Modified aramid nanofiber / rubber composite material and preparation method thereof

Abstract

The invention discloses a modified aramid nanofiber / rubber composite material and a preparation method thereof.Aramid nanofibers with good water dispersibility are prepared through epoxy modification, the in-situ polycondensation effect of a silicate ester compound on the surfaces of the nanofibers is improved through a nucleophilic substitution reaction of epoxy groups and amino groups, ANFs (at) SiO2 is formed, and the modified aramid nanofiber / rubber composite material is prepared. The composite material with excellent physical and mechanical properties and ablation resistance can be obtained by using the ANFs (at) SiO2 reinforced rubber with lower parts by weight. In the ablation process, the nano silicon dioxide is firstly melted to form a protective film to coat the surface of the aramid nano fiber, so that the aramid nano fiber is prevented from being corroded and decomposed by heat flow, ceramic structures such as SiC and Si3N4 are generated in situ to promote densification of a carbon layer, and the ablation resistance of the rubber is remarkably enhanced.

Description

Technical Field

[0001] This invention belongs to the field of rubber composite materials and relates to a modified aramid nanofiber and its application in rubber. Background Technology

[0002] Thermal protection materials are a crucial component of spacecraft. However, developing thermal protection materials with lightweight properties, excellent mechanical properties, high-temperature resistance, and ablation resistance remains a challenge. Rubber, due to its good thermal stability, low density, and excellent ablation resistance, is considered a good matrix for ablation-resistant composite materials and has great potential in the application of thermal protection layers in spacecraft. However, hollow rubber has poor mechanical properties and low carbon residue, requiring the addition of reinforcing fillers to achieve better mechanical strength and ablation resistance. Chinese patent CN118085462A discloses an aramid pulp / EPDM rubber composite material and its preparation method. Using 20 parts of aramid pulp to reinforce the EPDM rubber composite material reduces the linear ablation rate to 0.118 mm / s; however, the tensile strength and elongation at break are only 8.018 MPa and 81%, respectively. While a large amount of aramid pulp reduces the ablation rate of the EPDM rubber, it also impairs the mechanical properties of the composite material and increases its density, significantly reducing its utilization value. Therefore, finding an effective filler to reinforce rubber-based thermal insulation materials is urgently needed.

[0003] Aramid nanofibers (ANFs) are high-performance nanofibers. Due to their high aspect ratio (diameter 3–30 nm, length 5–10 μm), high tensile strength (3.6 GPa), and high modulus (90 GPa), even very small amounts can provide strong reinforcement to the polymer matrix. Chinese patent CN108424563A reports an aramid nanofiber / carboxylated nitrile rubber composite material and its preparation method. After adding 5 parts of aramid nanofibers, the tensile strength and elongation at break of the composite material increased to 13.12 MPa and 128%, respectively. Currently, the applications of aramid nanofibers mainly focus on improving the mechanical properties of composite materials; research on improving the ablation resistance of thermal protection materials has not yet been reported.

[0004] Current reports on rubber-based ablation-resistant composites mostly focus on improving ablation resistance. However, improving ablation resistance inevitably reduces mechanical properties. Balancing ablation rate, tensile strength, and elongation at break is a pressing challenge for researchers. Summary of the Invention

[0005] The present invention aims to provide a modified aramid nanofiber and a modified aramid nanofiber / rubber composite material and a method for preparing the same.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing aramid nanofibers (ANFs@SiO2) with in-situ grown nano-silica on the surface, comprising the following steps:

[0008] Step 1: Add an epoxy modifier to the dimethyl sulfoxide dispersion of aramid nanofibers under stirring conditions, and then dialyze with deionized water until the pH value is 7 to obtain an aqueous dispersion of epoxy-modified aramid nanofibers (m-ANFs).

[0009] Step 2: At a certain temperature, add silane coupling agent to the m-ANFs aqueous dispersion described in Step 1 and stir for a period of time to initiate the in-situ growth of nano-silica. After filtration and washing, modified aramid nanofibers (mk-ANFs) are obtained and redispersed in an aqueous solution to obtain mk-ANF aqueous dispersion.

