Recyclable high-performance carbon fiber reinforced polymer

Abstract

To provide a method of recycling a fiber-reinforced polymer.SOLUTION: A method of recycling a fiber-reinforced polymer comprises: grinding a used fiber reinforced polymer material to produce ground particles; functionalizing the ground particles to produce functionalized particles; dispersing the functionalized particles into a base resin; dispensing the resin with functionalized particles into one or more layers of continuous fiber mats; molding the resin with functionalized particles and the continuous fiber mats into a form of a desired part; and curing the form to produce the part. The used fiber-reinforced polymer material may be a carbon fiber-reinforced polymer or a glass fiber-reinforced polymer material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to and the benefit of U.S. Provisional Application No. 62 / 979,513, filed February 21, 2020, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present disclosure relates to fiber reinforced polymers (FRPs), and more particularly to recyclable FRPs. [Background technology]

[0003] Vehicle lightweighting involves building lighter cars and trucks to achieve better fuel efficiency and handling. Many governments and automakers around the world have made it a top priority. The primary benefits are improved fuel economy and reduced greenhouse gas emissions for vehicles. Due to their high specific strength, stiffness, and excellent corrosion resistance, carbon fiber reinforced polymers (CFRPs) have the greatest potential to reduce the weight of vehicle body panels by approximately 70%, far outperforming alternative, lower-risk solutions, including aluminum, which is at least 40% heavier, and multi-materials, which are at least 45% heavier.

[0004] However, today's cost of CFRP compared to various steels and aluminum materials makes it too expensive to be a viable economic option for the automotive industry. Vehicle weighing is often performed at the body-in-white (BIW) stage, which refers to the stage when the body components are bonded together, before painting and before the motor, chassis assembly, and trim are assembled. A recent techno-economic analysis showed that replacing the BIW of an average sedan with CFRP could reduce its weight by 52%, from 717 pounds to 344 pounds. However, this would increase BIW costs by $1,287 to $6,546 [A. Mascarin et al. Vehicle Lightweighting: Mass Reduction Spectrum Analysis and Process Cost Modeling (2016)]. This represents a cost increase associated with mass reduction of approximately $14.00 per pound of mass reduction. The target cost of mass reduction is approximately $5.00 per pound of mass reduction, which is offset by the fuel savings over the vehicle's lifetime enabled by the weight reduction. Current CFRPs cannot achieve this goal.

[0005] Low cost requires fast cycle times of less than three minutes per part, which is difficult to achieve with today's materials and manufacturing methods. Additionally, the need to recycle CFRP parts at the end of their life to reduce their environmental impact creates other challenging tasks. It is often necessary not only to achieve weight and target cost reductions with new materials, but also to achieve sufficient requirements to allow the manufactured parts to be used. For example, visible parts of automobiles, including hoods, roof panels, and other panels, must meet the highest surface appearance requirements, which poses a current challenge for CFRP. CFRP exhibits print-through defects after molding, preventing it from meeting these requirements. This challenge is currently solved by expensive post-molding processing steps. Another issue is the loss of dimensional stability at the high temperatures required for painting. Similar challenges apply to other industries that use CFRP, including aerospace, equipment manufacturing, sporting goods, and other specialty goods.

[0006] The primary barrier to the adoption of CFRP by the automotive industry is the cost of carbon fiber (CF) and part manufacturing. Current approaches to reducing the cost of carbon fiber, which involve the use of lower-cost fiber precursor raw materials, have been widely investigated, but progress has been relatively slow. The goal of a cost increase of less than $5.00 per pound reduced is not achievable with current CF, which is still approximately $12.5 / lb.

[0007] The second approach is to reduce the manufacturing cost of CFRP parts. The industry's largest manufacturing process for CFRP parts is high-pressure resin transfer molding (HP-RTR). It has very strict requirements for low-viscosity resin and is relatively slow. This process also requires expensive high-pressure equipment to pump the resin into the carbon fiber fabric. Therefore, CFRP manufacturing costs remain high at approximately $11 / lb.

