Flexible organic silicon resin-based heat prevention and insulation composite material and preparation method thereof

Abstract

The invention relates to a flexible organic silicon resin-based heat prevention and insulation composite material and a preparation method thereof, and belongs to the technical field of thermal protection materials, and the preparation method comprises the following steps: preparing a star-shaped block copolymerized polyvinyl phenyl organic silicon resin prepolymer; weaving the PAN fibers to prepare a PAN fiber woven body of which the porosity is gradually increased from the outer side to the inner side in a gradient manner in the thickness direction; on the basis of a cyclic pulsating pressure impregnation process, star-shaped block organic silicon resin prepolymer solutions with different solid contents are used for impregnating a PAN fiber woven body for multiple times, heating and curing are carried out, the flexible organic silicon resin-based heat prevention and insulation composite material is obtained, and different porosity areas of the PAN fiber woven body in the composite material are filled with organic silicon resin with different solid contents. According to the method, the technical problems of poor high-temperature strength and stability, high-temperature layering failure easily caused by interface stress concentration, low ablation resistance and coordination of contradiction between the surface ablation resistance requirement of the material and the internal heat insulation function in the flexible organic silicon resin based heat prevention and insulation composite material in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat protection materials, in particular to a flexible silicone resin-based heat protection and insulation composite material and a preparation method thereof. BACKGROUND

[0002] Traditional silicone heat protection materials are mainly single silicone rubber or short fiber reinforced composites. Although they have a certain flexibility, their high temperature resistance is limited, and they are prone to thermal decomposition in high-speed and high-heat environments, resulting in a significant increase in ablation rate, which is difficult to meet the simultaneous requirements of ablation resistance, long-term high-temperature stability and structural flexibility in the technical field of heat protection materials.

[0003] In addition, conventional fiber-reinforced silicone materials rely on physical infiltration to achieve interface bonding. Due to the significant difference in thermal expansion coefficient between the fiber and the matrix, interface stress concentration is easily generated during thermal cycling, resulting in delamination of the protective layer. At the same time, conventional fiber-reinforced silicone materials are difficult to reconcile the contradiction between the surface ablation resistance requirement and the internal thermal insulation function, often resulting in the single compromise of protection efficiency. SUMMARY

[0004] In view of the above analysis, the present application aims to provide a flexible silicone resin-based heat protection and insulation composite material and a preparation method thereof, to solve at least one of the technical problems of the prior art, such as poor high-temperature strength and stability, interface stress concentration, high-temperature delamination failure, low ablation resistance, and the contradiction between the surface ablation resistance requirement and the internal thermal insulation function.

[0005] A preparation method of a flexible silicone resin-based heat protection and insulation composite material, comprising:

[0006] S1: preparing a star-shaped block copolymerized vinylphenyl silicone resin prepolymer;

[0007] S2: weaving PAN fibers to prepare a PAN fiber woven body with a porosity gradient increasing from the outside to the inside in the thickness direction;

[0008] S3: based on a cyclic pulsating pressure impregnation process, impregnating the PAN fiber woven body with star-shaped block silicone resin prepolymer solutions with different solid contents multiple times and heating and curing to obtain a flexible silicone resin-based heat protection and insulation composite material, and the PAN fiber woven body in different porosity regions of the composite material is filled with silicone resin with different solid contents.

[0009] Preferably, the star-shaped block silicone resin prepolymer comprises a star-shaped prepolymer component, a second block component, a crosslinking agent and a catalyst; wherein the star-shaped prepolymer component comprises a plurality of arms, each arm comprising a first block component;

[0010] One of the first block component and the second block component contains no less than two vinyl groups, and the other contains at least one silicon-hydrogen bond;

[0011] The crosslinking agent contains at least two silicon-hydrogen bonds.

[0012] Preferably, the step S1 comprises:

[0013] The step S101 comprises:

[0014] The step S102 comprises:

[0015] The step S103 comprises:

[0016] Preferably, the step S101 comprises:

[0017] S1011, adding the star modifier and the monomers of the first block component into toluene according to the designed molar ratio, and controlling the reaction temperature and the reaction time to prepare the star pre-polymer with the target polymerization degree;

[0018] S1012, selecting a suitable end-capping agent to end-cap the first block component according to the monomers of the first block component, and preparing the star pre-polymer component with the first block component connected to the arms.

[0019] Preferably, the star modifier can be hexamethyldisilazane.

[0020] Preferably, the step S1011 comprises:

[0021] Step (1): adding the star modifier hexamethyldisilazane, the monomer phenyltrichlorosilane, and the monomer diphenyldichlorosilane into toluene according to the target molar ratio, and placing in a water bath at 40-50°C for hydrolysis for 2-3 hours;

[0022] Step (2): continuing to pre-polymerize at 50-60°C for 2-3 hours;

[0023] Step (3): adding hydrochloric acid, and continuing to terminate polymerization for 2-3 hours to obtain the un-end-capped star pre-polymer component.

[0024] Preferably, the step S1012 comprises:

[0025] Step (1): filtering the un-end-capped star pre-polymer component, and cleaning with ethanol and vacuum drying treatment;

[0026] Step (2): dissolving the un-end-capped star pre-polymer component after the drying treatment in toluene, and reacting at 70-90°C for 4-8 hours in an inert atmosphere.

[0027] Preferably, the step S102 comprises:

[0028] S1021, the monomers of the second block component are added to toluene according to the designed molar ratio, and the reaction temperature and reaction time are controlled to prepare a second block component prepolymer with a target polymerization degree;

[0029] S1022, a suitable end-capping agent is selected according to the monomers of the second block component to cap the second block component, thereby preparing the second block component.

[0030] A flexible silicone resin-based heat protection composite material is prepared by the above-mentioned method for preparing a flexible silicone resin-based heat protection composite material, comprising:

[0031] A PAN fiber woven body, a silicone resin dispersed in the pores of the PAN fiber woven body, and an RTV silicone rubber layer connecting the silicone resin and the PAN fiber, wherein the porosity of the PAN fiber woven body increases from the outside to the inside in the thickness direction, and different porosity regions of the PAN fiber woven body are filled with silicone resins with different solid contents.

[0032] An application of a flexible silicone resin-based heat protection composite material, the flexible silicone resin-based heat protection composite material prepared by the above-mentioned method is used as a high-temperature heat insulation layer in a temperature range of -60℃ to 300℃.

[0033] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0034] (1) The star-shaped block silicone resin used in the present application makes the resin have higher bending resilience on the basis of maintaining a certain flexibility, which can provide better stability, so that it performs better in applications requiring high strength and impact resistance; at the same time, it has better flowability at room temperature and maintains good processing performance; different solid content silicone resin solutions are used to batchwise impregnate the modified PAN fiber woven body and heat curing treatment, which helps to build a thermal conductivity gradient change structure of the organic silicon heat protection material from the inside to the outside, which cooperates with the porosity gradient change of the PAN fiber woven body and the star-shaped block silicone resin, helps to build a one-way heat channel, improves the ablation oxidation resistance of the PAN fiber, makes the material realize the cross-scale collaborative bearing of thermal and mechanical load, improves the high-temperature stability and bending strength of the material, reduces the linear ablation rate, and overcomes the defects of the prior art flexible silicone resin-based heat protection composite material, which is easy to fail at high temperature and coordinates the contradiction between the surface ablation resistance requirement and the internal heat insulation function.

[0035] (2) The present application obtains a star-shaped block organosilicon resin with a first block component-second block component and a first block component-crosslinking agent-second block component block structure by setting multiple arms in the star-shaped prepolymer component, each arm containing a first block component, and one of the first block component and the second block component is provided with not less than two vinyl groups, and the other is provided with at least one silicon-hydrogen bond, realizing high regularity of the block structure, and further improving high-temperature stability, bending resilience and bending strength performance.

[0036] (3) The present application realizes high selectivity of the first block component-second block component connection by selecting a suitable end-capping agent for the first block component and the second block component according to the monomers of the first block component and the second block component, greatly reduces the side reactions, obtains a star-shaped block organosilicon resin with a first block component-second block component and a first block component-crosslinking agent-second block component block structure, ensures high regularity of the block structure, and further improves high-temperature stability and mechanical properties.

[0037] (4) The present application realizes directional dispersion and dredging of heat flow from the low-porosity side to the high-porosity side by forming a heat flow channel between the pores in the thickness direction of the PAN fiber woven body, and further improves stability and bending strength at high temperature.

