A sizing agent for surface modification of PBO fibers, and a preparation method and application thereof

Abstract

The application belongs to the technical field of composite material preparation, and particularly relates to a sizing agent for a surface modification method of PBO fibers, a preparation method and application of the sizing agent, the sizing agent being used for surface modification of PBO fibers, the sizing agent comprising PBO nanofiber sol and inorganic salt, the PBO nanosol comprising mixed acid solution in which PBO nanofibers are dispersed, the PBO nanofibers having a branched morphology with a diameter of 5-20 nm and interpenetrating each other to form a three-dimensional network structure. The PBO nanofibers in the sizing agent adhere to the surface of the PBO fibers, which can increase the specific surface area of the fiber surface, facilitate the penetration and infiltration of resin glue on the surface of the PBO fibers, increase the contact area with the resin matrix, and improve the interface performance of the PBO fiber composite material.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, and particularly relates to a sizing agent for surface modification of PBO fibers, its preparation method and application, specifically a preparation method and application of poly(p-phenylenebenzobisoxazole) (PBO) fiber composite material with high strength and excellent interfacial properties. Background Technology

[0002] PBO fibers have the molecular structure shown in Formula I.

[0003]

[0004] PBO fibers possess rigid molecular chains highly oriented along the fiber axis, endowing them with superior mechanical strength, high modulus, high temperature resistance, flame retardancy, and light weight, while also exhibiting excellent dimensional stability, making them a recognized super fiber of the 21st century. However, the absence of polar groups in PBO molecules and their inert surface result in poor interfacial properties, hindering their composite application with other materials. Currently, surface modification of PBO fibers is typically achieved through coating to alter their interfacial properties. Coating modification, as a physical modification method, is non-destructive to bulk properties, simple, and mild, and has been extensively studied, demonstrating significant application potential in the field of interfacial reinforced composites.

[0005] In recent years, progress has been made in the field of surface modification by coating nanoscale reinforcing materials on fiber surfaces to improve the mechanical interaction between fibers and matrices. Among them, polymer nanofibers and their derivatives have attracted widespread attention for the interface reinforcement of composite materials due to their high porosity, large specific surface area, high surface energy, high activity, and nanoscale size effect. Nassar et al. used a deprotonation method to decompose large-scale aramid fibers into nanofibers. The aramid nanofibers possess a similar crystal structure and excellent mechanical properties to aramid fibers, and their surfaces are rich in polar functional groups such as amines and carboxylic acids. Coating the surface of aramid fibers with aramid nanofibers increased the interfacial shear strength of the aramid fiber composites by 70.29% (Nasser J, Lin J, Steinke K, et al. Enhanced interfacial strength of aramid fiber reinforced composites through adsorbed aramid nanofiber coatings[J]. Composites Science and Technology, 2019, 174: 125-133.). Steinke K et al. used aramid nanofibers (ANF) to impregnate ultra-high molecular weight polyethylene (UHMWPE) fibers. The surface roughness of the coated UHMWPE fibers increased by 197%, and the interfacial shear strength increased by 73%, while the tensile strength of the monofilament fibers remained unchanged, demonstrating excellent modification properties (Steinke K, Sodano H A. Aramid Nanofiber). Interphase for EnhancedInterfacial Shear Strength in Ultra-High Molecular Weight Polyethylene / EpoxyComposites[J]. Advanced Materials Interfaces, 2022,9(7):2102030.).

[0006] Currently, aramid nanofibers and cellulose nanofibers are commonly used in polymer nanofiber dispersions. These nanofibers have significant differences in molecular structure from PBO. When used for surface modification of PBO fibers, the structural differences lead to poor interfacial compatibility of the modified PBO fibers, making it difficult to effectively improve the interfacial properties of PBO fibers. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention uses a mixed acid / inorganic salt sizing agent to sizing PBO fibers, thereby treating PBO fibers with PBO nanofibers without damaging the fiber body.

[0008] In a first aspect, the present invention provides a sizing agent for surface modification of PBO fibers, the sizing agent comprising PBO nanofiber sol and inorganic salt, the PBO nanosol comprising a mixed acid solution in which PBO nanofibers are dispersed, the PBO nanofibers having a branched morphology with a diameter of 5 to 20 nm and forming a three-dimensional network structure through interconnection.

[0009] According to an embodiment of the present invention, the PBO nanofibers have the following characteristics: Figure 1 The morphology shown in the TEM image.

