An impact-resistant epoxy-polyurethane hybrid composite suitable for use in extreme cold environments and its use in exoskeleton joint components

Abstract

This invention discloses an impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments and its application in exoskeleton joint components. The impact-resistant epoxy-polyurethane hybrid composite material comprises component A and component B. Component A includes epoxy resin, a double-ended epoxy-terminated polyurethane prepolymer, a flexible spacer segment component, and nano-elastic particles with a three-layer structure of rigid core-soft shell-reactive bridge. Component B includes an amine curing agent. The nano-elastic particles, from the inside out, consist of an inorganic rigid core, an elastic polymer shell, and a reactive bridge outer layer containing epoxy reactive groups. The impact-resistant epoxy-polyurethane hybrid composite material provided by this invention exhibits significantly improved impact resistance and crack propagation resistance in extremely cold environments (-50°C), and significantly enhanced notched Izod impact strength and plane strain fracture toughness at -50°C.

Description

Technical Field

[0001] This invention relates to the field of epoxy-polyurethane hybrid composite materials, and in particular to an impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments and its application in exoskeleton joint components. Background Technology

[0002] Epoxy resins are widely used in structural adhesives, composite matrix, and precision component molding due to their high mechanical strength, modulus, and dimensional stability. However, after curing, single epoxy resins form a highly cross-linked three-dimensional network. The chain segments have limited mobility at low temperatures, exhibiting typical brittle fracture characteristics, and cracks are prone to rapid propagation in stress concentration areas. In components such as joint side plates, bearing housing outer walls, limiting blocks, reducer end caps, sensor protective covers, and metal insert outer coatings in exoskeletons (knee, ankle, hip joints, etc.), geometric discontinuities exist due to structural features such as bolt holes, corners, and limiting collision zones. Furthermore, these components must withstand impacts from falling ice, drops, low-temperature start-stop cycles, and transient impact loads from complex terrain during service. When ambient temperatures drop below -40°C, especially under extreme cold conditions of -50°C, traditional epoxy-based composite materials are more prone to penetrating brittle fracture and catastrophic failure in the aforementioned stress concentration areas.

[0003] To improve the low-temperature toughness of epoxy resins, several toughening modification routes have been proposed in existing technologies. One route involves physically blending epoxy resin with low-temperature polyurethane to toughen it, utilizing the low-temperature segment mobility of the polyurethane soft segments to provide flexible energy dissipation. However, the physically blended polyurethane exists only as a dispersed phase, lacking chemical bonding with the epoxy main network. Under low-temperature and high-stress conditions, it is prone to interfacial debonding and macroscopic phase separation, thus becoming a weak interfacial defect. Another route involves using core-shell rubber particles or nano-silica particles for single-component toughening. However, while purely elastic core-shell particles improve toughness, they often significantly sacrifice modulus, while purely rigid nanoparticles have limited ability to inhibit crack propagation. When the two are simply physically mixed, due to unreasonable particle size distribution and interfacial coupling, agglomeration and size mismatch are easily generated, which dulls or even cancels out the toughening benefits. Another approach is to use free isocyanate-terminated polyurethane prepolymers as toughening components. However, these prepolymers have drawbacks such as demanding storage and transportation conditions, self-curing at high addition levels, and a sharp increase in system viscosity, making it difficult to balance high addition modification with stable production.

[0004] In summary, for exoskeleton joint components designed for operation in extremely cold environments down to -50°C, existing epoxy-based composite materials are insufficient to simultaneously meet the requirements for impact resistance and crack propagation resistance at low temperatures. Furthermore, the introduction of toughening components to improve low-temperature impact toughness often results in a decrease in static stiffness, a reduction in glass transition temperature, an increase in system viscosity, and uncontrolled phase separation, making it difficult to comprehensively address the stiffness, formability, and service stability requirements of exoskeleton joint components. Therefore, there is an urgent need for an epoxy-polyurethane hybrid composite material that can simultaneously solve both of these problems. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments. The impact-resistant epoxy-polyurethane hybrid composite material comprises component A and component B. Component A includes epoxy resin, a double-ended epoxy-capped polyurethane prepolymer, a flexible spacer segment component, and nano-elastic particles with a three-layer structure of rigid core-soft shell-reactive bridge. Component B includes an amine curing agent. The double-ended epoxy-capped polyurethane prepolymer has epoxy groups at both ends, and is obtained by reacting polyether polyol soft segments, a diisocyanate component, and glycidyl ether. The nano-elastic particles, from the inside out, sequentially comprise an inorganic rigid core, an elastic polymer shell, and a reactive bridge outer layer containing epoxy reactive groups.

[0006] According to one aspect of the present invention, the epoxy resin in component A serves as the main load-bearing skeleton, providing the material with static modulus, stiffness, and dimensional stability. Both ends of the double-epoxy-terminated polyurethane prepolymer are epoxy groups. In the presence of the amine curing agent in component B, it can undergo a ring-opening addition reaction between the terminal epoxy groups and the amine groups, thereby covalently embedding itself into the main network constructed from epoxy resin, forming a covalently embedded hybrid crosslinked network structure. Specifically, the epoxy resin is cured by amine to form a rigid main crosslinked network, and the polyether soft segments of the double-epoxy-terminated polyurethane prepolymer are embedded between the crosslinking nodes of this rigid network as covalently bonded flexible segments. Thus, rigid aromatic segments and flexible polyether segments coexist in the same network topology, combining the load-bearing function of the rigid network with the low-temperature energy dissipation function of the flexible segments. Compared to polyurethane prepolymers with free isocyanate end groups or physically blended polyurethane toughening agents, the epoxy-terminated structure avoids the problems of self-curing and rapid thickening of free isocyanate end-group prepolymers during storage, transportation, and at high addition levels. Furthermore, it ensures that the polyurethane soft segments no longer exist solely as free dispersed phases, thus suppressing macroscopic phase separation and interfacial debinding at low temperatures and retaining activatable flexible segments at -50°C. The flexible spacer segment components, through their polyether segments, insert between adjacent rigid aromatic segments, reducing the local crosslinking density gradient and internal stress peak, preventing the segments from being completely locked at low temperatures. The inorganic rigid core of the nanoelastic particles maintains the static modulus, while the elastic polymer shell preferentially cavitates under impact loads and induces shear yielding in the surrounding matrix. The reactive bridge outer layer containing epoxy reactive groups forms a covalent anchor with the epoxy / amine curing network and the double-ended epoxy-terminated polyurethane prepolymer, preventing the particles from being pulled out entirely under low-temperature, high-stress conditions and becoming defect sources. The four components work synergistically to cause the crack tip to successively experience the local plasticization zone of the flexible spacer chain segment, the energy dissipation of cavitation by the nano-elastic particles, the shear yielding of the matrix, and the crack deflection / branching under the traction of the polyurethane-enriched phase, thus transforming the single main crack propagation mode into a multi-stage energy-dissipating propagation mode.

[0007] Preferably, the epoxy resin comprises a first epoxy component and a second epoxy component; the first epoxy component is a bisphenol A type liquid epoxy resin, and the epoxy equivalent of the first epoxy component is 180 g / eq to 195 g / eq; the second epoxy component is selected from at least one of phenolic epoxy resin and bisphenol F type epoxy resin. When the epoxy equivalent of the first epoxy component is in the range of 180 g / eq to 195 g / eq, the system has suitable initial viscosity and reactivity, which facilitates thorough mixing and dispersion with the double-ended epoxy-terminated polyurethane prepolymer and nano-elastic particles; if the epoxy equivalent is lower than 180 g / eq, the crosslinking density is too high, and the brittleness of the system after curing increases significantly, which is not conducive to low-temperature impact resistance; if it is higher than 195 g / eq, the crosslinking density is insufficient, and the static modulus and heat resistance of the material decrease. The phenolic epoxy resin in the second epoxy component contains multiple epoxy functional groups, which can introduce multifunctional crosslinking points into the main network and restore some of the stiffness and thermal stability lost due to the introduction of flexible components. Compared with bisphenol A, bisphenol F type epoxy resin has lower viscosity and retains better heat resistance, which makes it easier to maintain processability when a higher proportion of flexible components is introduced.