[0008] Another approach is to use resin-reinforced CFRP, where the mechanical properties of the CFRP are increased by the resin without changing the carbon fiber material or processing. Previous attempts have revealed mixed results, including negative effects, such as CFRP improvements of -10% to 27%. These have been achieved with both expensive carbon nanotubes and graphene, which add significant cost to the CFRP material or low-cost organoclay, and they have higher densities than carbon, making CFRP recycling difficult. Furthermore, these CFRPs are made with low-temperature curing agents, and low-glass transition temperature resins are made in the 120°C range, which cannot sustain high temperatures and are prone to defects. This represents a current challenge with CFRPs displaying print-through defects after molding. As is well known in the composites industry, the use of reinforced / filled resins for CFRP manufacturing, such as nano-filled epoxies as described above, can improve dimensional stability and shrinkage. There is a problem with reducing the friction that holds the carbon fiber-epoxy interface together, which typically increases as the epoxy shrinks due to the normal forces imposed by shrinkage. Thus, typical reinforced / filled resins may have greater dimensional stability, but may subsequently be prone to delamination at high temperatures or high stresses.

[0009] To reduce the environmental impact of fiber-reinforced plastics (FRPs), including materials, recycling of waste FRPs is required. This is an extremely difficult task. Due to changes in surface chemistry and morphology throughout the recycling process, which dramatically affect the performance of CFRPs, the performance (e.g., mechanical properties) of recycled continuous carbon fibers is lower than that of the original carbon fibers. Today, recycled CFRPs can only be used in applications requiring dramatically lower performance than the original material. To date, all CFRP recycling processes involve removing the organic components (polymers) in CFRPs and recovering and using the inorganic carbon fibers. There is no direct method for recycling CFRPs as a whole. Therefore, methods are needed to upcycle waste FRPs, especially CFRPs, i.e., to use them in applications where recycled materials offer unique properties, resulting in high-value, high-performance materials. Summary of the Invention

[0010] 1. A method for recycling fiber reinforced polymers, comprising: grinding post-consumer fiber reinforced polymer material to form ground particles; functionalizing the ground particles to form functionalized particles; and dispersing the functionalized particles in a base resin,

[0011] A method comprising dispensing a resin having functionalized particles into one or more layers of a continuous fiber mat, molding the resin having functionalized particles and the continuous fiber mat into the shape of a desired part, and curing the shape to produce the part.

[0012] According to aspects presented herein, there is provided a method for recycling carbon fiber reinforced polymers, including grinding used carbon fiber reinforced polymer material to form ground particles, functionalizing the ground particles to form functionalized particles, dispersing the functionalized particles in a base resin, dispensing the resin with the functionalized particles into one or more layers of a carbon fiber mat, molding the resin with the functionalized particles and the carbon fiber mat into the form of a desired part, and curing the form to produce the part.

[0013] According to aspects presented herein, there is provided a method for recycling fiberglass reinforced polymers, including grinding post-consumer fiberglass reinforced polymer material to form ground particles, functionalizing the ground particles to form functionalized particles, dispersing the functionalized particles in a base resin, dispensing the resin with the functionalized particles into one or more layers of a fiberglass mat, molding the resin with the functionalized particles and the fiberglass mat into the form of a desired part, and curing the form to form the part. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows a flow chart of one embodiment of a method for manufacturing a part using recycled carbon fiber reinforced polymer particles.

[0015] [Figure 2] 2A and 2B show a process for molding a part using carbon fiber reinforced polymer. DETAILED DESCRIPTION OF THE INVENTION

[0016] The embodiments described herein enable the production of lightweight, paintable CFRP parts with a premium surface finish that reduces weight by over 70% when compared to steel roofing, and with an acceptable cost increase of less than $5.00 per pound, offset by the fuel savings enabled by the weight reduction, while allowing for recycling of the CFRP at end of life. CFRP parts may also be made from other recycled fiber reinforced polymers (FRPs), including fiber reinforced plastics.

[0017] Embodiments described herein include composite resin formulations incorporating high glass transition epoxy resins after curing, meaning they have a glass transition temperature greater than 150° C. The formulations include functionalized recycled CFRP particles with functional groups that are similar to or compatible with the epoxy resin and react with the epoxy resin upon curing, thereby producing a crosslinked structure with a network of chemically bonded CFRP particles dispersed within the cured resin.

[0018] Embodiments include carbon fiber reinforced polymer structures made with the above composite resins in place of commercial resins.

[0019] Embodiments include a process for manufacturing CFRP parts by an improved and refined wet compression molding process.

[0020] Embodiments include processes for processing recyclable CFRPs and using them as performance-enhancing fillers in epoxy resins.