[0010] According to an embodiment of the present invention, the intrinsic viscosity of the PBO fiber dissolved in methanesulfonic acid is 20-40 dl / g.

[0011] According to an embodiment of the present invention, the concentration of PBO nanofibers in the PBO nanofiber sol is 0.01-2 wt%, preferably 0.05-1 wt%, for example, any value among 0.02 wt%, 0.04 wt%, 0.06 wt%, 0.08 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, and 1.8 wt%, or any intermediate value among any two values.

[0012] According to an embodiment of the present invention, the mixed acid is selected from a mixture of methanesulfonic acid or chlorosulfonic acid and other strong protic acids, wherein the strong protic acid is selected from at least one of trifluoroacetic acid, concentrated sulfuric acid, hydrochloric acid, and perchloric acid, for example, a mixed solution of trifluoroacetic acid and methanesulfonic acid.

[0013] According to an embodiment of the present invention, the salt is selected from water-soluble inorganic salts. The salt is selected from one or more of sodium sulfate, potassium sulfate, sodium bisulfate, sodium sulfite, magnesium nitrate, lithium chloride, lithium sulfate, ammonium chloride, aluminum chloride, magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium carbonate, sodium carbonate, sodium sulfate, potassium chloride, potassium carbonate, potassium nitrate, sodium phosphate, sodium nitrate, ammonium nitrate, aluminum sulfate, and aluminum nitrate, for example, at least one of sodium bisulfate, sodium sulfite, sodium carbonate, sodium sulfate, and potassium chloride.

[0014] According to an embodiment of the present invention, the salt concentration in the sizing agent is 0.01 to 10 wt%, preferably 0.1 to 8 wt%, for example, any value among 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, and 8 wt%, or any intermediate value among any two of these values.

[0015] Secondly, the present invention also provides a method for preparing the above-mentioned sizing agent, comprising the following steps: adding PBO fibers to a mixed acid solution to disperse and form a sol, and adding salt to the sol and dispersing it.

[0016] According to an embodiment of the present invention, the mixed acid solution is a mixture of methanesulfonic acid or chlorosulfonic acid and other strong protic acids, wherein the strong protic acid is selected from at least one of trifluoroacetic acid, concentrated sulfuric acid, hydrochloric acid, and perchloric acid, for example, a mixed solution of trifluoroacetic acid and methanesulfonic acid.

[0017] According to an embodiment of the present invention, when the mixed acid solution is a mixed solution of trifluoroacetic acid and methanesulfonic acid, the mass ratio of trifluoroacetic acid to methanesulfonic acid is 1:(0.05-20), preferably the mass ratio of trifluoroacetic acid to methanesulfonic acid is 1:(1-5).

[0018] According to an embodiment of the present invention, the dispersion time is 1 to 36 hours, preferably 5 to 24 hours.

[0019] According to an embodiment of the present invention, the dispersion is carried out under stirring conditions, and the stirring speed is 100-800 rpm.

[0020] Thirdly, the present invention also provides a modified PBO fiber, wherein the surface of the PBO fiber is coated with PBO nanofibers as described above, and there is a π-π interaction between the nanofibers and the PBO fiber.

[0021] Fourthly, the present invention also provides a method for preparing PBO fiber composite materials, comprising the following steps:

[0022] S1. The surface of the PBO fiber material is brought into contact with the above sizing agent to form a modified PBO fiber material;

[0023] S2. Composite the modified PBO fiber material with the matrix.

[0024] According to an embodiment of the present invention, step S1 includes the following steps: contacting the surface of the PBO fiber material with the above-mentioned sizing agent, removing it and allowing it to stand until a gel forms on the surface of the PBO fiber material, adjusting the pH of the surface of the PBO fiber material to neutral, and drying to obtain the modified PBO fiber material.

[0025] Preferably, the contact is, for example, wetting or coating.

[0026] According to an embodiment of the present invention, the soaking time is 10 to 300 seconds, preferably 50 to 200 seconds, and more preferably 100 to 150 seconds.

[0027] According to an embodiment of the present invention, the settling temperature is 60-150°C, preferably 80-120°C, and more preferably 100-110°C.

[0028] According to an embodiment of the present invention, the settling time is 60 to 300 minutes, preferably 100 to 200 minutes.