[0008] More preferably, the polyether polyol soft segments comprise polytetrahydrofuran diol and polypropylene glycol, and based on the total mass of the polyether polyol soft segments, the polytetrahydrofuran diol comprises 60% to 85% by mass, and the polypropylene glycol comprises 15% to 40% by mass; the diisocyanate component is selected from at least one of isophorone diisocyanate and dicyclohexylmethane diisocyanate. The polytetrahydrofuran diol backbone contains regularly distributed... The polyether segment, with its low glass transition temperature and excellent molecular chain flexibility, maintains segment mobility even at -50℃, thus contributing significantly to the material's low-temperature flexibility and hydrolysis resistance. If its mass percentage is below 60%, the soft segment is prone to cryogenic hardening at low temperatures, reducing the material's impact resistance. If it is above 85%, the tendency for orderly packing of the soft segment increases, making it susceptible to ordered cold crystallization in the low-temperature region, which conversely reduces low-temperature toughness. A small amount of polypropylene glycol (PPG) is used as a co-soft segment; its methyl side chains exert a steric hindrance effect on the orderly packing of the polytetrahydrofuran glycol backbone, further suppressing the tendency for cryogenic hardening of the soft segment. If the PPG mass percentage is below 15%, the above-mentioned inhibitory effect is not significant; if it is above 40%, the low-temperature flexibility of the polyether soft segment decreases. The diisocyanate component is selected from isophorone diisocyanate or dicyclohexylmethane diisocyanate with an alicyclic structure. Compared with aromatic diisocyanates, it has lower hard segment rigidity and does not produce low-temperature brittleness caused by benzene ring stacking, and has better yellowing resistance.

[0009] More preferably, the number-average molecular weight of the double-ended epoxy-terminated polyurethane prepolymer is 3000 to 8000, and the end-epoxy value is 0.025 eq / 100g to 0.067 eq / 100g. It should be noted that for prepolymers with double-ended functionality, each molecular chain contains two end-epoxy groups; therefore, its end-epoxy value (eq / 100g) is related to its number-average molecular weight M. n The epoxy value between them must be 200 / M. n The stoichiometric relationship of M above; n The lower limit of the range, 3000, corresponds to a theoretical end epoxy value of 0.067 eq / 100g, M n The upper limit of the range, 8000, corresponds to a theoretical epoxy value of 0.025 eq / 100g, with both components exhibiting strict closed-loop structure. When the number-average molecular weight is below 3000, the soft segments of the prepolymer are too short to provide sufficient space for low-temperature chain segment movement, resulting in limited toughening effect. When the number-average molecular weight is above 8000, the viscosity of the prepolymer increases significantly, its compatibility with the epoxy main resin deteriorates, mixing and dispersion become more difficult, and coarse phase separation is easily induced. The infrared spectrum shows no characteristic absorption peak of isocyanate at 2270 cm⁻¹, indicating that the -NCO groups in the prepolymer have been completely capped by glycidyl ether, avoiding uncontrollable side reactions during subsequent storage and compounding.

[0010] Preferably, the flexible spacer segment component is selected from at least one of polypropylene glycol diglycidyl ether and polytetrahydrofuran diglycidyl ether. Both ends of the aforementioned flexible spacer segment component are glycidyl ether groups, which can participate in the co-curing reaction with amine curing agents and enter the main network. The internal rotation barrier of the C-O-C ether bond in its molecular backbone is significantly lower than that of the aromatic ring-methylene linkage in the epoxy main resin. Therefore, it acts as an "inter-chain buffer bridge" in the main network, transforming the stress originally concentrated at bolt hole edges, acute angles, and abrupt thickness changes into more dispersed bulk deformation, reducing the probability of crack initiation in stress concentration areas at low temperatures.

[0011] According to one aspect of the present invention, the inorganic rigid core is silica; the elastic polymer shell is polybutyl acrylate; and the outer reactive bridge layer is a copolymer of methyl methacrylate and glycidyl methacrylate. The silica core has high modulus and good thermal stability, providing rigid support at the particle scale and preventing excessive deformation of the overall particles under stress, similar to pure rubber particles, thereby maintaining the static modulus of the composite material. The polybutyl acrylate elastic shell has a low glass transition temperature (approximately -49°C) and remains in a highly elastic state at -50°C, possessing the ability to cavitate and induce matrix shear yielding. The glycidyl methacrylate units in the outer copolymer contain glycidyl groups, which can form covalent chemical bonds with amine curing agents and the terminal epoxy groups of the double-ended epoxy-capped polyurethane prepolymer, thereby stably anchoring the nano-elastic particles in the hybrid hybrid network structure.

[0012] More preferably, the average particle size of the inorganic rigid core is 60 nm to 200 nm; the thickness of the outer layer of the reactive bridge is 2 nm to 10 nm; and the thickness of the elastic polymer shell is controlled by the ratio of its size to the average particle size of the inorganic rigid core, which is 0.04 to 0.12. When the average particle size of the inorganic rigid core is less than 60 nm, the particle specific surface area is too large, making it prone to agglomeration during dispersion; when it is greater than 200 nm, the particle size is close to the upper limit of the characteristic scale of the plastic zone at the crack tip, weakening the inhibitory effect on crack propagation. When the thickness of the outer layer of the reactive bridge is less than 2 nm, the number of reactive groups that can participate in chemical anchoring is insufficient; when it is greater than 10 nm, the proportion of non-epoxy reactive chain segments in the outer layer of the reactive bridge is too high, which will weaken the overall chemical coupling efficiency between the particles and the matrix. The ratio of the elastic polymer shell thickness to the average particle size of the inorganic rigid core is controlled between 0.04 and 0.12, which is the critical geometric condition for ensuring the effective brittle-ductile transition of the material. If it is below 0.04, the shell cannot trigger an effective cavitation energy dissipation mechanism at the particle scale, and the brittle-ductile transition threshold is not reached. If it is above 0.12, the relative volume fraction of the rigid core decreases, and the modulus retention capability weakens. Within this ratio range, the corresponding absolute thickness of the elastic polymer shell automatically falls within the range of approximately 2.4 nm to 24 nm depending on the core particle size, which can cover the minimum shell size required for cavitation triggering.

[0013] Preferably, component B comprises isophorone diamine, polyetheramine, and imidazole accelerators; the ratio of active hydrogen equivalent in component B to epoxy equivalent in component A is 0.95:1 to 1.05:1. Isophorone diamine is an alicyclic diamine with a molecular structure that combines rigidity and flexibility. The network formed after curing has a high glass transition temperature and maintains moderate segment mobility. The polyetheramine backbone contains polyether segments, which help to further introduce flexibility at the molecular scale and synergistically regulate the crosslinking density distribution of the cured network with isophorone diamine. Imidazole accelerators can accelerate the amine-epoxy curing reaction at the intermediate temperature stage, in conjunction with the subsequent segmented curing regime. The epoxy equivalent in component A includes the total contribution of epoxy resin, epoxy groups of the double-ended epoxy-terminated polyurethane prepolymer, glycidyl ether groups of the flexible spacer segment component, epoxy groups of the coupling dispersion component, and glycidyl ester groups of the outer layer of the nano-elastic particle reactive bridge. When the ratio of active hydrogen equivalent to epoxy group equivalent is less than 0.95:1, excess epoxy groups can easily lead to unreacted epoxy groups in the network, which may cause post-curing and performance drift under long-term service. When it is greater than 1.05:1, excess amine will introduce unreacted active hydrogen groups, affecting the water resistance and electrical properties of the material.