[0021] PARC is developing a chemically bonded particle network composite platform in which up to 50% highly loaded epoxy-compatible dispersible functionalized particles are chemically bonded to each other by flexible polymer linkers that achieve extremely high mechanical properties, up to five times higher than the base resin.

[0022] A key advantage of using CFRP particle-based resins from these embodiments is that they enable the complete recycling of CFRP components at the end of their life. CFRP composites incorporating inorganic particles such as carbon nanotubes, graphene, or clay would result in inhomogeneous new CFRP composites due to the uncontrollable composition. In contrast, the composite resins in these embodiments incorporate CFRP particles with the exact same primary components (carbon fiber + epoxy resin) that closely match the composition of conventional CFRP. Recycled waste CFRP made with CFRP particles from these embodiments produces new CFRP particles, enabling the fabrication of new CFRP objects with consistent and controllable compositions. This is not possible if the reinforcing particles are materials other than CFRP. Raw recycled CFRP particles are produced by grinding CFRP parts. An additional advantage of recycled particles as resin reinforcements is their very low cost, approximately $0.25 / kg. By comparison, graphene and carbon nanotubes, which may be more suitable for recycling purposes (because they are carbon materials like carbon fiber), can cost approximately $1,000 / kg.

[0023] Regarding CFRPs manufactured with resins, it has traditionally been known that the mechanical properties (strength, modulus) of CFRPs are determined by the CF alone, as the properties of the resin are several orders of magnitude lower, with strengths exceeding 60 MPa and moduli below 3 GPa. The mechanical properties of composite resins are sufficiently high, with estimated strengths of approximately 110 MPa, moduli up to 10 GPa, and elongations at break of up to 2%, allowing the resin to increase the mechanical properties of CFRPs beyond those possible with carbon fiber (CF) alone.

[0024] The embodiments described herein enable dimensional stability at elevated temperatures in several ways. These include high glass transition temperature (Tg) epoxy resin-based systems achieved through high crosslink density, resulting in cured resins with significantly lower coefficients of thermal expansion (CTE), minimizing mismatch with low-CTE carbon fibers. For example, EPON resin 164, available from Hexion, has a Tg of 17-22 x 10, three times lower than conventional RTM resins. -6 It has a CTE of only m / (m K).

[0025] Another beneficial aspect resides in the CFRP particle fillers, which further reduce the likelihood of delamination primarily by increasing the resin's elastic modulus, further contributing to greater dimensional stability and minimizing CTE mismatch.

[0026] Another effective aspect is in the chemically bonded particle network. Chemical bonding of particles via epoxy resins can further increase the elastic modulus of the composite material beyond the basic reinforcing effect, and additional crosslinking can further prevent delamination at high temperatures. For example, U.S. Patent Application Publication No. 2019 / 0194417 by Wei Junhua et al., published June 27, 2019, shows that materials incorporating chemically bonded particles have significantly increased elastic modulus and strength compared to the same unbonded particles.

[0027] The embodiments enable the highest surface quality in several ways, including using reinforced / particle-filled resins, not traditionally used to create the highest surface quality. The primary challenge in achieving the highest surface quality arises from the poor dispersion of most filler particles in epoxy resins. The composite resin materials from these proposed embodiments achieve the highest surface quality while simultaneously increasing the mechanical properties of CFRP. A unique and inherent feature of the composite resins from the embodiments is the excellent dispersion of functionalized CFRP particles, which are highly compatible with the resin base material. This differs from other traditional particles, which can form large agglomerates that result in undesirable roughness.

[0028] Another possible factor is minimizing the effect of fiber print-through. The primary reason for print-through is resin shrinkage while the carbon fiber does not. The composite resin of the present embodiment is an excellent solution to this problem because high glass transition resins have an inherently low free volume achieved by dense cross-linking, and the chemical bonding of particles can further strengthen the resin matrix and further reduce volumetric shrinkage beyond the effect of high transition temperature resins. This is another distinct feature of our materials that cannot be achieved with traditional RTM or plain resin systems.

[0029] The embodiments described herein offer unique advantages not previously available together. These include a 25% CFRP weight reduction and approximately 40% cost reduction of CFRP objects achieved by reducing the amount of CFRP per part, enabled by a chemically bonded particle network. Another advantage is the short cycle time of less than 3 minutes enabled by commercially available fast-curing agents and wet compression molding (WCM) and in-situ impregnation molding processes, which has the potential to reduce manufacturing costs by approximately $8 / lb to $5 / lb. Another advantage is recycling waste CFRP by grinding to produce new, low-cost CFRP particles at over $0.25 / lb.