[0029] According to an embodiment of the present invention, adjusting the pH of the PBO fiber material surface to neutral includes the following steps: immersing the PBO fiber material with gel on the surface in water to remove the mixed acid solvent and inorganic salts on the PBO fiber surface until the pH value is neutral.

[0030] According to an embodiment of the present invention, the composite of modified PBO fiber material with a matrix includes the following steps: coating the surface of the modified PBO fiber material with a matrix resin solution and drying it, then hot-pressing it in a hot press.

[0031] According to an embodiment of the present invention, the drying temperature is 40–120°C and the drying time is 60–100 min.

[0032] According to an embodiment of the present invention, the PBO fiber material is, for example, PBO fiber cloth, which is plain weave, satin weave, twill weave, square plain weave, or unidirectional weave.

[0033] According to an embodiment of the present invention, the surface density of the PBO fiber cloth is 100-400 g / m². 2 Preferably, the surface density of the PBO fiber cloth is 100-200 g / m². 2 .

[0034] According to an embodiment of the present invention, the matrix resin is selected from one of epoxy resin, cyanate ester resin, phenolic resin, bismaleimide resin, benzoxazine, and polyimide resin.

[0035] According to an embodiment of the present invention, the drying temperature after coating the base resin adhesive is 80-120°C, and the drying time is 20-60 min.

[0036] According to an embodiment of the present invention, the hot pressing temperature for hot pressing after drying is 70-370°C, the pressure is 5-20 MPa, the total hot pressing time is 70-230 min, and the venting time during the hot pressing process is 1-20 min.

[0037] Fifthly, the present invention also provides a PBO fiber composite material prepared by the method described above, comprising a matrix on which the modified PBO fiber material described above is composited.

[0038] Beneficial effects

[0039] (1) All raw materials involved in this invention are commercially available raw materials. This invention involves adding PBO fibers to a mixed acid solution to form a sol through a sol-gel reaction. The PBO nanofibers prepared by the sol-gel method retain the original structural units of PBO fibers and are completely consistent with the chemical structure of PBO. The interface layer has excellent compatibility with the fiber body. The peeled PBO nanofibers have a branched morphology with a diameter of 5-20 nm and form a three-dimensional network structure through mutual interconnection. The PBO nanofibers attached to the surface of PBO fibers can increase the specific surface area of ​​the fiber surface, which is beneficial to the penetration and wetting of the resin liquid on the surface of PBO fibers. The increased contact area with the resin matrix can improve the interfacial properties of PBO fiber composite materials.

[0040] (2) The heat resistance temperature of PBO nanofibers is consistent with that of PBO fibers, which solves the problem that the heat resistance temperature of modified PBO fibers is reduced due to the low heat resistance temperature of the sizing agent itself. This helps to promote the application of PBO fiber composite materials in the field of heat protection technology for aerospace vehicles and other ultra-high temperature extreme environments.

[0041] (3) Compared with traditional mixed acid sizing agents, the salt in the sizing agent of the present invention can react with the residual MSA and TFA in the sol, thereby inhibiting the peeling effect of the residual acid on PBO fibers, effectively protecting the integrity of the PBO fiber structure, inhibiting the PBO fiber body from being etched, and the mechanical properties of the PBO fiber body after surface treatment with the sizing agent remain basically unchanged.

[0042] (4) The interfacial shear strength and interlaminar shear strength of the PBO fiber composite material of the present invention have been significantly improved. The significant improvement in the interfacial properties of the PBO fiber composite material is of great significance for promoting the large-scale application of PBO fiber composite material in aerospace, mechanical chemical industry and nuclear energy industry. Attached Figure Description

[0043] Figure 1 This is a TEM image of the PBO nanofibers prepared in Example 3 of the present invention. Detailed Implementation

[0044] The following detailed description, in conjunction with specific embodiments, will further illustrate the sizing agent of the present invention, its preparation method, and its application. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0045] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0046] The experimental methods for the following embodiments are as follows:

[0047] In the following examples, the hot press used for hot pressing of PBO fiber composite materials was manufactured by IDM, model L003.

[0048] Example 1

[0049] Preparation of S101. PBO fiber surface-modified sizing agent

[0050] 0.008g of commercial PBO fiber (JQS type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 76.2g MSA (methanesulfonic acid) and 3.8g TFA (trifluoroacetic acid), and mechanically stirred at 600rpm for 12h until completely dissolved to obtain PBO nanofiber sol. 1.6g of sodium bisulfate was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, yielding a PBO nanofiber sol sizing agent.

