Thermosetting resins containing ionically cleavable disiloxanes

Abstract

A thermosetting resin comprising a plurality of crosslinked, ionically cleavable disiloxane units derived from disiloxane monomers incorporated therein. The thermosetting resin is a polyester, vinyl ester, polyurethane epoxy, polyurea, rubber, crosslinked thermoplastic, or a combination thereof. The plurality of crosslinked, ionically cleavable disiloxane units are cleavable by fluoride ions. A composite material comprising a cured matrix formed from the thermosetting resin and a plurality of reinforcing fibers embedded therein. The reinforcing fibers are glass, carbon, aramid, natural, basalt, boron, silicon carbide, polymer, or a combination thereof. The composite material is fully recyclable. A process for recycling the composite material includes adding the composite material to a solvent in a container, introducing fluoride ions into the solvent in the container, and maintaining under conditions to dissolve the matrix material and liberate more than 95% by weight of the reinforcing fibers from the matrix material.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 443,112, filed February 3, 2023, the contents of which are incorporated herein by reference.

[0002] The present invention relates generally to composite materials such as sheet molding compounds, and more particularly to ionically severable thermoset resins that can be readily recycled to recover reinforcing fibers therefrom. [Background technology]

[0003] The use of composite materials, including fiber-reinforced composites, has continued to increase in recent years in applications such as vehicle components, building materials, and industrial equipment. With the increased use of composite materials, the need to recycle discarded composites has become more urgent to avoid composite-based materials being disposed of in landfills and to conserve the resources used to form these composites. Generally, thermoplastic polymers such as polyethylene and polypropylene can be recycled through remelt processing. However, for thermoset composites, such as fiber-reinforced composites (FRCs), melt recycling is difficult due to the cross-linked nature of the resin. That is, the same properties that make thermosets strong and suitable for structural applications also make them extremely difficult to recycle efficiently.

[0004] Current recycling techniques for thermoset polymer composites involve either mechanically, thermally, or chemically processing the composites. These techniques are characterized by high energy input, harsh chemicals (many with toxic VOCs), and / or expensive capital equipment. Furthermore, recycled products tend to be of low quality due to factors such as process-related residual resin retention and fiber damage. Theoretically, the recycling of thermoset resins would be facilitated if high-value carbon fiber could be recovered from them.

[0005] One recycling method that has been attempted to recycle FRC-based materials is solvolysis, which uses reactive solvents such as benzyl alcohol, diethylene glycol, and diethylene glycol monomethyl ether in the presence of a catalyst under an inert atmosphere and elevated temperatures to break down the ester bonds in polyester thermoset resins while preserving the properties of the reinforcing fibers. While this method proved effective in separating the resin from the glass fibers, the resulting glass fibers were damaged during the process, and the cost of the solvent and reaction time made the process impractical. (H. Fukuzawa et al., 2nd International Symposium on Feedstock Recycling of Plastics and Other Innovative Plastics Recycling Techniques, Ostend, Belgium, September 8-11, 2002.)

[0006] Another technique for recycling FRC has been to solubilize epoxy resin matrices containing carbon or glass fibers using poly(ethylene glycol) in sodium hydroxide solution. Carbon fibers and non-alkaline fibers recovered after matrix solvolysis retained greater than 94% of their original strength, but this method has had limited acceptance due to the specificity of the chemistry to the epoxy matrix and low overall recycling efficiency. (P Yang et al., J. Reinforced Plastics and Composites, 2014, 33(22):2106-2114)

[0007] Aminolysis of FRC is attractive because it can yield carbon fibers with 97% purity. (Vallee, M., Tersac, G., Destais-Orvoen, N., Durand, G., "Chemical Recycling of Class Surface Quality Sheet-Molding Composites," Ind. Eng. Chem. Res., 43, 6317-6324 (2004).) The method involves high-temperature solvent digestion in the presence of a catalyst, such as glacial acetic acid, sodium acetate, or potassium sulfate, in excess ethanolamine, followed by washing, sonication, and drying of the recovered carbon fibers in a boiling solvent, such as methyl ethyl ketone (MEK). While the aminolysis process has been somewhat effective, the method has limited acceptance due to long process times (up to 48 hours) and the expense and toxicity of the solvent.

[0008] Further processes have been developed for regenerating carbon fibers from a cured thermoset matrix using low-cost, low-toxicity solvents, which involve adding a thermoset to a polyol solvent composition under conditions to liberate greater than 95% by weight of the carbon fibers from the particles. However, such processes still rely on techniques such as solvent pre-swelling of the particles, size reduction, microwave heating, and sonication to promote digestion of the thermoset matrix and liberate the reinforcing carbon fibers.

[0009] Fluoride cleavage of other polymeric materials has previously been explored in mixed organic-inorganic systems, but the hydrophobic nature of additives to thermosets (including reinforcing fibers dispersed therein) and the hydrophobicity of the resulting cured articles has previously precluded the application of this chemistry to thermosets (Krug et al.). Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need for thermoset resins that are more easily recyclable and for more efficient recycling processes to decompose the thermoset resin matrix and regenerate a high percentage of reinforcing fibers therefrom, such that the recovered fibers are suitable for subsequent reuse. [Means for solving the problem]

[0011] The present invention provides a thermosetting resin comprising a plurality of crosslinked, ionically cleavable disiloxane units derived from a disiloxane monomer incorporated therein. The thermosetting resin may be a polyester, vinyl ester, polyurethane epoxy, polyurea, rubber, crosslinked thermoplastic, or a combination thereof. The plurality of crosslinked, ionically cleavable disiloxane units are cleavable by fluoride ions.

[0012] The present invention further provides a composite material comprising a cured matrix formed from the thermosetting resin of the present invention and a plurality of reinforcing fibers embedded therein, the reinforcing fibers being glass fiber, carbon fiber, aramid fiber, all-natural fiber, basalt fiber, boron fiber, silicon carbide fiber, polymer fiber, or combinations thereof, and the composite material is fully recyclable.

[0013] The present invention further provides a process for recycling the composite material of the present invention, comprising the steps of adding the composite material to a solvent in a vessel; introducing fluoride ions into the solvent in the vessel; and maintaining the composite material, solvent, and fluoride ions in the vessel for a period of time under conditions to dissolve the matrix material and to liberate greater than 95% by weight of the reinforcing fibers from the matrix material to form free reinforcing fibers.