[0030] The highest paintable surface is achieved through the high glass transition temperature (Tg) of the highly crosslinked epoxy resin (>180°C) with a low coefficient of thermal expansion (CTE) and increased resin modulus. These enhance the part's dimensional stability at high temperatures and eliminate print-through issues related to resin shrinkage. Chemical bonding of the carbon fibers through the epoxy-functionalized recycled CFRP particle network increases the interfacial strength between the chemically reinforced resin and the carbon fibers. This reduces resin shrinkage, preventing delamination and offsetting friction losses.

[0031] Because CFRP is a composite thermosetting material made from a cross-linked polymer structure, it does not melt and, as a result, cannot be simply recycled by methods applicable to meltable plastics. The thermoplastic material can be removed by simply melting and reclaiming, leaving clean carbon fiber that can potentially be used to create new parts. The embodiments described herein use CFRP particles obtained by grinding CFRP, such as end-of-life waste. Processes for grinding particles are known [Vo Dong et al., Economic and environmental assessment of recovery and disposal pathways for CFRP waste management. Resources, Conservation and Recycling, 133, 63-75 (2018)]. These can provide two types of CFRP particles: particles containing a portion of the previously cured epoxy on their surface, composite particles, or pure carbon fiber particles, with the epoxy removed from the particle surface.

[0032] Figure 1 shows a flowchart of a method for manufacturing CFRP parts. In one embodiment, an FRP structure or other formed object is milled into crushed FRP particles, which are used as starting material for the production of functionalized CFRP particles. These CFRP particles can consist of crushed or chopped carbon fiber particles, with or without significant residual epoxy attached to them. The particles may have maximum dimensions ranging from 100 nm to 5 mm. The key design rule is that the functionalized CFRP particles have terminal epoxy functional groups. This is required to enhance the compatibility and dispersibility of the particles in the resin. In this way, a high particle concentration in the epoxy resin base can be achieved, which is a key requirement for achieving composite resin benefits such as improved mechanical properties and reduced shrinkage.

[0033] It should be noted that alternative raw materials, such as crushed or chopped glass fiber composite particles (GFRP), polymer fiber reinforced particles (PFRP), metals, and ceramics such as alumina and titania, can be functionalized in the same or similar manner to obtain dispersible particles. In these cases, similar gains in mechanical properties, dimensional stability, reduced shrinkage, etc., can be achieved by adjusting particle functionalization, dispersion, and concentration in the resulting filled resin. The particles used are referred to herein as FRP, which includes CFRP.

[0034] In these alternative embodiments, the resulting CFRP reinforcement may still achieve weight savings for vehicle applications, but may not be recyclable as made with recycled CFRP particles. In these embodiments, the resulting FRP may be made recyclable by using FRP particles having the same material as the fibers intended for the final composite part, such as using chopped or crushed Kevlar fiber composite particles to make Kevlar FRP parts, or using chopped or crushed glass fiber composite particles, referred to herein as fiberglass, to make glass FRP parts.

[0035] Specific methods for functionalizing various types of raw material particles are disclosed in U.S. Pat. No. 10,138,317 to Iftime et al. and U.S. Pat. No. 9,718,914 to Iftime et al., both of which are incorporated herein in their entireties.

[0036] Further specific methods for functionalizing carbon-based materials are also disclosed in U.S. Patent Application Publication No. 2019 / 0194417 by Wei Junhua et al., published June 27, 2019. Functionalized CFRP containing pure carbon fiber particles can be produced by any method that produces particles terminated with epoxy functional groups, including those described above.

[0037] In many cases, recycled carbon fiber particles may contain some functional groups, residues from the so-called sizing process during the initial production of continuous fibers. For epoxy-based sizing materials, groups such as COR, C═O, and COOR are generated to promote wetting of the carbon fiber with the epoxy while covering the surface roughness of the carbon fiber. [J. Moosburger Will et al. / Applied Surface Science 439(2018)305-312]. In this process, the particles are functionalized. Some particles, referred to herein as composite particles, may contain a portion of the previously cured epoxy on their surface. In this case, functionalization refers to the attachment of new epoxy-terminated material to the particle surface. Functionalization can be achieved either by a reaction to attach new groups to the surface of the carbon material by one of the methods disclosed above, or by a reaction to attach new groups to the surface of the cured epoxy.

