Composite sponge for automobile engine hood and preparation method of composite sponge

Abstract

The invention relates to a composite sponge for an automobile engine hood and a preparation method of the composite sponge. The composite sponge is prepared from the following components in parts by weight: 100 to 130 parts of polyurethane prepolymer, 20 to 30 parts of bismaleimide and furyl polyether copolymer, 12 to 20 parts of 6-(diphenoxy phosphine)-6H-dibenzoxphosphine or a derivative thereof, 12 to 20 parts of ammonium polyphosphate, 8 to 15 parts of nano silicon dioxide or montmorillonite, 12 to 20 parts of self-healing microcapsule, 1 to 3 parts of azodicarbonamide and 1 to 2 parts of zinc stearate. And 5 to 8 parts of a diisocyanate crosslinking agent. Wherein the self-healing microcapsule takes an aromatic ester or epoxy prepolymer as a core material and a urea formaldehyde condensate as a shell material, and the particle size is 20-80 microns. All the components are compounded under a specific process path to form a foam network structure with high-temperature shape memory and self-healing functions and efficient flame retardance, and the foam network structure is suitable for thermal protection application of an automobile engine compartment under complex working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of sponges, and more particularly to a composite sponge for an automobile hood. Background Art

[0002] At present, sponge-like heat insulation materials widely used in automobile engine hoods are mainly polyurethane foams, and their main functions include heat insulation, vibration absorption and noise attenuation. However, traditional polyurethane foam materials have a series of structural and performance defects under high-temperature heat fields and long-term vibration environments: on the one hand, the materials are prone to irreversible compression deformation and collapse under long-term hot pressing or mechanical stress, affecting their dimensional stability and buffering ability; on the other hand, their thermal stability and flame retardancy are limited, and they are prone to rapid decomposition and combustion when exposed to high temperatures or open flames, making it difficult to meet the high safety-level flame retardancy requirements of the engine compartment. In addition, during actual service, the materials often suffer from mechanical property degradation due to microscopic defects such as surface damage and crack initiation, but traditional foam materials do not have the ability of active repair and are prone to early failure.

[0003] Therefore, there is an urgent need for a new type of composite foam material to meet the comprehensive requirements of modern automotive power systems for high temperature resistance, flame retardancy, safety and service life. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a composite sponge for an automobile hood and a preparation method thereof.

[0005] A composite sponge for an automobile hood, the composite sponge comprising the following components in parts by weight: 100-130 parts of polyurethane prepolymer; 12-20 parts of bismaleimide and furan-based polyether copolymer; 12-20 parts of 6-(diphenoxyphosphine)-6H-dibenzophosphole or its derivatives; 20-30 parts of ammonium polyphosphate; 8-15 parts of nano-silica or montmorillonite; 20-30 parts of self-healing microcapsules; 1-3 parts of azodicarbonamide; 1-2 parts of zinc stearate; 5-8 parts of diisocyanate crosslinking agent; The self-healing microcapsules are formed by a urea-formaldehyde condensation reaction with an aromatic ester or epoxy prepolymer as the core material to form a shell-coated structure, and the particle size is 20-80 μm.

[0006] Based on a single polyurethane structure, the above-mentioned composite sponge material constructs a multifunctional composite foam structure with triple properties of thermally activated memory recovery, self-healing repair, and high flame retardant protection by introducing a dynamic reversible copolymer, self-healing microcapsules, and a phosphorus-phosphorus synergistic flame retardant system, combined with nanoparticle interface regulation and efficient foaming adjustment. This solves the problem of performance instability of traditional polyurethane foams under high temperature, mechanical impact, and fire risks, and provides a new systematic functional integration material solution for the thermal protection structure of automotive engine hoods.

[0007] Further, the preparation method of the polyurethane prepolymer is as follows: 1) Poly(tetramethylene ether) glycol with a number average molecular weight of 1800 - 2200 is dehydrated under vacuum at 100 °C for 1 h, and then dried by introducing nitrogen at 110 °C for another 0.5 h, controlling the water content in the system to be no higher than 0.05%. 2) The dehydrated poly(tetramethylene ether) glycol obtained in step 1) is cooled to 70 °C, and 4,4'-diphenylmethane diisocyanate is added under nitrogen protection, so that the molar ratio of isocyanate groups to hydroxyl groups is 1.65 - 1.75:1, and stirred to form a homogeneous reaction system. 3) Dibutyltin dilaurate catalyst is added to the system obtained in step 2), and the catalyst dosage is 0.05 - 0.1 parts based on the weight of poly(tetramethylene ether) glycol, and the reaction is carried out at 80 °C for 1.5 - 2.0 h while maintaining the stirring rate at 300 - 500 rpm. 4) The reaction end point is monitored by isocyanate titration method, and the reaction is terminated when the mass content of free isocyanate groups in the system reaches 6.5% - 7.5% to obtain the polyurethane prepolymer.

[0008] The present invention first introduces parameter optimization design in the preparation process of the polyurethane prepolymer, and improves the structural coupling degree between the prepolymer and each functional component by regulating multiple process steps.

[0009] Specifically, a two-step dehydration process is adopted in the prepolymer synthesis stage. First, vacuum dehydration is carried out at 100 °C for 1 hour, and then nitrogen is introduced at 110 °C for drying for 0.5 hour to reduce the water content in the system to no higher than 0.05%, so as to ensure that the isocyanate group does not undergo hydrolysis reaction during the subsequent reaction process, causing by-product bubbles and cell structure defects. Subsequently, polytetramethylene ether glycol with a number average molecular weight of 1800-2200 and 4,4'-diphenylmethane diisocyanate are subjected to a prepolymerization reaction under a nitrogen atmosphere, controlling the molar ratio of NCO to OH to be 1.65:1-1.75:1, and fully mixing evenly at 70 °C. 0.05-0.1 parts by mass of dibutyltin dilaurate catalyst is added at 80 °C and reacted for 1.5-2.0 hours. Finally, the content of free isocyanate groups is controlled to be 6.5%-7.5% by titration method to obtain a shape memory polyurethane prepolymer with moderate reaction activity, regular molecular structure and controllable subsequent foaming.