[0014] The present invention will be further described with reference to the following drawings, which are intended to illustrate various aspects of the invention and are not intended to be limiting as to its practice. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows a conventional styrene cross-linked unsaturated polyester. [Figure 2] FIG. 1 shows the replacement of styrene monomer with a divinylsiloxane crosslinking agent to provide a crosslinked unsaturated polyester that is easily de-crosslinked in the presence of fluoride ions (F−) at room temperature, according to an embodiment of the present invention. [Figure 3] FIG. 1 illustrates a reaction for incorporating cleavable silicon functionality into a thermosetting monomer, according to an embodiment of the present invention. [Figure 4A-4B] FIG. 1 shows a depiction of a conventional epoxy amine material. [Figures 5A-5D] FIG. 1 illustrates an inventive recycling method according to an embodiment of the present invention. [Figures 6A-6D] FIG. 1 illustrates an inventive recycling method according to an embodiment of the present invention. [Figure 7A] 1 is a graph showing water contact angle versus number of abrasion cycles for prime coatings at various cure temperatures. [Figure 7B] 1 is a graph showing water contact angle versus number of abrasion cycles for recycled (0.01 M TBAF / THF) silicone resin coatings cured at various cure temperatures. [Figure 7C] 1 is a graph showing water contact angle versus number of abrasion cycles for varying [F-] for recycling silicone resin cured at 250°C. [Figure 7D] FIG. 1 illustrates a silicon recycling loop according to an embodiment of the present invention. [Figures 8A-8D] Figure 1 shows SEM-EDS images and WCA photo insets of the silicone resin coating cured at 250°C after 200 abrasion cycles, and crosshatch tape adhesion test for prime and recycled coatings. Abrasion micrograph magnification 100x, scale bar 300 μm; crosshatch magnification 35x, scale bar 800 μm; EDS map: yellow = Si, blue = A. [Figures 8E-8H]Figure 1 shows SEM-EDS images and WCA photo insets of a silicone resin coating cured at 250°C after 200 abrasion cycles and a crosshatch tape adhesion test for 0.002M TBAF. Abrasion micrograph magnification 100x, scale bar 300 μm; crosshatch magnification 35x, scale bar 800 μm; EDS map: yellow = Si, blue = A. [Figures 8I-8L] Figure 1 shows SEM-EDS images and WCA photo insets of a silicone resin coating cured at 250°C after 200 abrasion cycles and a crosshatch tape adhesion test for 20.01M TBAF. Abrasion micrograph magnification 100x, scale bar 300 μm; crosshatch magnification 35x, scale bar 800 μm; EDS map: yellow = Si, blue = A. [Figure 8M-8P] ) SEM-EDS images and WCA photo insets of a silicone resin coating cured at 250°C after 200 abrasion cycles and a crosshatch tape adhesion test for 0.01-0.1M TBAF. Abrasion micrograph magnification 100x, scale bar 300 μm; crosshatch magnification 35x, scale bar 800 μm; EDS map: yellow = Si, blue = A. [Figure 9A] 1 is a graph showing a typical TGA in air of prime and recycled (0.01M TBAF) silicone resins cured at various temperatures, comparing thermal stability defined as the temperature at 5% mass loss, Td5%, with error corresponding to the standard deviation of three experiments for each resin replicate. [Figure 9B] 1 shows a typical TGA in air of prime and recycled silicone resins cured at 250°C with various TBAF concentrations, comparing thermal stability defined as the temperature at 5% mass loss, Td5%, with errors corresponding to the standard deviation of three experiments for each resin replicate. [Figure 10A] FIG. 1 shows GC-MS of prime silicone resin cured at 150°C and tested from 150 to 200°C to determine volatile content at various cure temperatures. [Figure 10B]FIG. 10 shows GC-MS of prime silicone resin cured at 200°C and tested at 200-250°C to determine volatile content at various cure temperatures. [Figure 11A] 1 is a graph showing water contact angle versus number of abrasion cycles for prime and recycled SILRES REN 50 coatings cured at 250C. [Figure 11B] 1 is a graph showing a typical TGA in air of prime and recycled SILRES REN 50 cured at 250° C. [Figures 11C-11E] FIG. 10 shows SEM images of prime coating after 0 abrasion cycles, 200 abrasion cycles, and tape adhesion testing. [Figures 11F-11H] FIG. 1 shows SEM images of recycled coatings after 0 abrasion cycles, 200 abrasion cycles, and tape adhesion testing. [Figures 11I-11J] FIG. 1 shows EDS maps (27× magnification, scale bar 1000 μm) of a primed coating before and after rubbing one half with 0.01 M TBAF solution. [Figure 12A] FIG. 1 shows the chemical structures of siloxanes designated as Es and As. [Figure 12B] FIG. 1 shows a casting of a siloxane combination. [Figure 13A] FIG. 12C is a graph showing the TGA plot of the sample of FIG. 12B. [Figure 13B] FIG. 13B is a graph showing the TGA plot of the combination of FIG. 13A and two additional siloxanes. [Figures 14A-14D] FIG. 2 illustrates the inventive recycling method according to another embodiment of the present invention. [Figure 15] 1 is a schematic diagram showing an unsaturated polyester (UPE) resin monomer containing a clipable crosslinker and a reaction schematic for its synthesis. [Figure 16] 1 is a schematic diagram of a batch reactor vessel in which the process of the present invention is carried out. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention has utility as an ionically cleavable thermoset resin that can be readily recycled and formed into a thermoset composite from which reinforcing fibers can be easily recovered. The present invention has further utility as an energy-efficient, cost-effective, and environmentally friendly recycling process for decomposing a thermoset resin matrix and recovering therefrom a high percentage of reinforcing fibers suitable for subsequent reuse. The recovered fibers retain most of the reinforcing properties of similar fibers in their virgin form. Notably, the process of the present invention occurs at room temperature in a suitable solvent, such as tetrahydrofuran (THF). The present invention is applicable to all thermosets capable of incorporating cleavable siloxane bonds, including, but not limited to, polyester, vinyl ester, polyurethane, or epoxy matrices, polyureas, and rubbers, as well as crosslinked thermoplastics, i.e., thermoplastics crosslinked with unsaturated units that allow crosslinking, such as crosslinked polystyrene, crosslinked polyethylene (XPE), thermoplastic elastomers, and the like. The present invention can recover a large number of reinforcing fibers from matrices formed from any of the aforementioned thermoset resins. For example, the process of the present invention can regenerate reinforcing fibers including glass fibers, carbon fibers, aramid fibers, all-natural fibers, basalt fibers, boron fibers, silicon carbide fibers, and polymer fibers such as polyesters (PER, PBT, PCDT), polyolefins (PE, PP), polyvinyl derivatives (PVC, PVA, polyacrylonitrile), and polyurethanes.

[0017] While prior art attempts to chop a thermoset cured matrix to produce reactive monomers and oligomers from it, the present invention is optimized for recycling reinforcing fibers from such matrices. Reinforcing fibers, as inert inclusions in a thermoset matrix, are significantly easier to regenerate into a reusable form compared to the matrix precursor. Furthermore, with carbon fiber costing approximately $22 per kilogram, there are economic and environmental incentives to prevent such fibers from going to waste.

[0018] In certain embodiments of the present invention, the cost of materials and processing to regenerate reinforcing fibers is less than the cost of new reinforcing fibers when the cost of disposing of used reinforcing fiber-containing thermoset articles is taken into account. It should be understood that the use of certain solvents and catalysts, while effective for breaking covalent bonds in the thermoset matrix, has inherent costs, handling hazards, or disposal costs that render the resulting process merely an academic curiosity. Illustrative examples of such processes are those described in the prior art. While processing time and energy input are factors in the efficiency of the process of the present invention, it has been found that room-temperature processes amenable to being carried out in aqueous solutions are feasible for recycling reinforcing fibers on an industrial scale.