[0038] Both direct and indirect processes can be used to achieve functionalization on the surface of cured epoxy. The direct process involves converting other chemical groups present in the cured epoxy into new epoxy groups using a reagent such as m-CPBA. The indirect process involves generating functional groups on the cured epoxy resin, which then react with new reagents containing at least an epoxy group to ultimately have reactive functional groups on the surface of the cured epoxy. This generally requires the attachment of another small molecule. For example, hydroxyl groups can be generated by treating the cured epoxy using acidic cleavage of an ether.

[0039] Further reaction results in an epoxy resin containing two epoxy groups per molecule. One of the epoxies reacts with the alcohol resulting from the acidic cleavage to epoxy-functionalize the surface, and when the particles are used as resin fillers, the second epoxy is available to chemically crosslink with the epoxy from the resin base.

[0040] Particle size is controlled by the milling method, which may include a grinding machine, conventional ball milling, high power planetary ball milling, or other methods. Ball media may include stainless steel, alumina, zirconia, yttrium zirconia oxide, tungsten carbide, and any other media harder than carbon fiber.

[0041] Particle size in at least one dimension can range from 10 nm to 10 mm, depending on the CFRP milling experimental process parameters. Generally, higher energy input, longer processing time, and smaller milling balls produce smaller sized CFRP particles.

[0042] The degree of functionalization, meaning the amount of functional organic material incorporated onto the surface of the particle, may range from 0.05% to 60% or even more depending on the functionalization method or functional organic molecule.

[0043] Returning to Figure 1, the process then disperses the functionalized FRP particles into the base resin at 14. The process generally requires dispersion of the functionalized FRP particles into the base resin. High quality dispersion is achieved by any mixing method, including but not limited to, shear mixing such as centrifugal mixing, rheometer mixing, cutting and folding mechanisms in screw-barrel extruders, compression mixing, flow mixing, other mixing methods used in polymer compounding, etc., or by energy dispersion methods such as ultrasonic dispersion.

[0044] After the particles are dispersed in the resin at 14, the resin with particles is dispersed into one or more layers of continuous fiber mat at 15. The fiber mat may include one of continuous carbon fiber, fiberglass, silicon carbide (SiC), aluminum oxide (Al2O2), and Kevlar fiber. After dispersion into one or more layers of mat, the resin with particles and mat are formed into the shape of a desired part at 16 and then cured at 18.

[0045] The dispersion process may be performed in a batch, semi-continuous, or continuous process, depending on the downstream processing method to make the final CFRP part. The dispersed functionalized particles may already have epoxy groups or groups that can be used to react with resins.

[0046] Conventional resins produce cured epoxies with low glass transition temperatures (Tg). When heated, for example for painting or sealing to other components, the resin softens, causing the CFRP object to lose dimensional stability. High-Tg epoxy resins minimize this effect. They generally achieve a high Tg (greater than 180°C) through high crosslink density or by using longer or bulkier monomers. The cured resins have significantly lower coefficients of thermal expansion (CTE), minimizing mismatch with low-CTE carbon fibers. For example, EPON Resin 164 has a CTE of only 17-22 × 10-6 m / (m K), approximately three times lower than conventional RTM resins.

[0047] Conventional low Tg epoxies contain two epoxy groups per resin molecule, which produces a cured resin with a low Tg. High Tg is achieved with resins with more than two functional groups per molecule, e.g., 2.5 to 6 or more, which produces a densely crosslinked structure.

[0048] Examples of suitable resins with high crosslink density, meaning more than two epoxy groups per resin molecule, include epoxy novolac resins, or other multifunctional resins, having the general chemical structure shown below: [ka]

[0049] Some of these resins are commercially available, for example, from Hexion, such as Epon Resin SU-8 (Tg 195-230; epoxy functionality of 8 epoxy per molecule), Epon Resin 1031 (Tg 195-230°C; epoxy functionality 3.5), and Epon Resin 164 (Tg 200-240°C; epoxy functionality 4.1). Other high Tg resins are available from Masterbond, such as EP13, EP121CL, and EP46HT-1, or from DIC Corporation, such as EPICLON HP-4710, an ultra-high heat resistant epoxy resin with a Tg of 350°C.