[0010] When the optimized polyurethane prepolymer is coordinated with the self-healing microcapsules, it has good interfacial compatibility and thermal response window matching characteristics. The microcapsules used have aromatic esters or epoxy prepolymers as the core material and urea-formaldehyde resin as the shell material, and the particle size is controlled between 20 and 80 microns. The polar structure of the shell material is compatible with the main chain of the polyether-type prepolymer, enabling the microcapsules to be evenly dispersed in the matrix without agglomeration. At the same time, the microcapsule release temperature range is about 90-120 °C, which highly coincides with the shape memory response temperature window (90-150 °C) of the prepolymer, making the microscopic repair behavior at the crack occur synchronously with the deformation recovery of the foam body, realizing the synchronous self-adaptive closure and structural rebound under thermal triggering.

[0011] In addition, the prepolymer also forms a good interfacial physical anchoring and thermal decomposition synergistic mechanism with the phosphorus-based flame retardant. DOPO derivatives provide phosphorylated intermediates at high temperatures to guide the formation of carbon layers, while ammonium polyphosphate releases polyphosphoric acid and ammonia during pyrolysis, synergistically forming an intumescent flame-retardant carbon shell structure. The residual NCO groups in the optimized prepolymer can undergo boundary bonding with the polar sites on the surface of ammonium polyphosphate, improving the dispersion stability of the phosphorus-based flame-retardant components in the matrix, enhancing the uniformity and persistence of the carbon layer, and improving the smoke suppression, oxygen isolation and thermal resistance performance of the material in a high-temperature combustion environment.

[0012] The present invention further introduces surface-modified nano-silica or montmorillonite with a particle size of 20-50 nm as a structural stability enhancing component. By forming hydrogen bond adsorption or physical embedding with the polar segments of the prepolymer, it can assist in constructing a local auxiliary network structure, enhancing the strength and thermal stability of the cell walls; at the same time, the nanoparticles can act on the bubble nucleation and cell expansion interfaces, and under the action of azodicarbonamide blowing agent and zinc stearate cell expansion aid, form a delicate and uniform cell distribution, improving the resilience, compression recovery ability and heat insulation performance of the foam material.

[0013] Through the coordinated parameter control of the above polyurethane prepolymer preparation method and the interface and reaction timing coupling structure formed between the self-healing component, flame retardant component, and nano-enhancing component in the composite system, the composite sponge material prepared by the present invention has achieved multi-dimensional breakthroughs in performance. After testing, the thermal trigger shape recovery rate of this material can reach more than 95% at 100 °C, the permanent deformation rate under the condition of compression at 80 °C for 24 hours is less than 8%, and the mechanical strength recovery is more than 80% within 48 hours after the crack area is formed; at the same time, the oxygen index test result is more than 30%, and it reaches V-0 level in the UL-94 vertical burning test, showing excellent flame retardant properties and comprehensive stability.

[0014] Further, the mass ratio of 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivative to ammonium polyphosphate is 1:1.8 to 1:2.2. The two are subjected to hot melt mixing treatment at 180 °C for 30 to 60 minutes and then cooled and crushed into solid particles, and the solid particles are used to be incorporated into the composite material before foaming.

[0015] Pre-mixing 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivative with ammonium polyphosphate at a mass ratio of 1:1.8 to 1:2.2, and carrying out hot melt compounding at 180 °C for 30 to 60 minutes, and then cooling and crushing to obtain flame retardant solid particles, effectively optimizing the synergistic pyrolysis behavior between the phosphorus-based flame retardants. During the hot melt pretreatment process, the phosphorus-oxygen structure of the DOPO derivative undergoes interfacial intercalation and preliminary cross-linking with the polyphosphate chain of ammonium polyphosphate, which is beneficial to the formation of a denser and more complete carbonized skeleton, reducing the migration and delamination phenomena of the flame retardant during the compounding process, and improving the dispersion uniformity of the flame retardant in the polyurethane matrix. This treatment method significantly enhances the smoke suppression, drip suppression, and heat shielding capabilities of the foam material in the combustion state.

[0016] Further, ammonium polyphosphate reacts with γ-aminopropyltriethoxysilane at 70-90 °C for 1-2 hours before the hot melt mixing treatment, and the pH value of the reaction system is controlled at 4.5-6.0, and the modified ammonium polyphosphate particles are used for the hot melt mixing treatment.

[0017] By using γ-aminopropyltriethoxysilane to carry out surface modification treatment on ammonium polyphosphate before the above hot melt compounding, an organosilane coating structure is formed under the conditions of 70-90 °C and pH of 4.5-6.0. This modification strategy introduces organosilane groups on the surface of ammonium polyphosphate, significantly enhancing its interfacial affinity and reaction compatibility in the organic foam system, and reducing the agglomeration and precipitation phenomena of the flame retardant caused by polarity differences. At the same time, the organosilicon structure has excellent thermal stability and carbonization induction ability, and not only participates in the carbonization reaction during combustion, but also synergizes with the phosphorus-phosphorus flame retardant system to further enhance the density and continuity of the flame retardant carbon layer of the foam material.

[0018] Furthermore, before being added to the composite material, the nano-silica or montmorillonite is coated with a urethane group prepolymer, which is prepared by reacting a small molecule chain extender containing an isocyanate group with a hydroxyl-terminated polyether at 60-80 °C for 1-2 hours.