[0019] Where a range of values ​​is provided, it is to be understood that the range is intended to encompass not only the endpoints of the range, but also values ​​intermediate to the range as expressly included within the range and varied by the last significant digit of the range. By way of example, a recited range of 1 to 4 is intended to include 1 to 2, 1 to 3, 2 to 4, 3 to 4, and 1 to 4.

[0020] It has been surprisingly discovered that incorporating siloxane bonds into thermosetting monomers prior to forming a thermosetting composite results in a robust yet facile bond. This bond allows for easy recycling of the cured thermosetting composite by de-crosslinking the thermosetting polymer at room temperature without the need for sophisticated equipment or hazardous chemicals. Notably, there are several ions capable of breaking (and subsequently reorganizing) Si-O-Si bonds—e.g., X = Cl, Br, or I in AlX3, or alkali metals such as K+—but these typically occur at elevated temperatures and pressures, conditions that have proven unfavorable for large-scale recycling attempts. Thus, it has been advantageously discovered that incorporating siloxane bonds into thermosetting monomers uniquely enables de-crosslinking of thermosetting polymers at room temperature without the need for sophisticated equipment or hazardous chemicals. For example, conventional styrene-crosslinked unsaturated polyesters (i.e., sheet molding compounds, SMCs) such as those shown in Figure 1 are not easily recycled. However, according to embodiments of the present invention, replacing styrene monomer or any other typical thermosetting monomer with a cleavable siloxane bond, such as a divinylsiloxane crosslinking agent, provides a crosslinked thermosetting monomer that readily decrosslinks at room temperature in the presence of scission ions, thereby facilitating the easy recovery of any reinforcing fibers contained within the thermosetting resin. Advantageously, upon removal of the scission ions, the siloxane bond reforms, allowing the recovered polymer and reinforcing fibers to be reused, thereby creating a closed-loop recycling process in some embodiments of the present invention. According to yet another embodiment of the present invention, replacing styrene monomer with a divinylsiloxane crosslinking agent provides a crosslinked unsaturated polyester that readily decrosslinks at room temperature in the presence of fluoride ions (F-) as a scission ion, as shown in Figure 2. The present invention is usable in aqueous solutions at temperatures between 0 and 95 degrees Celsius. Notably, upon removal of the fluoride ions (F-), the siloxane bond reforms, allowing the recovered polymer (and fibers) to be reused for the same application.Additional benefits of using siloxane-based crosslinkers include increased thermal / oxidative stability (Si-O = 452 kJ / mol), enhanced flame retardancy (inorganic, char accelerators), increased UV stability, and low volatile organic content (styrene-free).

[0021] A significant difference between the present invention and previous work on recycled siloxane polymers is that the present invention is a hybrid siloxane / conventional hydrocarbon system. In such systems, trapping F- is essential for reusing / recycling the polymer matrix. Leaving F-ions with the solvate results in a viscous polymer that never re-hardens, even when heat is applied. Therefore, in the present invention, F- must be trapped to recreate a usable solid matrix. In previous work on recycled siloxane polymers, these were not hybrid systems, so F- was not sequestered after recycling; F- was still present, allowing the siloxane to still be recast and reused. Further work explored trapping F-ions by reacting with CaCl2 to create insoluble CaF2, which resulted in the precipitation of the intended mixed solid silsesquioxane cages.

[0022] Disiloxane monomers that can be used in the present invention have the formula (I): R 1 -[Si(R2)-O] n - Si(R2)-R 1 (I) [In the formula, R 1 are independently in each occurrence H2C=CH-, H2C=CH-R-, H2C(O)CH-, H2C(O)CH-R-, H2N-R, H2C=CH-SiR2-O-, CH2=C(CH3)COO-, CH2=CHCOO-, (CHOH) m -, R-NCO, or (RCO)O(O)-, where R is independently in each occurrence C1 to C 12 Straight chain alkyl, C1-C 12 Branched alkyl, C5-C12 Cyclic alkyl, C1-C 12 Linear alkoxy, (C1-C 12 Alkyl)-C(O))-(C1-C 12 Alkyl)-O-(C1-C 12 Straight-chain alkyl), (C1-C 12 Alkyl)-O-(C1-C 12 Straight-chain alkyl), C6-C 12 Aryl, -O-Si(C1-C 12 Linear alkyl)3, or tri(C1-C 12 In some embodiments of the invention, R is the same in all occurrences. In other embodiments of the invention, R 1 In yet another embodiment of the invention, in one monomer, R is the same in all occurrences and R 1 is the same in all occurrences. Other disiloxane monomers that can be used in the present invention include their cyclic analogs. Specific disiloxane monomers that can be used in the present invention include, by way of example, [ka] Karstedt's catalyst, and combinations thereof. It will be appreciated that to achieve the inventive results of aqueous and room temperature recycle, only a portion of the conventional styrene monomer need be replaced with the disiloxane monomer of the present invention.

[0023] Figure 3 shows the reaction for incorporating cleavable silicon functionality into a thermosetting monomer. When a thermosetting resin incorporating disiloxane functionality is cured, the thermosetting resin crosslinks with the siloxane, retaining moieties susceptible to ionic scission. This can be used to form a thermosetting composite suitable for structural components. When the thermosetting composite is ready to be recycled, the cured thermosetting composite is exposed to a scission ion, such as fluoride (F-), in an aqueous solution. In some embodiments of the present invention, this reaction occurs at any temperature at which the solution is liquid, including room temperature. The solution can be a solution of an organic solvent miscible with water, while in other embodiments, the solvent is simply water, with or without common contaminants present. As shown in Figure 3, upon exposure to fluoride ions (F-), the thermosetting resin decrosslinks with the siloxane crosslinks, allowing for the recovery of any reinforcing fibers and the thermosetting resin.

[0024] Formula (I) includes the structures of various disiloxane monomers according to the present invention that are fluoride ion (F-) cleavable. It should be understood that through the inclusion of small amounts of tri-, tetra-, or higher mer siloxane monomers along with the curing divalent disiloxane monomers, a higher degree of cross-linking and three-dimensional matrix formation is achieved. Figures 4A and 4B show depictions of conventional prior art epoxy amine materials.

[0025] Figures 5A-5D show photographs of the inventive recycling method according to an embodiment of the present invention. Figure 5A shows a photograph of a small piece of cast unsaturated polyester (UPE) resin using a cleavable siloxane crosslinker. Figure 5B shows the cast UPE resin of Figure 5A in a container containing water into which fluoride ions (F-) have been introduced at room temperature. Figure 5C shows the container of Figure 5B after 1-3 days, at which point the thermosetting resin dissolves based on the F- concentration. Figure 5D shows a photograph of the recast resin solution after removal of the water solvent and F-ions. This process can be repeated as a continuous loop.