[0051] S102.PBO fiber surface coating treatment

[0052] Plain weave (106g / m) 2 PBO fiber cloth is immersed in PBO nanofiber sol sizing agent for 10 seconds and then removed. It is first left to stand at 25℃ for 6 hours to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. Then it is soaked in deionized water to remove the mixed acid solvent and inorganic salts on the surface of the PBO fiber cloth until the pH value of the PBO fiber surface is neutral. Finally, it is placed in a 100℃ oven for 60 minutes to dry and remove water, thus obtaining PBO nanofiber modified PBO fiber (hereinafter referred to as modified PBO fiber cloth).

[0053] Preparation of S103.PBO fiber / resin composite material

[0054] A mixture of 50g epoxy resin and 10g 4,4'-methylenebis(2-ethyl)aniline curing agent was brushed onto the surface of modified PBO fiber cloth. The mixture was then dried at 100℃ for 20 minutes to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was then stacked neatly and placed in a hot press. The press was first held at 80℃ and 5MPa for 30 minutes, then heated to 90℃ at a rate of 5℃ / min, held for 5 minutes, and the pressure was vented for 5 minutes. Finally, the temperature was increased to 120℃ at a rate of 5℃ / min, and the pressure was 10MPa. The press was then held for 30 minutes to obtain a PBO nanofiber interface-reinforced PBO fiber / epoxy resin composite material.

[0055] Example 2

[0056] Preparation of S201. PBO fiber surface-modified sizing agent

[0057] 0.16g of commercial PBO fiber (JQS type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 3.8g MSA and 76.2g TFA, and mechanically stirred at 800rpm for 36h until completely dissolved to obtain PBO nanofiber sol. 0.008g of magnesium phosphate was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, thus obtaining a PBO nanofiber sol sizing agent.

[0058] S202.PBO fiber surface coating treatment

[0059] Twill (106g / m) 2 After immersing the PBO fiber cloth in the PBO nanofiber sol sizing agent prepared in step S201 for 300s, it is taken out and left to stand at -60℃ for 24h to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. Then, it is soaked in deionized water to remove the mixed acid solvent and inorganic salts on the surface of the PBO fiber cloth until the pH value of the PBO fiber cloth surface is neutral. Finally, the PBO fibers are placed in an oven at 60℃ for 150min to dry and remove water, thus obtaining the PBO nanofiber coated modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0060] Preparation of S203.PBO fiber / resin composite materials

[0061] Phenolic resin (containing 25 wt% ethanol) was brushed onto the surface of modified PBO fiber cloth, and dried at 80℃ for 60 min to remove the ethanol from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was stacked neatly and placed in a hot press. First, it was held at 130℃ and 10 MPa for 60 min; then the temperature was increased to 150℃ at 5℃ / min and held for 20 min, followed by venting for 10 min; finally, the temperature was increased to 170℃ at 5℃ / min and the pressure was increased to 20 MPa, and the hot press was held for 60 min to obtain a PBO fiber / phenolic resin composite material with PBO nanofiber interface reinforcement.

[0062] Example 3

[0063] 301. Preparation of PBO fiber surface-modified sizing agent

[0064] 0.8g of commercial PBO fiber (JQS type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 40g MSA and 40g TFA, and mechanically stirred at 200rpm for 8 hours until completely dissolved to obtain PBO nanofiber sol. 0.04g of magnesium sulfate was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, yielding a PBO nanofiber sol sizing agent.

[0065] 302. PBO fiber surface coating treatment

[0066] Satin weave (113g / m) 2 PBO fiber cloth is immersed in the PBO nanofiber sol sizing agent prepared in step S301 for 200s, then removed and left to stand at -40℃ for 18h to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. Then it is soaked in deionized water to remove the mixed acid solvent and inorganic salts on the surface of the PBO fiber cloth until the pH value of the PBO fiber cloth surface is neutral. Finally, it is placed in an oven at 150℃ for 30min to dry and remove water, thus obtaining PBO nanofiber coated modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0067] 303. Preparation of PBO fiber / resin composite materials

[0068] A mixture of 50g bismaleimide resin and 5g diallyl bisphenol A curing agent was brushed onto the surface of modified PBO fiber cloth. The mixture was then dried at 80℃ for 60min to remove the solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was then stacked neatly and placed in a hot press. The press was first held at 120℃ and 5MPa for 20min; then the temperature was increased to 135℃ at a rate of 5℃ / min, held for 20min, and the pressure was released for 30min; then the temperature was increased to 160℃ at a rate of 5℃ / min, and the pressure was increased to 15MPa, held for 60min; then the temperature was increased to 180℃ at a rate of 5℃ / min, held for 60min; finally, the temperature was increased to 240℃ at a rate of 5℃ / min, and the press was held for 60min to obtain a PBO fiber / bismaleimide resin composite material with PBO nanofiber interface reinforcement.