[0019] By performing surface coating treatment of inorganic nanoparticles such as nano-silica or montmorillonite with a urethane group prepolymer, significant improvement in structural stability and interfacial synergistic enhancement have been achieved in the composite foam material. Due to the strong surface polarity of inorganic particles themselves, it is difficult for them to be uniformly dispersed in the hydrophobic polyurethane system, and problems such as agglomeration, interfacial detachment or stress concentration are likely to occur, thereby weakening the overall mechanical properties and flame retardancy of the foam. By introducing a prepolymer coating layer with a matching polar structure, the wettability and adhesion of the particles in the polyurethane prepolymer have been significantly improved, enabling them to be stably embedded in the organic network structure at the microscale, avoiding particle detachment and interfacial failure, and ensuring the stable growth of the cell structure.

[0020] Secondly, the urethane structure in the coating layer contains multiple polar interaction points, such as hydrogen bond donors / acceptors and flexible chain segments, which can migrate directionally to the cell wall interface region during the foaming and expansion process and participate in the construction of the cell wall structure in the form of network anchoring. This "confined enhancement" mechanism enables the particles to preferentially accumulate on the cell surface rather than being randomly distributed inside the bubbles, thereby effectively improving the structural integrity and thermal stability of the cell wall, making the pore size of the final foam material more uniform, enhancing the hot pressing deformation ability, and possessing more excellent mechanical buffering and energy absorption properties.

[0021] In addition, the urethane structure has a certain tendency of thermal crosslinking under high-temperature conditions. During the combustion process of the foam, this type of structure coated on the surface of the nanoparticles can form a local thermal crosslinking network in cooperation with the carbon layer, thereby enhancing the continuity, adhesiveness and density of the carbon layer. The spatial structure of the nanoparticles and the co-configuration morphology of the carbon layer residue can significantly enhance the heat erosion resistance of the carbonized skeleton, effectively inhibit flame propagation and oxygen exchange, and improve the overall flame retardancy level.

[0022] Furthermore, the preparation method of the urethane group prepolymer includes the following steps: 1) Add 40-60 parts by mass of the hydroxyl-terminated polyether to a reaction vessel, stir and heat up at 70-80 °C, then dropwise add 20-30 parts by mass of a small molecule chain extender containing two isocyanate groups, and react for 1-2 hours under a nitrogen atmosphere to generate an intermediate prepolymer containing free isocyanate groups; 2) Add 10 - 20 parts by mass of a functional small molecule with a secondary amine or primary amine structure to the reaction system obtained in step 1), and continue the reaction at 60 - 70 °C for 0.5 - 1 hour. Control the molar ratio of isocyanate groups to amino groups to be 1.05∶1 - 1.2∶1, so that the residual amount of free isocyanate is less than 0.5%.

[0023] By introducing a small amount of amine small molecules under the reaction conditions of a specific chain extender and a hydroxyl - terminated polyether, a flexible prepolymer containing urethane groups is formed. This prepolymer has a low residual NCO content and good molecular flexibility, and is suitable for coating nanoparticles under low - temperature conditions. The prepared coating layer forms a continuous coating film on the surface of the nanoparticles, improving the dispersion stability of the particles in the polyurethane system and the interfacial adaptation ability of the cell walls. During the foaming and combustion processes, this structure can maintain the physical anchoring state of the particles in the interfacial region, enhance the binding force between the particles and the carbon layer and the heat conduction inhibition performance, and further improve the overall thermal stability and structural integrity of the composite material.

[0024] Furthermore, the molar ratio of maleimide to furan in the maleimide - furan - based polyether copolymer is 1 - 1.2∶1.

[0025] The molar ratio of maleimide to furan - based polyether is limited to 1∶1 - 1.2∶1, achieving precise control of the thermally controllable cross - link density in the reversible Diels–Alder structure. This ratio window is in the optimal balance range of the reversible reaction rate and the degree of cross - linking, and can rapidly break and recombine the bonding structure under the thermal activation conditions of 100 - 130 °C, enabling the crack - closing process to have good timeliness and stress - release ability, avoiding material embrittlement caused by excessive cross - linking, and preventing recovery lag caused by insufficient continuity of the repair network under low cross - link density. More notably, when this dynamic copolymer network acts simultaneously with the polyurethane prepolymer backbone and the microcapsule core material, its thermal response range and elastic window are highly compatible, establishing a coordinated reaction path for micro - self - healing and macro - shape recovery in the composite foam system, and further strengthening the structural integrity and multi - scale repair ability of the material in a high - temperature stress environment.

[0026] Furthermore, the mass ratio of azodicarbonamide to zinc stearate is 1∶0.8 - 1.5. After premixing them evenly at 70 - 75 °C, they are added to the system.

[0027] The mass ratio of azodicarbonamide to zinc stearate is controlled to be 1:0.8 - 1:1.5, and addition is carried out by premixing at 70 - 75 °C, effectively avoiding the problems of intense local reaction and non-uniform cell expansion caused by the one-step addition of traditional blowing agents. As a gas release source, azodicarbonamide has a moderate release rate under controlled conditions, while zinc stearate delays the closing speed of cell walls through its dual functions of lubrication and pore expansion, making the overall cell structure more uniform and the cell walls denser, effectively improving the compression resilience and dimensional retention rate of the composite sponge. Especially under the synergistic regulation with the distribution of nano-fillers and the morphology of thermal flame-retardant particles, the uniformity of this cell structure and the porous mechanical transmission path are further optimized, laying a stable foundation for the improvement of the continuity of the subsequent carbon layer structure and the energy dissipation capacity.

