A room-temperature self-healing flexible ablation-resistant material, its preparation method and applications

Abstract

This invention provides a flexible room-temperature self-healing ablation-resistant material, its preparation method, and its applications. It is prepared from oligomeric polyols, isocyanates, metal hydroxide flame retardants, boron-containing compounds, chain extenders, and crosslinking agents. This material exhibits good mechanical strength and room-temperature self-healing properties, along with excellent heat resistance and ablation resistance, demonstrating superior overall performance. This flexible room-temperature self-healing ablation-resistant material exhibits stable performance, a wide range of applications, and a long service life. It can be applied to various flexible materials, coatings, potting materials, and adhesives, especially in high-temperature environments or for external protective coatings and flexible components requiring heat resistance and ablation resistance, such as flexible heat-resistant coatings. It offers advantages such as maintenance-free operation and high reliability, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of advanced functional materials, specifically relating to a flexible room temperature self-healing ablation-resistant material, its preparation method, and its applications. Background Technology

[0002] Ablation-resistant thermal protection materials play an irreplaceable and crucial role in spacecraft. Flexible ablation-resistant materials that can meet the requirements of thermal stress matching, large deformation coordination, and dynamic thermal protection are key materials for developing next-generation spacecraft. Currently, heat-resistant coatings with flexible structural characteristics are becoming increasingly important. Flexible materials, due to their long-term exposure to static or dynamic mechanical forces such as tension, compression, shearing, and torsion, are more prone to developing microcracks. Cracks and other defects pose a significant safety hazard to thermal protection structures. Therefore, modifying flexible thermal protection materials to enable them to automatically heal cracks and maintain the integrity of the material structure before ablation is of great significance, thereby extending service life and reducing maintenance costs.

[0003] The formation of a stable carbon layer during ablation is fundamental to achieving high ablation resistance in flexible ablation-resistant heat-insulating materials. A stable, dense carbon layer with sufficient strength can effectively resist the erosion of high-temperature, high-pressure combustion gases and prevent the transfer of external heat and oxidizing gases to the interior, inhibiting temperature rise and slowing material damage, thereby improving the ablation resistance of the flexible composite system. However, to achieve efficient self-healing, intrinsic self-healing materials introduce a large number of reversible dynamic bonds and supramolecular interactions with low bond energy, and are generally linear structures or low cross-linking degrees, resulting in very poor thermal stability, low initial decomposition temperature, and low thermal char residue. Under high-temperature ablation conditions, they degrade rapidly and are not prone to forming a protective carbon layer. In this case, reinforcing and functional fillers play an important role in the ablation resistance of the material, but the introduction of fillers usually restricts molecular chain movement or creates some defects, leading to a significant reduction in the material's self-healing performance.

[0004] Chinese patent CN 114369222 B discloses a high-strength, room-temperature, rapid self-healing flexible material, its preparation method, and its applications. This self-healing flexible material is prepared from oligomeric polyols, isocyanates, chain extenders, and crosslinking agents. While this self-healing flexible material exhibits both good mechanical strength and good room-temperature self-healing properties, its heat resistance and ablation resistance require further improvement.

[0005] Currently, there is limited research on the impact of fillers on the intrinsic self-healing behavior and performance of materials. There are only a few literature reports on small-sized or low-addition blends of carbon nanotubes, nano-metal oxides, boron nitride, graphene, etc., and most of them require external stimuli (light, heat, pressure, etc.) to repair. Research on the impact of larger-scale inorganic particle fillers on self-healing performance at higher addition levels is still insufficient, and there are no research reports on self-healing ablation-resistant materials.

[0006] Therefore, there is an urgent need to develop self-healing and ablation-resistant materials that can achieve a harmonious balance between the material's physical and mechanical properties, room-temperature self-healing characteristics, and ablation resistance. Summary of the Invention

[0007] The purpose of this invention is to provide a flexible room temperature self-healing ablation-resistant material, its preparation method, and its applications.

[0008] This invention provides a room-temperature self-healing flexible ablation-resistant material, which is prepared from oligomeric polyols, isocyanates, metal hydroxide flame retardants, boron-containing compounds, chain extenders, and crosslinking agents as raw materials; wherein the mass ratio of the oligomeric polyols, isocyanates, metal hydroxide flame retardants, boron-containing compounds, chain extenders, and crosslinking agents is (45-80):(20-40):(0-30):(1-20):(5-20):(1-5).