[0014] Preferably, in component A, the mass ratio of the epoxy resin, the double-ended epoxy-terminated polyurethane prepolymer, the flexible spacer segment component, and the nano-elastic particles is (50 to 70):(12 to 28):(4 to 12):(1 to 6). More preferably, the mass ratio of the aforementioned four components is (60 to 70):(20 to 26):(5 to 8):(3 to 5). When the mass ratio of the double-ended epoxy-terminated polyurethane prepolymer to the epoxy resin is lower than 12:70, the provided flexible sub-network density is insufficient, the low-temperature plastic zone area is insufficient, and the toughening effect is limited; when it is higher than 28:50, the proportion of flexible soft segments in the main network is too high, and the static stiffness and heat distortion temperature of the material decrease significantly. When the mass ratio of the flexible spacer segment component to the epoxy resin is too low, the inter-chain buffering effect is not significant; when it is too high, the overall crosslinking density of the main network is too low, and the difficulty in maintaining the glass transition temperature increases. When the mass ratio of nanoelastic particles to epoxy resin is too low, the number of triggerable nanoenergy-consuming centers is insufficient; when it is too high, the particle spacing is too small, significantly increasing the risk of agglomeration and interfacial inhomogeneity, and the viscosity of the composite resin system also increases significantly, reducing processability. Within a further optimized range, the material simultaneously possesses superior low-temperature impact resistance, static stiffness retention, and process stability.

[0015] Preferably, component A further includes a coupling dispersion component and an antifoaming and leveling component; the coupling dispersion component is selected from at least one of γ-glycidyl etheroxypropyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; component A further includes chopped reinforcing fibers, which are selected from at least one of chopped carbon fibers, aramid slurry, and basalt short fibers. The siloxymethyl groups of the coupling dispersion component undergo hydrolysis and condensation reactions under the action of trace amounts of moisture in the system, generating silanol groups and forming Si-O-Si condensation bonds with the residual silanol groups or hydroxyl groups on the surface of the nano-elastic particles and optionally on the surface of the chopped reinforcing fibers, thereby anchoring them to the inorganic / fiber interface; the trace amounts of methanol byproducts released during the hydrolysis process are effectively extracted in the subsequent vacuum degassing process (under an operating vacuum of approximately 0.01 MPa, the boiling point of methanol drops to approximately 15°C, far below the system operating temperature, and can be fully evaporated), and will not remain in the subsequent closed mold curing stage and cause porosity defects. The coupling dispersion component contains active epoxy groups at its organic ends, which can covalently embed into the main curing network via an amine-epoxy ring-opening addition reaction with the amine curing agent in component B. This creates a continuous chemical bonding pathway within the curing system, bridging the inorganic / fiber interface to the main network via the coupling dispersion component. The defoaming and leveling component assists in eliminating bubbles and improving surface leveling during high-shear dispersion and vacuum defoaming, further ensuring that no internal porosity defects are formed during the molding of exoskeleton joint components. The chopped reinforcing fibers further enhance the load-bearing capacity of the material in areas requiring higher bending stiffness, such as the exoskeleton joint side plates and bearing housing outer walls, and can be selectively added according to the mechanical requirements of specific components. For systems containing chopped reinforcing fibers, the molding method is changed from gravity casting to pressure injection molding or compression molding to ensure the integrity of the mold filling of the fiber-containing system.

[0016] According to another aspect of the present invention, the impact-resistant epoxy-polyurethane hybrid composite material can be molded by the following staged curing regime: first, pre-gelling at 45°C to 55°C for 1 to 2 hours, then holding at 75°C to 90°C for 2 to 4 hours, and finally curing at 110°C to 125°C for 2 to 3 hours. The segmented curing regime is based on the fact that the multi-component system used in this invention includes a double-ended epoxy-terminated polyurethane prepolymer, flexible spacer segment components, and three-layer structured nanoelastic particles. The polarity, molecular weight, and reactivity of each component are quite different. In the pre-gelling stage, the viscosity of the system slowly increases at a lower temperature, providing a time window for the nanoelastic particles and polyurethane-enriched phase to fully relax and distribute evenly after the residual shear field of component A disappears, thus avoiding the gravitational sedimentation and agglomeration of nanoparticles caused by a sudden drop in viscosity during the heating process. In the medium-temperature holding stage, the epoxy main network gradually undergoes an amine-epoxy ring-opening addition reaction and approaches the gel point, thereby locking the morphology of the already formed uniformly dispersed polyurethane-enriched phase at the submicron level and solidifying the spatial position of the nanoparticles. The post-curing stage supplements the crosslinking density and dimensional stability of the main network. If a conventional curing regime that involves rapid heating to the final curing temperature in one go is directly adopted, the nano-elastic particles in component A lack dispersion and relaxation time during the initial viscosity drop phase of heating, making them prone to particle agglomeration. At the same time, the reactions of each component proceed simultaneously and rapidly, and the uneven local composition and uneven exothermic reaction will further aggravate morphological defects, making it difficult for the low-temperature impact resistance of the material to meet expectations.

[0017] According to another aspect of the present invention, the impact-resistant epoxy-polyurethane hybrid composite material can be applied to exoskeleton joint components, the exoskeleton joint components including at least one of the following: joint side plates of the exoskeleton knee joint, ankle joint, or hip joint; bearing housing outer wall; limiting block; tether guide wheel housing; reducer end cap; sensor protective cover; bolt hole periphery reinforcement area; and metal hinge outer covering buffer layer. When using metal insert overmolding, the surface of the metal insert is sandblasted to a surface roughness Ra of 2 μm to 5 μm, and coated with an epoxy / aminosilane primer before in-mold casting to improve the peel resistance of the metal / composite material interface.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The impact-resistant epoxy-polyurethane hybrid composite material provided by this invention, suitable for extremely cold environments, significantly improves the material's impact resistance and crack propagation resistance in extremely cold environments down to -50°C by synergistically introducing a double-ended epoxy-terminated polyurethane prepolymer, a flexible spacer segment component, and nano-elastic particles with a rigid core-soft shell-reactive bridge three-layer structure into the epoxy resin system, and constructing a covalently embedded hybrid hybrid network structure via an amine curing agent. Because the double-ended epoxy-terminated polyurethane prepolymer covalently embeds into the main network through its terminal epoxy groups, it avoids the macroscopic phase separation and interfacial debonding problems of traditional physically blended polyurethane toughening agents at low temperatures; the reactive bridge outer layer of the nano-elastic particles forms a chemical anchor with the matrix, avoiding the agglomeration, size mismatch, and toughening benefit passivation problems that easily occur when rigid nanoparticles and core-shell rubber particles are simply physically mixed; the flexible spacer segment component reduces the local crosslinking density gradient through polyether segments, alleviating the chain segment locking phenomenon in stress concentration areas such as bolt hole edges and corners at low temperatures.