[0038] (5) The present application is conducive to forming a uniform and dense RTV silicone rubber modified layer in the pre-oxidized PAN fiber by gradient temperature curing, reduces interface defects, and improves mechanical properties; selecting different pressures at different stages of curing can reduce material stress, further reduce interface delamination, and improve stability at high temperature.

[0039] (6) The present application modifies the pre-oxidized PAN fiber with epoxy-modified RTV silicone rubber, realizes good compatibility of the PAN fiber and the RTV silicone rubber, not only improves the bonding strength and reduces interface delamination, but also improves the bending strength and stability at high temperature of the flexible organosilicon resin-based heat shielding composite material, and the Si-O-C chemical bond at the modified interface can form a continuous Si-O-C ceramic layer at high temperature ablation, effectively inhibits fiber oxidation damage, reduces linear ablation rate, and overcomes the defects of the prior art, such as poor high-temperature strength and stability, low high-temperature interface strength, easy high-temperature delamination failure, and low ablation resistance.

[0040] (7) The present application adopts organic silicon resin solutions with different solid contents to impregnate the modified PAN fiber braided body in batches and heat curing treatment, which helps to build the thermal conductivity gradient change structure of the organic silicon heat protection material from the inside to the outside, cooperates with the porosity gradient change of the PAN fiber braided body, helps to build the heat one-way channel, improves the oxidation resistance of the PAN fiber, makes the material realize the cross-scale collaborative bearing of thermal and mechanical load, improves the high temperature stability and bending strength of the material, reduces the linear ablation rate, and overcomes the defects that the existing flexible organic silicon resin based heat protection composite material is easy to delaminate at high temperature.

[0041] The above technical solutions in the present application can also be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained through the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated herein and constitute a part of the detailed description. The drawings illustrate embodiments of the present application and, together with the detailed description, serve to explain the principles of the present application.

[0043] Figure 1 Preparation method flow chart of the flexible organic silicon resin based heat protection composite material of the present application;

[0044] Figure 2 Infrared spectra of the modified PAN fiber and the unmodified PAN fiber in Example 1 of the present application. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present application will be specifically described below in combination with the drawings, wherein the drawings constitute a part of the present application, and are used to explain the principles of the embodiments of the present application, and are not used to limit the scope of the present application.

[0046] Term definition:

[0047] The outside of the flexible organic silicon resin based heat protection composite material or the PAN fiber braided body refers to the side in contact with the outside world;

[0048] The inside of the flexible organic silicon resin based heat protection composite material or the PAN fiber braided body refers to the side in contact with the substrate in need of protection.

[0049] In the first aspect, the present application provides a preparation method of a flexible organic silicon resin based heat protection composite material, comprising:

[0050] S1: preparing a star-shaped block copolymerized vinylbenzyl silicone resin prepolymer;

[0051] S2: weaving PAN fibers to prepare a PAN fiber woven body with the porosity gradient increasing from the outside to the inside in the thickness direction;

[0052] S3: multiple times of impregnating the PAN fiber woven body with the star-shaped block organosilicon resin pre-polymer solutions with different solid contents based on the cyclic pulsating pressure impregnation process and heating and curing to obtain a flexible organosilicon resin-based heat protection composite material, and the PAN fiber woven body in different porosity regions in the composite material is filled with organosilicon resins with different solid contents.

[0053] Compared with the prior art, the star-shaped block organosilicon resin adopted in the present application can provide better stability on the basis of maintaining a certain flexibility, which makes it perform better in applications requiring high strength and impact resistance; at the same time, the star-shaped block organosilicon resin has better flowability at room temperature and maintains good processing performance; the modified PAN fiber woven body is impregnated with organosilicon resin solutions with different solid contents in batches and is subjected to heating and curing treatment, which helps to build a structure with a thermal conductivity gradient varying from the inside to the outside of the organosilicon heat protection material, and cooperates with the star-shaped block organosilicon resin and the porosity gradient variation of the PAN fiber woven body to help build a one-way heat channel, improve the ablation oxidation resistance of the PAN fiber, and make the material realize cross-scale collaborative bearing of thermal and mechanical loads, improve the high-temperature stability and bending strength of the material, and reduce the linear ablation rate, overcoming the defects of the prior art flexible organosilicon resin-based heat protection composite material, such as easy high-temperature delamination failure and the contradiction between the surface ablation resistance requirement and the internal heat insulation function.

[0054] It should be noted that the block copolymerized vinylphenyl organosilicon resin belongs to an addition type curing resin due to the presence of vinyl groups, and the curing process of the block copolymerized vinylphenyl organosilicon resin does not produce small molecule products, has no small molecule escape channel, has high mechanical strength, and has low thermal conductivity, which can further improve the high-temperature stability and reduce the linear ablation rate.

[0055] Specifically, the star-shaped block organosilicon resin pre-polymer comprises a star-shaped pre-polymer component, a second block component, a crosslinking agent, and a catalyst; the star-shaped pre-polymer component comprises a plurality of arms, and each arm comprises a first block component;

[0056] One of the first block component and the second block component contains not less than two vinyl groups, and the other contains at least one silicon-hydrogen bond.

[0057] The crosslinking agent contains at least two silicon-hydrogen bonds.

[0058] In the implementation, after the curing treatment in step S3, the vinyl groups in the first block component or the second block component in the star block organosilicon resin prepolymer respectively react with the silicon hydrogen bonds in the crosslinking agent and the silicon hydrogen bonds in the other component, thereby realizing the direct connection of the first block component and the second block component or the indirect connection of the first block component and the second block component through the crosslinking agent, and further obtaining the star block copolymerized vinyl phenyl organosilicon resin with the direct connection of the first block component and the second block component or the sequential connection of the first block component-crosslinking agent-second block component.

[0059] Compared with the prior art, the star block organosilicon resin with the first block component-second block component and the first block component-crosslinking agent-second block component block structure is selectively obtained by arranging multiple arms in the star prepolymer component, each arm containing a first block component, one of the first block component and the second block component being provided with no less than two vinyl groups, and the other being provided with at least one silicon hydrogen bond, thereby realizing the high regularity of the block structure and further improving the high-temperature stability, bending resilience and bending strength performance.

[0060] Specifically, step S1 comprises:

[0061] Step S101, star prepolymer component preparation;

[0062] Step S102, second block component preparation;

[0063] Step S103, mixing the star prepolymer component, the second block component, the crosslinking agent, the catalyst and the necessary solvent to obtain the star block organosilicon resin prepolymer preparation.

[0064] Specifically, step S101 comprises:

[0065] S1011, adding the star modifier and the monomer of the first block component into toluene according to the designed molar ratio, controlling the reaction temperature and the reaction time to prepare the star prepolymer with the target polymerization degree;

[0066] S1012, selecting a suitable end-capping agent to end-cap the first block component according to the monomer of the first block component, to prepare the star prepolymer component with the first block component connected to the arms.

[0067] Specifically, the star modifier can be hexamethyldisilazane (HMDSN).

[0068] It should be noted that, to prepare the block polymer, when the monomer of the first block component is a phenyl monomer, the monomer of the second block component is a vinyl monomer; when the monomer of the first block component is a vinyl monomer, the monomer of the second block component is a phenyl monomer; and the first block component (star prepolymer component) containing a phenyl group and the second block component containing a vinyl group are taken as examples.

[0069] Step S1011 comprises:

[0070] Step (1): The star modifier hexamethyldisilazane, monomer phenyltrichlorosilane, monomer diphenyldichlorosilane are added to toluene according to the target molar ratio, and hydrolysis is carried out at 40-50°C under water bath for 2-3 hours.

[0071] Step (2): Continue to pre-polymerize at 50-60°C for 2-3 hours.

[0072] Step (3): Add an acid catalyst, and continue to terminate polymerization for 2-3 hours to obtain an unblocked star-shaped prepolymer component.

[0073] The acid catalyst can be 3% by mass of 0.1 mol / L hydrochloric acid.

[0074] It should be noted that in step S1012, a suitable end-capping agent is selected according to the monomer of the first block component to satisfy:

[0075] The monomer of the first block component is a phenyl monomer, and an end-capping agent containing a silicon-hydrogen bond, such as dimethylhydrogen monochlorosilane (DMCS), can form a silicon-hydrogen bond at the end of the first block component.