[0009] Further, the mass ratio of the oligomeric polyol, isocyanate, flame retardant, boron-containing compound, chain extender and crosslinking agent is (55-65):(25:30):(0-20):(2.5-10):(10-12):(1-2);

[0010] The metal hydroxide flame retardant is one or more of magnesium hydroxide, aluminum hydroxide, or bimetallic hydroxide flame retardants;

[0011] The boron-containing compound is boron oxide, zinc borate, or pentaboric acid; the chain extender is an aliphatic or aromatic diamino disulfide containing a reversible disulfide bond;

[0012] The crosslinking agent is a trifunctional compound containing a pyridine or pyrimidine ring structure with a hydrogen bond acceptor and a donor, and with an amino or hydroxyl group as the active functional group.

[0013] Further, the mass ratio of the oligomeric polyol, isocyanate, metal hydroxide flame retardant, boron-containing compound, chain extender and crosslinking agent is 59.77:27.85:(0-15):(2.5-10):11.12:1.25;

[0014] The boron-containing compound is boron oxide.

[0015] Furthermore, the bimetallic hydroxide flame retardant is magnesium hydroxide and aluminum hydroxide;

[0016] The mass ratio of magnesium hydroxide to aluminum hydroxide is (0-10):(0-5);

[0017] The oligomeric polyol is polytetrahydrofuran, polyoxypropylene polyol, or copolyether polyol.

[0018] And / or, the isocyanate is a diisocyanate, preferably isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate or diphenylmethane diisocyanate;

[0019] And / or, the chain extender is 4,4'-diaminodiphenyl disulfide, 4,4'-dihydroxydiphenyl disulfide, 3,3'-dihydroxydiphenyl disulfide or 2-hydroxyethyl disulfide;

[0020] And / or, the crosslinking agent is 2,4-diamino-6-hydroxypyrimidine, 2,4,6-triaminopyrimidine, or 2,4,5-triaminopyridine.

[0021] Furthermore, the isocyanate is isophorone diisocyanate;

[0022] The chain extender is 4,4'-diaminodiphenyl disulfide;

[0023] The crosslinking agent is 2,4-diamino-6-hydroxypyrimidine.

[0024] The present invention also provides a method for preparing the above-mentioned room temperature self-healing flexible ablation-resistant material, which includes the following steps:

[0025] (1) Synthesis of prepolymer: Add a catalytic amount of catalyst to oligomeric polyol and isocyanate, react in solvent to obtain prepolymer solution;

[0026] (2) Composite filler: Add metal hydroxide flame retardant and boron-containing compound to the prepolymer solution and stir until evenly dispersed;

[0027] (3) Chain extension and crosslinking: Add a crosslinking agent and a chain extender soluble in solvent to the final product of step (2), react, and obtain the reactant;

[0028] (4) Curing: Pour the reactants into a mold and cure them to obtain the product.

[0029] Further

[0030] In step (1), the catalyst is dibutyltin dilaurate or stannous octoate;

[0031] And / or, in step (1), the solvent is dimethyl sulfoxide, diethyl sulfoxide, or water;

[0032] And / or, in step (3), the solvent is dimethyl sulfoxide, diethyl sulfoxide or water.

[0033] Further

[0034] In step (1), the reaction temperature is 60–100°C; and / or, the reaction environment is an inert gas environment; and / or, the reaction time is 1–6 h.

[0035] And / or, in step (3), the temperature of the reaction is 50 to 100°C; and / or, the reaction time is 0.5 to 5 hours;

[0036] And / or, in step (4), the curing conditions are to first maintain at 90-150℃ for 1-5 hours in a vacuum environment, and then maintain at 120-200℃ for 10-20 hours.

[0037] The present invention also provides the use of the above-mentioned room temperature self-healing flexible ablation-resistant material in the preparation of room temperature self-healing materials;

[0038] Preferably, the room temperature self-healing material is a flexible material, a coating material, a potting material, or an adhesive; or the room temperature self-healing material is an external protective coating and flexible component material used in high-temperature environments or requiring heat resistance and ablation resistance. Preferably, the room temperature self-healing material is a flexible heat-resistant coating material.

[0039] The present invention also provides a room temperature self-healing flexible ablation-resistant material, which is prepared from the aforementioned ablation-resistant material as raw material.