[0069] See Figure 1 As shown, the PBO nanofibers stripped from the sizing agent have a branched morphology with a diameter of 5-20 nm and a porous three-dimensional network structure. The PBO nanofibers attached to the surface of PBO fibers can increase the specific surface area of ​​the fiber surface and increase the contact area with the resin matrix. Furthermore, the structure of PBO nanofibers is consistent with that of PBO fibers, and the interfacial layer has excellent compatibility with the fiber body, which can improve the interfacial properties of PBO fiber composites.

[0070] Meanwhile, the sizing agent of the present invention also includes salt, which can react with the residual MSA and TFA in the sol, thereby inhibiting the peeling effect of residual acid on PBO fibers and effectively protecting the integrity of PBO fiber structure.

[0071] Example 4

[0072] Preparation of S401. PBO fiber surface-modified sizing agent

[0073] 1.6g of commercial PBO fiber (JQH type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 40g MSA and 40g TFA, and mechanically stirred at 600rpm for 5h to completely dissolve it, thus obtaining PBO nanofiber sol. 0.08g of sodium sulfite was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, thus obtaining a PBO nanofiber sol sizing agent.

[0074] S402.PBO fiber surface coating treatment

[0075] One-way (115g / m 2 PBO fiber cloth was immersed in PBO nanofiber sol sizing agent for 50 seconds to form a sizing agent coating on the surface of the PBO fiber cloth. After removal, it was allowed to stand at 0℃ for 12 hours to allow the sizing agent coating on the surface of the PBO fiber cloth to gel. Then, it was immersed in deionized water to remove the mixed acid solvent and inorganic salts from the surface of the PBO fiber cloth until the pH value of the PBO fiber cloth surface was neutral. Subsequently, the PBO fibers were dried in a 100℃ oven for 120 minutes to remove water, resulting in PBO nanofiber modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0076] Preparation of S403.PBO fiber / resin composite materials

[0077] Allyl benzoxazine resin solution (containing 40 wt% acetone) was brushed onto the surface of modified PBO fiber cloth, and dried at 60℃ for 40 min to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was stacked neatly and placed in a hot press. First, it was hot-pressed at 150℃ and 5 MPa for 30 min, and then degassed for 20 min. Then, the temperature was increased to 190℃ at 5℃ / min, the pressure was increased to 10 MPa, and the temperature was held for 60 min. Next, the temperature was increased to 210℃ at 5℃ / min and the temperature was held for 60 min. Finally, the temperature was increased to 230℃ at 5℃ / min and the temperature was held for 60 min to obtain a PBO fiber / benzoxazine resin composite material with PBO nanofiber interface reinforcement.

[0078] Example 5

[0079] Preparation of S501. PBO fiber surface-modified sizing agent

[0080] 0.4g of commercial PBO fiber (JQH type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 20g MSA and 60g TFA, and mechanically stirred at 700rpm for 5h to completely dissolve it, thus obtaining PBO nanofiber sol. 2.4g of lithium chloride was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, thus obtaining a PBO nanofiber sol sizing agent.

[0081] S502.PBO fiber surface coating treatment

[0082] Satin weave (113g / m) 2 PBO fiber cloth is immersed in PBO nanofiber sol sizing agent for 30 seconds and then removed. It is first left to stand at 20℃ for 12 hours to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. Then it is soaked in deionized water to remove the mixed acid solvent and inorganic salts on the surface of the PBO fiber cloth until the pH value of the surface of the PBO fiber cloth is neutral. Finally, it is placed in a 100℃ oven for 20 minutes to dry and remove water, thus obtaining PBO nanofiber modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0083] Preparation of S503.PBO fiber / resin composite material

