical fluid is charged to the reactor in their respective states.

[0086] In an embodiment, the first superheated fluid is superheated water, while the second superheated fluid or second supercritical fluid is a solvent such as ethanol. The third supercritical fluid is carbon dioxide. Treating the polymeric resin with supercritical ethanol during the treatment with the superheated water and / or superheated ethanol is optional.

[0087] In short, a superheated fluid is charged to the reactor in its superheated state and a supercritical fluid is charged to the reactor in its supercritical state. An optional fluid not in its superheated or supercritical state may also be fed to the reactor during the contact of the polymer with the second mixture. As noted above, this fluid is chosen to have its boiling point lie above the temperature and pressure of the reactor during the operation. The additional fluid used during the contact of the polymer with the second mixture may be different from the additional fluid using during the contact with first mixture. For example, during the contact between polymer and the first mixture, ethylene glycol may be selected to remain below its superheated and supercritical point, while during the contact with the second mixture, glycerol may be selected to remain below the supercritical and superheated point.

[0088] The introduction of a fluid not in its supercritical or superheated state may be done either prior to the introduction of the other superheated or supercritical fluids into the reactor, simultaneously with the introduction of the other superheated or supercritical fluids, or after the introduction of the other superheated or supercritical fluids into the reactor. In an embodiment, it is preferably conducted prior to the introduction of the other superheated or supercritical fluids into the reactor.

[0089] The polymer is fed to the reactor simultaneously with the respective superheated fluid(s) (e.g., water and ethanol) or a combination of the superheated fluid (e.g., water and ethanol) with the supercritical fluid (e.g., carbon dioxide) and is mixed in the presence of the fluid. The polymer may be fed to the reactor in the form of a melt (e.g., at a temperature above its glass transition temperature or above its melting point), a solid (e.g., a powder, pellets, a briquette, a composite), a suspension, or in a solution. When fed to the device in the form of a suspension or in the form of a solution, the fluid for forming the suspension or the solution can be chemically the same or different from the supercritical fluid or the superheated fluid. In an embodiment, the polymeric resin is fed to the reactor in the form it is obtained after treatment with the first mixture (e.g., a swollen and / or fragmented polymer).

[0090] It is to be noted that the reactor may be fitted with ancillary equipment that may be used to crosslink the polymer such as, for example, a UV lamp, gamma raygenerators, electron beam generators, micro wave generating magnetrons and associated waveguides for transporting the microwaves to the reactor. The reactor may be fitted with optical fibers, waveguides, and other mechanisms for transporting irradiation from a remote source to the reactor to facilitate crosslinking if desired.

[0091] The superheated fluid(s) (e.g., water, ethanol, ethylene glycol, or a mixture thereof) or the combination of the superheated fluid(s) (e.g., water) with the supercritical fluid (e.g., ethanol) from the second mixture penetrates the polymeric resin (now in swollen or fragmented form after being treated with the first mixture) and swells it. The swollen polymer may then be treated with the third supercritical fluid (e.g., carbon dioxide). In an embodiment, the third supercritical fluid is supercritical carbon dioxide.

[0092] It is to be noted that the polymeric resin may be treated sequentially with the first superheated fluid (e.g., water), the second superheated fluid (e.g., ethanol) and the second or third supercritical fluids (e.g., ethanol and carbon dioxide). In other words, each fluid may be introduced into the reactor sequentially until all fluids are present in the reactor simultaneously to impregnate the polymeric resin. In another embodiment, the polymeric resin may be treated with all of the fluids (all of the superheated and supercritical fluids) simultaneously from the start of the impregnation process. It should be noted that the compounds shown in the parenthesis are only examples of the first, second and third fluids. These compounds may be substituted by any or the other equivalent compounds disclosed herein. For example, when ethanol is shown next to the second superheated fluid in parenthesis, it does not mean that only ethanol may be used as the second superheated fluid. The second superheated fluid can be any solvent having a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2.

