Design of a catalytic sizing agent and preparation method of low moisture absorption composite material

Abstract

The present invention relates to a design of a catalytic sizing agent and a method for preparing a low-hygroscopic composite material. An organic silicon titanium epoxy resin prepared by reacting organic silicon titanium with an epoxy resin is used as a sizing agent, and the engineering fiber is continuously sized and dried, and then composited and cured with a cyanate resin system to obtain a low-hygroscopic composite material. In the present invention, the organic silicon titanium epoxy resin is used as a sizing agent for the engineering fiber and a catalyst for curing the cyanate resin, and contains a transition metal and a relatively small amount of hydroxyl groups, so that the catalytic resin at the interface is preferentially cured and a relatively high resin cross-linking density is achieved, the temperature resistance of the sizing agent on the fiber surface is improved, the interfacial bonding strength of the composite material is increased, the water absorption of the interfacial phase of the composite material is suppressed, and the moisture and heat resistance of the composite material is effectively improved. The method is simple and effective, and can improve the stability and safety of the application of cyanate resin-based composite materials in the fields of aerospace, military weapons, marine engineering, electronic appliances, and microwave communications.

Description

Technical Field

[0001] The invention belongs to the field of composite materials, and in particular relates to the design of a catalytic sizing agent and a preparation method of a low-hygroscopic composite material. Background Art

[0002] Cyanate resin is composed of monomers or prepolymers containing two or more cyanate functional groups. The cross-linking density of the polymer formed by curing is extremely high, especially the highly symmetrical triazine ring skeleton network, which gives it high modulus and high strength, low dielectric and low loss, extremely low vacuum mass loss, high heat resistance and extremely low moisture absorption rate. It is one of the widely used raw materials for electronic devices and the most promising spacecraft structural material for future aerospace and deep space exploration. However, the curing temperature of this resin is high, and a catalyst is often required to reduce the activation energy to promote the curing of the resin. At the same time, when it is used in engineering composite materials with fibers, the interface is easy to diffuse water molecules, resulting in problems such as interface debonding and moisture absorption failure, which will greatly deteriorate the service performance of fiber-reinforced cyanate resin-based composite materials.

[0003] In order to improve the hygrothermal performance of composite materials, it is urgent to optimize the interface of composite materials by modifying the fiber surface. The main component of commercial sizing agents for engineering fibers on the market is bisphenol A epoxy resin, which contains a large number of hydroxyl groups, has poor heat resistance and rigidity, and is easy to absorb water, which will greatly limit the excellent performance of the composite material interface bonding and interface phase mechanics, hygroscopicity and heat resistance. Chinese patent (CN115341392A) discloses a method for preparing a high temperature resistant epoxy resin emulsion carbon fiber sizing agent, by preparing a nano-SiO 2 The epoxy resin of the particle and the epoxy resin curing agent containing silicon oxygen bond are used to obtain the epoxy resin emulsion sizing agent, but the introduction of defoamer and silicon oxygen bond in the sizing agent can reduce the interface layer rigidity, and the untreated silica is poorly combined with the resin matrix interface, and it is easy to form stress concentration at the interface; Chinese patent (CN113736015A) discloses a biomimetic polymer containing dopamine functional group and its preparation method and uses it for fiber sizing agent, the introduction of polydopamine can effectively improve the interface bonding performance, but the patent also introduces more hydroxyl groups in the interface, so that the composite material hygroscopic resistance decreases, and the biomimetic polymer preparation process containing dopamine functional group is harsh, which is not conducive to large-scale production. Therefore, it is necessary to prepare a sizing agent that can improve the interface mechanical properties, does not damage the hygroscopic resistance of the composite material, and the production process is simpler, so as to improve the stability in the interface performance and humid heat environment of engineering fiber reinforced composite materials. Summary of the invention

[0004] The purpose of the present invention is to provide a design of a catalytic sizing agent and a method for preparing a low-hygroscopic composite material in order to solve the problem of poor interface performance and high moisture absorption rate of composite materials. Organic silicon titanium epoxy resin is prepared by reacting organic silicon titanium resin with epoxy resin as an engineering fiber sizing agent, which is coated on the fiber surface to catalyze the preferential curing of the resin at the interface and increase the crosslinking density, thereby improving the interface performance of the composite material and improving the moisture and heat resistance of the composite material.