[0040] In summary, this invention relates to a room-temperature self-healing flexible ablation-resistant material, its preparation method, and its applications. The room-temperature self-healing flexible ablation-resistant material is prepared by combining Al(OH)3, Mg(OH)2, and B2O3 as fillers with isocyanate-terminated prepolymers. This room-temperature self-healing flexible ablation-resistant material not only has high mechanical strength but also good room-temperature self-healing properties, as well as excellent heat resistance and ablation resistance, exhibiting superior overall performance.

[0041] This invention is the first to discover a room-temperature self-healing flexible ablation-resistant material made by combining isocyanate-terminated prepolymers with 0-10 parts Al(OH)3, 0-5 parts Mg(OH)2, and 2.5-10 parts B2O3 as fillers. This material significantly enhances the resistance to thermal ablation while maintaining the room-temperature self-healing capability of the ablation-resistant material, achieving maintenance-free characteristics and effectively extending its service life, filling a gap in this field. The self-healing flexible material of this invention exhibits stable performance, a wide range of applications, and a long service life. It can be applied to various flexible materials, coating materials, potting materials, and adhesives, especially in high-temperature environments or for external protective coatings and flexible components requiring heat resistance and ablation resistance, such as flexible heat-resistant coatings. It offers advantages such as maintenance-free operation and high reliability, and has broad application prospects.

[0042] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0043] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0044] Figure 1 An optical photograph of the B2O3 / PIDA-2.5 composite self-healing elastomer.

[0045] Figure 2 (a) FTIR spectrum and (b) XRD spectrum of the B2O3 / PIDA-2.5 composite system. Figure 3 Stress-strain curves of B2O3 / PIDA-2.5 composite systems (a) A0M0B5, (b) A10M5B0, (c) A10M5B2.5, (d) A10M5B5, (e) A10M5B10 after repair at room temperature (25℃) and 60℃ for different times.

[0046] Figure 4 The TG(a) and DTG(b) curves of the B2O3 / PIDA-2.5 composite system in nitrogen atmosphere and the TG(c) and DTG(d) curves in air atmosphere.

[0047] Figure 5The evolution of samples (a) A0M0B5, (b) A10M5B0, (c) A10M5B2.5, (d) A10M5B5, and (e) A10M5B10 of the B2O3 / PIDA-2.5 composite system at different ablation times during the ablation process. Figure 6 Optical morphology of the ablated surface of the B2O3 / PIDA-2.5 composite system.

[0048] Figure 7 Ablation and thermal conductivity data of the B2O3 / PIDA-2.5 composite system: (a) linear ablation rate, (b) mass ablation rate, (c) thermal conductivity, (d) backplate temperature. Detailed Implementation

[0049] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0050] Example 1: Preparation of the self-healing flexible material of the present invention

[0051] I. Experimental Methods

[0052] (I) Synthesis of isocyanate-terminated prepolymer PREP

[0053] (1) Raw material dehydration treatment: Pour the raw material polytetrahydrofuran (PTMEG) with a molecular weight of 1000 into a flask and vacuum at 110°C for 2 hours to remove residual water. Isophorone diisocyanate (IPDI) uses high-purity analytical grade reagent and does not require further purification treatment.

[0054] (2) Synthesis of prepolymer: 15g of PTMEG and 6.99g of IPDI were poured into a flask, 7.5g of DMSO was added and heated to 60℃, 3000ppm of dibutyltin dilaurate (DBTDL) was added, and the mixture was stirred with argon gas at 60℃ for 3h to obtain the isocyanate-terminated prepolymer PREP2.5 solution.

[0055] (II) Preparation of B2O3 / PIDA-2.5

[0056] (1) Add composite functional filler: According to the raw material ratio shown in Table 1, add Al(OH)3, Mg(OH)2 and B2O3 to PREP-2.5 solution and stir rapidly for 30 min to disperse the filler in the prepolymer PREP2.5 solution.

[0057] (2) Chain extension and crosslinking: According to the raw material ratio shown in Table 1, 2,4-diamino-6-hydroxypyrimidine (DAHP) and 4,4'-diaminodiphenyl disulfide (APDS) dissolved in 12g solvent DMSO were added to the PREP2.5 prepolymer solution of the above dispersion filler system, and stirred at 60°C for 2h to obtain a viscous reactant.