[0010] Step 3: Add an ethanol solution of silicate ester compound to the mk-ANF aqueous dispersion, stir and react for a period of time at a certain temperature, filter and wash to obtain ANFs@SiO2.

[0011] As a preferred embodiment of the present invention, in step one, the epoxy modifier is epichlorohydrin or epibromopropane; the mass ratio of aramid nanofibers to epoxy modifier is 1:0.5 to 1:1; and the stirring time is 12-24 hours.

[0012] As a preferred embodiment of the present invention, in step two, the silane coupling agent is a silane coupling agent containing a primary amino group, which may be one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β(aminoethyl)-γ-aminopropyltriethoxysilane; the mass ratio of aramid fiber to silane coupling agent is 1:0.5 to 1:1; the stirring reaction temperature is 60-80℃, and the stirring reaction time is 4-6h.

[0013] As a preferred embodiment of the present invention, in step three, the silicate ester compound is one of methyl orthosilicate, ethyl orthosilicate, and bis(trimethoxysilyl)ethane; the mass ratio of aramid nanofibers to silicate ester compound is 1:2 to 1:4; the stirring reaction temperature is 60-80℃, and the stirring reaction time is 4-6h.

[0014] In a second aspect, the present invention provides ANFs@SiO2 prepared by the method described in the first aspect.

[0015] Thirdly, the present invention provides an ANFs@SiO2 / rubber ablation resistant composite material, which, by weight, is composed of the following raw materials: 100 parts of rubber, 3-7 parts of ANFs@SiO2, 1-2 parts of silane coupling agent, 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 20-30 parts of flame retardant filler, 1-2 parts of vulcanization accelerator, and 3-6 parts of vulcanizing agent.

[0016] Preferably, the rubber is one of EPDM rubber, nitrile rubber, or silicone rubber.

[0017] Preferably, the silane coupling agent is one of bis-[γ-(triethoxysilyl)propyl]tetrasulfide (Si-69), 3-aminopropyltriethoxysilane (KH-550), 3-(trimethoxysilyl)propyl methacrylate (KH-570), or vinyltris(β-methoxyethoxy)silane (A-172).

[0018] Preferably, the flame-retardant filler is a mixture of zinc borate, zirconium oxide, zirconium silicide and benzoxazine resin in a mass ratio of 1:0.5 to 1.5.

[0019] Preferably, the vulcanization accelerator is one of 2-mercaptobenzothiazole (accelerator M), dibenzothiazole disulfide (accelerator DM), N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CZ), and tetramethylthiuram disulfide (accelerator TMTD).

[0020] Preferably, the vulcanizing agent is a mixture of one of di-tert-butyl peroxide (BIPB) and di-diisopropylbenzene peroxide (DCP) and sulfur (S) in a mass ratio of 1:0.5 to 1.

[0021] Fourthly, the present invention also discloses a method for preparing the ANFs@SiO2 / rubber composite material described in the third aspect, comprising the following steps:

[0022] Step 1: The ANFs@SiO2 is uniformly dispersed in water and blended with rubber under stirring conditions to obtain a pre-dispersion. After removing the solvent, the ANFs@SiO2 / rubber masterbatch is obtained.

[0023] Step 2: ANFs@SiO2 / rubber masterbatch, zinc oxide, stearic acid, flame retardant filler, coupling agent, vulcanization accelerator, and vulcanizing agent are sequentially placed into a two-roll mill for blending to obtain ANFs@SiO2 / rubber compound.

[0024] Step 3: After the ANFs@SiO2 / rubber compound is left to stand at room temperature for a period of time, it is vulcanized to obtain vulcanized rubber, namely ANFs@SiO2 / rubber ablation resistant composite material.

[0025] As a preferred embodiment of the present invention, the concentration of the aqueous dispersion of ANFs@SiO2 in step one is 0.01-0.1 wt%; the rubber is a solution or latex rubber; the method for removing the solvent includes, but is not limited to, flocculation with sodium chloride or calcium chloride aqueous solution, ethanol flocculation, and vacuum distillation.