[0026] Figures 6A-6D illustrate the inventive recycling method according to an embodiment of the present invention. Figure 6A shows a molded UPE resin using a cleavable siloxane crosslinker and glass reinforcing fibers. Figure 6B shows the molded UPE resin of Figure 6A in a vessel containing water to which fluoride ions (F-) have been introduced at room temperature. Figure 6C shows the dissolved thermosetting resin after 1-3 days based on the F- concentration. Notably, this resin can subsequently be collected and recast as described above in connection with Figures 5A-5D. Figure 6D shows the glass fibers of the molded UPE resin of Figure 6A after the reinforcing fibers have been recovered.

[0027] According to some embodiments of the present invention, the inventive recycling method of the inventive ionically severable thermosetting resin of the present invention results in dry reinforcing fibers at a yield of better than 95% by weight of the reinforcing fibers in the thermosetting resin. In other embodiments of the present invention, the yield of dry reinforcing fibers is better than 97% by weight of the reinforcing fibers in the thermosetting resin. In yet other embodiments of the present invention, the yield of dry reinforcing fibers is better than 99% by weight of the reinforcing fibers in the thermosetting material. It will be understood that the cured matrix from which reinforcing fibers can be recycled according to the present invention includes any thermosetting resin capable of introducing cleavable siloxane bonds according to embodiments of the present invention. Exemplary such thermosetting resins include vinyl esters, polyesters, and epoxies. Reinforcing fibers that are renewable according to embodiments of the present invention include carbon fiber and glass fiber.

[0028] The present invention provides an economical and environmentally friendly recycling process for degrading a thermoset matrix to the extent necessary to release reusable reinforcing fibers. It has surprisingly been found that digestion of the thermoset matrix to recover the reinforcing fibers can be accomplished at room temperature and without solvents other than water when the thermoset matrix of a composite material is formed from a thermoset resin in which cleavable siloxane bonds are provided in the polymer chain to allow the chains to break apart at various chain lengths to degrade the matrix.

[0029] Unlike silicone fluids and elastomers, silicone resins also contain T and Q units. These tri- and tetra-functional units create highly branched and cage-like networks with high cross-linking densities, especially when compared to silicone elastomers. A combination of units is typically used to balance properties. For example, pure T resins can be brittle, but the addition of D or M units increases elasticity and adhesion. (Moretto et al.) Silicone resins combine high-temperature, oxidative, and UV stability with resistance to acids, oils, and water, making them ideal for many coating applications, including release, hydrophobic, oleophobic, abrasion-resistant, chemical-resistant, corrosion-resistant, protective, decorative, insulating, stain-resistant, sealants, and paints. (Moretto et al.)

[0030] Many of silicone's favorable properties are due to its robust inorganic siloxane backbone and cross-linking. However, thermosets do not melt like thermoplastics, making them much more difficult to recycle and reuse. Recycling of thermoset polymers falls into three categories: mechanical, thermal, and chemical recycling. Mechanical recycling involves grinding the thermoset into a powder and using a low loading of the material as a filler in a chemically similar polymer, which often results in a loss of mechanical properties. (Ma et al., Yigor et al.) Thermosets can be thermally recycled (burned) to generate energy and recover the filler, but this process is energy-intensive and produces unwanted greenhouse gases due to the high thermal stability of silicone.

[0031] A silicone resin made from dodecaphenylsilsesquioxane (Ph-T12) and octamethylcyclotetrasiloxane (D4) has a ratio of 1 Me:1 Ph and 2 T:1 D units. At this ratio of T:D units, each T unit creates a crosslink, resulting in a very high crosslink density, especially compared to silicone rubber elastomers, which have far fewer crosslinkable functional groups. A consistent solution concentration (10 wt% silicone) in TBAF / THF ensures uniform spray coating thickness onto Al 2024 coupons. Resin monoliths were cast and cured to produce sufficient material for the recycling reaction, as shown in Figure 7D. The cured resin is insoluble in THF without an F source. Dissolution time decreases with increasing [F] and increases with increasing curing temperature. Abrasion resistance is evaluated by a linear abrasion test, measuring the change in water contact angle (WCA) after 50 abrasion cycle increments (one double abrasion cycle) using 100 g of weighted 2000-grit sandpaper. As shown in Figure 9A, all prime coatings have a consistent initial average WCA of 90–92° with minor deviations, but after 50–200 abrasion cycles, the coatings cured at 150° and 200°C have higher and more variable WCAs. The increase in WCA due to surface roughening from the sandpaper indicates that these coatings are not as hard and abrasion-resistant as the coating cured at 250°C, which shows a stable and consistent WCA after 200 abrasion cycles. Higher curing temperatures may reduce plasticizing volatiles and increase crosslink density, as evidenced below.

[0032] Coatings made from silicone resin recycled in 0.01 M TBAF and then cured at 150 and 200 °C had a higher WCA increase during abrasion testing compared to the prime coating, suggesting that the recycled resin was softer, as shown in Figure 9B. The recycled resin coating cured at 150 °C had a WCA of 103 ± 3° after 100 abrasion cycles, which then decreased to 96 ± 7° after 200 abrasion cycles. The WCA of the recycled resin coating cured at 200 °C peaked at 117 ± 4° after 150 abrasion cycles and then decreased, indicating that a 50 °C increase in cure temperature results in a coating that is softer (and can be roughened) but has better adhesive strength.

[0033] The recycled resin cured at 250 °C provided consistent WCA from 0 to 200 abrasion cycles, similar to the primed coating cured at 250 °C. The 250 °C cure temperature is necessary to produce a harder silicon that does not easily roughen, as indicated by the consistent WCA after abrasion. SEM-EDS images of the primed resin coating (Figures 8A and 8B) and the 0.01 M TBAF-recycled resin coating (Figures 8I and 8J) after 200 abrasion cycles both show intact and complete coating layers with no exposed Al coupon substrate. Coating adhesion, measured by crosshatch scoring and tape peel adhesion testing (ASTM D3359), had the highest score (5B) for both the primed resin coating (Figures 8C and 8D) and the 0.01 M TBAF-recycled resin coating (Figures 8K and 8L), indicating excellent adhesion to the Al substrate. When cured at 250°C, this model silicone resin forms a hard, adhesive, abrasion-resistant, and hydrophobic coating that can be easily recycled and reapplied with retained mechanical properties.

[0034] Figure 9C shows the effect of [F-] in the recycled solution on the abrasion resistance and adhesive properties of silicone resin coatings cured at 250°C. The initial WCA for coatings from resin recycled in 0.01M TBAF is similar to that of the primed coating. Coatings from resin recycled using the solution with the highest [F-], 0.1M TBAF, are hydrophilic, with an initial WCA of <90°. The coating is uneven, with patches of exposed Al substrate and significant loss of coating after 200 abrasion cycles, as shown in Figures 8M and 8N. High [F-] can lead to the formation of many Si-F bonds in the polymer, which are easily converted to hydrophilic Si-OH in the presence of exogenous water and are continuously replenished as new surfaces are created by abrasion. The formation of Si-F bonds also hinders the formation of Si-O3 / 2 or SQ linkages, thus reducing crosslink density and abrasion resistance. F is not detected by EDS in any of the thin films or monoliths of resins recycled with 0.002 or 0.01 M TBAF, but F is present in monoliths cast from resins recycled with a 0.1 M TBAF solution. Thus, although fluorine remains in the recycled resin, under optimal recycling conditions, 0.01 M TBAF, this amount is too low to be detected by EDS.