[0005] The technical solutions specifically adopted in the present invention are as follows:

[0006] First, the present invention provides a method for preparing a catalytic sizing agent, which comprises the following steps:

[0007] Dihydroxysilane is self-polymerized into siloxane oligomer at high temperature, organic titanate is added to react to generate organic silicon titanium resin, glycidyl ether epoxy resin is added to prepare organic silicon titanium epoxy resin, and then the organic silicon titanium epoxy resin is dissolved in a solvent to obtain a catalytic sizing agent.

[0008] As a preferred embodiment of the present invention, the temperature of the dihydroxysilane self-polymerization reaction is 130-180°C, and the reaction time is 1-3h; the reaction temperature after adding the organic titanate is 120-150°C, and the reaction time is 1-3h; the reaction temperature after adding the glycidyl ether epoxy resin is 140-160°C, and the reaction time is 1-3h; wherein the molar ratio of dihydroxysilane to organic titanate is 0-7:1, and the mass fraction of organic titanate relative to 100 parts of glycidyl ether epoxy resin is 1-8 parts.

[0009] As a preferred embodiment of the present invention, the molar ratio of dihydroxysilane to organic titanate is preferably 2-4:1.

[0010] As a preferred embodiment of the present invention, the dihydroxysilane is one or more of diphenyldihydroxysilane and dimethyldihydroxysilane.

[0011] As a preferred embodiment of the present invention, the organic titanate is one or more of tetra-n-butyl titanate, tetra-isobutyl titanate, tetra-isopropyl titanate, and tetra-n-propyl titanate.

[0012] As a preferred embodiment of the present invention, the glycidyl ether epoxy resin is one or more of bisphenol A glycidyl ether epoxy resin, bisphenol F glycidyl ether epoxy resin, bisphenol S glycidyl ether epoxy resin, phenolic glycidyl ether epoxy resin, aliphatic polyol glycidyl ether epoxy resin, and alicyclic glycidyl ether epoxy resin.

[0013] As a preferred embodiment of the present invention, the solvent is one or more of N,N-dimethylformamide, toluene, methanol, acetonitrile and ether solvents, wherein the mass fraction of the organic silicon titanium epoxy resin in the catalytic sizing agent is 1-5%.

[0014] Secondly, the present invention provides a method for preparing a low-hygroscopic composite material based on the above-mentioned catalytic sizing agent, which comprises the following steps:

[0015] S1: dipping the engineering fiber in a catalytic sizing agent for 1-10 minutes, and drying at high temperature to obtain sized engineering fiber, wherein the mass of the catalytic sizing agent in the sized engineering fiber is 1-3% of the mass of the engineering fiber;

[0016] S2: Compounding and curing the cyanate resin system with the engineering fiber containing the catalytic sizing agent to obtain a fiber-reinforced composite material with low moisture absorption.

[0017] Preferably, the engineering fiber described in step S1 is high-modulus carbon fiber, high-strength carbon fiber, glass fiber, basalt fiber, quartz fiber, polyimide fiber or aramid fiber.

[0018] Preferably, the cyanate resin system described in step S2 is one or more of bisphenol A type cyanate resin, dimethyl paraphenylene type cyanate, bisphenol M type cyanate, and dicyclopentadiene cyanate.

[0019] The present invention also provides a low-hygroscopic composite material prepared by the above method, wherein the interlaminar shear strength retention rate after moisture absorption is not less than 70%, and the water absorption rate is less than 1wt%.

[0020] The beneficial effects of the present invention are:

[0021] 1) The present invention introduces a stable -CO-Ti- bond through the molecular structure design of the organosilicon titanium modified epoxy resin, thereby improving the heat resistance of the epoxy sizing agent. At the same time, the molecular structure contains transition metal atoms and has the ability to catalyze the curing reaction of the cyanate resin.