[0026] Compared with existing technologies, the adopted technical solution has the following advantages:

[0027] (1) This invention first prepares aramid nanofibers with good water dispersibility through epoxy modification, and then improves the in-situ polycondensation effect of silicate compounds on the nanofiber surface through the nucleophilic substitution reaction of epoxy groups and amino groups, forming aramid nanofibers with in-situ grown nano-silica. Unlike physical interactions such as physical adsorption or hydrogen bonding, the nano-silica grown in-situ on the surface of aramid nanofibers through covalent interactions is more uniformly distributed and more tightly encapsulates the fibers, which can significantly improve the thermal stability of aramid nanofibers.

[0028] (2) The ANFs@SiO2 prepared by this invention exhibits excellent thermal stability and can entangle and adsorb more rubber molecular chains in the matrix, greatly improving the overall performance of the composite material. The tensile strength of the prepared ANFs@SiO2 / rubber ablation-resistant composite material is >20.0MPa, and the elongation at break is >700%. The linear ablation rate of the ablation-resistant composite material is as low as 0.05~0.06mm / s.

[0029] (3) This invention can obtain a composite material with excellent ablation resistance by using a relatively low weight fraction of ANFs@SiO2 to reinforce the rubber. During the ablation process, nano-silica first melts to form a protective film that coats the surface of aramid nanofibers, protecting the aramid nanofibers from thermal erosion and decomposition, and in situ generating ceramic structures such as SiC and Si3N4 to promote carbon layer densification, significantly enhancing the ablation resistance of the rubber.

[0030] In summary, the ANFs@SiO2 / rubber ablation-resistant composite material prepared by this invention has excellent mechanical and ablation resistance properties and can be used in the field of aerospace thermal protection. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of the preparation method of the ANFs@SiO2 / rubber ablation resistant composite material of the present invention;

[0032] Figure 2 Transmission electron microscopy image of ANFs@SiO2 prepared in Example 1;

[0033] Figure 3 Transmission electron microscopy (TEM) image of the modified aramid nanofibers prepared in Comparative Example 1;

[0034] Figure 4 Transmission electron microscopy (TEM) image of the modified aramid nanofibers prepared in Comparative Example 3;

[0035] Figure 5 Thermogravimetric analysis of ANFs@SiO2 prepared in Examples 1-4;

[0036] Figure 6 Thermogravimetric analysis of ANFs@SiO2 prepared in Example 1 and Comparative Examples 1-6;

[0037] Figure 7 This is a scanning electron microscope image of the carbon layer after ablation of the rubber ablation-resistant composite material prepared in Application Example 1;

[0038] Figure 8 To compare the scanning electron microscope images of the carbon layer after ablation of the rubber composite material prepared in Application Example 1;

[0039] Figure 9 For comparison, a scanning electron microscope image of the carbon layer after ablation of the rubber composite material prepared in Application Example 3. Detailed Implementation

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0041] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0042] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0043] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0044] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0045] Currently, when reinforcing insulation materials with fibers, problems exist such as the surface fibers being easily eroded and decomposed by heat flow, and the carbon layer being insufficiently dense with excessively large pores. Therefore, the inventors have developed a method to in-situ grow nano-silica (SiO2) on the surface of aramid nanofibers (ANFs) to protect the fibers from heat flow erosion, thereby promoting the integrity of the rubber carbon layer structure. However, ANFs can only be dispersed in a strong alkaline solution of dimethyl sulfoxide. Directly mixing ANFs with aqueous solutions of silicate compounds leads to ANF agglomeration, making it difficult for SiO2 to grow uniformly on the ANF surface. Therefore, the inventors first grafted epoxy groups onto the ANF molecular chain through nucleophilic substitution to shield the proton-phobic nature of nitrogen anions, obtaining ANFs with good water dispersibility. Then, a coupling agent was introduced through a nucleophilic substitution reaction between amino and epoxy groups, serving as a site for the dehydration condensation of silicate compounds, thus successfully growing SiO2 in situ on the ANF surface. Unlike coating nano-SiO2 onto the fiber surface through physical interactions, the covalent cross-linking strategy described above results in stronger interfacial interactions between nano-SiO2 and aramid nanofibers, leading to more uniform coating of nano-SiO2. Furthermore, compared to blending ANFs and SiO2, the ANFs@SiO2 nanofibers prepared using this strategy exhibit more effective reinforcement of mechanical and ablation resistance properties.