[0058] (3) Solvent removal: Pour the polymer solution obtained above into a mold, vacuum at 100°C for 3 hours, maintain vacuum at 80°C for 36 hours, and vacuum at 120°C for 12 hours to obtain the self-healing flexible composite material B2O3 / PIDA-2.5 of the present invention. According to the raw material ratio shown in Table 1, the self-healing flexible materials prepared are named A0M0B5, A10M5B0, A10M5B2.5, A10M5B5 and A10M5B10, respectively.

[0059] Because adding a large amount of filler increases the viscosity of the polymer solution and generates bubbles during curing, it cannot be directly prepared into test samples. Therefore, taking advantage of the material's excellent reshaping properties, the cured material was placed in a 1mm thick stainless steel mold frame for hot pressing and reshaping at 120℃ for 20 minutes.

[0060] The final image of the defect-free composite material is as follows: Figure 1 As shown.

[0061] Table 1. Raw material ratio of B2O3 / PIDA-2.5 composite system (unit: parts per phr)

[0062] A0M0B5 87.63 0 0 5 1.25 11.12 A10M5B0 87.63 10 5 0 1.25 11.12 A10M5B2.5 87.63 10 5 2.5 1.25 11.12 A10M5B5 87.63 10 5 5 1.25 11.12 A10M5B10 87.63 10 5 10 1.25 11.12

[0063] The above quantities are by weight.

[0064] The following experimental examples demonstrate the beneficial effects of the self-healing flexible composite material B2O3 / PIDA-2.5 prepared in this invention.

[0065] Comparative example, preparation of PIDA-2.5

[0066] (1) Chain extension and crosslinking: 1.25 parts by weight of 2,4-diamino-6-hydroxypyrimidine (DAHP) and 11.12 parts by weight of 4,4'-diaminodiphenyl disulfide (APDS) dissolved in 12g of solvent DMSO were added to 87.63 parts by weight of PREP-2.5 prepolymer and stirred at 60°C for 2h to obtain a viscous reactant.

[0067] (2) Solvent removal: Pour the viscous reactant into a polytetrafluoroethylene mold, place it in a 60°C oven and remove bubbles by vacuuming for 1 hour, then maintain the vacuum at 90°C for 36 hours and at 120°C for 12 hours, and vacuum at regular intervals during this period. Cool to room temperature to obtain a transparent flexible material, namely PIDA-2.5.

[0068] Experimental Example 1: Characterization of the B2O3 / PIDA-2.5 composite structure of the present invention

[0069] I. Experimental Methods

[0070] The B2O3 / PIDA-2.5 composite system was characterized by ATR-FTIR infrared analysis.

[0071] II. Experimental Results

[0072] The ATR-FTIR infrared characterization analysis results of the B2O3 / PIDA-2.5 composite system are as follows: Figure 2 As shown. The -NCO in PDI will be at 2259cm. -1 A peak was observed near the composite system's infrared spectrum, but this peak was not observed there, indicating that IPDI had reacted completely. The peaks for other functional groups were similar to those of PIDA-7.5, around 1700 cm⁻¹. -1 The C=O stretching vibration peaks and 1650 cm⁻¹ corresponding to carbamates are shown. -1 The presence of C=O stretching vibration peaks belonging to the polyurea structure indicates that the reaction was complete and the matrix was successfully prepared. After the addition of Al(OH)3 (ATH) and Mg(OH)2 (MH), A10M5B0 also showed strong and sharp peaks belonging to these two hydroxides, respectively. The XRD pattern also showed diffraction peaks belonging to B2O3, Al(OH)3, and Mg(OH)2, confirming the successful preparation of the composite material.

[0073] Experimental Example 2: Study on the Mechanical Properties and Self-Healing Properties of the B2O3 / PIDA-2.5 Composite System of the Present Invention I. Experimental Methods

[0074] Mechanical property evaluation: The tensile properties of the self-healing elastomer were tested using a universal testing machine according to GB / T 528-2009, with a tensile rate of 100 mm / min. The stress-strain relationship of the B2O3 / PIDA-2.5 composite system at room temperature and 60℃ for different repair times was investigated.

[0075] Evaluation of self-healing performance: First, use a sharp blade to cut the dumbbell-shaped sample in half, gently touch the cut surfaces together, and then place the sample at 25℃ and 60℃ for different times to repair. Finally, use a tensile testing machine to test the tensile properties of the material at room temperature (25℃).