[0093] The swollen polymer is treated with the second mixture for a period of time of 30 minutes to 5 days, preferably 60 minutes to 4 days, and more preferably 2 hours to 3 days. The extended period of time, for which the polymeric resin is exposed to the superheated and / or supercritical fluids (of the second mixture) permits the uptake of a large volume of the superheated and / or supercritical fluid. This uptake of a large volume of fluid leads to rupture (termed fragmentation) when the pressure is removed. This fragmentation is observed in both thermoplastic and thermosetting resins but is more pronounced in the thermosetting resins because the crosslinks prevent thermal deformation during the removal of the pressure. When the deformation of the polymer occurs more rapidly than the rate of chain relaxation, fragmentation occurs. The pressurization, retention pressure and depressurization conductedwith the second mixture can be the same or different as the pressurization, retention pressure and depressurization conducted with the first mixture.

[0094] In an embodiment, the temperature of the reactor during the uptake of the second mixture is greater than 150°C, preferably greater than 200°C, preferably greater than 225 °C, preferably greater than 240°C, preferably greater than 270°C, and preferably greater than 300°C. The temperature of the reactor is preferably less than 375°C, which is the supercritical point of water. The pressure of the reactor during the uptake of the second mixture is greater than 500 pounds per square inch (psi), preferably greater than 1000 psi, preferably greater than 1500 psi, preferably greater than 2000 psi, preferably greater than 4500 psi, preferably greater than 5000 psi, preferably greater than 6000 psi, preferably greater than 7000 psi, and more preferably greater than 8000 psi, preferably greater than 10,000 psi. The pressure in the reactor may be as high as 25,000 psi.

[0095] As noted above, the polymeric resin may be treated to one or more pressure cycles with the second mixture. In an embodiment, the polymeric resin is preferably treated to only one cycle of increased pressure and temperature in the reactor during which the polymer is impregnated with the superheated and / or supercritical fluids of the second mixture. In other words, after depressurization, the polymer may not be treated to another cycle of increased pressure and temperature (after it contacts the second mixture) in the reactor. The effects of depressurization are detailed below. In an embodiment, the volume of the polymeric resin during pressurization (with the second mixture) increases by over 100%, preferably over 200%, and more preferably over 300%, based on an initial volume of the polymeric resin obtained after being treated with the first mixture.

[0096] The swollen polymer after being treated for one cycle with the second mixture is subjected to depressurization to produce additional fragmentation of the polymeric resin. During the rapid depressurization, polymeric resins present in composites are delaminated and separated from fillers present in the polymeric composite. The fragmentation of the polymeric resin produces polymeric particles that have a higher surface area than that of the original polymeric resin (prior to being treated with the second mixture). This increase in surface area facilitates dissolution of the fragmented particles in the second mixture to produce liquification of the polymer. During the liquification, bond cleavage takes place in the liquified polymer producing depolymerization of the polymer. In an embodiment, the hydrolysis of the fragmented polymer results in the depolymerization of the polymer to produce an oligomer-rich phase in the second mixture. The term “oligomer” is inclusive ofmonomers, dimers, trimers, tetramers, pentamers, and so on having a number average molecular weight of 200 to 5000 grams per mole.

[0097] The depressurization rate after being treated with the second mixture is the same as that after the treatment with the first mixture. The depressurization can be conducted slowly or rapidly. The depressurization step begins with a release in pressure from the reactor after treatment with the second mixture and may be conducted rapidly at a rate of 5000 psi per second (psi / second) to 50,000 psi / second, 10,000 to 40,000 psi / minute, 20,000 to 35,000 psi / minute till ambient conditions are reached. Alternatively, the depressurization may be conducted slowly after treatment with the second mixture at a rate of 100 psi / second to less than 5000 psi / second, 200 psi / second to 3000 psi / second, 300 to 1000 psi / second till ambient conditions are reached.

[0098] In the case of a pure polymer, the oligomer-rich phase may be subjected to further treatment (such as distillation, centrifugation, filtration, washing, and the like) to isolate the oligomers. A library of different oligomers may be obtained from the depolymerization of the pure polymer in this manner. The polymers and oligomers derived from this process are never in the form of a foam.

[0099] In the case of a polymeric composite, the liquification will produce a polymer- rich phase along with an oligomer-rich phase and a filler-rich phase. By increasing the time of liquification a larger portion of the polymer-rich phase will gradually undergo conversion to the oligomer-rich phase. In other words, with the passage of time (during liquification see FIG 5), the polymer-rich phase will decrease relative to the oligomer-rich phase. The polymer-rich phase and / or the oligomer-rich phase is separated from the filler-rich phase by techniques such as centrifugation, filtration, or the like. The fillers may be segregated from the filler-rich phase by centrifugation and reused in a composite, while the polymers and oligomers are separated from the polymer-rich phase by techniques such as distillation, filtration, liquid chromatography, or the like.