[0046] The epoxy-modified aramid nanofibers (m-ANFs) prepared in the embodiments of the present invention are obtained by a nucleophilic substitution reaction between the halogen of the epoxy modifier and the amide group of the aramid nanofibers. Therefore, the epoxy modifier in the embodiments of the present invention includes, but is not limited to, epichlorohydrin. The modified aramid nanofibers (mk-ANFs) prepared in the embodiments of the present invention are obtained by a nucleophilic substitution reaction between the primary amine in the coupling agent and the epoxy group of m-ANFs. Therefore, the coupling agent in the embodiments of the present invention includes, but is not limited to, 3-aminopropyltriethoxysilane, and other coupling agents containing primary amine groups are also applicable.

[0047] The following detailed description of the ANFs@SiO2 and ANFs@SiO2 / rubber composite materials provided by the present invention is based on specific embodiments. These embodiments are only some, not all, of the embodiments of the present invention.

[0048] Example 1

[0049] Step 1: Add 5g of epichlorohydrin to 1L of 5g / L dimethyl sulfoxide dispersion of aramid nanofibers, stir and react for 12h, then dialyze with deionized water until the pH value is 7 to obtain an epoxy-modified aramid nanofiber (m-ANFs) aqueous dispersion.

[0050] Step 2: Add 5g of 3-aminopropyltriethoxysilane (KH550) to 1L of the 5g / L m-ANFs aqueous dispersion obtained in Step 1, stir and react at 60℃ for 4h, filter and wash to obtain modified aramid nanofibers (mk-ANFs), redisperse in water to obtain mk-ANF aqueous dispersion.

[0051] Step 3: Add 20g of tetraethyl orthosilicate (TEOS) to 1L of mk-ANFs aqueous dispersion with a concentration of 5g / L obtained in Step 3, stir and react at 60℃ for 4h, filter and wash to obtain ANFs@SiO2.

[0052] Figure 2 The image shows a transmission electron microscope (TEM) image of ANFs@SiO2 prepared in Example 1. It can be observed that spherical nano-silica particles grow uniformly on the surface of aramid nanofibers, which helps to improve the thermal stability of the modified particles.

[0053] Table 1 and Figure 5 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 606.3℃, and the residual weight at 800℃ was 74.6%. Further TGA analysis revealed that the content of nano-silica particles in the ANFs@SiO2 prepared by this method was 34.4 wt%.

[0054] Example 2

[0055] The difference between this embodiment and Embodiment 1 is that the mass of epichlorohydrin added in step one is changed to 2.5g. The remaining steps are the same as in Embodiment 1.

[0056] Table 1 and Figure 5 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 603.5℃, and the residual weight at 800℃ was 72.2%. Further TGA analysis revealed that the ANFs@SiO2 prepared by this method contained 32.0 wt% nano-silica particles.

[0057] Example 3

[0058] The difference between this embodiment and Embodiment 1 is that the mass of the silane coupling agent KH550 added in step two is changed to 2.5g. The remaining steps are the same as in Embodiment 1.

[0059] Table 1 and Figure 5 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 598.6℃, and the residual weight at 800℃ was 70.8%. Further TGA analysis revealed that the content of nano-silica particles in the ANFs@SiO2 prepared by this method was 30.6 wt%.

[0060] Example 4

[0061] The difference between this embodiment and Embodiment 1 is that the mass of tetraethyl orthosilicate added in step two is changed to 10g. The remaining steps are the same as in Embodiment 1.

[0062] Table 1 and Figure 5 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 595.8℃, and the residual weight at 800℃ was 69.2%. Further TGA analysis revealed that the content of nano-silica particles in the ANFs@SiO2 prepared by this method was 29.0 wt%.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that no epoxy modifier is added in step one. The remaining steps are the same as in Example 1.

[0065] Figure 3 The transmission electron microscope image of the modified aramid nanofibers prepared in Example 1 shows that the absence of epoxy groups means that nano-SiO2 can only be connected to the aramid nanofibers through hydrogen bonds, resulting in a reduced amount of nano-SiO2 coating and uneven coating.