[0028] Furthermore, the thermal response temperature range among the bismaleimide, furan-based polyether copolymer, self-healing microcapsules, and polyurethane prepolymer is controlled at 90 - 130 °C, and the mass ratio of self-healing microcapsules to bismaleimide and furan-based polyether copolymer is 1 - 1.5:1.

[0029] By uniformly defining the thermal response temperature range of the bismaleimide - furan copolymer, self-healing microcapsules, and polyurethane prepolymer at 90 - 130 °C and stipulating the mass ratio of microcapsules to copolymer as 1:1 - 1.5:1, the dynamic coordination of the microscopic repair reaction and the macroscopic structure recovery process is achieved. This setting enables the self-healing reaction and the shape memory behavior to be synergistically triggered under the same thermal field conditions, thus avoiding the phenomenon of "the structure has rebounded but microcracks still remain" in traditional composite self-healing foams, ensuring the overall recovery integrity and multi-cycle repeatability of the material under thermal shock conditions. In addition, the copolymer provides thermal trigger sites as a reversible network, and the core material of the microcapsules provides a dispersed repair medium. The regulation of the mass ratio of the two not only ensures the spatial coverage rate during the microscopic repair process but also maintains the mechanical continuity and elastic matching of the overall foam; in the overall configuration with the flame-retardant system and the foaming structure, it also shows a high degree of synchronization in time and space.

[0030] A preparation method of a composite sponge for an automobile engine hood, comprising the following steps: S1: Weigh raw materials in proportion, including polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives, ammonium polyphosphate, nano-silica or montmorillonite, self-healing microcapsules, azodicarbonamide, zinc stearate, and diisocyanate cross-linking agent; S2: Mix the 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives with ammonium polyphosphate according to a mass ratio of 1:1.8 - 1:2.2, and melt and mix evenly under heating conditions, keep warm for 30 - 60 minutes and then cool and crush to obtain flame-retardant solid particles; S3: Place nano-silica or montmorillonite in a reaction system at 60 - 80 °C, add a urethane group prepolymer obtained by reacting a hydroxyl-terminated polyether with a chain extender containing an isocyanate group, stir and coat for 1 - 2 hours to obtain surface-coated nanoparticles, and control the addition amount to be 2% - 5% of the total mass of the composite material; S4: Mix the polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, self-healing microcapsules, the flame retardant particles obtained in S2, and the coated nanoparticles obtained in S3 evenly at 60 - 70 °C, then add azodicarbonamide and zinc stearate, and continue to stir at 70 - 75 °C for 3 - 5 minutes to form a foaming mixture; S5: Inject the foaming mixture into a mold, foam and mold at 100 - 110 °C, and thermally cure at 110 - 130 °C for 1 - 2 hours to obtain the composite sponge.

[0031] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: (1) Through the synergistic construction of a thermally responsive reversible crosslinking network composed of shape memory polyurethane, self-healing microcapsules, and bismaleimide - furan-based polyether, the material can achieve self-structure recovery and crack closure in an environment of 90 - 130 °C, solving the problems of traditional foam structure fatigue and irreversible microcracks.

[0032] (2) The phosphorus-phosphorus synergistic flame retardant structure (6-(diphenoxyphosphino)-6H-dibenzophosphole oxide and ammonium polyphosphate) forms a dense flame retardant solid particle after hot melt compounding, combined with the organosilicon surface modification process, endowing the material with excellent carbon layer continuity and smoke suppression and flame retardant properties, reaching V-0 grade in the UL-94 test, and the oxygen index ≥ 30%.

[0033] (3) The nanoparticles coated with the urethane group prepolymer are evenly distributed around the cell walls, forming a local confinement enhancement network, effectively inhibiting cell collapse, improving dimensional stability and compression resistance, and assisting in constructing a highly dense carbon layer during combustion to improve the overall thermal stability.

[0034] (4) The thermal response ranges of each functional component (self-healing microcapsules, DA copolymer, polyurethane prepolymer) match 90 - 130 °C, realizing the synchronous action of macroscopic rebound and microscopic crack repair under thermal triggering, significantly improving the structure recovery ability and service life of the material during multiple thermal cycles. Specific embodiments

[0035] The present invention will be described in detail below with reference to the embodiments.

[0036] Example 1 A composite sponge for an automobile hood, comprising the following components in parts by weight: 100 parts of polyurethane prepolymer; 15 parts of bismaleimide and furan-based polyether copolymer; 12 parts of 6-(diphenoxyphosphino)-6H-dibenzophosphole; 24 parts of modified ammonium polyphosphate; 8 parts of nano-silica; 20 parts of self-healing microcapsules; 1 part of azodicarbonamide; 1 part of zinc stearate; 5 parts of diisocyanate crosslinking agent; The molar ratio of maleimide to furan in the bismaleimide and furan-based polyether copolymer is 1:1.

[0037] The self-healing microcapsules use epoxy prepolymer as the core material, and are formed into a shell-coated structure through urea-formaldehyde condensation reaction, with a particle size of 20 μm.

[0038] The preparation method of the polyurethane prepolymer is as follows: 1) Poly(tetrahydrofuran) diol with a number average molecular weight of 1800 is dehydrated under vacuum at 100 °C for 1 h, and then dried by passing nitrogen at 110 °C for another 0.5 h to control the water content in the system not higher than 0.05%; 2) The dehydrated poly(tetrahydrofuran) diol obtained in step 1) is cooled to 70 °C, and 4,4'-diphenylmethane diisocyanate is added under nitrogen protection to make the molar ratio of isocyanate groups to hydroxyl groups 1.65:1, and stirred to form a homogeneous reaction system; 3) Dibutyltin dilaurate catalyst is added to the system obtained in step 2), and the catalyst dosage is 0.05 parts based on the weight of poly(tetrahydrofuran) diol, and the reaction is carried out at 80 °C for 1.5 h to 2.0 h while maintaining the stirring rate at 300 rpm; 4) The reaction end point is monitored by isocyanate titration method, and the reaction is terminated when the mass content of free isocyanate groups in the system reaches 6.5% to obtain the polyurethane prepolymer.