[0050] Fast-curing agents are necessary to achieve fast cycle times during the manufacture of CFRP objects, ideally less than 3 minutes per part. They typically cure in 1-3 minutes at temperatures above 100°C. Usable curing temperatures can generally range from 100°C to 250°C. Higher curing temperatures generally further reduce cure times and increase the mechanical properties of the cured resin.

[0051] Two types of curing agents are suitable for the purposes of these embodiments. The first type uses a fast-curing amino curing agent. These are used in an A+B system, where the A component is the epoxy resin and the B component is the amine curing agent. They are premixed immediately before use and applied immediately. Suitable examples of fast-curing amine curing agents include Aradur® 3475 and Hardener XB 3458, available from Huntsman, or fast curing agents available from Hexion. The second type of curing agent is a so-called latent curing agent, which, when mixed with an epoxy-based resin, including the composite resin of this embodiment, provides a stable solution that does not cure at room temperature. These are used in one-component resin systems. They cure rapidly when heated above 120°C. Generally, higher curing temperatures require a latent curing agent compared to an amino curing agent. Suitable examples of latent curing agents include ionic liquids such as 1-ethyl-3-methylimidazolium dicyanamide, 2-ethyl-4-methylimidazole, and dicyanidiamide (DICY). These are often used in conjunction with accelerators and catalysts such as tertiary amines.

[0052] The reinforced resin system from this embodiment is designed to be compatible with common, well-known methods for manufacturing CFRP parts. These may include any of the following, among others: wet compression molding, resin transfer molding, wet layup processing, pultrusion molding, and prepreg processing. Figure 2 shows an example of a process for molding a resin with functionalized particles. This is included as an example for ease of understanding and is not intended to limit any embodiment to any particular type of molding.

[0053] 2 shows a process according to a first embodiment. Recycled FRP is put into some type of grinder, shredder, or both 20 to obtain FRP material and product particles. These particles are then functionalized 22 either separately or by dispersion into a base resin.

[0054] A dispensing head 26 dispenses a defined volume of liquid resin 20 into either a single layer or a stack 28 of multiple layers of carbon fiber mats 24, forming a generally uniform film on top. The carbon fiber mats may consist of woven carbon fiber fabric, uniaxially oriented, or biaxially oriented fiber mats. When building stacks of oriented fiber mats, the relative orientation of the mats between each stack can be set depending on the intended mechanical properties of the resulting part.

[0055] The goal is to dispense a well-defined amount of liquid resin that covers nearly the complete lateral area of ​​the mat to minimize the need for significant resin spreading during the compression molding step. This can be done by a single-point dispense in the center of the fiber mat, as is currently done, which is applicable for low-viscosity resins, or by extruding the resin through a slotted die 26 to apply a uniform volume over a larger area, which is applicable for both low- and high-viscosity resins. The resulting resin film contains enough resin volume to completely wet the part, resulting in a final volume fraction of approximately 20–60% resin. The resulting resin film can have a thickness as low as 100 microns, but is likely to be thicker (1–10 millimeters). It is expected that the resin will be primarily contained on top of the first fabric layer, although some level of wetting may occur if the fabric mesh is larger and the resin has a sufficiently low viscosity.

[0056] Because reinforced resins contain fillers, recycled CFRP particles, with sizes in the multi-micron to nanometer range, are expected to have low viscosities, typically below 100 centipoise, and are more viscous than commonly used unfilled resins, which can be easily dispensed at 100 centipoise or less. Reinforced resins may have higher viscosities, at least greater than 100 centipoise, requiring greater pressure drops for rapid extrusion of precise volumes. Such hardware for dispensing fluids may include pressure multipliers, hydraulic piston-based force multipliers, or pneumatically driven fluid systems with screw and barrel extruder systems that can thin and shear the resin before dispensing. These may also include other hardware elements known to those skilled in the art.

[0057] In this likely application, a single layer of resin with a precise volume is dispensed onto a single carbon fiber (CF) mat or a stack of several CF mats. Other variations on this may include extruding multiple layers of resin onto a single CF mat or a stack of several CF mats to obtain the correct resin volume. Some methods may also choose to extrude a volume of resin onto each CF mat before they are assembled into a stack to reduce the wetting time of the resin through the mats. Other methods may place the resin in the center of a stack of CF mats, sandwiched between two mat layers, to enhance its penetration.

