Epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material and preparation method thereof

Abstract

The invention discloses an epoxy POSS modified benzoxazine / ethylene propylene rubber ablation resistant composite material and a preparation method thereof. The composite material is composed of the following raw materials by weight: 100 parts of ethylene propylene rubber, 10-20 parts of benzoxazine resin, 1-2 parts of epoxy POSS, 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 30-40 parts of flame retardant filler, 3-5 parts of coupling agent, 1-2 parts of vulcanizing accelerator, and 3-5 parts of vulcanizing agent. The present invention significantly improves the compatibility of benzoxazine resin and ethylene propylene rubber by epoxy POSS modification of benzoxazine resin, so that benzoxazine resin can produce appropriate cross-linking sites with EPDM, and the prepared composite material has excellent physical and mechanical properties and ablation resistance, and can be used in the field of aerospace thermal protection.

Description

Technical Field

[0001] The invention belongs to the field of heat protection materials and relates to an epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material and a preparation method thereof. Background Art

[0002] Thermal protection materials are materials used to protect solid rocket engine casings and electronic components of hypersonic vehicles from high temperatures. Ablative materials have become the most widely used thermal protection materials due to their high thermal protection efficiency. Ablative materials need to have good thermal stability and ablation resistance, as well as good mechanical properties. The development of ablative resistant materials with good heat resistance, high mechanical properties, and controllable ablation behavior is the future development direction.

[0003] Due to its saturated main chain structure, EPDM has high thermal stability. In addition, it has the advantages of low density, good aging resistance, corrosion resistance, and processability. It has been proven to be an ideal matrix for ablation-resistant materials and has great application prospects in the field of aerospace thermal protection. However, it has disadvantages such as relatively low carbon residue rate, weak carbon layer strength, and easy mechanical stripping, which makes it difficult to meet the more demanding use environment. Therefore, fillers and flame retardants are usually added to modify it to improve its comprehensive properties such as ablation resistance.

[0004] Benzoxazine resin is a new type of thermosetting resin, which is developed on the basis of traditional phenolic resin and has a three-dimensional cross-linked network similar to phenolic resin. The structure of benzoxazine resin contains six-membered heterocyclic rings of N and O, and has the characteristics of low curing shrinkage, good ablation resistance, and excellent dielectric properties. In addition, it has attracted extensive attention from researchers due to its flexible molecular structure and simple synthesis process.

[0005] Patent CN110760131B discloses a benzoxazine resin / ethylene propylene diene monomer rubber composite material and its preparation method. The prepared ethylene propylene diene monomer rubber composite material has a linear ablation rate of 0.07 mm / s, a tensile strength of 9 MPa, an elongation at break of 286%, and a density of 1.13 g / cm 3 However, due to the addition of a large amount of benzoxazine resin, the density of EPDM is increased, and its mechanical properties are greatly reduced, which cannot meet the mechanical and thermal insulation performance requirements of the current aerospace field. In addition, the vulcanization conditions of benzoxazine resin and EPDM are not matched, and the poor compatibility between the two has not been solved.

[0006] In summary, most of the existing research on EPDM ablation-resistant composite materials focuses on improving flame retardant properties. However, improving ablation properties will inevitably reduce mechanical properties. How to balance ablation rate, tensile strength and elongation at break has always been a difficult problem that researchers urgently need to solve. Summary of the invention

[0007] In view of the problem that it is difficult to simultaneously improve the ablation resistance and mechanical properties of existing EPDM-based composite materials, the present invention provides an epoxy polyhedral oligomeric silsesquioxane (epoxy POSS) modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material and a preparation method thereof. The present invention adds epoxy POSS modified benzoxazine resin to the EPDM matrix to create appropriate cross-linking sites, thereby forming an EPDM composite material with excellent physical and mechanical properties and ablation resistance.