[0039] A preparation method of the composite sponge for automobile hood according to the above, comprising the following steps: S1: Weigh the raw materials according to the weight part ratio of each component, including polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives, ammonium polyphosphate, nano-silica or montmorillonite, self-healing microcapsules, azodicarbonamide, zinc stearate and diisocyanate crosslinking agent; S2: Mix 6-(diphenoxyphosphino)-6H-dibenzophosphole and modified ammonium polyphosphate according to a mass ratio of 1:2, melt them evenly at 180 °C, keep warm for 60 minutes and then cool and crush to obtain flame-retardant solid particles; Among them, the modified ammonium polyphosphate is obtained by reacting ammonium polyphosphate with γ-aminopropyltriethoxysilane at 70 °C for 2 hours, and the pH value of the reaction system is controlled at 4.5.

[0040] S3: Place nano-silica or montmorillonite in a reaction system at 60 °C, add a urethane group prepolymer obtained by reacting a hydroxyl-terminated polyether with a chain extender containing an isocyanate group, and stir and coat for 2 hours to obtain surface-coated nanoparticles; Among them, the urethane group prepolymer is prepared through the following steps: 1) Add 40 parts by mass of the hydroxyl-terminated polyether to a reaction vessel, stir and heat up at 70 °C, and then dropwise add 20 parts by mass of a small molecule chain extender containing two isocyanate groups, and react for 2 hours under a nitrogen atmosphere to generate an intermediate prepolymer containing free isocyanate groups; 2) Add 10 parts by mass of a functional small molecule with a secondary amine or primary amine structure to the reaction system obtained in step 1), continue to react at 60 °C for 1 hour, and control the molar ratio of isocyanate groups to amine groups to be 1.05:1, so that the residual amount of free isocyanate is less than 0.5%.

[0041] S4: Mix the polyurethane prepolymer, the copolymer of bismaleimide and furyl polyether, the self-healing microcapsules, the flame retardant particles obtained in S2, and the coated nanoparticles obtained in S3 evenly at 60 °C, and then premix azodicarbonamide and zinc stearate evenly at a mass ratio of 1:1 at 70 °C and add them to the system, and continue to stir at 70 °C for 5 minutes to form a foaming mixture; S5: Inject the foaming mixture into a mold, foam and mold at 100 °C, and thermally cure at 110 °C for 2 hours to obtain the composite sponge.

[0042] Example 2 A composite sponge for an automobile hood, comprising the following components in parts by weight: 130 parts of polyurethane prepolymer; 15 parts of copolymer of bismaleimide and furyl polyether; 12 parts of 6-(diphenoxyphosphino)-6H-dibenzophosphole; 21.6 parts of modified ammonium polyphosphate; 15 parts of nano-silica; 20 parts of self-healing microcapsules; 2 parts of azodicarbonamide; 1.6 parts of zinc stearate; 8 parts of diisocyanate crosslinking agent; The molar ratio of maleimide to furan in the copolymer of bismaleimide and furyl polyether is 1.2:1.

[0043] The self-healing microcapsules use epoxy prepolymer as the core material, and form a shell-coated structure through urea-formaldehyde condensation reaction, with a particle size of 80 μm.

[0044] The preparation method of the polyurethane prepolymer is as follows: 1) Poly(tetramethylene ether) glycol with a number-average molecular weight of 2200 is dehydrated under vacuum at 100 °C for 1 h, and then dried by introducing nitrogen at 110 °C for another 0.5 h, controlling the water content in the system to be no higher than 0.05%; 2) The dehydrated poly(tetramethylene ether) glycol obtained in step 1) is cooled to 70 °C, and 4,4'-diphenylmethane diisocyanate is added under nitrogen protection, so that the molar ratio of isocyanate group to hydroxyl group is 1.75∶1, and stirred to form a homogeneous reaction system; 3) Dibutyltin dilaurate catalyst is added to the system obtained in step 2), and the amount of the catalyst is 0.1 part based on the weight of poly(tetramethylene ether) glycol, and the reaction is carried out at 80 °C for 1.5 h to 2.0 h, while maintaining the stirring rate at 500 rpm; 4) The reaction end point is monitored by isocyanate titration method, and the reaction is terminated when the mass content of free isocyanate groups in the system reaches 7.5% to obtain the polyurethane prepolymer.

[0045] A preparation method of the composite sponge for the automobile hood according to the above, comprising the following steps: S1: Weigh the raw materials according to the weight part ratio of each component, including polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives, ammonium polyphosphate, nano-silica or montmorillonite, self-healing microcapsules, azodicarbonamide, zinc stearate and diisocyanate crosslinking agent; S2: Mix 6-(diphenoxyphosphino)-6H-dibenzophosphole and modified ammonium polyphosphate according to a mass ratio of 1∶1.8, and melt them evenly at 180 °C, keep warm for 30 minutes and then cool and crush to obtain flame-retardant solid particles; Among them, the modified ammonium polyphosphate is obtained by reacting ammonium polyphosphate with γ-aminopropyltriethoxysilane at 90 °C for 1 h, and controlling the pH value of the reaction system at 6.0.