[0035] Dissolution of resin cured at 250 °C in 0.001 M TBAF was attempted, but after 7 days of stirring, the solution remained cloudy with solids. After increasing [F-] to 0.002 M TBAF, the solution became clear within 24 hours, thereby identifying the minimum threshold of F- required to dissociate the silicon network into soluble oligomers. Spray coatings from recycled solutions with this minimum [F-] were also heterogeneous, hydrophilic both initially and after 200 abrasion cycles, as shown in Figure 9C, and soft enough to roughen after 50 abrasion cycles, as suggested by the increase in WCA from 87 ± 2° to 106 ± 3°. As shown in Figures 8E and 8F, F-deficient systems may result in an insufficient number of reactive Si atoms required to reform a highly cross-linked network upon solvent removal, resulting in poor abrasion resistance.

[0036] As shown in Figure 9A, the thermal stability of silicone resins, determined via TGA in air as the average temperature at 5% mass loss (Td5%), increased with cure temperature, reaching a maximum of 483 ± 7 °C when cured at 250 °C. The Td5% of the resin cured at 200 °C was slightly lower at 470 ± 6 °C, but both resins exhibit two major mass losses between 400 and 575 °C and 575 and 700 °C, attributed to methyl / phenyl groups and residual carbon, respectively. The resin cured at the lowest temperature of 150 °C had a 130 °C lower Td5% (353 ± 5 °C), due to a third mass loss below 400 °C attributed to volatiles, as revealed by GC-MS.

[0037] As shown in Figure 10A, to generate only the volatiles that would be lost from increasing the cure temperature from 150 to 200°C, a sample of silicone resin cured at 150°C was heated to 200°C in a closed thermal desorption system and then injected into a GC-MS. The most abundant compound detected was tributylamine (413 ppm, 46% of total volatiles), which has a boiling point of 214°C and is the main decomposition product of TBAF. The second most abundant compound was butylated hydroxytoluene (BHT, 123 ppm, 14% of total volatiles), which has a boiling point of 265°C and is an inhibitor in THF. These and other TBAF and BHT decomposition products accounted for >90% of the total volatiles detected. These by-products may act as plasticizing impurities that reduce network integrity, crosslink density, thermal stability, abrasion resistance, and adhesion. Common silicone decomposition products, cyclic siloxane oligomers D3, D4, and D5, were detected in small amounts, totaling 2.5% of the volatiles.

[0038] As shown in Figure 12B, to generate only the volatiles that would be lost by increasing the curing temperature from 200 to 250°C, a silicone resin cured at 200°C was heated to 250°C under similar conditions and then analyzed by GC-MS. The total amount of tributylamine, BHT, and TBAF / BHT decomposition products decreased to 116 ppm, 86% less than that of the resin cured at 150°C. Cyclic siloxane oligomer decomposition products accounted for 10% of the total volatiles. The major compound detected was benzene (243 ppm), which accounted for 60% of all volatiles. Benzene was only detected in the resin upon heating to 250°C. A widely accepted free radical sequence, first proposed by Sobolevski, explains the generation of benzene from mixed methyl / phenyl polysiloxanes. 31-33 Si-C cleavages result in the removal of hydrogen from the methyl group to produce a phenyl group (CH), which forms benzene (boiling point = 80°C). This also forms a methylene group that attacks another Si atom, creating a cross-link and replacing another phenyl radical. This process increases the cross-link density while producing benzene. Continuing the process produces decomposition products of small sections of the silicon network, such as bis(di(trimethylsiloxy)phenylsiloxy)-trimethylsiloxyphenylsiloxane, as shown in Figure 12B.

[0039] The increase in Td5% from increasing the cure temperature from 200 to 250 °C can be explained by GC-MS findings of a decrease in total volatile species, an increase in crosslink density, and a decrease in organic content from benzene production. As shown in Figure 9B, at a given cure temperature, the resin recycled with 0.01 M TBAF had nearly the same Td5% as the primed resin, indicating no significant loss of thermal stability. GC-MS showed similar levels of volatiles in both the primed resin cured at 250 °C and the resin recycled with 0.01 M TBAF (Figure S3). However, the Td5% of the silicone resin recycled with 0.1 M TBAF decreased by 51 °C to 432 ± 6 °C due to a mass loss event below 400 °C. This is due to an order of magnitude increase in TBAF concentration, which resulted in a five-fold increase in TBAF decomposition products.

[0040] Using optimized recycling conditions (0.01M TBAF / THF at room temperature), the present technology is evaluated against a commercially available mixed phenyl / methyl silicone resin. SILRES REN 50 (Wacker Chemie) cured at 250°C is stirred in 0.01M TBAF / THF at room temperature until completely dissolved, which takes 55 minutes. The cured resin is insoluble in THF alone, as well as in toluene and xylene. Prime and recycled SILRES solutions (10 wt%) spray-coated onto clean Al coupons and cured at 250°C are tested for hydrophobicity, abrasion resistance, adhesion, and thermal stability. The initial WCA of both coatings was 90°. After 50–200 abrasion cycles, the prime coating roughens and then significantly wears away, as indicated by the sudden increase in WCA to 116 ± 4° after 50 cycles, followed by a drop ( Figure 11A ), and a large amount of substrate is exposed after 200 abrasion cycles ( Figure 11D ).

[0041] The recycled SILRES coating shows minimal WCA change and less wear after 200 cycles (Figure 11G). Coating adhesion of the recycled coating is comparable to or better than that of the primed coating (Figures 11E and 11H). The thermal stability of SILRES is 73 °C higher after recycling (Figure 11B). The increase in mechanical and thermal properties after recycling is due to the formation of a more cross-linked network, as evidenced by GC-MS spectra showing fewer silicon network decomposition products and the generation of benzene due to cross-linking upon heating. Finally, to demonstrate the modification, patterning, and repair capabilities of our technique, a cotton swab soaked in 0.01 M TBAF is used to selectively remove portions of cured SILRES (Figures 11I and 11J). This technique also works with silicone rubber, which is not surprising since rubber has a lower cross-link density than resin. A common room temperature curing silicone rubber, ELASTOSIL E10 (Wacker Chemie), dissolved in 0.01 M TBAF / THF in less than 15 minutes when stirred.

[0042] According to some embodiments of the present invention, the inventive recycling method of the inventive ionically severable thermosetting resin of the present invention results in dry reinforcing fibers at a yield of better than 95% by weight of the reinforcing fibers in the thermosetting resin. In other embodiments of the present invention, the yield of dry reinforcing fibers is better than 97% by weight of the reinforcing fibers in the thermosetting resin. In yet other embodiments of the present invention, the yield of dry reinforcing fibers is better than 99% by weight of the reinforcing fibers in the thermosetting material. It will be understood that the cured matrix from which reinforcing fibers can be recycled according to the present invention includes any thermosetting resin capable of introducing cleavable siloxane bonds according to embodiments of the present invention. Exemplary such thermosetting resins include vinyl esters, polyesters, and epoxies. Reinforcing fibers that are renewable according to embodiments of the present invention include carbon fiber and glass fiber.