[0066] Table 1 and Figure 6 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 583.3℃, ​​and the residual weight at 800℃ was 54.0%. Further TGA analysis revealed that the content of nano-silica particles in the ANFs@SiO2 prepared by this method was 13.8 wt%.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that 10g of epoxy modifier was added in step one. The remaining steps are the same as in Example 1.

[0069] Table 1 and Figure 6Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 593.8℃, and the residual weight at 800℃ was 56.1%. Further TGA analysis revealed that the content of nano-silica particles in the ANFs@SiO2 prepared by this method was 15.9 wt%.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is that no silane coupling agent is added in step two. The remaining steps are the same as in Example 1.

[0072] Figure 4 The transmission electron microscope image of the modified aramid nanofibers prepared in Example 3 shows that the lack of silane coupling agent resulted in a lack of effective interaction between nano-SiO2 and aramid nanofibers, causing nano-SiO2 to agglomerate in large quantities outside the fibers, making it difficult to enhance the thermal stability of the fibers.

[0073] Table 1 and Figure 6 Thermogravimetric analysis results showed that the maximum thermogravimetric temperature of the sample was 581.5℃, and the residual weight at 800℃ was 40.8%.

[0074] Comparative Example 4

[0075] The difference between this comparative example and Example 1 is that 10g of silane coupling agent was added in step two. The remaining steps are the same as in Example 1.

[0076] Table 1 and Figure 6 Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 591.3℃, and the residual weight at 800℃ was 50.8%. Further TGA analysis revealed that the ANFs@SiO2 prepared by this method contained 10.6 wt% nano-silica particles.

[0077] Comparative Example 5

[0078] The difference between this comparative example and Example 1 is that no silicate ester compound is added in step three. The remaining steps are the same as in Example 1.

[0079] Table 1 and Figure 6 Thermogravimetric analysis results showed that the maximum thermogravimetric temperature of the sample was 582.6℃, and the residual weight at 800℃ was 40.2%.

[0080] Comparative Example 6

[0081] The difference between this comparative example and Example 1 is that 30g of silicate compound was added in step three. The remaining steps are the same as in Example 1.

[0082] Table 1 and Figure 6Thermogravimetric analysis (TGA) results showed that the maximum thermogravimetric temperature of the sample was 585.8℃, and the residual weight at 800℃ was 45.3%. Further TGA analysis revealed that the content of nano-SiO2 particles in the ANFs@SiO2 prepared by this method was 5.1 wt%.

[0083] Table 1 summarizes the thermal decomposition data of the samples prepared in the examples and comparative examples. The ANFs@SiO2 described in the examples has a higher 5% thermogravimetric temperature (T5) and a higher maximum thermogravimetric temperature (T). max ) and residual weight at 800℃ (R 800 This indicates that the samples prepared in the examples have excellent thermal stability. In subsequent application examples, ANFs@SiO2 refers to the samples described in Example 1.

[0084] Application Example 1

[0085] Step 1: 5 parts by weight of ANFs@SiO2 prepared in Example 1 are uniformly dispersed in water to prepare an aqueous dispersion. Under stirring conditions, it is mixed with a rubber solution containing 100 parts by weight of EPDM rubber (EPDM rubber is a solid and needs to be mixed with an organic solvent to prepare a rubber solution for easy mixing with the aqueous dispersion of aramid nanofibers) to obtain a pre-dispersion. After removing the solvent, 105 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch is obtained.

[0086] Step 2: 105 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch (containing 5 parts by weight of ANFs@SiO2), 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 2 parts by weight of silane coupling agent A-172, 10 parts by weight of benzoxazine resin, 10 parts by weight of zinc borate, 1 part by weight of accelerator TMTD, 2 parts by weight of sulfur, and 2 parts by weight of DCP are put into a two-roll mill for blending to obtain ANFs@SiO2 / EPDM rubber compound.

[0087] Step 3: After the ANFs@SiO2 / EPDM rubber compound is left to stand at room temperature for a period of time, it is vulcanized to obtain vulcanized rubber, namely ANFs@SiO2 / EPDM rubber ablation resistant composite material.