[0076] II. Experimental Results

[0077] The mechanical properties of the B2O3 / PIDA-2.5 composite system were studied, and the results are as follows: Figure 3 As shown, it can be seen that adding only B2O3 or only hydroxide has drastically different effects on the mechanical properties of the composite system.

[0078] Based on the pure PIDA-2.5 matrix, the addition of 5 phr B2O3 (i.e., A0M0B5) reduced the initial tensile strength of the uncut material from 14.8 MPa to 11.4 MPa. However, the addition of 10 phr Al(OH)3 and 5 phr Mg(OH)2 (i.e., A10M5B0) increased the initial tensile strength to 31.7 MPa. This may be due to the slightly poor compatibility of B2O3 with polyurethane; B2O3 precipitation was observed on the sample surface, while the hydroxide was uniformly dispersed. Figure 1 As the B2O3 content gradually increased from 0 phr to 10 phr, the tensile strength of the composite system gradually decreased, especially the tensile strength of A10M5B10, which dropped to 12.1 MPa, indicating that too much B2O3 should not be added.

[0079] Figure 3 It can be seen that only A10M5B2.5 and A10M5B5 exhibit good self-healing properties. A10M5B2.5 achieves a tensile strength self-healing efficiency of 88.5% after 24 hours at 60℃, but its repair ability is lower at room temperature. A10M5B5 recovers its tensile strength to 18.5MPa after 48 hours at 25℃, with a self-healing efficiency as high as 92.5%, while it only takes 1 hour to fully recover at 60℃.

[0080] Experimental Example 3: Thermal stability of the B2O3 / PIDA-2.5 composite system of the present invention

[0081] The thermal stability of the B2O3 / PIDA-2.5 composite system was analyzed by thermogravimetric analysis (TGA). Samples weighing 3-8 mg were heated from 40 °C to 800 °C at a rate of 10 °C / min under N2 and air conditions. -1 The TG and DTG curves obtained from the test are as follows: Figure 4 As shown.

[0082] Table 2 shows the thermal decomposition characteristic parameters of the B2O3 / PIDA-2.5 composite system in a nitrogen atmosphere, and Table 3 shows the thermal decomposition characteristic parameters of the B2O3 / PIDA-2.5 composite system in an air atmosphere; where T 5％ The temperature at which a 5% weight loss occurs on the thermogravimetric curve is represented by T. max Represents the peak temperature corresponding to the maximum thermal decomposition rate in each thermal decomposition stage on the differential thermogravimetric curve; measured R 800 (°C) represents the residual weight at 800°C obtained from actual material testing using TGA; theoretical R 800 (°C) refers to the residual carbon content at 800°C, calculated under the assumption that the matrix and filler do not affect each other. Generally speaking, the higher the residual carbon content, the higher the quality of the carbon layer formed at high temperatures, and the stronger the protection of the underlying matrix from thermal erosion.

[0083] As can be seen from Tables 1 and 2, the T values ​​of the material under air and nitrogen atmospheres after adding B2O3, ATH, and MH are... 5％ All of them decreased compared to the pure matrix PIDA-2.5, and the T of A0M0B5 was lower. 5％ The lower value of A10M5B0 indicates that B2O3 has a greater impact on the initial decomposition temperature of the material than the mixed filler of ATH and MH. Furthermore, it can be observed that as the B2O3 content increases, the T value of the B2O3 / PIDA-2.5 composite system decreases. 5％ Further reduction. The addition of ATH and MH further improved the thermal stability of the B2O3-containing system materials. Simultaneously, the addition of fillers significantly increased the carbon residue at 800℃ in the composite system, and the actual carbon residue of the B2O3-added composite material at 800℃ was significantly higher than the theoretical value, demonstrating the advantage of the B2O3 composite filler system in improving the thermal carbon residue of the material. The melting of B2O3 and the barrier effect of the filler effectively protect the PIDA matrix and pyrolysis residues from further oxidation and decomposition. Meanwhile, the initial decomposition temperature of ATH is about 50℃ lower than the first weight loss peak (hard segment degradation) temperature of the matrix, and the initial decomposition temperature of MH is about 50℃ lower than the second weight loss peak (soft segment degradation) temperature. This filler-matrix degradation temperature matching design allows the filler to decompose before the matrix pyrolysis, thereby carrying away heat and delaying the pyrolysis of the matrix. Figure 4 The weakening of the peak in the DTG curve also indicates the delay and inhibition of the degradation process.