[0100] One of the novel compositions obtained from this process is a combination of the second mixture with both polymers and oligomers derived from depolymerization of the polymeric resin.

[0101] The fillers obtained from the filler-rich phase may be washed using the same fluids contained in the second mixture.

[0102] In an embodiment, vapors from the reactor may be collected during the depressurization after treatment with the second mixture and any valuable byproducts (such as, for example, monomers and other volatiles) recovered for further use.

[0103] As noted above, the fillers recovered from a composite do not suffer any substantial change in physical properties or chemical properties from those used initially. The aspect ratio (length divided by diameter) of the recovered fibers is substantially the same as that of the initial fibers. The lack of mechanical abrasion or thermal degradation during the recovery process prevents reduction in fiber quality, dimensions or chemical properties. The fibers recovered in this process can be reused to produce another component.

[0104] The process of recovering fillers and of depolymerizing the polymer may be a batch process, a semi-continuous process or a continuous process.

[0105] This method of treating the polymeric resin (in pure form or in composite form) via pressure cycling in a first mixture followed by treatment with a second mixture (that is compositionally different from the first mixture) is particularly effective for recycling crosslinked polymers. This method of recycling polymeric composites is useful for recycling wind turbine airfoils (epoxy based resin and glass), aerospace components (carbon fiber and epoxy based), automotive components (epoxy based and carbon or glass) as well as marine components (vinyl ester resin glass fiber based).

[0106] In an exemplary embodiment, composites containing glass fibers and epoxies (a crosslinked polymer) may be recycled using the aforementioned method. The epoxycontaining composite may be first treated with the second mixture containing superheated water (the first superheated fluid) and optionally with superheated ethanol (the second superheated fluid) or with supercritical ethanol (the first supercritical fluid). It is then treated with supercritical carbon dioxide. This treatment (with 3 fluids - superheated water, superheated ethanol or supercritical ethanol, and supercritical carbon dioxide) occurs at a pressure of 500 to 9000 psi, preferably 3000 to 8500 psi, preferably 4500 to 8000 psi and a temperature of greater than 240°C, preferably greater than or equal to 245°C up to a temperature of 370°C for a time period of 24 to 120 hours, preferably 48 to 80 hours.

[0107] The second mixture in the reactor comprises water and ethanol in a 45:55 to 55:45 volume ratio. The supercritical carbon dioxide constitutes the remainder of the second mixture in the reactor. The combination of water, ethanol and carbon dioxide facilitates an efficient liquification of the polymeric resin (the epoxy) present in the composite. The liquified product comprises water, ethanol, carbon dioxide, a polymer-rich phase and anoligomer-rich phase. The oligomer-rich phase can be extracted from the reactor and repeatedly washed to obtain the oligomer. The fibers may also be extracted from the reactor and repeatedly washed to obtain glass fibers that may be used to produce another composite.The oligomers may also be repolymerized and used to produce another composite. The composites produced in this manner may be used to produce another wind turbine airfoil

[0108] In an embodiment, a composition obtained from the process may contain a mixture of aromatic species and aliphatic species. The mixture of aromatic species may include those having the structures (1), (2) and (3) shown below.where for structure (1), each Rhis independently a C1-20 hydrocarbyl group such as a C1-20 alkyl, a substituted C1-20 alkyl, a Ce-io aryl, or substituted Ce-io aryl, and n is 0 to 5. The substituted C1-20 alkyl or substituted Ce-io aryls may include P, O, S, N or halogen substitution.

[0109] In a preferred embodiment, for structure (1), Rhis a Ci to C3 alkyl, while n may be 1 or 2.

[0110] In another preferred embodiment, moiety of structure 1 may have the structure 1A shown below.where R5, Re and R7 may each independently be a substituted or unsubstituted Ci to C20 alkyl or a Ci to C20 cycloalkyl. The substitution may include P, O, S, N atoms.