[0022] 2) The engineering fiber is treated with a catalytic sizing agent, which preferentially catalyzes the curing of the cyanate resin at the interface of the composite material, forming an interface phase with a high cross-linking density resin structure mainly composed of triazine rings, thereby increasing the modulus of the interface phase and forming a modulus transition zone, thereby increasing the bonding effect between the interface phase and the carbon fiber surface and achieving interface enhancement of the composite material.

[0023] 3) Compared with commercial sizing agents, the treatment with the catalytic sizing agent of the present invention can reduce the number of water-absorbing groups such as hydroxyl groups in the interface phase of the composite material, increase the crosslinking density of the interface phase of the composite material, reduce the interface defects of the composite material, inhibit the diffusion of water molecules in the interface phase of the composite material, and combine the low water absorption performance of the cyanate resin to ensure the stability of the composite material in a hot and humid environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the sizing process on the surface of engineering fibers.

[0025] Figure 2 This is the SEM image of the surface morphology of carbon fiber without surface treatment.

[0026] Figure 3 This is the SEM image of the surface morphology of the carbon fiber after commercial sizing in Example 3.

[0027] Figure 4 This is a SEM image of the surface morphology of the carbon fiber after surface treatment with the catalytic sizing agent in Example 3.

[0028] Figure 5 This is the fracture morphology of the commercial carbon fiber reinforced cyanate ester resin composite material of Example 3 after it absorbs moisture.

[0029] Figure 6 This is the fracture morphology of the carbon fiber reinforced cyanate ester resin composite material of Example 3 after absorbing moisture. DETAILED DESCRIPTION

[0030] The present invention will be further described and illustrated below in conjunction with the accompanying drawings and specific implementation methods.

[0031] Example 1

[0032] 1) Weigh 18g of dimethyldihydroxysilane in a beaker, stir at 150°C for 2h, then drop 6g of tetraisobutyl titanate, stir at 140°C to make it dissolve evenly and continue to react for 1.5h, then add 100g of bisphenol F type glycidyl ether epoxy resin, stir at 150°C for 2h, and finally obtain a transparent organosilicon titanium epoxy resin. Take 3g of the resin and dissolve it in 100g of methanol to obtain a catalytic sizing agent.

[0033] 2) If Figure 1 As shown, the unsized T800 carbon fiber is immersed in a catalytic sizing agent for 5 minutes through a surface sizing treatment device, and then dried in high temperature vacuum to obtain the sized T800 carbon fiber. The mass of the surface sizing agent after the immersion is 2.5% of the mass of the T800 carbon fiber.

[0034] 3) The dimethyl paraphenylene cyanate resin system and the T800 carbon fiber containing a catalytic sizing agent are cured at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a high-strength T800 carbon fiber reinforced cyanate-based composite material with low moisture absorption.

[0035] Example 2

[0036] 1) Weigh 8g of diphenyldihydroxysilane in a beaker, stir at 160°C for 4h, then drop 4.8g of tetrapropyl titanate, stir at 145°C to make it evenly dissolved and continue to react for 2h, then add 100g of aliphatic polyol glycidyl ether epoxy resin, react at the same temperature for 2.5h, and finally obtain a transparent organosilicon titanium epoxy resin. Take 2g of the resin and dissolve it in 100g of methanol. The resin is dissolved in acetone to obtain a catalytic sizing agent.

[0037] 2) If Figure 1 As shown, unsized glass fibers are immersed in a catalytic sizing agent for 3 minutes through a surface sizing treatment device, and then vacuum dried to obtain sized glass fibers. The mass of the surface sizing agent after the immersion is 1.4% of the mass of the glass fibers.

[0038] 3) The dicyclopentadiene cyanate resin system and the glass fiber containing the catalytic sizing agent are cured at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a glass fiber reinforced cyanate-based composite material with low moisture absorption.