[0043] The present invention provides an economical and environmentally friendly recycling process for degrading a thermoset matrix to the extent necessary to release reusable reinforcing fibers. It has surprisingly been found that digestion of the thermoset matrix to recover the reinforcing fibers can be accomplished at room temperature and without solvents other than water when the thermoset matrix of a composite material is formed from a thermoset resin in which cleavable siloxane bonds are provided in the polymer chain to allow the chains to break apart at various chain lengths to degrade the matrix.

[0044] An embodiment of the recycling process of the present invention may be carried out in the following manner: The cured thermoset matrix is ​​optionally ground to a particle size that increases surface area while limiting shearing of the reinforcing fibers. Typical lengths of carbon fibers in an SMC matrix are 6 to 40 millimeters (mm). Grind particle sizes for the process of the present invention typically range from 1 to 25 mm in diameter for spherical particles, with an average longest linear extent in the XYZ coordinate system of 5 to 80 mm for anisotropic particles. The cured resin grind is combined with water in a resin:water ratio of 1:2 to 20 by weight. To achieve economies of scale, according to the present invention, a batch process involving at least 0.75 kilograms of reinforcing fibers is carried out. The solvent is present in a sufficient amount to liberate greater than 95% by weight of the reinforcing fibers from the composite. Advantageously, typical reaction temperatures range from 15 to 25 degrees Celsius. According to some embodiments of the present invention, other components, such as surfactants, antifoaming agents, viscosity reducing agents, or boiling chips, are easily added.

[0045] Exemplary co-reactants that can be used in the present invention include alkali metal hydroxides, carbonates, bicarbonates, and phosphates, such as sodium carbonate, sodium hydroxide, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, tripotassium phosphate, or combinations thereof. Typical catalyst loadings range from 0 to 5 total weight percent.

[0046] After the reaction, the separated reinforcing fibers are washed and optionally sonicated. Washing is performed with water. The resulting separated fibers are dried. According to some embodiments of the present invention, the separated fibers may undergo antistatic, coupling, film-forming, or other sizing, which may be applied as an outer coating to the dried, recycled reinforcing fibers.

[0047] An embodiment of the process of the present invention can be a closed-loop process in which by-products obtained during fiber recovery are used in the form of novel FRC materials, as shown in Figures 7A-7D and 8A-8D.

[0048] In some embodiments of the invention, the reaction mixture is exposed to ultrasonic treatment before or during exposure to the reaction mixture, which appears to loosen the reinforcing fibers from the cured resin matrix and also clean and untangle the fibers.

[0049] In yet another embodiment, the reaction mixture is exposed to microwave irradiation to accelerate matrix digestion. Microwaves have frequencies between 100 MHz and 1000 GHz. 915 MHz and 2450 MHz are common klystron output frequencies. Reaction vessels particularly well suited for use with microwave irradiation have limited absorption at these wavelengths, and illustrative examples include glass, ceramic, or fluoropolymer. It should be understood that large reaction vessels are readily equipped with quartz glass or heat-resistant glass windows that act as microwave-transparent portals. Alternatively, a metal waveguide can serve to allow microwaves to be delivered into a microwave-absorbing vessel. After the reaction, the separated reinforcing fibers are washed and optionally sonicated. Washing is performed using water. The resulting separated fibers are then dried. According to some embodiments of the present invention, the separated fibers may undergo antistatic, coupling, film-forming, or other sizing treatments, which may then be applied as an outer coating to the dried, regenerated reinforcing fibers.

[0050] Figure 12A shows the E s and A sFigure 12B shows the chemical structures of siloxanes, shown as: Figure 12B shows casts of equal parts by weight combinations of siloxanes and the corresponding glass transition temperatures of polymers formed from these siloxanes.

[0051] FIG. 13A is a graph showing the TGA plot of the sample of FIG. 12B. The glass transition temperature is noted therein. FIG. 13B is a graph showing the TGA plot of the sample of FIG. 13A as well as the 50:50 E c / E s +A s and 75:25 E by weight c / E s +A s 1 is a graph showing a TGA plot of a combination of two additional siloxanes in parts by weight of 100%.

[0052] 14A-14D illustrate a recycling method of the present invention according to another embodiment of the present invention consistent with one of the compositions of FIG. 13B, showing steps consistent with those detailed in FIGS. 5A-5B, the details of which are incorporated herein by reference.

[0053] FIG. 15 is a schematic diagram showing an unsaturated polyester (UPE) resin monomer containing a clipable crosslinker and a reaction scheme for its synthesis.

[0054] An exemplary reactor for the process of the present invention is generally shown at 10 in FIG. 16. Hopper 12 contains small pieces of cured thermoset-based composite material containing reinforcing fibers. Screw 14 conveys the particles from hopper 12 to reaction vessel 16, which is adapted to contain water and any catalyst and other materials as they are metered into vessel 16 via screw 14. Motor 18 drives mechanical agitator 20 to homogenize reaction conditions. An ion introduction conduit 22 is provided so that scission ions can be introduced into the reaction vessel. A microwave generator or sonicator 24 is provided to impart energy to the reactants in vessel 16. A drain 26 is provided to facilitate removal of liquid from vessel 16. A filter 28 allows permeation and collection of size-excluded materials, such as filler particles, from the reaction mixture, as well as collection of scissionable ions, via side siphon valve 30.

[0055] Upon digestion of the matrix to free the reinforcing fibers, the fibers are collected after permeation through filter 18 or decanted from the reaction mixture and settled sediment. In some embodiments, the collected reinforcing fibers are further filtered to remove various insoluble fillers present in typical SMCs, illustratively including calcium carbonate, thickeners, glass beads, glass microspheres, paint pigments, and natural fibers. The weight of water added to wash the resulting carbon fibers is typically 10 to 100 times the weight of the reinforcing fibers released from the thermoset matrix.

[0056] The resulting recycled reinforcing fibers are briefly dried in a conventional or vacuum oven to remove residual water from the reinforcing fibers. The resulting reinforcing fibers are used as if they were virgin reinforcing fibers or chemically treated to apply a sizing coating thereto. The sizing is used to modify the surface properties of the fibers so that the recycled carbon fibers interact with the new matrix in which they are embedded.

[0057] The collected filtrate can be distilled to recover the cleavable ions, which can then be used in subsequent reinforcing fiber recovery reactions while maintaining a purity of the recovered reinforcing fibers of >95%.

[0058] In some embodiments of the present invention, the recovered and concentrated organics, after neutralization, are incorporated into novel polymer systems due to and depending on the nature of the functional groups present. At loadings of 5-50 wt.% recovered organics and 95-50 wt.% virgin polymer, the properties are similar to a 100% virgin system. Alternatively, the recovered organics can be used as fuel.