[0084] Polyimide resin solution (containing 40 wt% N-N'-dimethylacetamide) was brushed onto the surface of modified PBO fiber cloth and dried at 120℃ for 60 min to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was stacked neatly and placed in a hot press. First, it was held at 200℃ and 5 MPa for 30 min; then the temperature was increased to 260℃ at 5℃ / min and held for 30 min; then the temperature was increased to 300℃ at 5℃ / min and held for 30 min; next, the temperature was increased to 350℃ at 5℃ / min, the pressure was vented for 20 min, and held at 10 MPa for 10 min; finally, the temperature was increased to 370℃ at 5℃ / min and hot-pressed for 60 min to obtain a PBO fiber / polyimide resin composite material with PBO nanofiber interface reinforcement.

[0085] Example 6

[0086] Preparation of S601.PBO fiber surface-modified sizing agent

[0087] 0.8g of commercial PBO fiber (JQX type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 13.3g MSA and 66.7g TFA, and mechanically stirred at 500rpm for 5h until completely dissolved to obtain PBO nanofiber sol. 8g of potassium chloride was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, thus obtaining a PBO nanofiber sol sizing agent.

[0088] S602.PBO fiber surface coating treatment

[0089] Square plain weave (163g / m) 2PBO fiber cloth was immersed in PBO nanofiber sol sizing agent for 20 seconds, then removed and left to stand at -20℃ for 16 hours to allow the sizing agent layer on the surface of the PBO fiber cloth to form a gel. It was then immersed in deionized water to remove the mixed acid solvent and inorganic salts from the surface of the PBO fiber cloth until the pH value of the PBO fiber cloth surface was neutral. Subsequently, the PBO fibers were dried in a 100℃ oven for 60 minutes to remove water, resulting in PBO nanofiber coated and modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0090] Preparation of S603.PBO fiber / resin composite material

[0091] A cyanate ester resin solution (containing 50 wt% acetone) was brushed onto the surface of the modified PBO fiber cloth, and dried at 60℃ for 20 min to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was stacked neatly and placed in a hot press. It was first held at 70℃ and 12 MPa for 60 min, then heated to 80℃ at a rate of 5℃ / min and held for 30 min, followed by venting for 15 min. Finally, it was heated to 100℃ at a rate of 5℃ / min and pressurized to 15 MPa for 60 min to obtain a PBO nanofiber interface-reinforced PBO fiber / cyanate ester resin composite material.

[0092] Example 7

[0093] Preparation of S701. PBO fiber surface-modified sizing agent

[0094] 1.2g of commercial PBO fiber (JQX type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 7.3g MSA and 72.7g TFA, and mechanically stirred at 100rpm for 24h until completely dissolved to obtain PBO nanofiber sol. 0.16g of aluminum chloride was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, yielding a PBO nanofiber sol sizing agent.

[0095] S702.PBO fiber surface coating treatment

[0096] Plain weave (113g / m) 2 PBO fiber cloth is immersed in PBO nanofiber sol sizing agent for 10 seconds, then removed and left to stand at 25℃ for 6 hours to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. Then it is immersed in deionized water to remove the mixed acid solvent and inorganic salts on the surface of the PBO fiber cloth until the pH value of the PBO fiber cloth surface is neutral. Finally, the PBO fibers are placed in an oven at 170℃ for 60 minutes to dry and remove water, thus obtaining PBO nanofiber modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0097] Preparation of S703.PBO fiber / resin composite material

[0098] A mixture of 50g bismaleimide resin and 5g diallyl bisphenol A curing agent was brushed onto the surface of modified PBO fiber cloth. The mixture was then dried at 100℃ for 80min to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth was then stacked neatly and placed in a hot press. The press was first held at 120℃ and 5MPa for 20min; then the temperature was increased to 135℃ at a rate of 5℃ / min, held for 20min, and the pressure was released for 30min; next, the temperature was increased to 160℃ at a rate of 5℃ / min, and the pressure was increased to 15MPa, held for 60min; then the temperature was increased to 180℃ at a rate of 5℃ / min, held for 60min; finally, the temperature was increased to 240℃ at a rate of 5℃ / min, and the hot press was held for 60min to obtain a PBO fiber / bismaleimide resin composite material with PBO nanofiber interface reinforcement.