[0111] For structure (2), Raand Rbare each independently a C1-20 alkoxy or C1-20 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than4, the valence of each carbon of the ring is filled by hydrogen. In an aspect, p and q is each 0, or p and q is each 1, and Raand Rbare each a C1-3 alkyl group, preferably methyl, disposed meta to the hydroxy group on each arylene group. Xais a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each Ce arylene group are disposed ortho, meta, or para (preferably para) to each other on the C<> arylene group, for example, a single bond, -O-, -S-, -S(O)-, -S(O)2-, -C(O)-, or a C1-18 organic group, which can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous.For example, Xacan be a substituted or unsubstituted C3-18 cycloalkylidene; a C1-25 alkylidene of the formula -C(Rc)(Rd) - wherein Rcand Rdare each independently hydrogen, C1-12 alkyl, C1-12 cycloalkyl, C7-12 arylalkyl, C1-12 heteroalkyl, or cyclic C7-12 heteroarylalkyl; or a group of the formula -C(=Re)- wherein Reis a divalent C1-12 hydrocarbon group.

[0112] In a preferred embodiment, for structure (2) Xais a Ci to Cis organic group, preferably a Ci to Ce organic group, which can be cyclic or acyclic, aromatic or non- aromatic; and Raand Rbare each independently a Ci to C20 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen.

[0113] In yet another embodiment, structure (2) may reduce to structure (2A):where R7, Rs and R9 can be the same or different and can independently be a hydrocarbyl group having 1 to 20 carbon atoms, where the hydrocarbyl unit can be linear, branched, cyclic, or any combination thereof. Moreover, the hydrocarbyl fragment may be saturated or unsaturated and may include one or more of the following hetero atoms: N, O, S, and / or P.

[0114] For structure (3), Ri, R2, and R3 can be the same or different and can independently be a hydrogen; a saturated or unsaturated hydrocarbyl, having between 1 and 20 carbon atoms, where the hydrocarbyl unit can be linear, branched or cyclic and may be substituted or unsubstituted. Substitution may occur with N, O, S, and / or P.

[0115] In an embodiment, when a polymeric composite that comprises a polymer having aryl groups (e.g., epoxies, phenolics, aromatic polyesters, or the like) is subjected to pressurization and depressurization in the presence of supercritical and / or superheated fluids, a mixture that comprises aromatic and aliphatic species may be obtained. The aromatic species and aliphatic species may be monomers, dimers, trimers or oligomers and may be reacted to undergo polymerization. In other words, at least one or more of the aromatic and / or aliphatic species derived from the cleavage of polymers may be capable of being polymerized.

[0116] The molar ratios of aromatic species to aliphatic species can vary from 0.05:1.10 to 0.15:1.00. In other words, the molar ratio of aromatic to aliphatic species expressed as a percentage (of the sum of aromatic and aliphatic species) can vary from about 3% to about 20%, preferably about 5% to about 15%, and more preferably 6 to 10%, based on the total moles of aromatic and aliphatic species derived from the liquefaction of the polymers in the polymeric composite.

[0117] The fillers obtained from the filler-rich phase may be washed using the same fluids contained in the fluid composition.

[0118] In an embodiment, vapors from the reactor may be collected during the depressurization and any valuable byproducts (such as, for example, monomers and other volatiles) recovered for further use.

[0119] The first mixture, the second mixture and the method of using these respective mixtures to depolymerize the polymeric resin is exemplified by the following non-limiting example.EXAMPLEExample 1

[0120] This example is conducted to demonstrate the use of a pressure cycle with the first mixture on a polyepoxide-glass fiber composite. It exemplifies the methodology detailed above for separating the fibers from an epoxy containing composite using the first mixture detailed herein. Epoxy based thermosets are not soluble in common solvents, do not melt, and generally cannot be reprocessed.

[0121] In this example, the epoxy containing composite is treated with 2 different fluid compositions. One fluid composition contained only superheated water (shlLO) at 6000 psi for 72 hours. The epoxy containing composite was treated with this fluid afterwhich the insoluble polymeric content in the composite was determined. The second fluid composition contained supercritical carbon dioxide (scCCh) and superheated water (shH O). This fluid composition is covered by the first mixture detailed in this disclosure. One epoxy containing composite was treated to a first cycle. The samples were subjected to the first cycle at temperatures of 200, 210, 215, 220, 225 and 240°C. The pressure soak for each cycle was conducted at these temperatures at 6000 psi for 72 hours. In this example, the epoxy containing composite was subjected to a slow depressurization (between 100 psi / second to less than 5000 psi / second) after the pressure soak step. The results are shown in the Table 2 below.Table 2

[0122] The percentage of insoluble polymer was measured after each cycle for each sample. The results are shown in Table 2 above.