[0046] S3: Place nano-silica or montmorillonite in a reaction system at 80 °C, add a urethane group prepolymer obtained by reacting a hydroxyl-terminated polyether with a chain extender containing an isocyanate group, and stir and coat for 1 h to obtain surface-coated nanoparticles; Among them, the urethane group prepolymer is prepared through the following steps: 1) Add 60 parts by mass of the hydroxyl-terminated polyether to a reaction vessel, stir and heat it up at 80 °C, then dropwise add 30 parts by mass of a small molecule chain extender containing two isocyanate groups, and react for 1 hour under a nitrogen atmosphere to form an intermediate prepolymer containing free isocyanate groups; 2) Add 20 parts by mass of a functional small molecule with a secondary amine or primary amine structure to the reaction system obtained in step 1), continue to react at 70 °C for 0.5 hour, control the molar ratio of isocyanate groups to amino groups to be 1.2:1, and make the residual amount of free isocyanate less than 0.5%.

[0047] S4: Mix the polyurethane prepolymer, the copolymer of bismaleimide and furyl polyether, the self-healing microcapsules, the flame retardant particles obtained in S2, and the coated nanoparticles obtained in S3 evenly at 70 °C. Then, azodicarbonamide and zinc stearate are premixed evenly at a mass ratio of 1:0.8 at 75 °C and added to the system, and continue to stir for 3 minutes at 75 °C to form a foaming mixture; S5: Inject the foaming mixture into a mold, foam and mold it at 110 °C, and thermally cure it at 130 °C for 1 hour to obtain the composite sponge.

[0048] Example 3 A composite sponge for an automobile engine hood, comprising the following components in parts by weight: 120 parts of polyurethane prepolymer; 20 parts of copolymer of bismaleimide and furyl polyether; 13.7 parts of 6-(diphenoxyphosphino)-6H-dibenzophosphole; 30 parts of modified ammonium polyphosphate; 11 parts of nano-silica; 30 parts of self-healing microcapsules; 3 parts of azodicarbonamide; 2 parts of zinc stearate; 6 parts of diisocyanate crosslinking agent; The molar ratio of maleimide to furan in the copolymer of bismaleimide and furyl polyether is 1.1:1.

[0049] The self-healing microcapsules use epoxy prepolymer as the core material, and form a shell-core structure through urea-formaldehyde condensation reaction, with a particle size of 50 μm.

[0050] The preparation method of the polyurethane prepolymer is as follows: 1) Dehydrate polytetrahydrofuran diol with a number average molecular weight of 2000 at 100 °C under vacuum for 1 h, then continue to dry it by introducing nitrogen at 110 °C for 0.5 h, and control the water content in the system to be no higher than 0.05%; 2) Cool the dehydrated polytetrahydrofuran diol obtained in step 1) to 70 °C, and add 4,4'-diphenylmethane diisocyanate under nitrogen protection, so that the molar ratio of isocyanate groups to hydroxyl groups is 1.7∶1, and stir to form a homogeneous reaction system; 3) Add dibutyltin dilaurate catalyst to the system obtained in step 2), and the catalyst dosage is 0.08 parts based on the weight of polytetrahydrofuran diol, and react at 80 °C for 1.5 h to 2.0 h while maintaining the stirring rate at 400 rpm; 4) Monitor the reaction end point by isocyanate titration method, and terminate the reaction when the mass content of free isocyanate groups in the system reaches 7% to obtain a polyurethane prepolymer.

[0051] A preparation method of the composite sponge for automobile hood according to the above, comprising the following steps: S1: Weigh raw materials according to the weight ratio of each component, including polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, 6-(diphenoxyphosphine)-6H-dibenzophosphole or its derivatives, ammonium polyphosphate, nano-silica or montmorillonite, self-healing microcapsules, azodicarbonamide, zinc stearate and diisocyanate crosslinking agent; S2: Mix 6-(diphenoxyphosphine)-6H-dibenzophosphole and modified ammonium polyphosphate according to a mass ratio of 1∶2.2, melt them evenly at 180 °C, keep warm for 45 minutes and then cool and crush to obtain flame retardant solid particles; Among them, the modified ammonium polyphosphate is obtained by reacting ammonium polyphosphate with γ-aminopropyltriethoxysilane at 80 °C for 1.5 hours, and controlling the pH value of the reaction system at 5.

[0052] S3: Place nano-silica or montmorillonite in a reaction system at 70 °C, add a urethane group prepolymer obtained by reacting a hydroxyl-terminated polyether with a chain extender containing isocyanate groups, and stir and coat for 1.5 hours to obtain surface-coated nanoparticles; Among them, the urethane group prepolymer is prepared by the following steps: 1) Add 50 parts by mass of hydroxyl-terminated polyether to a reaction vessel, stir and heat up at 75 °C, then dropwise add 25 parts by mass of a small molecule chain extender containing two isocyanate groups, and react for 1.5 hours under a nitrogen atmosphere to generate an intermediate prepolymer containing free isocyanate groups; 2) Add 15 parts by mass of a functional small molecule with a secondary amine or primary amine structure to the reaction system obtained in step 1), and continue to react at 65 °C for 0.75 hours, controlling the molar ratio of isocyanate groups to amine groups to be 1.1∶1, so that the residual amount of free isocyanate is less than 0.5%.

[0053] S4: Mix the polyurethane prepolymer, bismaleimide, furan-based polyether copolymer, self-healing microcapsules, the flame retardant particles obtained in S2, and the coated nanoparticles obtained in S3 evenly at 65 °C. Subsequently, azodicarbonamide and zinc stearate are premixed evenly at a mass ratio of 1:1.5 at 72 °C and then added to the system, and stirring is continued at 73 °C for 4 minutes to form a foaming mixture; S5: Inject the foaming mixture into a mold, foam-mold it at 105 °C, and thermally cure it at 120 °C for 1.5 hours to obtain the composite sponge.