[0019] Compared to the unmodified bisphenol A type epoxy baseline system under the same curing regime, the impact-resistant epoxy-polyurethane hybrid composite material of this invention exhibits significantly improved notched Izod impact strength and plane strain fracture toughness at -50℃. Although the introduction of the flexible component inevitably leads to a certain decrease in room temperature tensile strength, flexural modulus, and glass transition temperature, the inorganic rigid core of the nano-elastic particles maintains a considerable contribution to the static modulus at the particle size. Furthermore, the segmented curing regime controls the size of the polyurethane-enriched phase to the submicron level, preventing nanoparticle aggregation. Consequently, the decrease in flexural modulus, glass transition temperature, and thermal deformation stability is significantly less than that of the traditional pure polyurethane toughening system. In addition, since the polyurethane component is end-capped with epoxy rather than free isocyanate, the material system does not suffer from the self-curing and rapid thickening issues associated with free isocyanate-end-group prepolymers during storage, transportation, and high addition levels, which is beneficial for process stability and raw material safety. When the material is applied to components such as the joint side plates, bearing housing outer walls, limiting blocks, and metal insert outer buffer layers of exoskeleton knee, ankle, and hip joints, it can improve the impact resistance safety margin of stress concentration areas in extremely cold environments while maintaining the lightweight and geometric accuracy of the exoskeleton joints. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] The main raw materials and their specifications used in the following examples and comparative examples are as follows: bisphenol A type liquid epoxy resin is E-51 (Baling Petrochemical), with an epoxy equivalent of 184 g / eq to 194 g / eq; phenolic epoxy resin is F-44 (Nantong Xingchen Synthetic Materials Co., Ltd.), with an epoxy equivalent of 175 g / eq to 185 g / eq; bisphenol F type epoxy resin is NPEF-170, with an epoxy equivalent of 165 g / eq to 175 g / eq; polypropylene glycol diglycidyl ether (number average molecular weight approximately 640, epoxy equivalent approximately 320 g / eq) and... Polytetrahydrofuran diglycidyl ether (number average molecular weight approximately 750, epoxy equivalent approximately 375 g / eq) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; polytetrahydrofuran diol (PTMG-3000, number average molecular weight approximately 3000) was purchased from BASF; polypropylene glycol (PPG-2000, number average molecular weight approximately 2000) was purchased from Shandong Lanxing Dongda Co., Ltd.; isophorone diisocyanate (IPDI, molecular weight 222) and dicyclohexylmethane diisocyanate (H12MDI, molecular weight 262) were purchased from Wanhua Chemical Group Co., Ltd. Glycidyl ether (purity ≥96%), dibutyltin dilaurate (DBTDL), and 2-ethyl-4-methylimidazole were purchased from Sinopharm Chemical Reagent Co., Ltd.; γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) was purchased from Nanjing Shuguang Chemical Group Co., Ltd.; γ-methacryloyloxypropyltrimethoxysilane (KH-570, used only in the emulsion polymerization process for pre-modification of nanoparticle surfaces) was purchased from Nanjing Shuguang Chemical Group Co., Ltd.; tetraethyl orthosilicate (TEOS), butyl acrylate (BA), methyl methacrylate (MMA), and... Glycidyl methacrylate (GMA) was purchased from Shanghai Aladdin; isophorone diamine (IPDA, molecular weight 170, active hydrogen equivalent 42.5) was purchased from Wanhua Chemical Group Co., Ltd.; polyetheramine D230 (number average molecular weight approximately 230, active hydrogen equivalent approximately 60) was purchased from Huntsman Advanced Materials; chopped carbon fibers (PAN-based, average length 3 mm) were purchased from Zhongfu Shenying Carbon Fiber Co., Ltd.; and methyl methacrylate-butadiene-styrene copolymer core-shell rubber particles (MBS, average particle size approximately 150 nm) used for comparative examples were purchased from Zhongyuan Chemical.

[0022] The double-ended epoxy-capped polyurethane prepolymer (hereinafter referred to as EPU) is prepared as follows: PTMG-3000 and PPG-2000 are mixed at a mass ratio of 75:25 (i.e., polytetrahydrofuran diol accounts for 75% of the total mass of the polyether polyol soft segment, and polypropylene glycol accounts for 25%), and vacuum dehydrated at 110℃ for 2 hours. After the moisture content is lower than 0.05%, the temperature is lowered to 80℃; IPDI is weighed according to an NCO / OH molar ratio of 2.0 and added to the reaction system (i.e., each mole of total -OH corresponds to 1 mole of I). PDI was added, and DBTDL (0.05% of the total mass of reactants) was added as a catalyst. The reaction was carried out at 80℃ for 2.5 h. The residual -NCO value was measured every 30 min. After reaching the theoretical value (i.e., one free -NCO is retained at each end of each polyether chain), the temperature was lowered to 75℃. Glycidyl ether was added at 1.05 equivalents of the remaining -NCO, and the reaction was continued at 75℃ for 3 h. The reaction was stopped when the characteristic absorption peak of -NCO at 2270 cm⁻¹ in the infrared spectrum completely disappeared. After the reaction was completed, vacuum thin-film distillation was carried out at 75℃ and absolute pressure ≤500 Pa for 30 min to remove unreacted excess glycidyl ether (the boiling point of glycidyl ether is 167℃, and the boiling point drops to about 70℃ under this vacuum, so it can be effectively distilled off). Gas chromatography analysis showed that the residual free glycidyl ether content in the system after distillation was less than 0.1%, which did not affect the accurate determination of the subsequent epoxy value. The obtained EPU structure is a bi-epoxy-terminated ABA-type prepolymer of glycidyl-IPDI-polyether polyol-IPDI-glycidyl. Mo was determined by gel permeation chromatography. n The value is 3260. The measured terminal epoxy value using the hydrochloric acid-acetone method is 0.0612 eq / 100g. This is related to the stoichiometry of the dual-terminal functionality (terminal epoxy value = 200 / M). n The theoretical deviation is less than 0.2%, confirming that the prepolymer is indeed a double-ended epoxy-capped structure, and that excess glycidyl ether has been effectively removed. In this process, the two -NCO groups of IPDI first undergo an addition reaction with the -OH groups at both ends of the polyether polyol soft segment to form urethane bonds and a -NCO-capped intermediate. Since the NCO / OH molar ratio is 2.0, no chain extension reaction occurs, and each polyether chain retains one unreacted free -NCO group at each end. Subsequently, this free -NCO group further undergoes an addition reaction with the -OH groups of glycidyl ether, converting both ends of the prepolymer into glycidyl ether epoxy groups.

[0023] The rigid core-soft shell-reactive bridge three-layer structure nanoelastic particles are prepared by the following method: First, a silica core with an average particle size of about 100 nm is prepared in an ethanol / ammonia system using TEOS as a precursor via the Stöber method. After centrifugation and washing, the silica core is dispersed in ethanol. Then, 5% KH-570 relative to the mass of silica is added, and the mixture is refluxed at 60°C for 4 h to graft methacryloyloxy double bonds that can participate in free radical polymerization onto the silica surface. After centrifugation and washing to remove ungrafted silanes, surface-modified silica is obtained. Surface-modified silica was first dispersed in butyl acrylate monomer (utilizing the hydrophobicity of the KH-570 grafted silica surface to preferentially wet the monomer phase), and treated in an ultrasonic bath for 10 min to fully depolymerize the powder. Then, this silica / monomer dispersion was slowly added at a solid content of 5% by weight to an aqueous solution containing sodium dodecyl sulfate (SDS concentration 0.15% w / w, below its critical micelle concentration). After ultrasonic treatment (frequency 20 kHz, power 600 W) in an ice-water bath for 15 min using cell disruption ultrasonication, it was emulsified for 10 min using a high-shear homogenizer at 10000 rpm to form a microemulsion with silica / monomer droplets as the dispersed phase. Seeded emulsion polymerization was carried out at 70℃ using potassium persulfate (KPS) as an initiator and a starved semi-continuous dropwise addition method: the remaining butyl acrylate monomer (according to…) was… A pre-emulsion was prepared by calculating the total mass ratio of butyl acrylate to polybutyl acrylate (1:0.30, excluding the portion already added with silica). This pre-emulsion was then added to the reaction system at a uniform dropping rate of 0.5 mL / min over 4 hours to maintain an extremely low instantaneous free monomer concentration, thus inhibiting homogeneous nucleation in the aqueous phase and ensuring preferential polymerization of the monomer on the KH-570 grafted silica surface to form a shell, yielding silica / butyl acrylate core-shell particles. Subsequently, methyl methacrylate and glycidyl methacrylate (according to...) were... A pre-emulsion (prepared with a mass ratio of MMA to GMA of 1:0.20, where the molar ratio of MMA to GMA is 4:1) was also added dropwise over 3 hours using a starved semi-continuous method to coat the surface of silica / polybutyl acrylate core-shell particles, forming an outer layer of methyl methacrylate-glycidyl methacrylate copolymer. After demulsification, washing, and freeze-drying, the product yielded three-layered nanoelastic particles. Statistical analysis using transmission electron microscopy showed that the average particle size of the inorganic rigid core was 100 nm, the thickness of the elastic polymer shell was 8 nm, and the thickness of the reaction bridge outer layer was 4 nm. The ratio of the elastic polymer shell thickness to the average particle size of the inorganic rigid core was 0.08, falling within the range of 0.04 to 0.12 defined in claim 7. Morphological analysis of 200 randomly selected particles by transmission electron microscopy showed that pure core-shell structure particles accounted for ≥92%, while bare silica without shell and independent polymer latex particles accounted for ≤8% in total. This indicates that the starved state semi-continuous feeding process effectively suppressed secondary nucleation.