[0058] After the dispensing step, the now-wet CF mat or wet stack of CF mats is placed in the lower half 32 of a compression mold for use with the upper half 30 for hot compression molding. Mat placement can be manual or, in the anticipated application, automated to minimize the required placement time. In compression molding, the two halves of the mold are closed to form a nearly closed volume around the wet CF mat or wet stack of CF mats, forming the assembly into the desired part shape. The molding tool is preheated to a sufficiently high temperature to minimize the time required to fully heat the part to the cure temperature of the base resin.

[0059] The mold provides enough hydrostatic pressure to force the resin to infiltrate through the CF mat(s). This can be achieved by methods known in the art by designing the correct mold shape and applying the correct pressure during compression. This process results in the formation of a fully cured or nearly fully cured solid CFRP part with the desired shape, with the resin completely infiltrating the CF mat layers and with few voids in the resin, producing part 34. In the target application, the process also obtains the highest quality surface with aesthetic value suitable for commercial automotive applications with minimal post-processing.

[0060] In some applications, the mold halves 30 and 32 have seal and pump valves that create a vacuum within the chamber for better void control of the CFRP part.

[0061] As seen in Figure 2, an exploded view of the highest surface includes CFRP particles, such as 36, in the resin. Because the CFRP particles are functionalized with reactive groups capable of reacting with the base epoxy, they are expected to covalently bond to the resulting thermoset network, which is also chemically bonded to the carbon fiber. The presence of this chemically bonded, percolated covalent network is responsible for the increased mechanical properties when using the proposed resin. These CFRP particles, as shown at 36, are intended to be well dispersed throughout the resin and, in some cases, may also exhibit alignment or orientation relative to the CF surface. This relative alignment may be desirable and contribute to increased mechanical properties.

[0062] It is expected that the combination of the two processes, dispense molding and compression molding, can be performed with a cycle time of less than 3 minutes. Possible modifications, such as a longer hold time in the mold, can increase this cycle time but may also lead to better performing parts. The proposed resin system can also be used for other CFRP processing methods that may have similar or longer cycle times but may offer advantages in other properties. For example, the reinforced resin of the embodiment may also be used in a resin transfer molding process, in which a dry fiber mat is placed in a mold of the desired shape and resin dispensing occurs within the mold, for example, through one or more sprues.

[0063] For RTM (resin transfer molding), resin transfer time may have the greatest impact on cycle time. Resin transfer time refers to the time required for the resin to spread around the mold, across the part, and through the gaps in the mat(s). This may be 30 to 60 minutes, depending on the resin viscosity and part size and shape. High-pressure RTM methods are also known in the art and may result in shorter cycle times, such as 1 to 10 minutes, and may require higher-pressure dispensing systems, such as those mentioned in the dispensing step for wet compression molding and known in the art. The proposed liquid resin system can also be used in prepreg-molding techniques, where a prepreg of resin-infiltrated laminates of CF mat(s) is formed at elevated temperatures to mold the prepreg into the desired part shape.

[0064] In the case of prepregs, a reinforced resin system containing particles is used to produce the prepreg. These manufacturing methods can include a wet-stretch process in which a fiber mat is immersed in a vat of liquid resin and drawn from the vat after the required holding temperature. The method can also include spray application of the resin onto a CF mat or pultrusion process without a holding period for resin infiltration, slot coating dispensing of the resin onto the fiber mat, and final curing and / or solidification. The resulting prepreg can be wet, semi-wet, or semi-solid, depending on the non-cure solidification process of the parent epoxy. In either the prepreg case or the flat mat example, the resin with particles is dispensed into a mat, referred to herein as a resin mat.

[0065] The choice of prepreg manufacturing process can have advantages depending on the actual properties of the reinforced resin system. Wet stretch or pultrusion processes are common and established processes in prepreg manufacturing, but do not offer strict control over the resin composition, taking into account the percentage of dispersed filler. However, these processes can work with resins of almost any viscosity. Slot coating and spray-type application of resin to the CF mat(s) provides better control of the resin composition, but are viscosity-limited and may not work for very high viscosity resins.

[0066] Regardless of the manufacturing process, after removal from the mold, the part may be subjected to additional heating, which may be beneficial to complete the cure of the part if the cure in the mold was incomplete. This provides CFRP parts with improved properties compared to partially cured or cold-cured compositions. The additional heating after demolding can be performed at a temperature lower than, the same as, or higher than the molding temperature. Post-cure times can range from <1 minute to up to 24 hours, depending on the material and the desired mechanical performance.