[0039] Example 3

[0040] 1) Weigh 1g of dimethyldihydroxysilane in a beaker, stir at 150°C for 3h, then drop 3g of tetrabutyl titanate, stir at 130°C to make it dissolve evenly and continue to react for 1h, then add 100g of bisphenol A glycidyl ether epoxy resin, react at the same temperature for 1h, and finally obtain a transparent organosilicon titanium epoxy resin. Dissolve 2.5g of the resin in N,N-dimethylformamide to obtain a catalytic sizing agent.

[0041] 2) If Figure 1 As shown, the unsized M40J carbon fiber is immersed in a catalytic sizing agent for 7 minutes through a surface sizing treatment device, and then dried in high temperature vacuum to obtain the sized M40J carbon fiber. The mass of the surface sizing agent after impregnation is 1.8% of the mass of the M55J carbon fiber.

[0042] 3) The bisphenol A cyanate resin system and the M40J carbon fiber containing a catalytic sizing agent are cured at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a low-hygroscopic M40J high-modulus carbon fiber reinforced cyanate-based composite material.

[0043] Comparative Example 1

[0044] Using exactly the same cyanate resin system as in Example 1, the cyanate resin system was cured with commercial sized T800 carbon fiber (Toray, Japan) at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a commercial T800 carbon fiber reinforced cyanate resin-based composite material.

[0045] Comparative Example 2

[0046] Using exactly the same cyanate resin system as in Example 2, the cyanate resin system was cured with commercially sized E6 glass fiber (China Jushi) at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a commercial glass fiber reinforced cyanate resin-based composite material.

[0047] Comparative Example 3

[0048] Using exactly the same cyanate resin system as in Example 3, the cyanate resin system was cured with commercial sized M40J carbon fiber (Toray, Japan) at 150°C / 1h+180°C / 4h+200°C / 2h to obtain a commercial M40J carbon fiber reinforced cyanate resin-based composite material.

[0049] Figure 2-4 The surface morphology SEM images of carbon fiber without surface treatment, carbon fiber after commercial sizing in comparative example 3, and carbon fiber after surface treatment with catalytic sizing agent in example 3 of the present invention are shown in the figure. Figure 2 The surface of unsizing carbon fiber is densely covered with grooves, which are deep; Figure 3 After commercial sizing, the grooves on the carbon fiber surface become flat, mainly because the original deeper grooves are filled and covered by the sizing agent after sizing; Figure 4 The surface of the carbon fiber after being treated with the catalytic sizing agent also appears flat, similar to the surface of commercial carbon fiber, indicating that the sizing effect of the present invention on carbon fiber is equivalent to that of commercial carbon fiber.

[0050] Figure 5 This is the fracture morphology of the commercial carbon fiber reinforced cyanate ester resin composite material of Example 3 after it absorbs moisture. Figure 6 This is the fracture morphology of the carbon fiber reinforced cyanate resin composite material of Example 3 after moisture absorption. Figure 5 and Figure 6 It can be seen that after the commercial carbon fiber composite material absorbs moisture, the interface of the composite material is corroded by water, and the carbon fiber is peeled off and debonded. This is mainly because the commercial sizing agent has strong water absorption, which leads to the water absorption capacity of the interface phase of the composite material after curing; the catalytic sizing agent modified composite material has no obvious interface debonding after moisture absorption, which is mainly attributed to the lower hydroxyl and other water-absorbing functional groups in the catalytic sizing agent, and the high cross-linking density triazine ring structure interface phase formed by catalysis, which greatly inhibits the diffusion and corrosion of water in the interface phase of the composite material and improves the interface bonding performance of the composite material in a hot and humid environment.

[0051] Table 1 is a comparison of the interfacial shear strength, dry and wet interlaminar shear strength, interlaminar shear strength retention rate after moisture absorption and water absorption rate of different engineering fiber dry and wet composites (the composite material is a unidirectional continuous fiber composite material, in which the fiber volume fraction is 60%; the moisture absorption process is carried out in a humid and hot environment, specifically boiling in water at 80°C for 60 days).