[0059] The patent documents and publications cited in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains and are hereby incorporated by reference to the same extent as if each individual document or publication was specifically and individually indicated to be incorporated by reference herein.

[0060] The foregoing description is illustrative of particular embodiments of the present invention but is not intended to be a limitation on its practice. The following claims, including all equivalents thereof, are intended to define the scope of the invention.

[0061] References

[0062] Moretto, HH; Schulze, M.; Wagner, G. Silicones. In Ullmann's Encyclopedia of Industrial Chemistry; Wiley-VCH: Weinheim, Germany, 2012; pp 675-712 DOI: 10.1002 / 14356.

[0063] Murphy, C. M.; Saunders, C. E.; Smith, D. C. Thermal and Oxidation Stability of Polymethylphenylsiloxanes. Ind. Eng. Chem. 1950, 42, 2462-2468.

[0064] Hanu, L. G.; Simon, G. P.; Cheng, Y. -B. Thermal Stability and Flammability of Silicone Polymer Composites. Polym. Degrad. Stab. 2006, 91, 1373-1379.

[0065] Hamdani, S.; Longuet, C.; Perrin, D.; Lopez-Cuesta, J. M.; Ganachaud, F. Flame Retardancy of Silicone-Based Materials. Polym. Degrad. Stab. 2009, 94, 465-495.

[0066] Abbasi, F.; Mirzadeh, H.; Katbab, A. A. Modification of Polysiloxane Polymers for Biomedical Applications: A Review. Polym. Int. 2001, 50, 1279-1287.

[0067] Lucas, P.; Robin, J. J. Silicone-Based Polymer Blends: An Overview of the Materials and Processes. In Advances in Polymer Science: Functional Materials and Biomaterials; Springer-Verlag: Berlin, Germany, 2007; Vol. 209, pp 111-147 DOI: 10.1007 / 12_2007.

[0068] Ma, M.; Hill, R. M. Superhydrophobic Surfaces. Curr. Opin. Colloid Interface Sci. 2006, 11, 193-202.

[0069] Yilgor, E.; Yilgor, I. Silicone Containing Copolymers: Synthesis, Properties and Applications. Prog. Polym. Sci. 2014, 39, 1165-1195. (9) Gong, D.; Long, J.; Jiang, D.; Fan, P.; Zhang, H.; Li, L.; Zhong, M. Robust and Stable Transparent Superhydrophobic Polydimethylsiloxane Films by Duplicating via a Femtosecond Laser-Ablated Template. ACS Appl. Mater. Interfaces 2016, 8, 17511-17518.

[0070] Ghosh, A.; Antony, P.; Bhattacharya, A. K.; Bhowmick, A. K.; De, S. K. Replacement of Virgin Rubbers by Waste Ground Vulcanizates in Blends of Silicone Rubber and Fluororubber Based on Tetrafluoroethylene / Propylene / Vinylidene Fluoride Terpolymer. J. Appl. Polym. Sci. 2001, 82, 326-2341.

[0071] Ghosh, A.; Rajeev, R. S.; Bhattacharya, A. K.; Bhowmick, A. K.; De, S. K. Recycling of Silicone Rubber Waste: Effect of Ground Silicone Rubber Vulcanizate Powder on the Properties of Silicone Rubber. Polym. Eng. Sci. 2003, 43, 279-296. (12) Hsiao, Y.-C.; Hill, L. W.; Pappas, S. P. Reversible Amine Solubilization of Cured Siloxane Polymers. J. Appl. Polym. Sci. 1975, 19, 2817-2820.

[0072] Pappas, S. P.; Just, R. L. Aminolysis of Crosslinked Polysiloxanes: Tautomeric Catalysis by 2-Pyridone. J. Polym. Sci., Polym. Chem. Ed. 1980, 18, 527-531.

[0073] Okamoto, M.; Suzuki, S.; Suzuki, E. Polysiloxane Depolymerization with Dimethyl Carbonate Using Alkali Metal Halide Catalysts. Appl. Catal., A 2004, 261, 239-245.

[0074] Enthaler, S. Zinc-Catalyzed Depolymerization of End-of-Life Polysiloxanes. Angew. Chem., Int. Ed. 2014, 53, 2716-2721.

[0075] Enthaler, S.; Kretschmer, R. Low-Temperature Depolymerization of Polysiloxanes with Iron Catalysis. ChemSusChem 2014, 7, 2030-2036.

[0076] Enthaler, S. Iron-Catalyzed Depolymerization of Polysiloxanes to Produce Dichlorodimethylsilane, Diacetoxydimethylsilane, or Dimethoxydimethylsilane. J. Appl. Polym. Sci. 2015, 132, 41287.

[0077] Weidauer, M.; Heyber, B.; Woelki, D.; Tschiersch, M.; Kohler- Krutzfeldt, A.; Enthaler, S. Iron-Catalyzed Depolymerizations of Silicones with Hexanoic Anhydride Provide a Potential Recycling Method for End-of-Life Polymers. Eur. J. Lipid Sci. Technol. 2015, 117, 778-785.

[0078] Dohlert, P.; Pfrommer, J.; Enthaler, S. Recycling Concept for End-of-Life Silicones: Boron Trifluoride Diethyl Etherate as Depolymerization Reagent to Produce Difluorodimethylsilane as Useful Commodity. ACS Sustainable Chem. Eng. 2015, 3, 163-169.

[0079] Dohlert, P.; Enthaler, S. Depolymerization Protocol for Linear, Branched, and Crosslinked End-of-Life Silicones with Boron Trifluoride Diethyl Etherate as the Depolymerization Reagent. J. Appl. Polym. Sci. 2015, 132, 1-7.

[0080] Gou, Z.; Zuo, Y.; Feng, S. Thermally Self-Healing Silicone- Based Networks with Potential Application in Recycling Adhesives. RSC Adv. 2016, 6, 73140-73147.

[0081] Xiang, H. P.; Rong, M. Z.; Zhang, M. Q. A Facile Method for Imparting Sunlight Driven Catalyst-Free Self-Healability and Recyclability to Commercial Silicone Elastomer. Polymer 2017, 108, 339-347.

[0082] Asuncion, M. Z.; Laine, R. M. Fluoride Rearrangement Reactions of Polyphenyl- and Polyvinylsilsesquioxanes as a Facile Route to Mixed Functional Phenyl, Vinyl T10 and T12 Silsesquioxanes. J. Am. Chem. Soc. 2010, 132, 3723-3736.

[0083] Ronchi, M.; Sulaiman, S.; Boston, N. R.; Laine, R. M. Fluoride Catalyzed Rearrangements of Polysilsesquioxanes, Mixed Me, Vinyl T8, Me, Vinyl T10 and T12 Cages. Appl. Organomet. Chem. 2010, 24, 551-557.