[0084] Table 2. Thermal decomposition characteristic parameters of the B2O3 / PIDA-2.5 composite system in nitrogen atmosphere.

[0085] PIDA-2.5 284.4 307.2 / 402.7 0 0 A0M0B5 254.6 321.5 / 402.7 6.1 4.7 A10M5B0 277.9 303.0 / 405.2 11.1 8.7 A10M5B2.5 269.4 303.4 / 410.1 14.3 9.4 A10M5B5 256.9 304.3 / 400.9 14.2 10.0 A10M5B10 240.6 302.8 / 392.1 17.3 11.2

[0086] Table 3. Thermal decomposition characteristic parameters of the B2O3 / PIDA-2.5 composite system in air atmosphere.

[0087] PIDA-2.5 287.3 355.6 / 538.3 0.2 0.2 A0M0B5 252.8 315.3 / 400.7 / 545.9 6.0 4.7 A10M5B0 280.7 328.4 / 398.5 / 514.5 9.9 8.7 A10M5B2.5 269.7 303.5 / 402.9 / 535.1 12.4 9.4 A10M5B5 261.0 303.7 / 401.9 / 545.7 13.1 10.0 A10M5B10 250.9 298.6 / 378.7 / 545.6 13.9 11.2

[0088] Experimental results show that the heat resistance of the B2O3 / PIDA-2.5 composite system of the present invention is improved, especially with a higher thermal residual weight. This improves the char-forming ability of self-healing materials containing a large number of weak bonds with low bond energy, which is crucial for improving the char-forming ability of the composite system during the ablation process and enhancing the ablation resistance of the material.

[0089] Experimental Example 4: Study on the thermal ablation performance of the B2O3 / PIDA-2.5 composite system of the present invention

[0090] 1. Ablation resistance of the B2O3 / PIDA-2.5 composite system

[0091] The ablation resistance of the B2O3 / PIDA-2.5 composite system was tested.

[0092] All samples were ablated for 30 seconds in a butane flame at approximately 1300℃ and a heat flux of 0.25 MW. Images of the ablation process and the optical morphology after ablation are shown below. Figure 5 and Figure 6 As shown.

[0093] It can be seen that different samples exhibit significant differences in their phenomena during and after ablation. The most important difference is that the introduction of B2O3 enables the formation of a carbon layer during ablation, while PIDA-2.5 and A10M5B0, which do not contain B2O3, show a smoother surface after ablation, with a sticky pyrolysis layer exposed, and no carbon layer formed. During the ablation process, from... Figure 5 It can be seen that when the ablation time is 2s, the sample surface with added hydroxide begins to show a white mist, which may be due to the decomposition of hydroxide at high temperature to produce water. When the ablation time reaches 7s, the sample surface with added B2O3 begins to show bright red spots, and the higher the content of B2O3, the more obvious the spots become. This is because boron oxide reaches a molten state at high temperature and radiates heat outward. When the ablation time reaches 15s, A10M5B0 without B2O3 shows severe thermal degradation and produces a large number of oligomer droplets, with no carbon layer forming on the surface. A0M0B5 with only B2O3 shows a carbon layer, but it is scattered on the ablated surface and is not dense. Other composite materials containing B2O3 and hydroxide show that the carbon layer gradually becomes denser as the content of B2O3 increases. It is worth noting that although a carbon layer was formed for A10M5B2.5 containing 2.5 phr B2O3, the carbon layer began to slide downwards along with the pyrolyzed matrix below as the ablation time increased, indicating that more B2O3 needs to be added to stabilize the carbon layer.

[0094] The linear ablation rate and mass ablation rate of the B2O3 / PIDA-2.5 composite system after 30 s of ablation were calculated, and the results are as follows: Figure 7 a and Figure 7 As shown in b, the linear ablation rate of A0M0B5 is only 0.0248 mm / s, a decrease of 74.8% compared to PIDA-2.5, while the linear ablation rate of A10M5B0 is 0.047 mm / s, a decrease of 52.2% compared to PIDA-2.5. Whether only hydroxide or only B2O3 is added, both the linear ablation rate and the mass ablation rate are significantly reduced compared to the PIDA-2.5 matrix, indicating that the ablation resistance of this invention is greatly improved compared to the PIDA-2.5 matrix.