[0088] Figure 7 The image shows a scanning electron microscope (SEM) image of the carbon layer of the ANFs@SiO2 / EPDM ablation-resistant composite material prepared in Example 1 after oxyacetylene ablation. The uniformly distributed, thermally stable nano-SiO2 particles on the surface of the carbon layer of the ANFs@SiO2 / EPDM ablation-resistant composite material fill the pores between the carbon layers, helping to form a dense and compact carbon layer, which significantly reduces the ablation rate of the composite material.

[0089] The obtained ablation-resistant composite material has a linear ablation rate of 0.052 mm / s, a tensile strength of 25.55 MPa, and an elongation at break of 727%.

[0090] Application Example 2

[0091] The difference between this application example and application example 1 is that in step two, 103 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch is used, which contains 3 parts by weight of ANFs@SiO2. The remaining steps are the same as in application example 1.

[0092] The obtained ablation-resistant composite material has a linear ablation rate of 0.058 mm / s, a tensile strength of 20.68 MPa, and an elongation at break of 705%.

[0093] Application Example 3

[0094] The difference between this application example and application example 1 is that in step two, 107 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch is used, which contains 7 parts by weight of ANFs@SiO2. The remaining steps are the same as in application example 1.

[0095] The obtained ablation-resistant composite material has a linear ablation rate of 0.055 mm / s, a tensile strength of 20.75 MPa, and an elongation at break of 701%.

[0096] Application Example 4

[0097] The difference between this application example and Application Example 1 is as follows: In step two, 105 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch (containing 5 parts by weight of ANFs@SiO2), 4 parts by weight of zinc oxide, 2 parts by weight of stearic acid, 2 parts by weight of silane coupling agent KH550, 15 parts by weight of benzoxazine resin, 10 parts by weight of zirconium oxide, 2 parts by weight of accelerator CZ, 3 parts by weight of sulfur, and 3 parts by weight of BIBP are sequentially placed into a two-roll mill for blending to obtain ANFs@SiO2 / EPDM rubber compound. The remaining steps are the same as in Application Example 1.

[0098] The obtained ablation-resistant composite material has a linear ablation rate of 0.057 mm / s, a tensile strength of 22.71 MPa, and an elongation at break of 744%.

[0099] Application Example 5

[0100] The difference between this application example and Application Example 1 is as follows: In step two, 105 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch (containing 5 parts by weight of ANFs@SiO2), 6 parts by weight of zinc oxide, 3 parts by weight of stearic acid, 2 parts by weight of silane coupling agent Si-69, 10 parts by weight of benzoxazine resin, 15 parts by weight of zirconium silicide, 1.5 parts by weight of accelerator DM, 1 part by weight of sulfur, and 2 parts by weight of DCP are sequentially placed into a two-roll mill for blending to obtain ANFs@SiO2 / EPDM rubber compound. The remaining steps are the same as in Application Example 1.

[0101] The obtained ablation-resistant composite material has a linear ablation rate of 0.059 mm / s, a tensile strength of 20.12 MPa, and an elongation at break of 701%.

[0102] Application Example 6

[0103] The difference between this application example and Application Example 1 is as follows: In step two, 105 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch (containing 5 parts by weight of ANFs@SiO2), 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1 part by weight of silane coupling agent KH570, 10 parts by weight of benzoxazine resin, 20 parts by weight of zinc borate, 1 part by weight of accelerator M, 2 parts by weight of sulfur, and 3 parts by weight of DCP are sequentially placed into a two-roll mill for blending to obtain ANFs@SiO2 / EPDM rubber compound. The remaining steps are the same as in Application Example 1.

[0104] The obtained ablation-resistant composite material has a linear ablation rate of 0.057 mm / s, a tensile strength of 23.65 MPa, and an elongation at break of 755%.

[0105] Application Example 7

[0106] The difference between this application example and application example 1 is that in step one, the EPDM rubber solution is replaced with acrylonitrile rubber latex to prepare ANFs@SiO2 / acrylonitrile rubber masterbatch; the remaining steps are the same as in application example 1.