[0054] Example 4 The difference between this example and Example 1 lies in the different addition amounts of the self-healing microcapsules, bismaleimide, and furan-based polyether copolymer, which are respectively: Bismaleimide and furan-based polyether copolymer: 120 parts; Self-healing microcapsules: 30 parts.

[0055] Example 5 The difference between this example and Example 1 lies in the different addition amounts of azodicarbonamide and zinc stearate, which are respectively: Azodicarbonamide: 2 parts; Zinc stearate: 1.4 parts.

[0056] Example 6 The difference between this example and Example 1 lies in the different addition methods of azodicarbonamide and zinc stearate. They are directly added instead of being added after premixing.

[0057] Example 7 The difference between this example and Example 1 lies in that the molar ratio of maleimide to furan in the bismaleimide and furan-based polyether copolymer is 1.3:1.

[0058] Example 8 The difference between this example and Example 1 lies in that the nano-silica is not treated with a urethane group prepolymer coating, but with a silane coupling agent (3-aminopropyltriethoxysilane).

[0059] Example 9 The difference between this example and Example 1 lies in that the ammonium polyphosphate is not modified.

[0060] Example 10 The difference between this example and Example 1 lies in the different addition amounts of 6-(diphenoxyphosphino)-6H-dibenzophosphole and ammonium polyphosphate, which are respectively: 6-(Diphenoxyphosphino)-6H-dibenzophosphole or its derivative: 12 parts; Ammonium polyphosphate: 30 parts.

[0061] Example 11 The difference between this example and Example 1 is that (diphenoxyphosphino)-6H-dibenzophosphole and ammonium polyphosphate are not subjected to hot melt mixing treatment and are directly added.

[0062] Comparative Example 1 The difference between this comparative example and Example 1 is that the bismaleimide and furan-based polyether copolymer and the self-healing microcapsules are not added.

[0063] Comparative Example 2 The difference between this comparative example and Example 1 is that the bismaleimide and furan-based polyether copolymer are not added.

[0064] Comparative Example 3 The difference between this comparative example and Example 1 is that the self-healing microcapsules are not added.

[0065] Comparative Example 4 The difference between this comparative example and Example 1 is that 6-(diphenoxyphosphino)-6H-dibenzophosphole is not added.

[0066] Comparative Example 5 The difference between this comparative example and Example 1 is that the modified ammonium polyphosphate is not added.

[0067] Testing Method 1. Thermal Shape Memory Performance Test Testing Method: Compress the sample by 50% and then cool it at room temperature to fix the shape; Put it into an oven at 100 °C and keep it for 10 min, and record the shape recovery situation; Measure the thickness after recovery and calculate the thermal recovery rate: H0: Original thickness; H1: Thickness after recovery; H2: Thickness after compression.

[0068] 2. Self-Healing Ability Test Testing Method: Artificially scratch the surface of the sample (scratch width is about 100 μm); Place it at room temperature and 100 °C for 24 h respectively; Use an optical microscope / SEM to observe the degree of scratch closure; And conduct tensile / compressive strength tests on the scratched area and calculate the recovery rate: 3. Flame Retardancy Performance Test (1)Limiting Oxygen Index (LOI): According to GB / T 2406.2-2009 Cut into test strips of 100 × 10 × 10 mm and detected by an LOI tester.

[0069] (2)UL-94 Vertical Burning Test: According to the UL-94 standard Use 3 specimens to measure the dripping, burning time, and residual length.

[0070] 4. Thermal stability (TGA analysis) Method: Heat at a rate of 10 °C / min in a nitrogen atmosphere from room temperature to 800 °C; Measure the char residue rate.

[0071] 5. Compression set rate (compression resilience) Test method: According to GB / T 6670-2008 Compress the sample to 50% of its original thickness and keep it at 80 °C for 24 h; Take it out and let it recover naturally, measure the final thickness, and calculate the compression set rate: H0: Original thickness; H1: Thickness after recovery; H2: Thickness after compression.

[0072] All the test results of the above tests are shown in Table 1 below.

[0073] Table 1 The test results show that Examples 1 to 3 perform optimally in all indicators, with a heat recovery rate exceeding 94.8%, a self-healing recovery strength reaching over 87%, an LOI value higher than 32.5%, and the compression set rate controlled within 7.6%, demonstrating excellent shape memory, self-healing ability, and structural stability. Examples 4 to 11 are slightly lower than the above optimal group in terms of heat recovery rate (91.0% - 93.0%), self-healing strength (80% - 84%), and LOI (30.0% - 31.9%), but are still significantly better than all comparative examples. The comparative examples are inferior to the examples in all performance dimensions, with the lowest heat recovery rate being only 30%, the self-healing strength being less than 50%, the LOI not reaching 30% in all cases, and the compression deformation rate generally greater than 9%. The overall data verifies the significant role of the bismaleimide-furan reversible network, self-healing microcapsules, and flame retardant synergistic structure in improving the deformation recovery, thermal stability, and flame retardant properties of composite foam materials.

[0074] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A composite sponge for a car hood, characterized in that, The composite sponge comprises the following components in parts by weight: 100 - 130 parts of polyurethane prepolymer; 12 - 20 parts of bismaleimide and furan - based polyether copolymer; 12 - 20 parts of 6 - (diphenoxyphosphino) - 6H - dibenzophosphole or its derivatives; 20 - 30 parts of ammonium polyphosphate; 8 - 15 parts of nano - silica or montmorillonite; 20 - 30 parts of self - healing microcapsules; 1 - 3 parts of azodicarbonamide; 1 - 2 parts of zinc stearate; 5 - 8 parts of diisocyanate cross - linker; The self - healing microcapsules use aromatic esters or epoxy prepolymers as the core material, and form a shell - coated structure through urea - formaldehyde condensation reaction, with a particle size of 20 - 80 μm.