[0008] The technical solution of the present invention is as follows:

[0009] The epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material is composed of the following raw materials in parts by weight: 100 parts of ethylene propylene diene monomer rubber, 10-20 parts of benzoxazine resin, 1-2 parts of epoxy POSS, 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 30-40 parts of flame retardant filler, 3-5 parts of coupling agent, 1-2 parts of vulcanization accelerator and 3-5 parts of vulcanizing agent.

[0010] The structural formula of the epoxy POSS of the present invention is shown in Formula I:

[0011]

[0012] The structural formula of the benzoxazine resin is shown in Formula II:

[0013]

[0014] Preferably, the mass ratio of epoxy POSS to benzoxazine resin is 1:10 to 1:15.

[0015] The flame retardant filler described in the present invention is a flame retardant filler commonly used in the art, and is selected from two or more of aramid fiber, silicon dioxide, zinc borate, zirconium oxide and zirconium silicide.

[0016] The coupling agent described in the present invention is a coupling agent conventionally used in the art, selected from bis-[γ-(triethoxysilyl)propyl]tetrasulfide (Si-69), 3-aminopropyltriethoxysilane (KH-550) or γ-(2,3-epoxypropyloxy)propyltrimethoxysilane (KH-560).

[0017] The vulcanization accelerator of the present invention is a vulcanization accelerator commonly used in the art, selected from 2-mercaptobenzothiazole (accelerator M), dibenzothiazole disulfide (accelerator DM) or N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CZ).

[0018] The vulcanizing agent described in the present invention is a vulcanizing agent conventionally used in the art, and is selected from one or more of sulfur (S), di-tert-butyl peroxide isopropylbenzene (BIPB) and diisopropylbenzene peroxide (DCP).

[0019] The present invention provides a method for preparing the epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material, comprising the following steps:

[0020] Step 1, according to the formula, EPDM rubber, zinc oxide, stearic acid, benzoxazine resin, epoxy POSS, flame retardant filler, coupling agent, vulcanization accelerator, and vulcanizing agent are put into an open mill for blending to obtain a rubber mixture;

[0021] Step 2, after the mixed rubber is allowed to stand at room temperature for a period of time, vulcanization is performed at 160-180° C. to obtain an epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material.

[0022] Preferably, the vulcanization time is 30 to 60 minutes, and the vulcanization pressure is 10 to 15 MPa.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention improves the compatibility of the benzoxazine resin and EPDM by performing epoxy POSS modification on the benzoxazine resin. The modified benzoxazine resin can be co-cured with EPDM at 160-180° C. The benzoxazine resin can generate appropriate crosslinking sites with EPDM. The prepared epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material has a tensile strength of more than 10.0 MPa, an elongation at break of more than 300%, a linear ablation rate as low as 0.05-0.08 mm / s, a hardness of 85-100, and a density of 1.00-1.06 g / cm 3 , meeting the technological requirements of light weight and high strength, while having good ablation resistance, and can be used in the field of aerospace thermal protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM image of the surface layer and carbonized layer of the epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation-resistant composite material of Example 3 after oxyacetylene ablation;

[0026] Figure 2 This is a SEM image of the surface layer and carbonized layer of the sample prepared in Comparative Example 1 after oxyacetylene ablation;

[0027] Figure 3 This is the SEM image of the surface layer and carbonized layer of the sample prepared in Comparative Example 2 after oxyacetylene ablation. DETAILED DESCRIPTION