[0076] Step S1012 comprises:

[0077] Step (1): After filtering the unblocked star-shaped prepolymer component, it is washed with ethanol and vacuum dried.

[0078] Step (2): Dissolve the unblocked star-shaped prepolymer component after drying treatment in toluene, and react at 70-90°C for 4-8 hours under an inert atmosphere.

[0079] Specifically, the molar ratio of the star modifier and the first block component is determined according to the polymerization degree of the first block component. When the first block component is polymerized from a phenyl monomer, the polymerization degree is 8000-12000, which can be 8000, 9000, 10000, 11000 or 12000; and the corresponding second block component is polymerized from a vinyl monomer, and the polymerization degree is 16000-20000; when the first block component is polymerized from a vinyl monomer, the polymerization degree is 16000-20000, which can be 16000, 17000, 18000, 19000 or 20000; and the corresponding second block component is polymerized from a phenyl monomer, and the polymerization degree is 8000-12000.

[0080] The above settings can ensure that the polymerization degree of the phenyl block in the star-shaped block organosilicon resin prepolymer is 8000-12000, and the polymerization degree of the vinyl monomer is 16000-20000.

[0081] The molar ratio of the end-capping agent to the star modifier is 6.1-6.3:1, which can be 6.1:1, 6.2:1 or 6.3:1.

[0082] It should be noted that the molar ratio of the star modifier to the first block component is related to the target polymerization degree, and the hexamethyldisilazane has 6 silicon hydroxyl branch arms after hydrolysis, and each branch arm can independently connect one first block component. When the polymerization degree of the first block component is 8000-12000, the molar ratio of the star modifier to the first block component is 1:48000-72000.

[0083] Specifically, the phenyl content in the star block copolymerized vinylphenyl silicone resin prepolymer is controlled to be 18wt%-22wt%, which can be 18wt%, 19wt%, 20wt%, 21wt% or 22wt%.

[0084] It should be noted that increasing the phenyl content helps to improve the high temperature resistance and thermal stability, but too high phenyl content will reduce the toughness.

[0085] In implementation, the molar ratio of different phenyl content monomers can be determined according to the phenyl content in the star block copolymerized vinylphenyl silicone resin prepolymer and the target polymerization degree of the first block component; for example, the phenyl content of monomer phenyltrichlorosilane and monomer diphenyldichlorosilane is different, by adjusting the ratio of the two, the phenyl mass content in the first block component can be adjusted to vary in the range of 40%-48%, and by adjusting the polymerization degree of the first block component and the second block component, the phenyl content in the star block copolymerized vinylphenyl silicone resin can be adjusted to vary in the range of 18wt%-22wt%; for example, when the polymerization degree of the first block component is 8000-12000, the polymerization degree of the second block component is 16000-18000.

[0086] Specifically, step S102 includes:

[0087] S1021, adding the monomers of the second block component into toluene according to the designed molar ratio, and controlling the reaction temperature and the reaction time to prepare the second block component prepolymer with the target polymerization degree;

[0088] S1022, selecting a suitable end-capping agent to end-cap the second block component to prepare the second block component.

[0089] The following continues to take the preparation of the first block component containing phenyl (star prepolymer component) and the second block component containing vinyl as an example to illustrate step S1021:

[0090] Step S1021 includes:

[0091] Step (1): monomer methylvinyl dichlorosilane, monomer vinyl trichlorosilane are added into toluene according to target molar ratio, hydrolysis for 2-3 hours under 40-50℃ water bath;

[0092] Step (2): continue pre-polymerization for 2-3 hours under 50-60℃;

[0093] Step (3): add 3% mass fraction of 0.1 mol / L hydrochloric acid, continue final polymerization for 2-3 hours to obtain un-capped star-shaped pre-polymer component.

[0094] It should be noted that in step S1022, a suitable end-capping agent is selected according to the monomer of the second block component to meet:

[0095] The monomer of the second block component is a vinyl monomer, and a disiloxane end-capping agent such as hexamethyl disiloxane (HMDSO) and 1,1,3,3-tetramethyl disiloxane is selected, wherein the siloxane bond (Si-O-Si) can react with the silicon hydroxyl (Si-OH) at the end of the polymer chain to form a stable inert end group, which cannot continue to react with silicon hydroxyl (Si-OH) or vinyl.

[0096] It should be noted that for another case, the first block component (star-shaped pre-polymer component) contains vinyl, and the second block component contains phenyl, the monomer of the first block component in step S1011 is changed to the vinyl monomer in step S1021, the monomer of the second block component in step S1021 is changed to the phenyl monomer in step S1011, and the end-capping agent is adjusted according to the adaptability of the monomer, and then the first block component containing vinyl and the second block component containing phenyl are prepared.

[0097] It should be noted that during the thermal curing of step S3, the first block component and the second block component contain almost no silicon hydroxyl or contain a small amount of silicon hydroxyl, and cannot be cured by silicon hydroxyl condensation without adding a silicon hydroxyl curing catalyst, and crosslinking curing can only be carried out by addition of silicon hydrogen bond and vinyl.

[0098] Compared with the prior art, the present application realizes high selectivity of the connection of the first block component and the second block component by selecting a suitable end-capping agent for the first block component and the second block component according to the monomers of the first block component and the second block component, greatly reduces the generation of side reactions, and obtains a star-shaped block organosilicon resin with a first block component-second block component and a first block component-crosslinking agent-second block component block structure, which ensures high regularity of the block structure and further improves high temperature stability and mechanical properties.

[0099] The star block copolymerization vinyl phenyl silicone resin prepolymer prepared by the above method has a polymerization degree of 24000-32000, a phenyl monomer polymerization unit polymerization degree of 8000-10000, a vinyl monomer polymerization unit polymerization degree of 16000-20000, a 25℃ rotary viscosity of 1200±200 mPa·s, a glass transition temperature (Tg) of -45 to -40℃, and a thermal decomposition temperature (T d 5%) ≥ 420℃.

[0100] Specifically, the crosslinking agent in the star block silicone resin prepolymer can be methyl hydrogen-containing silicone oil crosslinking agent, the SiH content is 0.5wt%-0.8wt%, and the amount of methyl hydrogen-containing silicone oil crosslinking agent satisfies that the molar ratio of SiH in the methyl hydrogen-containing silicone oil to the vinyl of the silicone resin is 1.05-1.1:1.

[0101] Specifically, the catalyst in the star block silicone resin prepolymer can be chloroplatinic acid-vinyl siloxane complex, and the amount satisfies that the mass concentration in the star block silicone resin prepolymer is 30ppm-100ppm.

[0102] Specifically, the porosity of the PAN fiber braid in step S2 is 25%-35%, the thickness of the PAN fiber braid is 2mm-5mm, and the fiber volume content is 40%-60%.

[0103] It should be noted that the fiber volume content is related to the fiber diameter and the porosity, and when the porosity is constant, the larger the fiber diameter, the greater the fiber volume content.

[0104] Further preferably, the PAN fiber braid can be provided with three fiber braid layers from the inside to the outside, and the porosities of the sections in each fiber braid layer are equal.

[0105] The porosity of the lower layer of the fiber braid layer is 25%-28%, the porosity of the middle layer of the fiber braid layer is 30%-32%, and the porosity of the higher layer of the fiber braid layer is 35%-38%.

[0106] In implementation, the PAN fiber braid with a step change in porosity can form a heat flow channel between the pores after being filled with the silicone resin solution, so as to realize directional dispersion and dissipation of heat flow from the low-porosity side to the high-porosity side; the high-porosity side buffers thermal strain through the pores, so as to realize cross-scale collaborative bearing of the material under thermal and mechanical loads.

[0107] Compared with the prior art, the present application realizes directional dispersion and dissipation of heat flow from the low-porosity side to the high-porosity side by forming a heat flow channel between the pores of the PAN fiber braid, which has a step decrease in porosity from the inside to the outside in the thickness direction, so as to further improve the stability and bending strength at high temperatures.

[0108] Preferably, the PAN fibers in step S2 can adopt pre-oxidized PAN fibers.

[0109] Specifically, the pre-oxidized PAN fibers can be obtained by oxidizing the PAN fibers at 200℃-230℃ for 80min-100min.

[0110] Specifically, the PAN fiber braid in step S2 is a 2.5D or three-dimensional braided structure.