[0107] The obtained ANFs@SiO2 / nitrile rubber ablation-resistant composite material has a linear ablation rate of 0.059 mm / s, a tensile strength of 22.35 MPa, and an elongation at break of 716%.

[0108] Application Example 8

[0109] The difference between this application example and application example 1 is that in step one, the EPDM rubber solution is replaced with a silicone rubber emulsion to prepare ANFs@SiO2 / silicone rubber masterbatch; the remaining steps are the same as in application example 1.

[0110] The obtained ANFs@SiO2 / silicone rubber ablation-resistant composite material has a linear ablation rate of 0.052 mm / s, a tensile strength of 20.15 MPa, and an elongation at break of 703%.

[0111] Comparative Application Example 1

[0112] The difference between this comparative application example and application example 1 is that in step two, the EPDM rubber masterbatch does not contain ANFs@SiO2, while the rest of the implementation method is the same as application example 1.

[0113] The obtained comparative sample had a linear ablation rate of 0.243 mm / s, a tensile strength of 5.88 MPa, and an elongation at break of 365%.

[0114] Figure 8 To compare the carbon layer scanning electron microscope images in Example 1, it was observed that the carbon layer formed after ablation of the EPDM rubber composite material without the addition of ANFs@SiO2 had a loose and porous structure, resulting in a higher ablation rate.

[0115] Comparative Application Example 2

[0116] The difference between this comparative application example and application example 1 is that in step two, 110 parts by weight of ANFs@SiO2 / EPDM rubber masterbatch is used, which contains 10 parts by weight of ANFs@SiO2. The remaining steps are the same as in application example 1.

[0117] The obtained comparative sample had a linear ablation rate of 0.104 mm / s, a tensile strength of 10.78 MPa, and an elongation at break of 275%.

[0118] Comparative Application Example 3

[0119] The difference between this comparative application example and application example 1 is that in step one, 2.5 parts by weight of ANFs and 2.5 parts by weight of SiO2 are used to replace 5 parts by weight of ANFs@SiO2 to prepare ANFs-SiO2 / EPDM rubber masterbatch.

[0120] The obtained comparative sample had a linear ablation rate of 0.125 mm / s, a tensile strength of 3.70 MPa, and an elongation at break of 404%.

[0121] Figure 9 To compare with the carbon layer scanning electron microscope image of Application Example 3, it was observed that the carbon layer surface of the composite material with ANFs and SiO2 added by blending has SiO2 particles with large diameters, and the carbon layer still has many pores, resulting in a high ablation rate of the composite material.

[0122] Comparative Application Example 4

[0123] The difference between this comparative application example and application example 1 is that in step one, 5 parts by weight of ANFs@SiO2 are replaced with 5 parts by weight of the sample prepared in comparative example 1, while the rest of the implementation method is the same as application example 1.

[0124] The obtained comparative sample had a linear ablation rate of 0.102 mm / s, a tensile strength of 15.45 MPa, and an elongation at break of 415%.

[0125] Comparative Application Example 5

[0126] The difference between this comparative application example and application example 1 is that in step one, 5 parts by weight of ANFs@SiO2 were replaced with 5 parts by weight of the sample prepared in comparative example 3. The rest of the implementation method is the same as application example 1.

[0127] The obtained comparative sample had a linear ablation rate of 0.116 mm / s, a tensile strength of 7.62 MPa, and an elongation at break of 293%.

[0128] Comparative Application Example 6

[0129] The difference between this comparative application example and application example 1 is that in step one, 5 parts by weight of ANFs@SiO2 are replaced with 5 parts by weight of ANFs. The rest of the implementation method is the same as application example 1.

[0130] The obtained comparative sample had a linear ablation rate of 0.206 mm / s, a tensile strength of 4.70 MPa, and an elongation at break of 374%.

[0131] Table 1 shows the thermal decomposition data for the examples and comparative examples.

[0132]

[0133]

[0134] Table 2 shows the linear ablation rate, tensile strength, and elongation at break data for the application example and the comparative application example.

[0135]

[0136] The above embodiments are merely preferred embodiments of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, or combinations made without departing from the spirit and principle of the present invention, such as various combinations of solutions in the embodiments, should be considered equivalent replacements and are all within the protection scope of the present invention.