[0123] In order to determine the percentage of soluble polymer removed from the epoxy composites, the sample were weighed prior to treatment. They were then treated with the desired fluid as shown in Table 2. The samples were dried and weighed after the treatment and the difference in weight was recorded as being the amount of polymer that was solubilized. The percentage of insoluble polymer is the amount of the polymer still on the sample that was subjected to the treatment with fluid.

[0124] From Table 2 it may be seen that treatment with superheated water only leaves a lot of the polymeric resin in the epoxy composite unsolubilized even at temperatures of 240°C. When samples were subjected to the first mixture of superheated water and supercritical carbon dioxide for one cycle (with slow depressurization), it may be seen thatthere is more polymer that is solubilized when compared with the sample that was exposed to only superheated water. For example, the sample treated at 220°C for one cycle of the first mixture (of superheated water and supercritical carbon dioxide with slow depressurization) contains about 63.1 wt% of insoluble matter, while the sample treated for only one cycle with superheated steam has 100 wt% of insoluble matter left.

[0125] From Table 2 it can be seen that samples subjected to the first cycle with a combination of supercritical carbon dioxide and superheated steam show a greater ability to solubilize the polymer at almost any temperature, thus demonstrating the effectiveness of pressure cycling with two fluids instead of just one in delaminating the polymer from the composite and solubilizing it.Example 2

[0126] In this example, the epoxy composite of Example 1 was treated to one pressure cycle of superheated water (shFhO) and supercritical carbon dioxide (scCCE) with rapid depressurization after the pressure soak step. As with Example 1, the pressure soak step was conducted at 6000 psi for 72 hours. The pressurization and pressure soak steps were conducted as in Example 1. The depressurization was rapid between 5000 psi / second to 50,000 psi / second. In the previous example, the depressurization step was slow between 100 psi / second to less than 5000 psi / second.

[0127] The results are shown in the Table 3. The Table 3 contains the results shown above in Table 2 for comparison.Table 3depressurization) shows a much greater of conversion of the polymer (the polyepoxide) to a soluble form. For example, after one pressure cycle at 220°C, it may be seen that the fast depressurization results in only 3.74 wt% of the polyepoxide being left as insoluble. The corresponding sample that was treated with the slow depressurization has by contrast 63.1 wt% of the polyepoxide that is insoluble.

[0129] From Table 3 it can be seen that samples subjected to the pressure cycle with rapid depressurization show a greater dissolution of the polymer at any temperature when compared with a slow depressurization, thus demonstrating the effectiveness of pressure cycling with rapid depressurization in delaminating the polymer from the composite and solubilizing it.

[0130] The Examples 1 and 2 also demonstrate the utility of treating the epoxy containing composites with the first mixture of a superheated fluid and a supercritical fluid as opposed to only one of the superheated fluid or the supercritical fluid. Rapid depressurization is more advantageous than slow depressurization at lower temperatures for the pressure soak step. A slow depressurization is effective as a rapid depressurization at higher temperatures.Example 3

[0131] This example is conducted to demonstrate the extraction of fibers and the depolymerization of an epoxy polymer from a composite that is treated with the second mixture. It exemplifies the methodology detailed above for separating the fibers from an epoxy containing composite using the second mixture of fluids detailed herein. Epoxy based thermosets are not soluble in common solvents, do not melt, and generally cannot be reprocessed.

[0132] In this example, the epoxy containing composite is treated with 3 different fluid compositions. The first two fluid compositions contained only 2 fluids, while the third fluid composition contained 3 fluids and is similar to the second mixture detailed herein. The first fluid composition comprises supercritical carbon dioxide and super critical ethanol. The second fluid composition comprises supercritical carbon dioxide and superheated water. The third fluid composition is similar to the second mixture and comprises supercritical carbon dioxide, supercritical ethanol and superheated water. In the third fluid composition, thevolume ratio of water to ethanol is 50:50. All epoxy containing composites were saturated with the respective fluid composition for 3 days (72 hours) at 245°C. Table 2 below shows the respective fluid compositions along with the pressure of the supercritical carbon dioxide.