[0111] Further preferably, step S2 further comprises modifying the epoxy-modified RTV silicone rubber to the PAN fiber braid to improve the connection strength of the silicone resin to the PAN fiber braid and the stability at high temperature.

[0112] Specifically, the modification of the epoxy-modified RTV silicone rubber to the PAN fiber braid in step S2 adopts vacuum impregnation assisted bonding and heating curing, and the thickness of the RTV silicone rubber layer is 10μm-50μm, which can be 10μm, 15μm, 20μm, 26μm, 30μm, 35μm, 40μm, 45μm, or 50μm.

[0113] Specifically, the vacuum degree of the vacuum impregnation assisted bonding is -0.09MPa--0.07MPa, the RTV silicone rubber is injected at a rate of 5mL / min-8mL / min to immerse the fiber braid, and the impregnation time is 30min-60min.

[0114] It should be noted that the vacuum degree, injection rate, and impregnation time of the vacuum impregnation assisted bonding can achieve better infiltration and flow within the above ranges.

[0115] Preferably, the heating curing treatment of the epoxy-modified RTV silicone rubber is gradient temperature curing.

[0116] Specifically, the heating curing treatment of the epoxy-modified RTV silicone rubber can be three-stage gradient temperature curing, and the temperature and holding time of the gradient temperature curing satisfy: 55℃-65℃ / 1.5h-2.5h / -0.07MPa--0.09MPa→85℃-90℃ / 3.5h-5h / -0.03MPa--0.06MPa→115℃-135℃ / 2.5h-4h / normal pressure. The temperature rising rate of each stage of the gradient temperature curing is 2℃ / min-5℃ / min.

[0117] The applicant has found that the self-curing of RTV silicone rubber is mainly affected by water vapor, and the curing is from the surface to the inside, and the reaction temperature is lower than the reaction temperature of pre-oxidized PAN fiber and epoxy group modified RTV silicone rubber, the pre-oxidized PAN fiber and the epoxy group modified RTV silicone rubber, the initial reaction temperature of the reaction is about 80 DEG C, and the complete reaction needs to reach about 150 DEG C; at a single temperature, direct high-temperature curing or too fast heating rate, on the one hand, the high temperature affects the water vapor entering the RTV silicone rubber, so that the RTV silicone rubber is difficult to fully cure; on the other hand, the high temperature leads to violent reaction, and small molecule products are difficult to fully discharge, and micro-pores and interface defects are easily generated.

[0118] At the same time, the viscosity of the RTV silicone rubber and the surface tension of the RTV silicone rubber are matched, so that the thickness of the RTV silicone rubber layer is in a relatively appropriate range, so that the modified layer of the RTV silicone rubber plays a better flexible transition layer role, and the interface separation under high temperature is reduced.

[0119] In addition, the gradient temperature curing process can realize multi-level interface bonding through molecular dynamics regulation, the first stage is low-temperature pre-curing under subcritical vacuum, the conversion rate of esterification reaction of epoxy group and fiber surface carboxyl is 45%;

[0120] The second stage is to promote the construction of three-dimensional cross-linked network through siloxane polycondensation reaction through medium-temperature gradient pressure retention, and the ether bond grafting rate is greater than or equal to 85%;

[0121] The third stage is to implement high-temperature post-curing under normal pressure, to eliminate residual stress through molecular chain relaxation, and the thickness of the interface transition layer is accurately controlled to be about 20 microns.

[0122] Compared with the prior art, the gradient temperature curing is beneficial to forming a uniform and dense RTV silicone rubber modified layer on the pre-oxidized PAN fiber, reducing interface defects and improving mechanical properties; different pressures are selected in different stages, so as to reduce material stress, further reduce interface division, and improve stability under high temperature.

[0123] Specifically, the epoxy group modified RTV silicone rubber can be introduced in the following ways:

[0124] (1) 3,4-epoxy cyclohexyl ethyl methyl dimethoxysilane is used as a modifier, and the addition amount is 5% to 15% of the mass of the RTV silicone rubber matrix;

[0125] (2) under inert gas protection, the modifier is reacted with the hydroxyl-terminated polydimethylsiloxane at 60-80 DEG C for 4-6 hours, the content of epoxy group is controlled to be 0.3-0.8 mol / kg, which can be 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 mol / kg; the viscosity of the epoxy-modified RTV silicone rubber at 25 DEG C is 5000-15000 mPa s, which can be 5000, 5600, 6000, 7000, 7500, 8000, 10000, 11000, 12000 or 15000 mPa s.

[0126] It should be noted that the RTV silicone rubber is mainly composed of polysiloxane, the main chain of which is Si-O-Si, and the side chain is usually an organic group such as methyl or phenyl. Polyacrylonitrile (PAN) is a polymer containing cyano groups (-CN), and the main chain thereof is composed of carbon atoms, and the surface energy is low. The chemical structures of the two materials are quite different, resulting in weak interaction and poor compatibility between them; at the same time, the cyano groups in PAN and the siloxane bonds in the RTV silicone rubber are difficult to form effective chemical bonding, and it is extremely difficult to modify PAN using RTV silicone rubber under normal circumstances.

[0127] In the implementation, the pre-oxidized PAN fiber and the epoxy-modified RTV silicone rubber used in the present application not only have better compatibility and achieve sufficient infiltration, but also the surface of the pre-oxidized PAN fiber has more fiber active groups (-C=O, -OH) and better reactivity with the epoxy group, so that a Si-O-C chemical bond can be formed to achieve stable chemical connection and realize the surface modification of PAN by the RTV silicone rubber.

[0128] Compared with the prior art, the pre-oxidized PAN fiber is modified by the epoxy-modified RTV silicone rubber in the present application, which realizes good compatibility between the PAN fiber and the RTV silicone rubber, improves the bonding strength, reduces the interface delamination, and improves the bending strength and high-temperature stability of the flexible organic silicone resin-based heat-resistant composite material. At the same time, the Si-O-C chemical bond at the modified interface can form a continuous Si-O-C ceramic layer during high-temperature ablation, effectively inhibits the oxidation damage of the fiber, reduces the linear ablation rate, and overcomes the defects of the prior art, such as poor high-temperature strength and stability, low high-temperature interface strength, easy high-temperature delamination failure, and low ablation resistance.

[0129] Preferably, the step S3 of impregnating the organic silicone resin solution is a cyclic pulsating pressure impregnation process.

[0130] The pressure range is 0.5-2.0 MPa, the pulsation frequency is 0.1-0.5 Hz, and the pressure waveform is a trapezoidal wave, with a pressure increase rate of 0.25±0.1 MPa / s, a pressure maintenance time of 30±5 s, and a pressure decrease rate of 0.12±0.05 MPa / s.

[0131] It should be noted that the cyclic pulsating pressure impregnation process is selected:

[0132] On the one hand, the cyclic pulsating pressure impregnation process can improve the impregnation efficiency: by periodically applying and releasing pressure, the cyclic pulsating pressure impregnation process can significantly speed up the speed of the impregnating liquid into the preform, and shorten the impregnation time;

[0133] On the other hand, the cyclic pulsating pressure impregnation process can improve the impregnation uniformity: the periodic change of pressure helps the impregnating liquid to be more uniformly distributed in the entire preform, reducing the incomplete or uneven impregnation phenomenon caused by uneven capillary force;

[0134] In addition, the cyclic pulsating pressure impregnation process can improve the material properties; the pulsating pressure can promote the chemical reaction between the impregnating liquid and the preform, help to refine the microstructure of the matrix, and thus improve the mechanical properties and durability of the material; by controlling the pressure and time, the porosity and defects in the material can be reduced, and the density and strength of the material can be improved.

[0135] Further preferably, step S3 comprises: batchwise impregnating the modified PAN fiber braid with organic silicon resin solutions of different solid contents and heating and curing treatment.

[0136] Specifically, the PAN fiber braid has an inner high-porosity layer and an outer low-porosity layer, and the filling organic silicon resin solution has a gradually increasing solid content.