[0028] Benzoxazine resin is self-ring-opening polymerization during the vulcanization process and polymerization process, without small molecule release, without the need to add curing agent, and has excellent mechanical properties and thermal properties. The inventors noticed that benzoxazine resin with olefins can undergo vulcanization cross-linking reaction with EPDM rubber under the action of a co-catalytic vulcanization system, and the obtained benzoxazine resin / EPDM rubber composite material has excellent tensile strength, ablation resistance and process performance. However, in order to maintain excellent ablation resistance, adding a large amount of benzoxazine resin not only increases the density of the material, but also greatly reduces the tensile strength and elongation at break of the composite material, greatly reducing the application range of the material. In addition, the temperature requirement of the self-polymerization reaction of benzoxazine resin is relatively high (≥200°C), and there is a problem of mismatching of the vulcanization conditions (temperature, time) with the EPDM insulation layer (vulcanization temperature 150°C to 160°C), and the two have poor compatibility, making it difficult to exert the excellent performance of the material. In view of the above problems, the present invention introduces epoxy POSS for covalent cross-linking when a large number of phenolic hydroxyl groups are generated by the ring-opening polymerization of benzoxazine resin. Since the introduced epoxy POSS has low density, high strength and excellent ablation resistance, the prepared composite material has excellent mechanical properties while maintaining excellent ablation performance. At the same time, the inventors established the mass ratio of epoxy POSS to benzoxazine resin through a large number of experimental studies, and then controlled the number of cross-linking reaction groups, so that the final EPDM composite material has appropriate cross-linking and does not have excessive cross-linking.

[0029] In the following embodiments, the tensile test of the composite material is carried out according to GB / T528-2009 standard, and the tensile test sample is dumbbell-shaped; the oxyacetylene ablation test of the composite material is carried out according to GJB-323A96 standard, and the diameter of the test sample is 29.5 mm.

[0030] The present invention is further described in detail below in conjunction with specific embodiments and accompanying drawings.

[0031] Example 1

[0032] According to weight, 100 parts of EPDM rubber, 5 parts of zinc oxide, 1 part of stearic acid, 10 parts of benzoxazine resin, 1 part of epoxy POSS, 10 parts of aramid fiber, 20 parts of silicon dioxide, 5 parts of zinc borate, 4 parts of Si-69, 1 part of accelerator M, 1 part of sulfur, and 3 parts of DCP are put into a double-roll mill for blending to obtain a mixed rubber. After standing at room temperature for 24 hours, it is put into a 180°C flat vulcanizer for vulcanization molding, the vulcanization pressure is 15MPa, and the vulcanization time is 30min to obtain a vulcanized rubber, that is, an epoxy POSS modified benzoxazine / EPDM rubber ablation-resistant composite material.

[0033] The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material prepared in this embodiment has a linear ablation rate of 0.074 mm / s, a tensile strength of 10.5 MPa, an elongation at break of 641.9%, and a density of 1.022 g / cm 3 .

[0034] Example 2

[0035] According to weight, 100 parts of EPDM, 4 parts of zinc oxide, 2 parts of stearic acid, 15 parts of benzoxazine resin, 1.5 parts of epoxy POSS, 10 parts of aramid fiber, 20 parts of silicon dioxide, 10 parts of zirconium silicide, 4 parts of Si-69, 1.5 parts of accelerator DM, 1 part of sulfur, and 3 parts of DCP are put into a double-roll mill for blending to obtain a mixed rubber. After standing at room temperature for 24 hours, it is put into a 160°C flat vulcanizer for vulcanization molding, the vulcanization pressure is 10MPa, and the vulcanization time is 60min to obtain a vulcanized rubber, that is, an epoxy POSS modified benzoxazine / EPDM ablation-resistant composite material.

[0036] The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material prepared in this embodiment has a linear ablation rate of 0.069 mm / s, a tensile strength of 13.0 MPa, an elongation at break of 525.2%, and a density of 1.045 g / cm 3 .

[0037] Example 3

[0038] According to weight, 100 parts of EPDM rubber, 5 parts of zinc oxide, 1 part of stearic acid, 20 parts of benzoxazine resin, 2 parts of epoxy POSS, 10 parts of aramid fiber, 20 parts of silica, 5 parts of zinc borate, 3 parts of KH-550, 2 parts of accelerator CZ, 2 parts of sulfur, and 3 parts of BIPB are put into a double-roll mill for blending to obtain a mixed rubber. After standing at room temperature for 24 hours, it is put into a 180°C flat vulcanizer for vulcanization molding, the vulcanization pressure is 15MPa, and the vulcanization time is 30min to obtain a vulcanized rubber, that is, an epoxy POSS modified benzoxazine / EPDM rubber ablation-resistant composite material.