[0133] The epoxy-containing composite was first treated with superheated water (the first superheated fluid) and then with supercritical ethanol (the first supercritical fluid). Following the impregnation of the epoxy-containing composite with the superheated water and supercritical ethanol, it is treated with supercritical carbon dioxide (the second supercritical fluid) at different pressures (shown in the Table 2 above), a temperature of 245 °C for a time period of 72 hours.

[0134] From the Table 2 it may be seen that the fiber cleaning efficiency improves with pressure. For example, it may be seen that when the composite is treated with water, ethanol and carbon dioxide the cleaning efficiency improves at pressures of 6000 to 8000 psi compared with the cleaning efficiency below 1000 psi. Similarly, it may be seen that at 6000 psi, the best cleaning efficiency is obtained when all three fluids (superheated water, supercritical ethanol and supercritical carbon dioxide) are used in the fluid composition versus those compositions that have only two fluids (supercritical carbon dioxide and superheated water or supercritical carbon dioxide and supercritical ethanol). This reveals that there is a synergy between the carbon dioxide, the ethanol and water that functions to clean the fibers very efficiently.

[0135] Cleaning efficiency is measured using ASTM D3171-22 “Standard Test Methods for Constituent Content of Composite Materials” This is a bum out test using a furnace to ascertain mass loss of the fiber. A higher “cleaning efficiency” is a recovered fiber batch that has very little mass loss after treatment in the furnace. Little or no polymeric matrix remaining.Table 2Key: scCC = supercritical carbon dioxide; shH O = superheated water; scEtOH = supercritical ethanolExample 4

[0136] This example was conducted to determine the different oligomeric products that are formed from the depolymerization of the poly epoxide in the epoxy -containing composite. As noted above, liquefication of crosslinked thermosets, and thermoset composites results in the formation of low molecular weight polymers and oligomers with a range of molecular weights between 200 and 5,000 g / mol.

[0137] FIG. 4 depicts the reaction between bisphenol A diglycidyl ether (commonly abbreviated BADGE or DGEBA) and JEFFAMINE D230. JEFFAMINE D230 is a polyetheramine - a difunctional, primary amine with an average molecular weight of about 230 g / mol. The primary amine groups are located on secondary carbon atoms at the end of the aliphatic polyether chain.

[0138] FIG. 5 is a schematic diagram that shows the potential moieties that may be formed as a result of the fragmentation of epoxy network.

[0139] The oligomer and polymers can be either linear, or branched, or a combination of both linear and branched mixtures. The chemical functionality present on the oligomer and polymer fragments is a combination of aliphatic and aromatic alcohols, including phenolic residues. Also present on the oligomer are primary and secondary amines, again a combination of aliphatic and aromatic from the liquefication of amine cured epoxy resins. The ratio of aliphatic to aromatic content is readily quantified by proton nuclear magneticresonance (^H NMR) spectroscopy and can vary between 5:95 to 95:5 mole percent. The ratio of alcohols; aliphatic, aromatic and phenolic can be identified by using phosphorus labeling and31P NMR, as described by Meng et al. in Nature Protocol 2019 (NATURE PROTOCOLS |VOL 14 [SEPTEMBER 2019 | 2627-2647 https: / / doi.org / 10.1038 / s41596- 019-0191-1). Similarly, the amine content and ratio of primary and secondary amines can similarly be determined by an adaptation of the procedure of Meng et al.

[0140] The amino-alcohol oligomeric and polymeric liquefied products were found to be soluble in a range of organic solvents, tetrahydrofuran, toluene, anisole, diethyl ether, chloroform, dichloromethane and acetone.

[0141] The depolymerization process of amine cured epoxy thermosets produces oligomeric products that are amino-alcohol functionalized. Various thermosets that are encountered for this process involve:1) an aromatic epoxide cured with an aliphatic amine.2) an aromatic epoxide cured with an aromatic amine.3) an aliphatic epoxide cured with an aliphatic amine.4) an aliphatic epoxide cured with an aromatic amine.5) various combinations of 1 through 4 above.

[0142] Amine cured epoxy thermosets, and amine cured epoxy thermoset composites, can have a range of aromatic and aliphatic content. The amino-alcohol oligomer produced by the depolymerization results in compositions having ranges of mole percentages of aromatic to aliphatic content as shown in the Tables 3 and 4 below.Table 3

[0143] More preferably compositions ranges of the aromatic to aliphatic content in the amino-alcohol oligomers would be as shown below in Table 4.Table 4Example 5

[0144] In this example was conducted to evaluate some of the different potentially commercially valuable species that are produced when the fragmentation of an epoxy network occurs under the conditions detailed above.