[0137] Specifically, step S3 comprises:

[0138] S301: Place the modified PAN fiber braid with the inner side facing down and the outer side facing up, and select a lower solid content organic silicon resin solution for the first impregnation of the modified PAN fiber braid;

[0139] S302: Curing and hot pressing the first impregnated modified PAN fiber braid to obtain a first-stage preform;

[0140] S303: Select a higher solid content organic silicon resin solution for the second impregnation of the first-stage preform;

[0141] S304: Curing and hot pressing the second impregnated first-stage preform to obtain a second-stage preform;

[0142] S305: Refer to steps S303-S304, the organic silicon resin solution with higher solid content is selected to impregnate, cure and hot-press the second stage preform, and the above steps are repeated to sequentially select the organic silicon resin solution with higher solid content to impregnate, cure and hot-press each stage preform to obtain the final flexible organic silicon resin-based heat protection and insulation composite material.

[0143] In the implementation, after the first impregnation, the organic silicon resin solution with the lowest solid content preferentially fills the high-porosity layer on the inside of the modified PAN fiber braid under the action of gravity and circulating pulsating pressure, and after curing and hot-pressing, a channel with lower cross-linking degree, higher softness and lower thermal conductivity is formed in the high-porosity layer; the softness makes the resin and the modified RTV silicone rubber layer have better adhesion, improves the stability and mechanical properties at high temperature; the lower thermal conductivity can form a heat insulation layer to improve the oxidation resistance of the PAN fiber; the organic silicon resin solution with higher solid content is filled in the high-porosity layer on the outside of the PAN fiber braid, and the high cross-linking degree helps to form a dense silicon-based ceramic layer.

[0144] Compared with the prior art, the present application adopts organic silicon resin solutions with different solid contents to impregnate the modified PAN fiber braid in batches and heat curing, which helps to build a thermal conductivity gradient structure of the organic silicon heat protection material from the inside to the outside, cooperates with the porosity gradient of the PAN fiber braid, helps to build a one-way heat channel, improves the oxidation resistance of the PAN fiber, makes the material realize the cross-scale collaborative bearing of thermal and mechanical load, improves the high-temperature stability and bending strength of the material, and reduces the linear ablation rate, overcoming the defect that the flexible organic silicon resin-based heat protection and insulation composite material of the prior art is easy to delaminate at high temperature.

[0145] It should be noted that the unique process of the present application of using organic silicon resin solutions with different solid contents to impregnate, heat and cure in batches needs to solve the problem that high-solid-content silicon resin is difficult to disperse in the PAN fiber braid during impregnation, and the above-mentioned circulating pulsating pressure impregnation process can realize the full dispersion of the organic silicon resin solution.

[0146] Preferably, the heating and curing treatment in step S3 is gradient temperature curing, and the temperature rising and holding time meet 80℃-90℃ / 1.0h-3h→110℃-130℃ / 1.0h-3h→150℃-160℃ / 1.0h-3h. The gradient temperature rising rate of each stage is 2℃ / min-5℃ / min.

[0147] It should be noted that the gradient temperature curing in step S3 can match different curing stages, release stress in stages, and avoid stress accumulation.

[0148] On the other hand, the present application provides a flexible organic silicon resin-based heat protection and insulation composite material, comprising:

[0149] A PAN fiber braid, an organic silicone resin dispersed in the pores of the PAN fiber braid, and an RTV silicone rubber layer connecting the organic silicone resin and the PAN fiber, wherein the porosity of the PAN fiber braid increases from the outside to the inside in the thickness direction of the PAN fiber braid, and the different porosity regions of the PAN fiber braid are filled with different solid contents of the organic silicone resin.

[0150] In a third aspect, the application relates to the application of the flexible organic silicone resin-based thermal insulation composite material as described above in the field of thermal protection materials, in particular to a high-temperature thermal insulation layer in a temperature range of-60-300 DEG C.

[0151] In order to better illustrate the application, the following preparation examples, examples and comparative examples are provided:

[0152] The RTV silicone rubber used is Ronsil RTV 6338 from Shanghai Rontex New Material Co., Ltd., with a viscosity of 2000 mPa·s.

[0153] Preparation Example 1

[0154] The preparation example discloses a preparation method of a star-shaped block copolymerized vinylphenyl silicone resin prepolymer:

[0155] Step S101, star-shaped prepolymer component preparation;

[0156] S1011, the star-shaped modifier and the monomers of the first block component are added to toluene according to the designed molar ratio, and the star-shaped prepolymer with a target polymerization degree is prepared by controlling the reaction temperature and the reaction time;

[0157] Step (1): the star-shaped modifier hexamethyldisilazane, the monomer phenyltrichlorosilane, and the monomer diphenyldichlorosilane are added to toluene according to the target molar ratio, and hydrolysis is carried out at 40 DEG C for 2 hours; the molar ratio of the star-shaped modifier and the first block monomer is 1:60000, so that the polymerization degree of the first block component is 10000; the molar ratio of the capping agent and the star-shaped modifier is 6.1:1; the molar ratio of the monomer phenyltrichlorosilane and the monomer diphenyldichlorosilane is set according to the phenyl content and the polymerization degree;

[0158] Step (2): continue to pre-polymerize at 50 DEG C for 2 hours;

[0159] Step (3): 3% mass fraction of 0.1 mol / L hydrochloric acid is added, and the final polymerization is continued for 3 hours to obtain an un-capped star-shaped prepolymer component;

[0160] S1012, a dimethylhydrochlorosilane (DMCS) capping agent is selected to cap the first block component, and a star-shaped prepolymer component connected with the first block component is prepared;

[0161] Step (1): After filtering the unblocked star-shaped prepolymer component, it is washed with ethanol and treated by vacuum drying;

[0162] Step (2): The unblocked star-shaped prepolymer component after drying treatment is dissolved in toluene, and reacted for 8 hours at 0℃ in an inert atmosphere.

[0163] Step S102, preparation of the second block component;

[0164] S1021, monomers of the second block component are added to toluene according to the designed molar ratio, and the second block component prepolymer with the target polymerization degree is prepared by controlling the reaction temperature and reaction time;

[0165] Step (1): monomers methylvinyl dichlorosilane and monomer vinyl trichlorosilane are added to toluene according to the target molar ratio, and hydrolysis is carried out at 50℃ for 3 hours; vinyl is selected as the second block component with a mass content of 22%, and the target polymerization degree is 18000; the molar ratio of monomers methylvinyl dichlorosilane and monomer vinyl trichlorosilane is set according to the vinyl content and the target polymerization degree;

[0166] Step (2): continue to pre-polymerize at 60℃ for 2 hours;

[0167] Step (3): 3% mass fraction of 0.1 mol / L hydrochloric acid is added, and the final polymerization is continued for 2-3 hours to obtain the unblocked star-shaped prepolymer component.

[0168] S1022, hexamethyl disiloxane (HMDSO) is selected as the blocking agent, in which the siloxane bond (Si-O-Si) can react with the silicon hydroxyl (Si-OH) at the end of the polymer chain to generate a stable inert end group, which cannot continue to react with the silicon hydroxyl (Si-OH) or vinyl, and the second block component is blocked to prepare the second block component.

[0169] Step S103, mixing the star-shaped prepolymer component, the second block component, the crosslinking agent, the catalyst and the necessary solvent to obtain the star-shaped block organosilicon resin prepolymer.

[0170] The phenyl content in the star-shaped block copolymer vinylphenyl organosilicon resin prepolymer is controlled at 20wt%.

[0171] The star-shaped block copolymer vinylphenyl organosilicon resin prepolymer is prepared by the above method, the first block component contains phenyl, the end group of the first block component contains silicon hydrogen bond, and the second block component contains vinyl.

[0172] According to the corresponding national standard test, the rotational viscosity at 25℃ is 1128 mPa·s, the glass transition temperature (Tg) is -45℃, and the thermal decomposition temperature (T d 5%) is 422℃.