[0099] Example 8

[0100] Preparation of S801.PBO fiber surface-modified sizing agent

[0101] 0.008g of commercial PBO fiber (JQX type PBO filament from Zhongke Jinqi New Material Technology Co., Ltd.) was added to a mixed solvent of 5g MSA and 75g TFA, and mechanically stirred at 500rpm for 1h to completely dissolve it, thus obtaining PBO nanofiber sol. 4g of magnesium nitrate was added to the PBO nanofiber sol and thoroughly mixed to achieve uniform dispersion, thus obtaining a PBO nanofiber sol sizing agent.

[0102] S802.PBO fiber surface coating treatment

[0103] Plain weave (300g / m²) 2 PBO fiber cloth was immersed in PBO nanofiber sol sizing agent for 40 seconds, then removed and left to stand at -40℃ for 18 hours to allow the PBO nanofiber sol coating on the surface of the PBO fiber cloth to form a gel. The cloth was then soaked in deionized water to remove the mixed acid solvent and inorganic salts from the surface until the pH of the PBO fiber cloth surface was neutral. Subsequently, the PBO fibers were dried in an 80℃ oven for 60 minutes to remove moisture, resulting in PBO nanofiber coated and modified PBO fiber cloth (hereinafter referred to as modified nanofiber cloth).

[0104] S803. A mixture of 50g bismaleimide resin and 5g diallyl bisphenol A curing agent is brushed onto the surface of modified PBO fiber cloth. The mixture is dried at 90℃ for 60min to remove the resin solvent from the surface of the modified PBO fiber cloth. The modified PBO fiber cloth is stacked neatly and placed in a hot press. First, it is held at 120℃ and 5MPa for 20min; then the temperature is increased to 135℃ at 5℃ / min, held for 20min, and the pressure is released for 30min; then the temperature is increased to 160℃ at 5℃ / min, the pressure is increased to 15MPa, and held for 60min; then the temperature is increased to 180℃ at 5℃ / min, held for 60min; finally, the temperature is increased to 240℃ at 5℃ / min, and the hot press is held for 60min to obtain a PBO fiber / bismaleimide resin composite material with PBO nanofiber interface reinforcement.

[0105] Test Example 1

[0106] a) Using a composite material interface performance evaluation device (HM-410, Toei Sangyo Co., Ltd., Japan), the interfacial shear strength between PBO fiber composite material and matrix resin before and after coating treatment was tested by microsphere debonding method. The fiber migration rate during the test was 0.1 mm / min, and 20 valid data were collected for each sample group.

[0107] b) In accordance with GB / T 35100-2018 standard "General Rules for Test Methods of Fiber Reinforced Plastics", the interlaminar shear strength of PBO fiber composites before and after coating treatment was tested using a universal tensile testing machine.

[0108] c) In accordance with ASTM-D3379 standard "Test Method for Tensile Strength and Young's Modulus of High Modulus Monofilament Materials", the tensile strength of PBO fibers before and after coating treatment was tested using a computer-controlled electronic tensile testing machine.

[0109] d) The maximum thermal decomposition temperature of PBO fiber refers to the temperature at which the surface-modified PBO fiber reaches its highest weight loss rate under heating conditions. The maximum thermal decomposition temperature of the PBO fibers prepared in Examples 1-8 was determined by thermogravimetric analyzer. The heating temperature during the test was 100-800℃, and the heating rate was 20℃ / min.

[0110] Table 1. Relevant properties of PBO nanofibers before and after surface modification and relevant properties of PBO fiber / resin composites.

[0111]

[0112] As can be seen from Table 1, compared with untreated PBO fiber composites, PBO fiber composites made with modified PBO fiber cloth treated with PBO nanofibers can improve IFSS by 79.6-101.8% and ILSS by 98.4-120.7%.

[0113] The modified fiber's thermogravimetric temperature remained essentially unchanged, maintaining good heat resistance. Tensile strength decreased slightly, but the maximum decrease was only 2%, and overall, it retained excellent mechanical properties. This indicates that adding inorganic salts to our sizing agent can disrupt the charge distribution of the acid solution on the nanofibers, thereby inhibiting the protonation effect of acid on the PBO fiber surface and mitigating acid etching of the PBO fiber surface. This sizing agent has excellent effects on the surface and interface modification of PBO fibers, which is of great significance for promoting the further application of nanofibers in the field of fiber composite materials and the large-scale application of PBO fiber composite materials in the field of spacecraft thermal protection technology.