[0145] For this example, some of the species seen in the FIG. 2 were quantified using phosphorus NMR spectroscopy. A mixture of liquified resin sample was subjected to a phosphitylation reaction following which phosphorus NMR was conducted. The nomenclature adopted for the samples seen in the Table 5 is shown in the FIG. 6A. From the FIG. 6A, it may be seen that samples liquified in a mixture of supercritical carbon dioxide and superheated water are labelled A, while those liquified in a mixture of supercritical carbon dioxide, superheated water and supercritical ethanol are labelled B. FIGS. 6B-1 and 6B-2 includes graphs of representative phosphorus NMR spectrum of the phosphitylation reaction mixture of liquified resin samples that was conducted in a mixture of supercritical carbon dioxide, superheated waster and supercritical alcohol. Peaks a, b and c in both the spectra represent aliphatic amino-alcohols, while peaks d and e in the spectra represent aromatic hydroxyl species.

[0146] The results of several liquified mixtures are shown in the FIG. 7. FIG. 7 contains a table (Table 5) that details the ratio of aromatic to aliphatic component ratios determined by phosphorus-31 NMR spectroscopy. From the Table 5 in FIG. 7 it may be seen that the molar ratio of aromatic to aliphatic species can vary from 0.05:1.10 to 0.15:1.00. In other words, the molar ratio of aromatic to aliphatic species expressed as a percentage (of the sum of aromatic and aliphatic species) can vary from about 4% to about 15%, preferably about 5% to about 12%. At least a portion of the aromatic species, the aliphatic species, or a combination thereof are polymerizable.

[0147] From the Table 5 in FIG. 7, it may be seen that the liquified mixtures contain the following aromatic and aliphatic species. These are shown in the Table 6.Table 6where in Table 6, for structure (1), each Rhis independently a C1-20 hydrocarbyl group such as a C1-20 alkyl, a substituted C1-20 alkyl, a Ce-io aryl, or substituted Ce-io aryl, and n is 0 to 5. The substituted C1-20 alkyl or substituted Ce-io aryls may include P, O, S, N or halogen substitution.

[0148] In Table 6, for structure (2), Raand Rbare each independently a C1-20 alkoxy or C1-20 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen. In an aspect, p and q is each 0, or p and q is each 1, and Raand Rbare each a C1-3 alkyl group, preferably methyl, disposed meta to the hydroxy group on each arylene group. Xais a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each Ce arylene group are disposed ortho, meta, or para (preferably para) to each other on the Ce arylene group, for example, a single bond, -O-, -S-, -S(O)-, - S(O)2-, -C(O)-, or a C1-18 organic group, which can be cyclic or acyclic, aromatic or nonaromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. For example, Xacan be a substituted or unsubstituted C3-18 cycloalkylidene; a C1-25 alkylidene of the formula -C(Rc)(Rd) - wherein Rcand Rdare each independently hydrogen, C1-12 alkyl, C1-12 cycloalkyl, C7-12 arylalkyl, C1-12 heteroalkyl, or cyclic C7-12 heteroarylalkyl; or a group of the formula -C(=Re)- wherein Reis a divalent C1-12 hydrocarbon group.

[0149] In Table 6, in structure (3), Ri, R2, and R3 can be the same or different and can independently be a hydrogen; a saturated or unsaturated hydrocarbyl, having between 1 and 20 carbon atoms, where the hydrocarbyl unit can be linear, branched or cyclic and may besubstituted or unsubstituted. Substitution may occur with N, O, S, P, a halogen, or a combination thereof.Example 6

[0150] This example is conducted to demonstrate the use of ethylene glycol (EG) and / or glycerol as potential solvents for the liquification of polymers and polymeric composites. In this example, glycerol was not superheated or transformed into its supercritical state. It was used in a non-superheated and non- supercritical state. FIG. 8 depicts the nomenclature adopted for determining sample compositions. Three different fluid compositions were used for liquification of the polymeric composite samples. The polymeric composite comprised an epoxy thermoset and glass fibers. The first fluid composition (Bl) included supercritical carbon dioxide and superheated water. The second fluid composition (B8) included supercritical carbon dioxide, superheated water and superheated ethanol. The superheated water and superheated ethanol were used in a volume ratio of 1 : 1. The third fluid composition (B5) included supercritical carbon dioxide, superheated water and glycerol. The water and glycerol was used in a 1:1 volume ratio. Each sample was pressurized to 3000 psi for a period of 72 hours. Samples with the letter “c” next to them were subjected to rapid depressurization after 24 hours followed by slow depressurization after 48 hours. The temperature during pressurization was 225°C.