[0173] Preparation Example 2

[0174] The present preparation example discloses a method for preparing a star-shaped block copolymer vinylphenyl silicone resin prepolymer:

[0175] Step S101, star prepolymer component preparation;

[0176] S1011, the star modifier, the monomers of the first block component are added to toluene according to the designed molar ratio, and the star prepolymer with the target degree of polymerization is prepared by controlling the reaction temperature and the reaction time;

[0177] Step (1): the star modifier hexamethyldisilazane, methylvinyl dichlorosilane, and monomer vinyltrichlorosilane are added to toluene according to the target molar ratio, and hydrolysis is carried out at 50°C for 2 hours in a water bath; the molar ratio of the star modifier and the first block monomer is 1:108000, so that the degree of polymerization of the first block component is 18000; the molar ratio of the end-capping agent to the star modifier is 6.3:1;

[0178] Step (2): continue to pre-polymerize at 60°C for 3 hours;

[0179] Step (3): 3% mass fraction of 0.1 mol / L hydrochloric acid is added, and the final polymerization is continued for 2 hours to obtain an unblocked star prepolymer component;

[0180] S1012, hexamethyldisiloxane (HMDSO) is selected as the end-capping agent, in which the siloxane bond (Si-O-Si) can react with the silicon hydroxyl group (Si-OH) at the end of the polymer chain to generate a stable inert end group, which cannot continue to react with the silicon hydroxyl group (Si-OH) or vinyl group to cap the first block component;

[0181] Step (1): after the unblocked star prepolymer component is filtered, it is washed with ethanol and vacuum dried;

[0182] Step (2): the unblocked star prepolymer component after drying treatment is dissolved in toluene, and reacted at 90°C for 4 hours in an inert atmosphere.

[0183] Step S102, second block component preparation;

[0184] S1021, the monomers of the second block component are added to toluene according to the designed molar ratio, and the second block component prepolymer with the target degree of polymerization is prepared by controlling the reaction temperature and the reaction time;

[0185] Step (1): the monomers phenyltrichlorosilane and diphenyldichlorosilane are added to toluene according to the target molar ratio, and hydrolysis is carried out at 50°C for 3 hours in a water bath;

[0186] Step (2): Continue pre-polymerization at 60℃ for 3 hours;

[0187] Step (3): Add 3% mass fraction of 0.1 mol / L hydrochloric acid, continue to terminate polymerization for 3 hours to obtain an unblocked star-shaped prepolymer component.

[0188] S1022, dimethyl hydrogen monochlorosilane (DMCS) is selected as the end-capping agent to prepare the second block component.

[0189] Step S103, mixing the star-shaped prepolymer component, the second block component, the crosslinking agent, the catalyst and the necessary solvent to obtain the star-shaped block organosilicon resin prepolymer.

[0190] The phenyl content in the star-shaped block copolymerized vinylphenyl organosilicon resin prepolymer is controlled at 22wt%.

[0191] The preparation example discloses a star-shaped block copolymerized vinylphenyl organosilicon resin prepolymer prepared by the above method, the second block component contains phenyl, the end group of the second block component contains a silicon-hydrogen bond, and the first block component contains vinyl.

[0192] According to the corresponding national standard test, the rotational viscosity at 25℃ is 1396 mPa·s, the glass transition temperature (Tg) is -41℃, and the thermal decomposition temperature (T d 5%) is 432℃.

[0193] Example 1

[0194] The example discloses a preparation method of a flexible organosilicon resin-based heat insulation composite material, and the specific preparation steps are as follows:

[0195] S1: The star-shaped block copolymerized vinylphenyl organosilicon resin prepolymer is obtained by the method in the preparation example 1.

[0196] S2: The pre-oxidized PAN fiber is woven to prepare a PAN fiber woven body; three-dimensional orthogonal woven PAN pre-oxidized fiber is selected as the reinforcing body, the fiber volume content is controlled to be 50%, the thickness of the woven body is 3mm, the interlayer porosity along the thickness direction is designed to be 28% (outer layer)→30% (middle)→32% (inner layer) three layers of equal thickness, and the fiber woven body is placed in a 100℃ oven for drying for 2 hours to remove adsorbed water;

[0197] The three-dimensional orthogonal woven PAN fiber is subjected to 200℃, 80min oxidation treatment to obtain PAN pre-oxidized fiber.

[0198] The epoxy-modified RTV silicone rubber is used to modify the PAN fiber woven body to prepare a modified PAN fiber woven body with Si-O-C on the surface of the PAN fiber. Figure 2The red curve is the infrared spectrum of the PAN fiber woven body surface modified by the epoxy-modified RTV silicone rubber prepared in Example 1, and the Si-O-C characteristic peak appears at 1018 cm -1 The Si-O-C characteristic peak appears, indicating that Si-O-C appears at the connection of the RTV silicone rubber and the PAN fiber woven body; Figure 2 The black curve in the middle is the infrared spectrum of the surface of the unmodified PAN fiber, and the Si-O-C characteristic peak at 1018 cm -1 does not appear, indicating that no Si-O-C is generated;

[0199] The epoxy-modified RTV silicone rubber is injected into a vacuum impregnation tank, the tank is pre-vacuumed to -0.08 MPa, the silicone rubber is injected at a rate of 6 mL / min, the fiber woven body is immersed, and the vacuum-assisted bonding is completed after 40 minutes of immersion, followed by a heating and curing treatment;

[0200] The heating and curing treatment is a gradient heating and curing, and the heating temperature, holding time, and vacuum degree meet 80℃ / 1.5h / -0.07MPa→120℃ / 4h / -0.04MPa→150℃ / 1.5h / normal pressure. The gradient heating rate is 3℃ / min for each stage; and the prepared RTV silicone rubber layer has a thickness of 20μm.

[0201] The epoxy-modified RTV silicone rubber can be introduced in the following ways:

[0202] (1) γ-glycidyl ether propyl trimethoxysilane is used as a modifier, and the addition amount is 15% of the mass of the RTV silicone rubber matrix;

[0203] (2) Under the protection of inert gas, the modifier is reacted with hydroxyl-terminated polydimethylsiloxane at 60℃ for 4h, and the content of epoxy functional groups is controlled to be 0.3mol / kg; and the viscosity of the epoxy-modified RTV silicone rubber at 25℃ is in the range of 5000mPa·s.

[0204] S3: The modified PAN fiber woven body immersed in the silicone resin solution is subjected to a heating and curing treatment to obtain a flexible silicone resin-based heat insulation composite material;

[0205] Amino-modified vinyl phenyl silicone resin toluene solutions with concentrations of 28%, 36%, and 40% are sequentially injected into the fiber preform.

[0206] The silicone resin solution in step S3 is selected to be subjected to a cyclic pulsating pressure impregnation process: the silicone resin solution is impregnated at a pressure in the range of 0.8MPa, the pulsating frequency is 0.3Hz, and the pressure waveform is a trapezoidal wave, the pressure is changed according to the rising rate of 0.2MPa / s→holding for 30s→falling rate of 0.1MPa / s, and the injection time is 8h.

[0207] The stepwise curing process is as follows: 80℃ / 2h→120℃ / 2h→150℃ / 2h, and the temperature increasing rate of each stage is 3℃ / min; the hot press is preheated to 180℃, and a pressure of 8MPa is applied, and the pressure is maintained for 60 minutes.

[0208] The embodiment discloses a flexible silicone resin-based thermal insulation composite material prepared by the preparation method.

[0209] The application of the flexible silicone resin-based thermal insulation composite material as described above, the silicone heat protection material is applied to the field of heat protection materials, and can be specifically used for high-temperature thermal insulation layers in the temperature range of-60-300℃.

[0210] Example 2

[0211] The embodiment discloses a preparation method of a flexible silicone resin-based thermal insulation composite material, and specific preparation steps are as follows:

[0212] S1: the star-shaped block copolymerized vinylphenyl silicone resin prepolymer is obtained by the method in the preparation example 1;

[0213] S2: the pre-oxidized PAN fiber is woven to prepare a PAN fiber woven body; three-dimensional orthogonal woven PAN pre-oxidized fiber is selected as a reinforcing body, the fiber volume content is controlled to be 45%, the thickness of the woven body is 4mm, the porosity along the thickness direction is designed to be 24%(outer layer)→31%(middle)→34%(inner layer) three layers of equal thickness, and the fiber woven body is placed in a 100℃ oven for drying for 2 hours to remove adsorbed water;

[0214] The three-dimensional orthogonal woven PAN fiber is subjected to 200℃, 80min oxidation treatment to obtain PAN pre-oxidized fiber;

[0215] The epoxy-modified RTV silicone rubber is used to modify the PAN fiber woven body to prepare a modified PAN fiber woven body with Si-O-C on the surface of the PAN fiber;

[0216] The epoxy-modified RTV silicone rubber is injected into a vacuum impregnation tank, the impregnation tank is pre-vacuumized to-0.08MPa, the silicone rubber is injected at a rate of 6mL / min to immerse the fiber woven body, and the silicone rubber is cured after being immersed for 40 minutes;

[0217] The heating and curing treatment in step S2 is gradient temperature rising curing, and the temperature rising, temperature maintaining time and vacuum degree meet 55℃ / 1h / -0.08MPa→85℃ / 3h / -0.05MPa→130℃ / 2h normal pressure. The temperature rising rate of each stage is 3℃ / min; and the thickness of the prepared RTV silicone rubber layer is 22μm.