[0052] Table 1

[0053]

[0054] As can be seen from Table 1, Examples 1-3 are composite materials treated with a catalytic sizing agent, and Comparative Examples 1-3 are corresponding commercial fiber composite materials. From the results of interface shear strength and interlaminar shear strength, it can be seen that the interface performance of the composite materials treated with the catalytic sizing agent is improved compared with the commercial fiber composite materials; the wet interlaminar shear strength, that is, the interlaminar shear strength measured after the composite material absorbs moisture, and the interlaminar performance of the composite material after moisture absorption are all reduced, but the interlaminar shear strength retention rate of the composite material treated with the catalytic sizing agent after moisture absorption (wet interlaminar shear strength / dry interlaminar shear strength) is greatly improved compared with the commercial fiber composite material; the water absorption rate of the composite material treated with the catalytic sizing agent is also lower than that of the commercial fiber composite material, and the water absorption rate of the modified composite material is basically less than 1%.

[0055] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a catalytic sizing agent, characterized in that: The steps include: The dihydroxysilane is self-polymerized into a siloxane oligomer at a high temperature, an organic titanate is added to react to generate an organic silicon titanium resin, a glycidyl ether epoxy resin is added to prepare an organic silicon titanium epoxy resin, and the organic silicon titanium epoxy resin is dissolved in a solvent to obtain a catalytic sizing agent; The molar ratio of dihydroxysilane to organic titanate is 0-7:1, and the mass fraction of organic titanate relative to 100 parts of glycidyl ether epoxy resin is 1-8 parts; the solvent is one or more of N,N-dimethylformamide, toluene, methanol, acetonitrile and ether solvents, and the mass fraction of organic silicon titanium epoxy resin in the catalytic sizing agent is 1-5%.

2. The method for preparing a catalytic sizing agent according to claim 1, characterized in that: The temperature of the self-polymerization reaction of dihydroxysilane is 130-180°C, and the reaction time is 1-3h; the reaction temperature after adding organic titanate is 120-150°C, and the reaction time is 1-3h; the reaction temperature after adding glycidyl ether epoxy resin is 140-160°C, and the reaction time is 1-3h.

3. The method for preparing a catalytic sizing agent according to claim 1, characterized in that: The dihydroxysilane is diphenyldihydroxysilane or dimethyldihydroxysilane.

4. The method for preparing a catalytic sizing agent according to claim 1, characterized in that: The organic titanate is one or more of tetra-n-butyl titanate, tetra-isobutyl titanate, tetra-isopropyl titanate and tetra-n-propyl titanate.

5. The method for preparing a catalytic sizing agent according to claim 1, characterized in that: The glycidyl ether epoxy resin is one or more of bisphenol A glycidyl ether epoxy resin, bisphenol F glycidyl ether epoxy resin, bisphenol S glycidyl ether epoxy resin, phenolic glycidyl ether epoxy resin, aliphatic polyol glycidyl ether epoxy resin, and alicyclic glycidyl ether epoxy resin.

6. A method for preparing a low-hygroscopic composite material of a catalytic sizing agent prepared by the method according to any one of claims 1 to 5, characterized in that The steps include: S1: dipping the engineering fiber in a catalytic sizing agent for 1-10 minutes, and drying at high temperature to obtain sized engineering fiber, wherein the mass of the catalytic sizing agent in the sized engineering fiber is 1-3% of the mass of the engineering fiber; S2: Compounding and curing the cyanate resin system with the engineering fiber containing the catalytic sizing agent to obtain a fiber-reinforced composite material with low moisture absorption.

7. The method according to claim 6, characterized in that The engineering fiber described in step S1 is high-modulus carbon fiber, high-strength carbon fiber, glass fiber, basalt fiber, quartz fiber, polyimide fiber or aramid fiber.

8. The method according to claim 6, characterized in that The cyanate resin system described in step S2 is one or more of bisphenol A type cyanate resin, dimethyl paraphenylene type cyanate, bisphenol M type cyanate, and dicyclopentadiene cyanate.

9. A low hygroscopic composite material prepared by the method of claim 6, characterized in that The interlaminar shear strength retention rate after moisture absorption is not less than 70%, and the water absorption rate is less than 1wt%.

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