[0151] The result of this exposure to pressure and the fluid composition produced the liquefaction results as seen in the FIG. 9. From the bar chart seen in FIG. 9, it may be seen that as the temperature of pressurization is increased, a larger fraction of the polymeric composite is liquified (i.e., it is converted to a soluble mixture of reactants).

[0152] At temperatures of 220°C or greater it may be seen that a substantial portion of the polymeric composite is converted into a soluble liquid that can be subjected to further fractionation and used for other reactions downstream. In summary, this method of liquification may be used to recover a large amount of polymeric resin from a polymeric article or a polymeric composite.

[0153] While the invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof.Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method of solubilizing a polymeric resin comprising: treating the polymeric resin or a composite comprising the polymeric resin with a first mixture of fluids for one or more pressure cycles; where the first mixture comprises a first superheated fluid and a first supercritical fluid; where each pressure cycle comprises a pressurization step, a pressure retention step and a depressurization step; and treating the polymeric resin or the composite comprising the polymeric resin to one or more pressure cycles with a second mixture of fluids; where the second mixture of fluids comprises superheated water, a second superheated or supercritical fluid and a third supercritical fluid; where the first superheated fluid and the second superheated or supercritical fluid comprise a solvent that has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2.

2. The method of Claim 1, where the first superheated fluid is superheated water or a superheated solvent that has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2.

3. The method of any one of the foregoing claims, where the first superheated fluid is present in an amount of 25 to 75 volume percent and where the first supercritical fluid is present in an amount of 25 to 75 volume percent, based on a total volume of the first mixture.

4. The method of any one of the foregoing claims, where the superheated solvent that has a Hildebrand solubility parameter between 15 and 40 (MPa)1 / 2is ethanol.

5. The method of any one of the foregoing claims, where the first superheated fluid is superheated water and where the first supercritical fluid is carbon dioxide.

6. The method of any one of the foregoing claims, where the second superheated fluid is ethanol and the third supercritical fluid is carbon dioxide.

7. The method of any one of the foregoing claims, where the second supercritical fluid is ethanol and the third supercritical fluid is carbon dioxide.

8. The method of any one of the foregoing claims, where the first mixture has a different chemical composition from the second mixture.

9. The method of any one of the foregoing claims, where the pressurization step with the first mixture is conducted to reach a pressure of greater than 4500 psi.

10. The method of any one of the foregoing claims, where the pressure retention step is conducted for 30 minutes to 5 days.

11. The method of any one of the foregoing claims, where the depressurization step is conducted at a rate of 5000 psi / second to 50000 psi / second.

12. The method of any one of the foregoing claims, where the depressurization step is conducted at a rate of 100 psi / second to less than 5000 psi / second.

13. The method of any one of the foregoing claims, where the first superheated fluid and the second superheated or supercritical fluid are a same solvent.

14. The method of any one of the foregoing claims, where the same solvent is ethanol.

15. The method of any one of the foregoing claims, where the treating the polymeric resin or the composite comprising the polymeric resin with a first mixture of fluids is conducted for 2 or more cycles.

16. The method of any one of the foregoing claims, where the first supercritical fluid and the third supercritical fluid are a same gas.

17. The method of any one of the foregoing claims, where the same gas is carbon dioxide.

18. The method of any one of the foregoing claims, further comprising condensing volatiles that are discharged during the depressurization step.

19. The method of any one of the foregoing claims, where the first mixture and / or the second mixture comprises at least one fluid that is not in the supercritical state or in the superheated state.

20. The method of any one of the foregoing claims, where the first mixture and / or the second mixture comprises an initiator and / or crosslinker that facilitates crosslinking in an uncrosslinked polymeric resin or lightly crosslinked polymeric resin.

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