Claims

1. A method for preparing aramid nanofibers with in-situ surface-grown nano-silica, characterized in that, Includes the following steps: Step 1: Add an epoxy modifier to the dimethyl sulfoxide dispersion of aramid nanofibers under stirring conditions, and then dialyze with deionized water until the pH value is 7 to obtain an epoxy-modified aramid nanofiber (m-ANFs) aqueous dispersion. Step 2: At a certain temperature, add silane coupling agent to the m-ANFs aqueous dispersion described in Step 1, stir and react for a period of time, filter and wash to obtain modified aramid nanofibers (mk-ANFs), redisperse them in an aqueous solution to obtain mk-ANF aqueous dispersion; Step 3: Add an ethanol solution of silicate ester compound to the mk-ANF aqueous dispersion, stir and react for a period of time at a certain temperature, filter and wash to obtain the aramid nanofibers ANFs@SiO2 with nano-silica grown on the surface in situ.

2. The method as described in claim 1, characterized in that, In step one, the epoxy modifier is epichlorohydrin or epibromopropane; the mass ratio of aramid nanofibers to epoxy modifier is 1:0.5 to 1:1; and the stirring time is 12-24 h.

3. The method as described in claim 1, characterized in that, In step two, the silane coupling agent is a silane coupling agent containing a primary amino group, specifically one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β(aminoethyl)-γ-aminopropyltriethoxysilane; the mass ratio of aramid fiber to silane coupling agent is 1:0.5 to 1:1; the stirring reaction temperature is 60-80 ℃, and the stirring reaction time is 4-6 h.

4. The method as described in claim 1, characterized in that, In step three, the silicate ester compound is one of methyl orthosilicate, ethyl orthosilicate, or bis(trimethoxysilyl)ethane; the mass ratio of aramid nanofibers to silicate ester compound is 1:2 to 1:4; the stirring reaction temperature is 60-80℃, and the stirring reaction time is 4-6 h.

5. An ANFs@SiO2 prepared by the method according to any one of claims 1-4.

6. An ANFs@SiO2 / rubber ablation-resistant composite material, characterized in that, The product is composed of the following raw materials by weight: 100 parts rubber, 3-7 parts ANFs@SiO2 prepared by any one of the methods described in claims 1-4, 1-2 parts silane coupling agent, 4-6 parts zinc oxide, 1-3 parts stearic acid, 20-30 parts flame retardant filler, 1-2 parts vulcanization accelerator, and 3-6 parts vulcanizing agent.

7. The ANFs@SiO2 / rubber ablation-resistant composite material as described in claim 6, characterized in that, The rubber is one of EPDM rubber, nitrile rubber, or silicone rubber.

8. The ANFs@SiO2 / rubber ablation-resistant composite material as described in claim 6, characterized in that, The flame-retardant filler is a mixture of zinc borate, zirconium oxide, zirconium silicide and benzoxazine resin, with a mass ratio of 1:0.5~1.

5.

9. The ANFs@SiO2 / rubber ablation-resistant composite material as described in claim 6, characterized in that, The vulcanizing agent is a mixture of one of di-tert-butylperoxyisopropylbenzene and di-diisopropylbenzene peroxide and sulfur, with a mass ratio of 1:0.5~1.

10. A method for preparing the ANFs@SiO2 / rubber composite material as described in any one of claims 6-9, characterized in that, Includes the following steps: Step 1: The ANFs@SiO2 is uniformly dispersed in water and blended with rubber under stirring conditions to obtain a pre-dispersion. After removing the solvent, the ANFs@SiO2 / rubber masterbatch is obtained. Step 2: ANFs@SiO2 / rubber masterbatch, zinc oxide, stearic acid, flame retardant filler, coupling agent, vulcanization accelerator, and vulcanizing agent are sequentially placed into a two-roll mill for blending to obtain ANFs@SiO2 / rubber compound. Step 3: After the ANFs@SiO2 / rubber compound is left to stand at room temperature for a period of time, it is vulcanized to obtain vulcanized rubber, namely ANFs@SiO2 / rubber ablation resistant composite material.

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