[0024] The molding of the impact-resistant epoxy-polyurethane hybrid composite material is carried out according to the following process: Bisphenol A type liquid epoxy resin, the second epoxy component and the flexible spacer segment component are added to a jacketed stirred reactor in a predetermined number of parts and mechanically stirred at 60°C for 25 min until uniformly mixed; a predetermined number of EPU is added and stirring is continued for 25 min; nano-elastic particles and coupling dispersion components are added and dispersed at 2000 rpm under high shear for 15 min. For the embodiment without chopped reinforcing fibers, a defoaming and leveling component was then added, and the mixture was defoamed for 15 minutes under a vacuum of -0.09 MPa (this vacuum defoaming process is carried out at an absolute pressure of approximately 0.01 MPa, which can effectively remove trace amounts of methanol byproducts generated by the hydrolysis of the methoxy group of the coupling dispersion component KH-560; the boiling point of methanol at normal pressure is 64.7°C, and under this vacuum, the boiling point drops to approximately 15°C, which is far below the current operating temperature of the system, so the methanol can be fully evaporated, ensuring that there are no volatile residues causing pore defects during the subsequent sealing and curing stage), to obtain component A; after cooling to 40°C, component B (IPDA, polyetheramine D230 and 2-ethyl-4-methylimidazole premixed) was added, stirred at low speed for 8 minutes, and poured into a mold preheated to 50°C. For the embodiment containing chopped reinforcing fibers (Example 6), after the aforementioned high-shear dispersion of nanoparticles is completed, defoaming and leveling components should be added first, and defoaming should be performed under a vacuum of -0.09 MPa for 15 min (to remove methanol byproducts as well). The speed should be reduced to 300 rpm to 500 rpm before adding chopped carbon fibers. The mixture should be stirred at this low speed for 15 min to ensure that the fibers are fully impregnated, thereby preventing the chopped fibers from being broken up and losing their bridging function during the initial high-shear dispersion process, resulting in fiber-containing component A. After cooling to 40°C, component B should be added, and the mixture should be stirred at a low speed for 8 min. The mixture should be injected into a mold preheated to 50°C using a pressure injection molding method of 2 MPa to 5 MPa to ensure the integrity of the mold filling and the uniformity of fiber distribution under the condition that the flow resistance is increased due to the overlap effect of chopped carbon fibers. Subsequently, a segmented curing process was adopted: first, pre-gelling was carried out at 50℃ for 1.5h, then the temperature was raised to 85℃ and held for 3h, and finally the temperature was raised to 120℃ and cured for 2.5h. After naturally cooling to room temperature, the product was demolded to obtain an impact-resistant epoxy-polyurethane hybrid composite material.

[0025] In all embodiments and comparative examples, the amount of component B was prepared at a ratio of 1.00:1 between the total equivalent of all epoxy groups in component A and the equivalent of active hydrogen in component B. The sources of the total equivalent of epoxy groups in component A include epoxy resin (E-51 and the second epoxy component), EPU terminal epoxy groups, flexible spacer segment components (polyether diglycidyl ether), epoxy groups in coupling dispersion component KH-560, and epoxy groups provided by GMA units in the outer layer of the nano-elastic particle reactive bridge.

[0026] Performance tests were conducted according to the following standards: tensile strength according to ASTM D638-14, using type I dumbbell specimens, with a tensile rate of 5 mm / min; flexural strength and flexural modulus according to ASTM D790-17, with a span-to-thickness ratio of 16:1 and a loading rate of 2 mm / min; notched Izod impact strength according to ASTM D256-10, using type A notch; plane strain fracture toughness K... IC With critical strain energy release rate G IC According to ASTM D5045-14, a single-sided notch bending (SENB) specimen is used; glass transition temperature T g According to ASTM E1640-18, dynamic mechanical analyzers were used to determine the temperature corresponding to the peak value of the loss factor tanδ, with a heating rate of 3℃ / min and a frequency of 1Hz. Samples for low-temperature mechanical property testing were first kept at -50℃ for 4 hours in an environmental chamber before testing. Microscopic phase structure observation was performed using a JEM-2100 transmission electron microscope (JEOL) and an S-4800 scanning electron microscope (Hitachi). To evaluate the service reliability of the material when used in exoskeleton joint components, a -50℃ / 25℃ thermal cycling test was conducted according to GB / T 2423.1—2008 and GB / T 2423.22—2012, with 100 cycles. A -50℃ low-temperature drop hammer impact test was performed on a 3mm thick, 100mm diameter disc sample according to ISO 6603-2 standard. Simultaneously, plate-shaped samples with M6 bolt holes were subjected to drop hammer impact at -50℃, followed by industrial CT inspection for hole edge crack integrity. Example 1

[0027] In component A, the mass ratio of epoxy resin, EPU, flexible spacer segment component, and nano-elastic particles is 66:24:6:4, falling within the further preferred range of claim 9. The specific composition is: 52 parts of bisphenol A type liquid epoxy resin E-51, 14 parts of phenolic epoxy resin F-44 (total epoxy resin 66 parts), 6 parts of polypropylene glycol diglycidyl ether, and EPU (M... n =3260, 24 parts of epoxy end value 0.0612eq / 100g, 4 parts of three-layer structured nano-elastic particles; 0.4 parts of KH-560 and 0.1 parts of BYK-A530 defoamer were added. Group B was composed of 12.6 parts of IPDA, 5.5 parts of polyetheramine D230 and 0.3 parts of 2-ethyl-4-methylimidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. The composite material of Example 1 was obtained by molding according to the aforementioned process and segmented curing regime. Example 2

[0028] Component A has a four-component mass ratio of 70:14:12:4, which falls within the scope of claim 9. The specific composition is: 6 parts E-515, 14 parts F-44 (70 parts total epoxy resin), 12 parts polypropylene glycol diglycidyl ether, 14 parts EPU, and 4 parts three-layer structured nano-elastic particles; plus 0.3 parts KH-560 and 0.1 parts BYK-A530 defoamer. Component B contains 13.7 parts IPDA, 6.0 parts D230, and 0.3 parts imidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. The remaining preparation process and segmented curing regime are the same as in Example 1. This example focuses on the performance under conditions of low flexible subnet density, taking values ​​near the upper limit of epoxy resin, the upper limit of flexible spacer segment components, and the lower limit of double-ended epoxy-capped polyurethane prepolymer within the scope of claim 9. Example 3