[0095] The ablation rate of A10M5B0 is still relatively high, indicating that the material lost a significant amount of mass during pyrolysis and droplet formation. However, compared to the pure PIDA-2.5 matrix, the linear ablation rate still decreased by 52.2% after the addition of hydroxide, demonstrating that the present invention successfully delayed the thermal decomposition of the matrix.

[0096] In the A10M5B2.5, A10M5B5 and A10M5B10 systems, the linear ablation rate further decreased with the increase of B2O3 content, while A10M5B10 showed a negative linear ablation rate. The carbon layer showed slight expansion, and the underlying matrix pyrolysis was less, indicating that the ablation resistance of the material was greatly improved.

[0097] Figure 7 c represents the thermal conductivity data of the B2O3 / PIDA-2.5 composite system. It can be seen that A0M0B5 has the lowest thermal conductivity due to the smallest amount of filler added, while the four groups of samples with 10 phr ATH and 5 phr MH show similar thermal conductivity.

[0098] In this invention, the backplate temperature of the sample was recorded using thermocouples before and after the ablation test. The results are as follows: Figure 7 As shown in Figure d, after 30 seconds of ablation, the backplate temperature of all samples with added filler was lower than PIDA-2.5. This is also related to the lower linear ablation rate of the material after adding filler, indicating that this invention reduces the downward erosion of heat. After 30 seconds of ablation, the backplate temperature continued to rise, and the results were closely related to the thermal conductivity of the material. A0M0B5 had the lowest thermal conductivity and the lowest peak backplate temperature; while A10M5B0 had the highest thermal conductivity and therefore the highest peak backplate temperature. Experimental results show that the B2O3 / PIDA-2.5 composite system of this invention exhibits excellent ablation resistance. The addition of B2O3 plays a decisive role in the ablation and charring of the PIDA-2.5 self-healing matrix. Its synergistic effect with hydroxides makes the char layer after ablation more continuous and dense. The linear ablation rates of A10M5B2.5 and A10M5B5 are 0.0263 mm / s and 0.0179 mm / s, respectively, which are reduced by 73.2% and 81.8% compared to the PIDA-2.5 matrix, demonstrating excellent ablation performance. The linear ablation rate and mass ablation rate of the B2O3 / PIDA-2.5 composite system of this invention are significantly reduced.

[0099] In summary, this invention relates to a room-temperature self-healing flexible ablation-resistant material, its preparation method, and its applications. The room-temperature self-healing flexible ablation-resistant material is prepared by combining Al(OH)3, Mg(OH)2, and B2O3 as fillers with isocyanate-terminated prepolymers. This room-temperature self-healing flexible ablation-resistant material not only has high mechanical strength but also good room-temperature self-healing properties, as well as excellent heat resistance and ablation resistance, exhibiting superior overall performance.

[0100] This invention is the first to discover a room-temperature self-healing flexible ablation-resistant material made by combining isocyanate-terminated prepolymers with 0-10 parts Al(OH)3, 0-5 parts Mg(OH)2, and 2.5-10 parts B2O3 as fillers. This material significantly enhances the resistance to thermal ablation while maintaining the room-temperature self-healing capability of the ablation-resistant material, achieving maintenance-free characteristics and effectively extending its service life, filling a gap in this field. The self-healing flexible material of this invention exhibits stable performance, a wide range of applications, and a long service life. It can be applied to various flexible materials, coating materials, potting materials, and adhesives, especially in high-temperature environments or for external protective coatings and flexible components requiring heat resistance and ablation resistance, such as flexible heat-resistant coatings. It offers advantages such as maintenance-free operation and high reliability, and has broad application prospects.

Claims

1. A room-temperature self-healing flexible ablation-resistant material, characterized in that: It is prepared from oligomeric polyols, isocyanates, metal hydroxide flame retardants, boron-containing compounds, chain extenders, and crosslinking agents as raw materials; wherein, the mass ratio of the oligomeric polyols, isocyanates, metal hydroxide flame retardants, boron-containing compounds, chain extenders, and crosslinking agents is (45~80):(20~40):(0~30):(1~20):(5~20):(1~5), and the mass fraction of the metal hydroxide flame retardant is not 0; the boron-containing compound is boron oxide or zinc borate; the chain extender is an aliphatic or aromatic diamino disulfide containing reversible disulfide bonds, and / or, the crosslinking agent is a trifunctional compound with a pyridine or pyrimidine ring structure containing hydrogen bond acceptors and donors and with amino or hydroxyl groups as active functional groups.