[0039] The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material prepared in this embodiment has a linear ablation rate of 0.055 mm / s, a tensile strength of 14.1 MPa, an elongation at break of 343.3%, and a density of 1.060 g / cm 3 .

[0040] Example 4

[0041] While other conditions in Example 3 remain unchanged, the mass ratio of epoxy POSS to benzoxazine resin is changed to 1:15, that is, 20 parts of benzoxazine resin and 1.3 parts of epoxy POSS.

[0042] The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material prepared in this embodiment has a linear ablation rate of 0.062 mm / s, a tensile strength of 13.7 MPa, an elongation at break of 365.3%, and a density of 1.057 g / cm 3 .

[0043] Example 5

[0044] According to weight, 100 parts of EPDM rubber, 6 parts of zinc oxide, 3 parts of stearic acid, 10 parts of benzoxazine resin, 1 part of epoxy POSS, 5 parts of aramid fiber, 15 parts of silica, 10 parts of zirconium oxide, 5 parts of KH-560, 1 part of accelerator M, and 5 parts of DCP are sequentially put into a double-roll mill for blending to obtain a mixed rubber. After standing at room temperature for 24 hours, the mixed rubber is put into a 180°C flat vulcanizer for vulcanization molding, the vulcanization pressure is 15MPa, and the vulcanization time is 60min to obtain a vulcanized rubber, i.e., epoxy POSS modified benzoxazine / EPDM rubber ablation-resistant composite material.

[0045] The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material prepared in this embodiment has a linear ablation rate of 0.078 mm / s, a tensile strength of 10.3 MPa, an elongation at break of 600.4%, and a density of 1.021 g / cm 3 .

[0046] Comparative Example 1

[0047] This comparative example is substantially the same as Example 3, except that no benzoxazine resin and epoxy POSS are added.

[0048] The linear ablation rate of the sample prepared in this comparative example is 0.149 mm / s, the tensile strength is 4.9 MPa, the elongation at break is 194.6%, and the density is 1.017 g / cm 3 .

[0049] Comparative Example 2

[0050] This comparative example is substantially the same as Example 3, except that epoxy POSS is not added.

[0051] The linear ablation rate of the sample prepared in this comparative example is 0.093 mm / s, the tensile strength is 9.2 MPa, the elongation at break is 283.3%, and the density is 1.050 g / cm 3 .

[0052] Comparative Example 3

[0053] This comparative example is substantially the same as Example 3, except that no benzoxazine resin is added.

[0054] The linear ablation rate of the sample prepared in this comparative example is 0.087 mm / s, the tensile strength is 6.9 MPa, the elongation at break is 223.8%, and the density is 1.025 g / cm 3 .

[0055] Comparative Example 4

[0056] This comparative example is substantially the same as Example 3, except that epoxy POSS is not added, and 20 parts of benzoxazine resin is changed to 20 parts of bisphenol A type benzoxazine resin (non-vinyl benzoxazine resin).

[0057] The linear ablation rate of the sample prepared in this comparative example is 0.091 mm / s, the tensile strength is 8.5 MPa, the elongation at break is 254.6%, and the density is 1.051 g / cm 3 .

[0058] Comparative Example 5

[0059] This comparative example is substantially the same as Example 3, except that no benzoxazine resin is added, and 2 parts of epoxy POSS are changed to 2 parts of norbornene-based POSS.

[0060] The linear ablation rate of the sample prepared in this comparative example is 0.085 mm / s, the tensile strength is 7.1 MPa, the elongation at break is 237.4%, and the density is 1.023 g / cm 3 .

[0061] Comparative Example 6

[0062] This comparative example is substantially the same as Example 3, except that 2 parts of epoxy POSS are replaced with 2 parts of norbornene-based POSS.