[0029] Component A has a four-component mass ratio of 56:28:10:6, which falls within the scope of claim 9. The specific composition is: 2 parts E-514, 14 parts F-44 (56 parts total epoxy resin), 10 parts polypropylene glycol diglycidyl ether, 28 parts EPU, and 6 parts three-layer structured nano-elastic particles; plus 0.5 parts KH-560 and 0.1 parts BYK-A530 defoamer. Component B contains 11.3 parts IPDA, 5.2 parts D230, and 0.3 parts imidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. The remaining preparation process and segmented curing regime are the same as in Example 1. This example uses values ​​near the upper limits of the double-ended epoxy-capped polyurethane prepolymer and the upper limit of the nano-elastic particles within the scope of claim 9 to examine the retention of static mechanical properties under conditions of high flexible subnet density and high nanoparticle content. Example 4

[0030] Group A was allocated the same as in Example 1, except that the flexible spacer segment component was replaced with an equal amount of polytetrahydrofuran diglycidyl ether instead of 6 parts of polypropylene glycol diglycidyl ether. Group B was allocated with 12.5 parts of IPDA, 5.5 parts of D230, and 0.3 parts of imidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. All other raw materials, preparation processes, and segmented curing regimes were the same as in Example 1. This example was used to investigate the effect of the type of flexible spacer segment component on low-temperature impact resistance. Example 5

[0031] In the EPU preparation process, the isocyanate component is replaced by an equivalent amount of H12MDI, resulting in an EPU with M nThe measured epoxy value was 0.0598 eq / 100g, with a value of 3339. Group A was prepared using the same proportions as in Example 1. Group B consisted of 12.6 parts IPDA, 5.5 parts D230, and 0.3 parts imidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. All other preparation processes and staged curing regimes were the same as in Example 1. This example was used to investigate the effect of alicyclic diisocyanate type on EPU performance and the low-temperature impact resistance of the final composite material. Example 6

[0032] Component A consists of four core components in the same proportions as in Example 1 (66:24:6:4); 0.4 parts of KH-560, 0.1 parts of BYK-A530 defoamer, and 5 parts of chopped carbon fiber are added. The process for the aforementioned system containing chopped reinforcing fibers is performed as follows: after high-shear dispersion of the nano-elastic particles, the defoaming and leveling components are added and vacuum defoamed for 15 minutes. The speed is then reduced to 400 rpm, and the chopped carbon fiber is added. The mixture is stirred at this low speed for 15 minutes to fully wet the fiber surface and prevent the fiber from being cut under high shear conditions, resulting in component A containing fibers. After cooling to 40°C, component B (with the same proportions as in Example 1) is added, and the mixture is stirred at low speed for 8 minutes. The mixture is then injected into a mold preheated to 50°C using a 3MPa pressure injection molding method. The segmented curing process is the same as in Example 1. This embodiment corresponds to the preferred embodiment of claim 10 containing chopped reinforcing fibers and is used to evaluate the comprehensive performance of the material when applied to exoskeleton joint side plates and other areas requiring higher bending stiffness.

[0033] Comparative Example 1 In component A, EPU was completely removed, and the reduced amount was made up by E-51 in equal mass. The specific composition is: 76 parts E-51, 14 parts F-44, 6 parts polypropylene glycol diglycidyl ether, and 4 parts three-layer structured nano-elastic particles; plus 0.4 parts KH-560 and 0.1 parts BYK-A530 defoamer. Component B contains 16.2 parts IPDA, 7.2 parts D230, and 0.3 parts imidazole, with an active hydrogen equivalent to epoxy group equivalent ratio of 1.00:1. The remaining preparation process and segmented curing regime are the same as in Example 1. This comparative example serves to demonstrate, in reverse, the necessity of the double-ended epoxy-capped polyurethane prepolymer as a core component for low-temperature impact resistance.

[0034] Comparative Example 2 The 24 parts of EPU in Example 1 were replaced with an equal amount of free -NCO-terminated polyurethane prepolymer (prepared using the same PTMG-3000 / PPG-2000 soft segments and IPDI, with the same NCO / OH ratio of 2.0, but without glycidyl end-capping, resulting in a residual -NCO content of approximately 2.6%). All other components, proportions, preparation processes, and segmented curing regimes were the same as in Example 1. It should be noted that this free -NCO-terminated prepolymer exhibits poor storage stability after mixing with other components of component A. After approximately 24 hours at 40°C, the viscosity of component A increased from approximately 2400 mPa·s to approximately 6500 mPa·s, indicating that -NCO underwent continuous side reactions with hydroxyl groups, trace amounts of moisture, and amine impurities in the system. To avoid macroscopic gelation that would prevent sample molding, this comparative example employed a fresh-mixing and immediate-use process; that is, component A was mixed with component B and cast into molds within 2 hours of preparation.

[0035] Comparative Example 3 Four parts of the three-layer structured nanoelastic particles in Example 1 were replaced with an equal amount of conventional MBS core-shell rubber particles (methyl methacrylate-butadiene-styrene copolymer, with an average particle size of approximately 150 nm, and without an epoxy-containing reactive bridge outer layer). All other components, proportions, preparation processes, and segmented curing regimes remained the same as in Example 1. This comparative example serves to demonstrate, in reverse, the necessity of the epoxy-containing reactive bridge outer layer for the chemical anchoring effect of the nanoelastic particles in the main network.

[0036] Comparative Example 4 The ratio of components A and B, raw materials, and the initial preparation process are the same as in Example 1, except that the segmented curing regime is replaced with a conventional single-stage heating curing regime: the temperature is directly increased from room temperature to 120°C at a heating rate of 2°C / min, held at that temperature for 4 hours, and then naturally cooled to room temperature for demolding. This comparative example is used to demonstrate, in reverse, the necessity of the segmented curing regime for the uniformity of nanoparticle dispersion, phase morphology uniformity, and final low-temperature impact resistance.

[0037] The main mechanical and thermal properties of the composite materials obtained in Examples 1-6 and Comparative Examples 1-4 are listed in Table 1, and the service reliability evaluation results related to the application of exoskeleton joint components are listed in Table 2.