[0218] The epoxy-modified RTV silicone rubber can be introduced in the following ways:

[0219] (1) 3,4-epoxycyclohexylethyl methyl dimethoxysilane as a modifier, the addition amount is 15% of the mass of the RTV silicone rubber matrix;

[0220] (2) under the protection of inert gas, the modifier is reacted with hydroxyl-terminated polydimethylsiloxane at 60℃ for 4h, and the content of epoxy group functional group is controlled to be 0.5 mol / kg; the viscosity of the epoxy group modified RTV silicone rubber ranges from 8000 mPa·s at 25℃.

[0221] S3: the modified PAN fiber braided body impregnated with the silicone resin solution is subjected to a heating and curing treatment to obtain a flexible silicone resin based heat protection and insulation composite material;

[0222] The amino-modified vinyl phenyl silicone resin toluene solutions with concentrations of 28%, 36% and 40% are sequentially injected into the fiber preform.

[0223] Step S3: the silicone resin solution is selected to be subjected to a cyclic pulsating pressure impregnation process, the impregnation pressure of the silicone resin solution ranges from 0.8 MPa, the pulsating frequency is 0.2 Hz, and the pressure waveform is a trapezoidal wave, the pressure is changed at a rising rate of 0.2 MPa / s→pressure maintaining for 35 s→falling rate of 0.15 MPa / s, and the injection time is 6h.

[0224] Step S3: the silicone resin solution is selected to be subjected to a cyclic pulsating pressure impregnation process, the impregnation pressure of the silicone resin solution ranges from 0.8 MPa, the pulsating frequency is 0.2 Hz, and the pressure waveform is a trapezoidal wave, the pressure is changed at a rising rate of 0.2 MPa / s→pressure maintaining for 35 s→falling rate of 0.15 MPa / s, and the injection time is 6h.

[0225] The flexible silicone resin based heat protection and insulation composite material is prepared by the preparation method.

[0226] The application of the flexible silicone resin based heat protection and insulation composite material as described above, the silicone heat protection material is applied to the field of heat protection materials, and can be specifically used for high-temperature heat insulation layers in the temperature range of-60-300℃.

[0227] Example 3

[0228] The preparation method of the flexible silicone resin based heat protection and insulation composite material is disclosed.

[0229] S1: the star-shaped block copolymerized vinyl phenyl silicone resin prepolymer is obtained by the method of Preparation Example 2;

[0230] S2: weaving the pre-oxidized PAN fibers to prepare a PAN fiber woven body; selecting three-dimensional orthogonal woven PAN pre-oxidized fiber as the reinforcing body, controlling the fiber volume content to be 55%, the woven body thickness to be 4 mm, and the interlayer porosity along the thickness direction to be designed as 28% (outer layer) → 32% (middle layer) → 36% (inner layer) three layers of equal thickness, placing the fiber woven body in a 100℃ oven for drying for 2 hours to remove adsorbed water;

[0231] S1: oxidizing the three-dimensional orthogonal woven PAN fibers at 200℃ for 80 minutes to obtain PAN pre-oxidized fiber;

[0232] S1: oxidizing the three-dimensional orthogonal woven PAN fibers at 200℃ for 80 minutes to obtain PAN pre-oxidized fiber;

[0233] S1: oxidizing the three-dimensional orthogonal woven PAN fibers at 200℃ for 80 minutes to obtain PAN pre-oxidized fiber;

[0234] The heating and curing treatment in step S2 is gradient heating and curing, and the heating temperature, holding time and vacuum degree meet 50℃ / 2h / -0.06MPa→90℃ / 3h / -0.03MPa→120℃ / 2h / -0.01MPa. The gradient heating rate of each stage is 3℃ / min; the prepared RTV silicone rubber layer thickness is 20μm.

[0235] The epoxy-modified RTV silicone rubber can be introduced in the following ways:

[0236] (1) 3,4-epoxycyclohexylethylmethyldimethoxysilane is used as a modifier, and the addition amount is 16% of the mass of the RTV silicone rubber matrix;

[0237] (2) under the protection of inert gas, the modifier is reacted with hydroxyl-terminated polydimethylsiloxane at 60℃ for 5h, and the epoxy functional group content is controlled to be 0.5mol / kg; the viscosity of the epoxy-modified RTV silicone rubber at 25℃ is in the range of 12000mPa·s.

[0238] S3: the modified PAN fiber woven body impregnated with the silicone resin solution is subjected to heating and curing treatment to obtain a flexible silicone resin-based heat-proof and heat-insulating composite material;

[0239] The amino-modified vinylphenyl silicone resin toluene solution with concentrations of 28%, 36% and 40% is injected into the fiber preform in sequence.

[0240] Step S3: the silicone resin solution is selected to be impregnated by a cyclic pulsating pressure impregnation process, the impregnation pressure range is 0.8 MPa, the pulsating frequency is 0.2 Hz, and the pressure waveform is a trapezoidal wave, the pressure is changed according to the rising rate of 0.2 MPa / s→pressure maintaining for 35 s→the falling rate of 0.15 MPa / s, and the glue injection time is 6 h.

[0241] Step S4: a ladder curing process is performed: 80℃ / 1h→120℃ / 1h→150℃ / 1h, the temperature rising rate of each stage is 4℃ / min; the hot press is preheated to 185℃, a pressure of 12 MPa is applied, and the pressure is maintained for 30 minutes.

[0242] The embodiment discloses a flexible silicone resin-based heat-proof and heat-insulating composite material prepared by the preparation method.

[0243] The application of the flexible silicone resin-based heat-proof and heat-insulating composite material as described above is applied to the field of heat-proof materials, and can be specifically used for a high-temperature heat-insulating layer in a temperature range of-60-300℃.

[0244] Comparative Example 1

[0245] The comparative example discloses a preparation method of a flexible silicone resin-based heat-proof and heat-insulating composite material, and the difference from Example 1 is that the RTV silicone rubber is not modified, and the rest is the same as Example 1.

[0246] The flexible silicone resin-based heat-proof and heat-insulating composite material is prepared by using the preparation method of the flexible silicone resin-based heat-proof and heat-insulating composite material.

[0247] Comparative Example 2

[0248] The comparative example discloses a preparation method of a flexible silicone resin-based heat-proof and heat-insulating composite material, and the difference from Example 1 is that the volume content of the PAN pre-oxidized fiber body is 65%, and the rest is the same as Example 1.

[0249] The flexible silicone resin-based heat-proof and heat-insulating composite material is prepared by using the preparation method of the flexible silicone resin-based heat-proof and heat-insulating composite material.

[0250] Comparative Example 3

[0251] The comparative example discloses a preparation method of a flexible silicone resin-based heat-proof and heat-insulating composite material, and the difference from Example 1 is that the porosity of the PAN fiber woven body is uniformly set to 28%, and the rest is the same as Example 1.

[0252] The flexible silicone resin-based heat-proof and heat-insulating composite material is prepared by using the preparation method of the flexible silicone resin-based heat-proof and heat-insulating composite material.

[0253] Comparative Example 4

[0254] The preparation method of the flexible silicone resin-based thermal insulation composite material is disclosed in this comparative example, and the difference between Example 1 is that step S2 does not use a three-stage gradient curing process, the curing temperature is uniformly selected as 80°C, the total curing time is the same as Example 1, and the rest is the same as Example 1.

[0255] The flexible silicone resin-based thermal insulation composite material is prepared by using the above-mentioned preparation method of the flexible silicone resin-based thermal insulation composite material.

[0256] Comparative Example 5

[0257] The preparation method of the flexible silicone resin-based thermal insulation composite material is disclosed in this comparative example, and the difference between Example 1 is that the star block copolymerization vinylphenyl silicone resin prepolymer is replaced by a mixed prepolymer of a phenyl resin terminated by a silicon-hydrogen bond at both ends with a polymerization degree of 10,000 and a vinyl resin terminated by hexamethyldisiloxane (HMDSO) at both ends with a polymerization degree of 18,000, the amount of crosslinking agent and catalyst is the same as Preparation Example 1, and there is no star structure connected by hexamethyldisilazane, and the rest is the same as Example 1.