[0063] The linear ablation rate of the sample prepared in this comparative example is 0.083 mm / s, the tensile strength is 8.7 MPa, the elongation at break is 233.6%, and the density is 1.058 g / cm 3 .

[0064] Table 1 Performance test data of samples prepared in various embodiments and comparative examples.

[0065]

[0066] Figure 1 This is an SEM image of the surface layer and carbonized layer of the epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation-resistant composite material of Example 3 after oxyacetylene ablation. It is observed that the fibers on the surface are surrounded by carbides, with a high level of residual carbon. The carbonized layer has a dense structure and the surface is covered with a variety of carbides.

[0067] Figure 2This is a SEM image of the surface layer and carbonized layer of the sample prepared in Comparative Example 1 after oxyacetylene ablation. It is observed that the surface layer and carbonized layer of the EPDM rubber without the addition of benzoxazine resin and epoxy POSS present a loose and porous structure.

[0068] Figure 3 The SEM images of the surface layer and carbonized layer of the sample prepared in Comparative Example 2 after oxyacetylene ablation show that the surface layer of the benzoxazine resin / EPDM rubber without the addition of epoxy POSS has an increased diameter of vapor-deposited reactive fibers, and the carbonized layer is denser than that in Comparative Example 1.

Claims

1. Epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material, characterized in that: The present invention is composed of the following raw materials by weight: 100 parts of EPDM rubber, 10-20 parts of benzoxazine resin, 1-2 parts of epoxy POSS, 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 30-40 parts of flame retardant filler, 3-5 parts of coupling agent, 1-2 parts of vulcanization accelerator and 3-5 parts of vulcanizing agent. The structural formula of the epoxy POSS is shown in Formula I: Formula I, The structural formula of the benzoxazine resin is shown in Formula II: Formula II.

2. The epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material according to claim 1, characterized in that, The mass ratio of epoxy POSS to benzoxazine resin is 1:10~1:

15.

3. The epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material according to claim 1, characterized in that, The flame retardant filler is selected from two or more of aramid fiber, silicon dioxide, zinc borate, zirconium oxide and zirconium silicide.

4. The epoxy POSS modified benzoxazine / EPDM ablation resistant composite material according to claim 1, characterized in that: The coupling agent is selected from bis-[γ-(triethoxysilyl)propyl]tetrasulfide, 3-aminopropyltriethoxysilane or γ-(2,3-epoxypropyloxy)propyltrimethoxysilane.

5. The epoxy POSS modified benzoxazine / EPDM ablation resistant composite material according to claim 1, characterized in that, The vulcanization accelerator is selected from 2-mercaptobenzothiazole, dibenzothiazole disulfide or N-cyclohexyl-2-benzothiazole sulfenamide.

6. The epoxy POSS modified benzoxazine / EPDM rubber ablation resistant composite material according to claim 1, characterized in that: The vulcanizing agent is one or more selected from sulfur, di-tert-butyl peroxide isopropylbenzene and diisopropylbenzene peroxide.

7. according to the preparation method of the arbitrary described epoxy POSS modified benzoxazine / ethylene propylene diene monomer rubber ablation resistant composite material of claim 1 to 6, it is characterized in that, The steps include: Step 1, according to the formula, EPDM rubber, zinc oxide, stearic acid, benzoxazine resin, epoxy POSS, flame retardant filler, coupling agent, vulcanization accelerator, and vulcanizing agent are put into an open mill for blending to obtain a rubber mixture; Step 2, after the mixed rubber is allowed to stand at room temperature for a period of time, vulcanization is performed at 160-180° C. to obtain an epoxy POSS modified benzoxazine / ethylene propylene diene rubber ablation resistant composite material.

8. The preparation method according to claim 7, characterized in that The vulcanization time is 30~60 min, and the vulcanization pressure is 10~15 MPa.

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