[0038] Table 1. Test results of main mechanical and thermal properties of Examples 1-6 and Comparative Examples 1-4 serial number -50℃ Notched Izod Impact Strength (J / m) <![CDATA[-50℃ K IC (MPa·m 1 / 2 )]]> <![CDATA[-50℃ G IC (J / m²)]]> Room temperature tensile strength (MPa) Room temperature flexural strength (MPa) Room temperature flexural modulus (GPa) Room temperature elongation at break (%) <![CDATA[T g (℃)]]> Example 1 124 1.76 378 67.5 113.4 2.86 7.6 107 Example 2 95 1.48 252 72.8 122.5 3.04 5.9 113 Example 3 138 1.85 408 60.2 102.6 2.58 9.4 95 Example 4 130 1.79 392 66.4 112.8 2.82 8.0 104 Example 5 121 1.74 369 68.7 115.6 2.92 7.2 109 Example 6 138 1.91 418 88.4 154.2 3.52 4.6 108 Comparative Example 1 32 0.78 92 78.5 131.6 3.31 3.4 117 Comparative Example 2 58 1.08 152 55.4 91.2 2.34 5.6 86 Comparative Example 3 74 1.24 185 59.3 97.5 2.45 5.9 97 Comparative Example 4 71 1.20 175 62.8 105.7 2.66 5.2 99 Table 2. Service reliability evaluation results of exoskeleton joint components in Examples 1 and 6 and Comparative Examples 1-4 serial number -50℃ drop hammer impact penetration energy (J) -50℃ bolt hole edge crack length (mm, after 5J drop hammer impact) Room temperature flexural strength retention rate (%) after 100 cycles of thermal cycling at -50℃ and 25℃ After 100 thermal cycles at -50℃ / 25℃, the retention rate of Izod impact strength at -50℃ is as follows (%). Area of ​​interface peeling after metal insert coating is dropped at low temperature (-50℃) (1.5m) (%) Example 1 18.4 0.9 94.8 91.2 0 Example 6 22.6 0.5 94.2 91.8 0 Comparative Example 1 4.8 8.2 (Penetration) 87.5 70.5 19.2 Comparative Example 2 9.4 4.5 76.8 62.4 13.6 Comparative Example 3 11.8 3.7 83.2 70.8 9.2 Comparative Example 4 10.7 4.0 81.5 67.6 10.4 As can be seen from the data in Tables 1 and 2, the notched Izod impact strength of the materials obtained in Examples 1 to 6 at -50℃ consistently falls within the target window of 90 J / m to 140 J / m, and the plane strain fracture toughness K IC Falling into 1.4 MPa·m 1 / 2 ~1.9MPa·m 1 / 2 Range, critical strain energy release rate G IC It falls within the range of 250J / m² to 420J / m², showing a significant advantage in low-temperature impact resistance compared to comparative examples 1 to 4. Meanwhile, the introduction of double-ended epoxy-terminated polyurethane prepolymer, flexible spacer segment components, and three-layer structured nanoelastic particles inevitably leads to a certain decrease in the room temperature tensile strength, flexural strength, and flexural modulus of the material compared to the unmodified epoxy reference system (Comparative Example 1). Taking Example 1 as an example, the room temperature tensile strength decreased from 78.5 MPa in Comparative Example 1 to 67.5 MPa (a decrease of about 14%), the flexural strength decreased from 131.6 MPa to 113.4 MPa (a decrease of about 14%), and the flexural modulus decreased from 3.31 GPa to 2.86 GPa (a decrease of about 14%). However, compared with Comparative Example 2 (tensile strength decrease of about 29%), Comparative Example 3 (tensile strength decrease of about 24%), and Comparative Example 4 (tensile strength decrease of about 20%), the decrease in static mechanical properties of the embodiment of the present invention is significantly controlled, and the glass transition temperature remains stable above 95°C. This verifies the balance achieved by the synergistic design described in the present invention between "improving low-temperature toughness" and "controlling static stiffness loss".

[0039] Example 1 falls within the more preferred range defined in claim 9, achieving an optimal balance between the material's low-temperature impact toughness, static strength, and glass transition temperature. In Example 2, because the EPU content is near the lower limit of the main range of claim 9 and the flexible spacer segment component is near the upper limit, the flexible subnet density is relatively low, and the rigid mainnet density is relatively high. Therefore, the low-temperature notched Izod impact strength decreases to 95 J / m, but correspondingly, the room temperature tensile and flexural moduli increase slightly, and the glass transition temperature also increases by 6°C compared to Example 1, demonstrating the effect of the flexible component content on stiffness / T. g Maintaining coordination between them. In Example 3, because the amounts of EPU and nano-elastic particles are both taken near the upper limit of the main range of claim 9, the low-temperature impact resistance is further improved to 138 J / m and 1.85 MPa·m. 1 / 2 However, the room temperature tensile strength decreased to 60.2 MPa, and the flexural modulus decreased to 2.58 GPa. gThe temperature was lowered to 95°C, consistent with the rigid recovery mechanism described in claim 2 and the upper limit of dosage set in claim 9. In Example 4, polypropylene glycol diglycidyl ether was replaced with polytetrahydrofuran diglycidyl ether. Because the polytetrahydrofuran segment has higher segment relaxation activity in the low-temperature region compared to the polypropylene glycol segment, but its… The unit density is slightly higher, thus slightly improving the low-temperature impact resistance, while T g A slight decrease of 3°C is within the preferred range of claim 5, and the difference is a reasonable fluctuation. In Example 5, after replacing IPDI in the EPU with H12MDI, the rigidity of the hard segment slightly increased, and the material's T... g The retention capacity was slightly improved (from 107°C to 109°C), and the low-temperature impact resistance remained within the optimal range, proving that the alicyclic diisocyanates described in claim 3 are all applicable. In Example 6, after introducing short-cut carbon fibers and employing a process sequence of high-shear dispersion of nanoparticles followed by low-speed fiber impregnation and then pressure injection molding, cross-sectional observation showed that the fiber length remained basically within the range of 2mm to 3mm, with no significant cutting. The fibers played a bridging and load-sharing role in the matrix, further improving the room-temperature flexural strength and flexural modulus. Furthermore, due to the synergistic contribution of the fiber pull-out energy dissipation mechanism, the low-temperature notched Izod impact strength increased to 138 J / m. IC Increased to 1.91 MPa·m 1 / 2 This verifies the applicability of the optional chopped reinforcing fiber component in claim 10 to parts requiring higher bending stiffness, such as the exoskeleton joint side plate, and also demonstrates the engineering feasibility of the feeding sequence and pressure injection molding process used.

[0040] In Comparative Example 1, due to the complete removal of the EPU component, the main network lacks chemically linked flexible segments, and the material essentially reverts to the typical mechanical behavior of brittle epoxy at -50℃: the notched Izod impact strength is only 32 J / m, K IC Only 0.78 MPa·m 1 / 2Furthermore, the bolt hole edge developed a through-crack under a 5J impact, and the interface peeling area of ​​the metal insert-coated part reached 19.2% after low-temperature drop. This result directly proves the irreplaceable nature of the double-ended epoxy-terminated polyurethane prepolymer described in claim 1 as a core component. That is, relying solely on the flexible spacer segment component and nano-elastic particles, it is impossible to form continuous low-temperature activatable flexible segments in the main network. The plastic zone at the crack tip is insufficient, and rapid brittle fracture still occurs when subjected to transient impact. Comparative Example 2 used a free -NCO-terminated polyurethane prepolymer to replace EPU. Because the -NCO end groups cannot quantitatively embed into the main network via controlled ring-opening addition with amine curing agents like epoxy groups, they react with trace amounts of hydroxyl, moisture, and amine groups in the system before curing to generate localized urea bonds and branched structures, leading to an imbalance in the crosslinking density distribution of the main network. Simultaneously, the viscosity of the -NCO-terminated prepolymer increased significantly during the storage stage of component A, resulting in decreased component dispersion uniformity. Ultimately, the polyurethane component in the material exists as a relatively coarse, non-reactive embedded dispersed phase, which debonds from the matrix interface under low temperature and high stress. Therefore, the low-temperature notched Izod impact strength is only 58 J / m, and the residual -NCO reaction leads to a decrease in network crosslinking density. g The temperature dropped to 86℃, reflecting the dual advantages of the epoxy-end-capped structure described in claim 1 over the free isocyanate end group in terms of both process and performance. Comparative Example 3 used ordinary MBS core-shell rubber particles to replace the three-layer structured nanoelastic particles. Since the MBS particles do not have a reactive bridge outer layer containing epoxy reactive groups on their surface, they only interact with the matrix through physical van der Waals forces. Under low temperature and high stress conditions, the particle-matrix interface preferentially debonds and evolves into a defect source, resulting in a low-temperature notched Izod impact strength of only 74 J / m. Furthermore, the MBS particles have relatively high overall elasticity and lack rigid core support, leading to a decrease in room temperature tensile strength and flexural modulus to 59.3 MPa and 2.45 GPa, respectively. This verifies the necessity of the rigid core-soft shell-reactive bridge three-layer structure described in claim 1 for synergistically achieving low-temperature toughening and modulus maintenance. Comparative Example 4 employed a one-step temperature-curing process. Due to the initial rapid decrease in viscosity of the multi-component A system containing EPU, flexible spacer segments, and nano-elastic particles as the temperature rose, followed by a rapid rebound due to the reaction, the nano-elastic particles lacked dispersion relaxation time within this low viscosity window, resulting in gravitational sedimentation and aggregation. Transmission electron microscopy revealed clusters of nanoparticles with a scale of approximately 300 nm to 600 nm, as well as locally enriched polyurethane strip-like discontinuous phases. The overall morphological uniformity was significantly worse than that of the sample in Example 1. Therefore, the low-temperature notched Izod impact strength of Comparative Example 4 was only 71 J / m. IC Reduced to 1.20 MPa·m 1 / 2 This demonstrates that the segmented curing system plays an irreplaceable role in the engineering control of the dispersion uniformity and phase morphology uniformity of nanoparticles.