[0258] The flexible silicone resin-based thermal insulation composite material is prepared by using the above-mentioned preparation method of the flexible silicone resin-based thermal insulation composite material.

[0259] Comparative Example 6

[0260] The preparation method of the flexible silicone resin-based thermal insulation composite material is disclosed in this comparative example, and the difference between Example 1 is that the star block copolymerization vinylphenyl silicone resin prepolymer is replaced by a random prepolymer of a vinylphenyl resin, and a catalyst is added for dehydration condensation curing, and the rest is the same as Example 1.

[0261] The flexible silicone resin-based thermal insulation composite material is prepared by using the above-mentioned preparation method of the flexible silicone resin-based thermal insulation composite material.

[0262] The flexible silicone composite materials obtained in the examples and comparative examples are subjected to corresponding performance tests, and Table 1 is a summary of the properties of the flexible silicone composite materials obtained in the examples and comparative examples. Among them, the density test adopts GB 1463-2005 method, the test method of thermal conductivity adopts GBT 10295-2008, the test method of linear ablation rate adopts GJB 323B-2018, the test method of bending modulus adopts GBT 9341-2008, the test method of residual stress adopts GBT 31231-2014, and the test method of bending resilience rate adopts GBT 2411-2008; wherein, the internal thermal conductivity gradient ratio refers to the ratio of the maximum thermal conductivity at one end to the minimum thermal conductivity at the other end in the thickness direction of the composite material, which is obtained by testing the material slices at different thicknesses.

[0263] Table 1 Properties of flexible silicone composite materials

[0264]

[0265] From the above, the bending modulus of the embodiment is 360MPa~380MPa, the thermal conductivity is 0.35W / m·K~0.40W / m·K, the linear ablation rate is 0.038~0.042mm / s, the density is 1.58g / cm 3 ~1.65g / cm 3 , the residual stress is 12~15MPa, the internal thermal conductivity gradient is 6.9~7.1, and the bending resilience is 92%~95%.

[0266] As can be seen from the comparative example and Comparative Example 1, Comparative Example 5 and Comparative Example 6, the addition of a star structure to the matrix resin can improve the bending strength and high temperature stability, and reduce the linear ablation rate; the introduction of a block structure significantly improves the bending strength and high temperature ablation resistance of the matrix resin.

[0267] As can be seen from the comparative example and Comparative Example 1, Comparative Example 1, the epoxy modified RTV silicone rubber can better combine with the PAN fiber, significantly improve the bending strength, high temperature ablation resistance, reduce the thermal conductivity and residual stress, improve the bending resilience, and reduce the high temperature delamination.

[0268] As can be seen from the comparative example and Comparative Example 1, Comparative Example 4, when the epoxy modified RTV silicone rubber is used to modify the PAN fiber, a suitable curing process can improve the interfacial bonding force, significantly improve the bending strength, high temperature ablation resistance, improve the bending resilience, and reduce the high temperature delamination.

[0269] As can be seen from the comparative example and Comparative Example 2, Comparative Example 3, a suitable PAN fiber braiding volume and PAN fiber braiding thickness direction porosity gradient setting can greatly improve the thermal conductivity and ablation resistance effect.

[0270] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for producing a flexible silicone resin-based thermal barrier composite material, characterized by, Comprising: S1: preparing a star-shaped block copolymerized vinylphenyl silicone resin prepolymer; S2: weaving PAN fibers to prepare a PAN fiber woven body with porosity gradient increasing from the outside to the inside in the thickness direction; S3: impregnating the PAN fiber woven body with star-shaped block silicone resin prepolymer solutions with different solid contents multiple times based on a cyclic pulsating pressure impregnation process and heating and curing to obtain a flexible silicone resin-based heat-proof and heat-insulating composite material, and the PAN fiber woven body in different porosity regions of the composite material is filled with silicone resins with different solid contents.

2. The method of claim 1, wherein the flexible silicone resin-based thermal barrier composite is prepared by the steps of: a) mixing a silicone resin, a curing agent, and a catalyst to form a mixture; b) applying the mixture to a substrate; c) curing the mixture to form a cured silicone resin; and d) applying a coating to the cured silicone resin. The star-shaped block silicone resin prepolymer comprises a star-shaped prepolymer component, a second block component, a crosslinking agent, and a catalyst; The star-shaped prepolymer component comprises a plurality of arms, and each arm comprises a first block component; One of the first block component and the second block component contains not less than two vinyl groups, and the other contains at least one silicon-hydrogen bond; The crosslinking agent contains at least two silicon-hydrogen bonds.

3. The method for preparing the flexible organosilicon resin-based heat-insulating composite material according to claim 2, characterized in that, Step S1 comprises: Step S101, star-shaped prepolymer component preparation; Step S102, second block component preparation; Step S103, mixing the star-shaped prepolymer component, the second block component, the crosslinking agent, the catalyst, and the necessary solvent to obtain the star-shaped block silicone resin prepolymer preparation.

4. The method for preparing the flexible organosilicon resin-based heat-insulating composite material according to claim 3, characterized in that, Step S101 comprises: S1011, adding the star modifier and the monomers of the first block component into toluene according to the designed molar ratio, controlling the reaction temperature and the reaction time to prepare the star-shaped prepolymer with the target polymerization degree; S1012, selecting a suitable end-capping agent according to the monomers of the first block component to end-cap the first block component to prepare the star-shaped prepolymer component with the first block component connected to the arms.

5. The method of claim 4, wherein the flexible silicone resin-based thermal barrier composite is prepared by the steps of: a) mixing the silicone resin, the filler, and the curing agent; b) applying the mixture to a surface of a substrate; and c) curing the mixture to form the flexible silicone resin-based thermal barrier composite. The star modifier is hexamethyldisilazane.

6. The method for preparing the flexible organosilicon resin-based heat-insulating composite material according to claim 5, characterized in that, Step S1011 comprises: Step (1): adding the star modifier hexamethyldisilazane, the monomer phenyltrichlorosilane, and the monomer diphenyldichlorosilane into toluene according to the target molar ratio, and placing the mixture in a water bath at 40-50°C for 2-3 hours of hydrolysis; Step (2): continuing to pre-polymerize at 50-60°C for 2-3 hours; Step (3): adding hydrochloric acid and continuing to post-polymerize for 2-3 hours to obtain the un-end-capped star-shaped prepolymer component.

7. The method of claim 6, wherein the flexible silicone resin-based thermal barrier composite is prepared by the steps of: a) providing a silicone resin; b) providing a reinforcing material; c) mixing the silicone resin and the reinforcing material to form a mixture; d) curing the mixture to form the flexible silicone resin-based thermal barrier composite. Step S1012 comprises: Step (1): filtering the un-end-capped star-shaped prepolymer component, washing it with ethanol, and vacuum drying; Step (2): dissolving the dried un-end-capped star-shaped prepolymer component in toluene, and reacting at 70-90°C for 4-8 hours in an inert atmosphere.

8. The method of claim 7, wherein the flexible silicone resin-based thermal barrier composite is prepared by the steps of: a) providing a silicone resin; b) providing a reinforcing material; c) mixing the silicone resin and the reinforcing material; d) curing the mixture of the silicone resin and the reinforcing material; and e) providing a coating layer on the cured mixture. Step S102 comprises: S1021, adding the monomers of the second block component into toluene according to the designed molar ratio, and controlling the reaction temperature and the reaction time to prepare the second block component prepolymer with the target polymerization degree; S1022, selecting a suitable end-capping agent according to the monomers of the second block component to end-cap the second block component to prepare the second block component.

9. A flexible silicone resin-based thermal barrier composite material, characterized by, Prepared by the method of any one of claims 1-8, comprising: A PAN fiber braid, an organic silicone resin dispersed in the pores of the PAN fiber braid, and an RTV silicone rubber layer connecting the organic silicone resin and the PAN fiber, wherein the porosity of the PAN fiber braid increases from the outside to the inside in the thickness direction, and the different porosity regions of the PAN fiber braid are filled with organic silicone resins of different solid contents.

10. Use of a flexible silicone resin-based thermal barrier composite material, characterized in that, The flexible organic silicone resin-based heat-proof and heat-insulating composite material prepared by the method of any one of claims 1-8 is used as a high-temperature heat-proof and heat-insulating layer in a temperature range of -60°C to 300°C.

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