[0067] As specified, the use of CFRP particle-reinforced resin increases the mechanical properties of the CFRP, including modulus, tensile strength, elongation, and other properties. The improvement can be at least 1% when compared to a CFRP made with the same resin matrix, but without the incorporated functionalized recycled CFRP particles. In other cases, it can be at least 10% or 25% or more. In other embodiments using other FRPs (Kevlar, glass, etc.) as resin fillers, similar improvements in the final FRP mechanical properties can be expected, depending on the degree of functionalization of the final FRP resin filler and its loading in the final FRP part.

[0068] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other different systems or applications. Various substitutions, modifications, variations, or improvements therein not presently anticipated or anticipated may subsequently occur to those skilled in the art.

Claims

1. 1. A method for recycling fiber reinforced polymers, comprising: grinding the used fiber reinforced polymer material to generate ground particles; functionalizing the ground particles to form functionalized particles; dispersing the functionalized particles in a base resin; dispensing the resin with functionalized particles into one or more layers of a continuous fiber mat; molding the resin with functionalized particles and the continuous fiber mat into the shape of a desired part; and hardening the form to produce the part. The method, wherein functionalizing the ground particles comprises an indirect process involving creating functional groups on a cured epoxy resin and reacting the functional groups with a reagent.

2. 10. The method of claim 1, wherein grinding the used fiber-reinforced polymer material comprises grinding at least one material from the group consisting of: ground fiber composite particles comprising at least one of continuous fibers, discontinuous fibers, and powdered fibers; polymer fiber-reinforced particles; carbon fiber-reinforced polymer; carbon composite particles; Kevlar; ceramic fiber composite particles; and glass fiber-reinforced particles.

3. 10. The method of claim 1, wherein the continuous fiber mat is selected from the group consisting of continuous carbon fiber, fiberglass, silicon carbide, aluminum oxide, and Kevlar fiber mats.

4. The method of claim 1 , wherein the indirect process is acidic cleavage.

5. 10. The method of claim 1, wherein the milling comprises one selected from the group consisting of grinding, ball milling, and high power planetary ball milling.

6. The method of claim 1, wherein providing the ground particles comprises providing ground particles having a size ranging from 10 nm to 10 mm.

7. 10. The method of claim 1, wherein dispersing the functionalized particles comprises one selected from the group consisting of shear mixing, centrifugal mixing, rheometer mixing, cutting and folding, compression mixing, flow mixing, and sonication dispersion.

8. 2. The method of claim 1, wherein the resin comprises one selected from the group consisting of an epoxy resin having a glass transition temperature of at least 150°C, a resin having more than two functional groups per molecule, a resin having eight functional groups per molecule, and a novolac resin.

9. The method of claim 1 , wherein the resin comprises a fast hardener comprising at least one of an amino hardener, a latent curing agent, or a catalyst.

10. The method of claim 1 , wherein dispensing the resin with functionalized particles into one or more layers of a continuous fiber mat forms a prepreg mat.

11. The method of claim 1 , wherein the molding comprises one of the group consisting of wet compression molding, resin transfer molding, wet layup processing, pultrusion, and prepreg processing.

12. 1. A method for recycling carbon fiber reinforced polymers, comprising: grinding the used carbon fiber reinforced polymer material to generate ground particles; functionalizing the ground particles to form functionalized particles; dispersing the functionalized particles in a base resin; dispensing the resin with functionalized particles into one or more layers of a carbon fiber mat; forming the resin with functionalized particles and the carbon fiber mat into the shape of a desired part; and hardening the form to produce the part. The method, wherein functionalizing the ground particles comprises an indirect process involving creating functional groups on a cured epoxy resin and reacting the functional groups with a reagent.

13. 13. The method of claim 12, wherein the molding comprises one of the group consisting of wet compression molding, resin transfer molding, wet layup processing, pultrusion, and prepreg processing.

14. 1. A method for recycling glass fiber reinforced polymers, comprising: grinding the used glass fiber reinforced polymer material to produce ground particles; functionalizing the ground particles to form functionalized particles; dispersing the functionalized particles in a base resin; dispensing the resin with functionalized particles into one or more layers of a fiberglass mat; molding the resin with functionalized particles and the fiberglass mat into the shape of a desired part; and hardening the form to produce the part. The method, wherein functionalizing the ground particles comprises an indirect process involving creating functional groups on a cured epoxy resin and reacting the functional groups with a reagent.

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