2. The room-temperature self-healing flexible ablation-resistant material according to claim 1, characterized in that: The mass ratio of the oligomeric polyol, isocyanate, metal hydroxide flame retardant, boron-containing compound, chain extender and crosslinking agent is (55~65):(25~30):(0~20):(2.5~10):(10~12):(1~2), and the mass fraction of the metal hydroxide flame retardant is not 0. The metal hydroxide flame retardant is one or more of magnesium hydroxide, aluminum hydroxide, or bimetallic hydroxide flame retardants.

3. The room-temperature self-healing flexible ablation-resistant material according to claim 1 or 2, characterized in that: The mass ratio of the oligomeric polyol, isocyanate, metal hydroxide flame retardant, boron-containing compound, chain extender and crosslinking agent is 59.77:27.85:(0~15):(2.5~10):11.12:1.25, and the mass of the metal hydroxide flame retardant is not 0 parts; The boron-containing compound is boron oxide.

4. The room-temperature self-healing flexible ablation-resistant material according to claim 3, characterized in that: The metal hydroxide flame retardant is magnesium hydroxide and aluminum hydroxide; The mass ratio of magnesium hydroxide to aluminum hydroxide is (0~10):(0~5); The oligomeric polyol is polytetrahydrofuran, polyoxypropylene polyol, or copolyether polyol. The isocyanate is a diisocyanate; The chain extender is 4,4'-diaminodiphenyl disulfide, 4,4'-dihydroxydiphenyl disulfide, 3,3'-dihydroxydiphenyl disulfide, or 2-hydroxyethyl disulfide, and / or the crosslinking agent is 2,4-diamino-6-hydroxypyrimidine, 2,4,6-triaminopyrimidine, or 2,4,5-triaminopyridine.

5. The room-temperature self-healing flexible ablation-resistant material according to claim 4, characterized in that: The diisocyanate is isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate, or diphenylmethane diisocyanate.

6. The room-temperature self-healing flexible ablation-resistant material according to claim 5, characterized in that: The isocyanate is isophorone diisocyanate; The chain extender is 4,4'-diaminodiphenyl disulfide; The crosslinking agent is 2,4-diamino-6-hydroxypyrimidine.

7. A method for preparing a room-temperature self-healing flexible ablation-resistant material according to any one of claims 1 to 6, characterized in that: It includes the following steps: (1) Synthesis of prepolymer: Add a catalytic amount of catalyst to oligomeric polyol and isocyanate, react in solvent to obtain prepolymer solution; (2) Composite filler: Add metal hydroxide flame retardant and boron-containing compound to the prepolymer solution and stir until evenly dispersed; (3) Chain extension and crosslinking: Add a crosslinking agent and a chain extender soluble in solvent to the final product of step (2), react, and obtain the reactant; (4) Curing: Pour the reactants into a mold and cure them to obtain the product; In step (1), the solvent is dimethyl sulfoxide or diethyl sulfoxide; In step (3), the solvent is dimethyl sulfoxide or diethyl sulfoxide.

8. The preparation method according to claim 7, characterized in that: In step (1), the catalyst is dibutyltin dilaurate or stannous octoate.

9. The preparation method according to claim 7, characterized in that: In step (1), the reaction temperature is 60~100℃; and / or, the reaction environment is an inert gas environment; and / or, the reaction time is 1~6h; And / or, in step (3), the temperature of the reaction is 50~100℃; and / or, the reaction time is 0.5~5h; And / or, in step (4), the curing conditions are to first maintain at 90~150℃ for 1~5h in a vacuum environment, and then maintain at 120~200℃ for 10~20h.

10. Use of the room temperature self-healing flexible ablation-resistant material according to any one of claims 1 to 9 in the preparation of room temperature self-healing materials.

11. The use according to claim 10, characterized in that, The room temperature self-healing material is a flexible material, coating material, potting material, or adhesive; or the room temperature self-healing material is an external protective coating and flexible component material used in high-temperature environments or with heat resistance and ablation resistance requirements.

12. The use according to claim 11, characterized in that, The room-temperature self-healing material is a flexible heat-resistant coating material.

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