[0041] Further analysis from the perspective of microstructure and mechanism: SEM observation of the fracture surface of Example 1 showed that the -50℃ impact fracture surface exhibited typical multi-level energy dissipation characteristics, with high surface roughness, and a large number of cavitation pits originating from nano-elastic particles, densely distributed shear yield bands, and crack deflection traces generated by the traction of polyurethane-enriched phases. TEM observation showed that the polyurethane-enriched phase was uniformly distributed in the epoxy main network, with characteristic sizes mainly distributed in the range of 150nm to 300nm. The three-layer structure nano-elastic particles were well dispersed in the matrix, and no obvious agglomeration was observed. The formation of this multi-stage energy-consuming morphology is based on the following mechanism: the terminal epoxy groups of the double-epoxy-terminated polyurethane prepolymer covalently embed into the epoxy main network through a ring-opening addition reaction with an amine curing agent. Due to the difference in solubility parameters between the polyurethane soft segments (containing polytetrahydrofuran glycol and a small amount of polypropylene glycol) and the epoxy main network, reaction-induced phase separation occurs in the system during the curing process, forming a covalently embedded hybrid hybrid network structure with epoxy as the continuous phase and polyurethane as the dispersed phase. The pregelation stage of the segmented curing regime provides sufficient dispersion and relaxation time for nanoparticles during the low viscosity change window to avoid agglomeration. The intermediate temperature stage allows the epoxy main network to gradually reach the gel point and locks in the uniform microphase separation morphology during formation. The post-curing stage replenishes the crosslinking density of the main network. In the flexible spacer segment component, polyether segments are inserted between adjacent rigid aromatic links. Based on the steric hindrance effect and the principle of rotational barrier within the main chain, the internal rotational barrier of the C-O-C ether bond is significantly lower than that of the aromatic ring-methylene linkage in the epoxy main resin. Therefore, under the same low-temperature conditions, it can still retain a certain chain relaxation ability, alleviating stress concentration at geometrically discontinuous locations such as bolt hole edges and corners. The silica core in the three-layer structured nanoelastic particles maintains the static modulus, and the polybutyl acrylate elastic shell remains in a highly elastic state at -50℃. During impact, cavitation preferentially occurs, inducing the formation of shear yield bands in the surrounding matrix. The epoxy groups in the outer methyl methacrylate-glycidyl methacrylate copolymer synergistically form covalent chemical bonds with the terminal epoxy groups of the amine curing agent and the double-ended epoxy-terminated polyurethane prepolymer, stably anchoring the particles in the hybrid hybrid network and preventing the particles from being pulled out as a whole under low-temperature, high-stress conditions.

[0042] As can be seen from the above embodiments and comparative data, the impact-resistant epoxy-polyurethane hybrid composite material of the present invention, through the synergistic design of double-ended epoxy-terminated polyurethane prepolymer, flexible spacer segment components, and nano-elastic particles with a three-layer structure of rigid core-soft shell-reactive bridge, and with the precise control of the dispersion uniformity and phase morphology uniformity of nanoparticles by a segmented curing regime, significantly improves the material's impact resistance and crack propagation resistance in extremely cold environments of -50℃. At the same time, the decrease in static stiffness, glass transition temperature, and process stability is controllable, meeting the service requirements of components such as joint side plates, bearing housing outer walls, limiting blocks, and metal insert outer buffer layers of exoskeletons such as knee, ankle, and hip joints.

[0043] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments, characterized in that, The impact-resistant epoxy-polyurethane hybrid composite material includes component A and component B; Component A includes epoxy resin, double-ended epoxy-terminated polyurethane prepolymer, flexible spacer segment components, and nano-elastic particles with a three-layer structure of rigid core-soft shell-reactive bridge. Component B includes an amine curing agent; The prepolymer with epoxy end capping has epoxy groups at both ends, and is obtained by reacting polyether polyol soft segments, diisocyanate components and glycidyl ether. The nanoelastic particles, from the inside out, consist of an inorganic rigid core, an elastic polymer shell, and a reaction bridge outer layer containing epoxy reactive groups.

2. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, The epoxy resin includes a first epoxy component and a second epoxy component; the first epoxy component is a bisphenol A type liquid epoxy resin, and the epoxy equivalent of the first epoxy component is 180 g / eq to 195 g / eq; the second epoxy component is selected from at least one of phenolic epoxy resin and bisphenol F type epoxy resin.

3. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, The polyether polyol soft segment comprises polytetrahydrofuran diol and polypropylene glycol, and based on the total mass of the polyether polyol soft segment, the mass percentage of polytetrahydrofuran diol is 60% to 85%, and the mass percentage of polypropylene glycol is 15% to 40%; the diisocyanate component is selected from at least one of isophorone diisocyanate and dicyclohexylmethane diisocyanate.

4. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 3, characterized in that, The number-average molecular weight of the double-epoxy-terminated polyurethane prepolymer is 3,000 to 8,000, and the end-epoxy value is 0.025 eq / 100g to 0.067 eq / 100g. The end-epoxy value and the number-average molecular weight satisfy the double-end functionality relationship of end-epoxy value (eq / 100g) = 200 / number-average molecular weight. Furthermore, the infrared spectrum of the double-epoxy-terminated polyurethane prepolymer does not show a characteristic absorption peak of isocyanate at 2270 cm⁻¹.

5. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, The flexible spacer segment component is selected from at least one of polypropylene glycol diglycidyl ether and polytetrahydrofuran diglycidyl ether.

6. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, The inorganic rigid core is silicon dioxide; the elastic polymer shell is polybutyl acrylate; and the outer layer of the reaction bridge is a copolymer of methyl methacrylate and glycidyl methacrylate.

7. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 6, characterized in that, The average particle size of the inorganic rigid core is 60 nm to 200 nm; the thickness of the outer layer of the reactive bridge is 2 nm to 10 nm; and the ratio of the thickness of the elastic polymer shell to the average particle size of the inorganic rigid core is 0.04 to 0.

12.

8. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, Component B includes isophorone diamine, polyetheramine, and imidazole accelerators; the ratio of active hydrogen equivalent in component B to epoxy equivalent in component A is 0.95:1 to 1.05:

1.

9. The impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments according to claim 1, characterized in that, In component A, the mass ratio of the epoxy resin, the double-ended epoxy-terminated polyurethane prepolymer, the flexible spacer segment component, and the nano-elastic particles is (50 to 70): (12 to 28): (4 to 12): (1 to 6). Component A further includes a coupling dispersion component and an antifoaming and leveling component; the coupling dispersion component is selected from at least one of γ-glycidyl etheroxypropyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; Component A further includes chopped reinforcing fibers, which are selected from at least one of chopped carbon fibers, aramid slurry and basalt short fibers.

10. The application of the impact-resistant epoxy-polyurethane hybrid composite material suitable for extremely cold environments, as described in any one of claims 1 to 9, in the manufacture of exoskeleton joint components, characterized in that, The exoskeleton joint components are selected from at least one of the following: joint side plates of the exoskeleton knee, ankle, or hip joints; outer wall of the bearing seat; limiting block; cable guide wheel housing; reducer end cover; sensor protective cover; reinforced area around bolt holes; and outer buffer layer covering metal hinges.