[0084] Jung, J. H.; Laine, R. M. Beads on a Chain (BOC) Polymers Formed from the Reaction of [NH2PhSiO 1.5 ] x [PhSiO 1.5 ] 10-x and [NH2PhSiO 1.5 ] x [PhSiO 1.5 ] 12-x Mixtures (x= 2-4) with the Diglycidyl Ether of Bisphenol A. Macromolecules 2011, 44, 7263-7272.

[0085] Jung, J. H.; Furgal, J. C.; Goodson III, T.; Mizumo, T.; Schwartz, M.; Chou, K.; Vonet, J.-F.; Laine, R. M. 3-D Molecular Mixtures of Catalytically Functionalized [vinylSiO 1.5 ] 10 / [vinyl-SiO 1.5 ] 12 . Photophysical Characterization of Second Generation Derivatives. Chem. Mater. 2012, 24, 1883-1895.

[0086] Furgal, J. C.; Jung, J. H.; Goodson III, T.; Laine, R. M. Analyzing Structure-Photophysical Property Relationships for Isolated T8, T10, and T12 Stilbenevinylsilsesquioxanes. J. Am. Chem. Soc. 2013, 135, 12259-12269.

[0087] Furgal, J. C.; Goodson III, T.; Laine, R. M. D5h [PhSiO1.5]10 Synthesis via F- Catalyzed Rearrangement of [PhSiO 1.5 ] n . An Experimental / Computational Analysis of Likely Reaction Pathways. Dalton Trans. 2016, 45, 1025-1039.

[0088] Krug, D. J.; Laine, R. M. Durable and Hydrophobic Organic- Inorganic Hybrid Coatings via Fluoride Rearrangement of Phenyl T12 Silsesquioxane and Siloxanes. ACS Appl. Mater. Interfaces 2017, 9, 8378-8383.

[0089] Milionis, A.; Loth, E.; Bayer, I. S. Recent Advances in the Mechanical Durability of Superhydrophobic Materials. Adv. Colloid Interface Sci. 2016, 229, 57-79.

[0090] Sobolevskii, M. V.; Skorokhodor, I. I.; Ditsent, V. Ye.; Sobolevskaya, L. V.; Vovshin, E. I.; Blekk, L. M. Study of Thermal Transformations of Oligomethylphenylsiloxanes. Vysokomol. Soedin., Ser. A 1974, 16, 729-734.

[0091] Grassie, N.; Macfarlane, IG; Francey, KF The Thermal Degradation of Polysiloxanes II. Poly(methylphenylsiloxane). Eur. Polym. J. 1979, 15, 415-422.

[0092] Deshpande, G.; Rezac, ME The Effect of Phenyl Content on the Degradation of Poly(dimethyl diphenyl) Siloxane Copolymers. Polym. Degrad. Stab. 2001, 74, 363-370. [Explanation of symbols]

[0093] 10 Exemplary Reactor 12 Hopper 14 Screw 16 Reaction vessel 18 motors 20 Mechanical stirrer 22 Iontophoretic conduit 24 Microwave generator or ultrasonic processor 26 Drain pipe 28 filters 30 Side siphon valve

Claims

1. A thermosetting resin, comprising a plurality of crosslinked ionically cleavable disiloxane units derived from disiloxane monomers incorporated therein; Thermosetting resin.

2. the thermosetting resin is a polyester, vinyl ester, polyurethane epoxy, polyurea, rubber, cross-linked thermoplastic, or a combination thereof; The thermosetting resin according to claim 1 .

3. the plurality of cross-linked ionically cleavable disiloxane units are cleavable by fluoride ions; The thermosetting resin according to claim 1 .

4. 2. The thermosetting resin of claim 1, wherein the disiloxane monomer usable in the present invention has formula (I): R １ -[Si(R ２ )-O] ｎ - Si(R ２ )-R １ (I) [In the formula, R １ independently in each occurrence, H ２ C=CH-, H ２ C=CH-R-, H ２ C(O)CH—, H ２ C(O)CH-R-, H ２ N-R, H ２ C=CH-SiR ２ -O-, CH ２ =C(CH ３ ) COO-, CH ２ =CHCOO-, (CHOH) ｍ -, R-NCO, or (RCO)O(O)-, wherein R is independently in each occurrence C １ ~C １２ Straight chain alkyl, C １ ~C １２ Branched alkyl, C ５ ~C １２ Cyclic alkyl, C １ ~C １２ Linear alkoxy, (C １ ~C １２ alkyl)-C(O))-(C １ ~C １２ alkyl)-O-(C １ ~C １２ Straight-chain alkyl), (C １ ~C １２ alkyl)-O-(C １ ~C １２ Straight-chain alkyl), C ６ ~C １２ Aryl, —O—Si(C １ ~C １２ Straight-chain alkyl) ３ , or tri (C １ ~C １２ alkyl)-Si-O-, wherein n is an integer from 1 to 20 (inclusive) and m is an integer from 1 to 4.

5. 5. The thermoset of claim 4, wherein the disiloxane monomer comprises at least one of the following: 【Chemistry 1】

6. a cured matrix formed from the thermosetting resin of claim 1; a plurality of reinforcing fibers embedded in said cured matrix; Composite material comprising:

7. the plurality of reinforcing fibers are glass fibers, carbon fibers, aramid fibers, all-natural fibers, basalt fibers, boron fibers, silicon carbide fibers, polymer fibers, or combinations thereof; The composite material of claim 6.

8. the composite material is fully recyclable; The composite material of claim 6.

9. adding the composite material to a solvent in a container; introducing fluoride ions into the solvent in the vessel; maintaining the composite material, the solvent, and the fluoride ions in the vessel for a period of time under conditions to dissolve the matrix material and to liberate greater than 95% by weight of the reinforcing fibers from the matrix material to form loose reinforcing fibers; Including, A method for recycling the composite material of claim 6.

10. further comprising the step of washing the loose reinforcement fibers.

10. The method of claim 9.

11. the washing step is with water; The method of claim 10.

12. the solvent is water; 10. The method of claim 9.

13. further comprising the step of drying the loose reinforcement fibers.

10. The method of claim 9.

14. further comprising the step of reusing the recycled reinforcing fibers in a new composite material.

10. The method of claim 9.

15. further comprising collecting the dissolved matrix material.

10. The method of claim 9.

16. further comprising leaching the fluoride ions from the collected dissolved matrix material. The method of claim 11.

17. further comprising the step of reusing the filtered dissolved matrix material in a new composite material. The method of claim 11.

18. further comprising the step of collecting the leached fluoride ions. The method of claim 11.

19. further comprising the step of reusing the collected filtered fluoride ions in a new recycling process.

15. The method of claim 14.

20. greater than 97% by weight of the reinforcing fibers are liberated from the matrix material; 16. The method according to any one of claims 9 to 15.

21. greater than 95% by weight of the matrix material is regenerated; 16. The method according to any one of claims 9 to 15.

22. the conditions include a temperature of 15 to 25°C; 16. The method according to any one of claims 9 to 15.

23. the conditions include atmospheric pressure; 16. The method according to any one of claims 9 to 15.

24. The period is 1 to 3 days.

16. The method according to any one of claims 9 to 15.

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