2. The composite sponge for an automobile hood according to claim 1, wherein, The preparation method of the polyurethane prepolymer is as follows: 1) Poly(tetramethylene ether) glycol with a number - average molecular weight of 1800 - 2200 is dehydrated under vacuum at 100 °C for 1 h, and then dried by introducing nitrogen at 110 °C for another 0.5 h, controlling the water content in the system to be no higher than 0.05%; 2) The dehydrated poly(tetramethylene ether) glycol obtained in step 1) is cooled to 70 °C, and 4,4'-diphenylmethane diisocyanate is added under nitrogen protection, so that the molar ratio of isocyanate groups to hydroxyl groups is 1.65 - 1.75∶1, and stirred to form a homogeneous reaction system; 3) Dibutyltin dilaurate catalyst is added to the system obtained in step 2), and the catalyst dosage is 0.05 - 0.1 part based on the weight of poly(tetramethylene ether) glycol, and the reaction is carried out at 80 °C for 1.5 - 2.0 h while maintaining the stirring rate at 300 - 500 rpm; 4) The reaction end - point is monitored by isocyanate titration method. When the mass content of free isocyanate groups in the system reaches 6.5% - 7.5%, the reaction is terminated to obtain the polyurethane prepolymer.

3. The composite sponge for the automobile hood according to claim 1, characterized in that, The mass ratio of 6 - (diphenoxyphosphino) - 6H - dibenzophosphole or its derivatives to ammonium polyphosphate is 1∶1.8 - 1∶2.

2. The two are subjected to hot - melt mixing treatment at 180 °C for 30 - 60 minutes and then cooled and crushed into solid particles, and the solid particles are incorporated into the composite sponge before foaming.

4. The composite sponge for an automobile hood according to claim 3, characterized in that, Before the hot - melt mixing treatment, ammonium polyphosphate reacts with γ - aminopropyltriethoxysilane at 70 - 90 °C for 1 - 2 hours, and the pH value of the reaction system is controlled at 4.5 - 6.

0. The modified ammonium polyphosphate particles are used for the hot - melt mixing treatment.

5. The composite sponge for an automobile hood according to claim 4, characterized in that, Before adding to the composite material, the nano - silica or montmorillonite is coated with a urethane - group prepolymer, and the prepolymer is prepared by reacting a small - molecule chain extender containing isocyanate groups with a hydroxyl - terminated polyether at 60 - 80 °C for 1 - 2 hours.

6. The composite sponge for an automobile hood according to claim 5, characterized in that, The preparation method of the urethane - group prepolymer includes the following steps: 1) 40 - 60 parts by mass of hydroxyl - terminated polyether are added to a reaction vessel, stirred and heated at 70 - 80 °C, and then 20 - 30 parts by mass of a small - molecule chain extender containing two isocyanate groups are added dropwise, and the reaction is carried out for 1 - 2 hours under a nitrogen atmosphere to generate an intermediate prepolymer containing free isocyanate groups; 2) Add 10 - 20 parts by mass of a functional small molecule having a secondary amine or primary amine structure to the reaction system obtained in step 1), and continue the reaction at 60 - 70 °C for 0.5 - 1 hour. Control the molar ratio of isocyanate groups to amino groups to be 1.05∶1 - 1.2∶1, so that the residual amount of free isocyanate is less than 0.5%.

7. The composite sponge for the automobile engine hood according to claim 1, wherein, In the bismaleimide and furan-based polyether copolymer, the molar ratio of maleimide to furan is 1 - 1.2∶1.

8. The composite sponge for an automobile hood according to claim 1, characterized in that, The mass ratio of azodicarbonamide to zinc stearate is 1∶0.8 - 1.

5. After premixing them evenly at 70 - 75 °C, add them to the system.

9. The composite sponge for an automobile hood according to claim 1, wherein The thermal response temperature range among the bismaleimide and furan-based polyether copolymer, the self-healing microcapsules, and the polyurethane prepolymer is controlled at 90 - 130 °C, and the mass ratio of the self-healing microcapsules to the bismaleimide and furan-based polyether copolymer is 1 - 1.5∶1.

10. A method for preparing the composite sponge for an automobile engine hood according to any one of claims 1 to 9, characterized in that, It includes the following steps: S1: Weigh the raw materials according to the weight parts ratio of each component, including polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives, ammonium polyphosphate, nano-silica or montmorillonite, self-healing microcapsules, azodicarbonamide, zinc stearate, and diisocyanate crosslinking agent; S2: Mix the 6-(diphenoxyphosphino)-6H-dibenzophosphole or its derivatives with ammonium polyphosphate according to a mass ratio of 1∶1.8 - 1∶2.2, and melt them evenly under heating conditions. Keep warm for 30 - 60 minutes and then cool and crush to obtain flame-retardant solid particles; S3: Place nano-silica or montmorillonite in the reaction system at 60 - 80 °C, add the urethane group prepolymer obtained by reacting a hydroxyl-terminated polyether with a chain extender containing isocyanate groups, and stir and coat for 1 - 2 hours to obtain surface-coated nanoparticles. Control its addition amount to account for 2% - 5% of the total mass of the composite sponge; S4: Mix the polyurethane prepolymer, bismaleimide and furan-based polyether copolymer, self-healing microcapsules, the flame-retardant particles obtained in S2, and the coated nanoparticles obtained in S3 evenly at 60 - 70 °C. Then add azodicarbonamide and zinc stearate, and continue to stir for 3 - 5 minutes at 70 - 75 °C to form a foaming mixture; S5: Inject the foaming mixture into a mold, foam and form at 100 - 110 °C, and thermally cure at 110 - 130 °C for 1 - 2 hours to obtain the composite sponge.

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