[0114] The specific embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A sizing agent, characterized by, It is used for surface modification of PBO fibers. The sizing agent includes PBO nanofiber sol and inorganic salt. The PBO nanofiber sol includes a mixed acid solution in which PBO nanofibers are dispersed. The PBO nanofibers have a branched morphology with a diameter of 5~20 nm, forming a three-dimensional network structure. The mixed acid is selected from a mixture of methanesulfonic acid or chlorosulfonic acid and other strong protic acids, wherein the strong protic acid is selected from at least one of trifluoroacetic acid, concentrated sulfuric acid, hydrochloric acid, and perchloric acid; The inorganic salt is selected from one or more of sodium sulfate, potassium sulfate, sodium bisulfate, sodium sulfite, magnesium nitrate, lithium chloride, lithium sulfate, ammonium chloride, aluminum chloride, magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium carbonate, sodium carbonate, sodium sulfate, potassium chloride, potassium carbonate, potassium nitrate, sodium phosphate, sodium nitrate, ammonium nitrate, aluminum sulfate, and aluminum nitrate.

2. The sizing agent according to claim 1, characterized by The intrinsic viscosity of the PBO fiber dissolved in methanesulfonic acid was measured to be 20~40 dl / g; And / or, the concentration of PBO nanofibers in the PBO nanofiber sol is 0.01 ~ 2 wt%; And / or, the mixed acid is a mixed solution of trifluoroacetic acid and methanesulfonic acid.

3. The sizing agent according to claim 1 or 2, characterized in that, The concentration of inorganic salts in the sizing agent is 0.01~10 wt%.

4. A method for preparing the sizing agent according to any one of claims 1-3, characterized in that, The process includes the following steps: dispersing PBO fibers in a mixed acid solution to form a sol, and adding salt to the sol and dispersing it.

5. The preparation method according to claim 4, characterized in that, The mixed acid solution is a mixture of trifluoroacetic acid and methanesulfonic acid.

6. The preparation method according to claim 5, characterized in that, The mass ratio of trifluoroacetic acid to methanesulfonic acid is 1: (0.05~20).

7. A modified PBO fiber, characterized in that, The surface of the PBO fiber is coated with PBO nanofibers as described in any one of claims 1-3, and there is a π-π interaction between the nanofibers and the PBO fiber.

8. A method for preparing a PBO fiber composite material, characterized in that, Includes the following steps: S1. The surface of the PBO fiber material is brought into contact with the sizing agent according to any one of claims 1-3 or the sizing agent prepared by the preparation method according to any one of claims 4-6 to form a modified PBO fiber material. S2. Composite the modified PBO fiber material with the matrix.

9. The method for preparing PBO fiber composite material according to claim 8, characterized in that, Step S1 includes the following steps: contacting the surface of the PBO fiber material with the above sizing agent, removing it and allowing it to stand until a gel forms on the surface of the PBO fiber material, adjusting the pH of the surface of the PBO fiber material to neutral, and drying to obtain the modified PBO fiber material.

10. The method for preparing the PBO fiber composite material according to claim 9, characterized in that, The contact is described as wetting or coating, and the wetting time is 10~300 s; And / or, the settling temperature is 60~150°C, and the settling time is 60~300 min; And / or, adjusting the pH of the PBO fiber material surface to neutral includes the following steps: immersing the PBO fiber material with gel on the surface in water to remove the mixed acid solvents and inorganic salts on the PBO fiber surface until the pH value is neutral.

11. The method for preparing PBO fiber composite material according to claim 8, characterized in that, The process of combining modified PBO fiber material with a matrix includes the following steps: coating the surface of the modified PBO fiber material with a matrix resin solution and drying it, then hot-pressing it in a hot press.

12. The method for preparing PBO fiber composite material according to claim 11, characterized in that, The drying temperature is 40~120℃, and the drying time is 60~100 min.

13. The method for preparing PBO fiber composite material according to claim 11, characterized in that, The matrix resin is selected from one of epoxy resin, cyanate ester resin, phenolic resin, bismaleimide resin, benzoxazine, and polyimide resin; And / or, after coating the base resin adhesive, the drying temperature is 80~120 ℃, and the drying time is 20~60 min; And / or, after drying, the hot pressing temperature in the hot press is 70~370 ℃, the pressure is 5~20 MPa, the total hot pressing time is 70 min~230 min, and the venting time during the hot pressing process is 1~20 min.

14. A PBO fiber composite material prepared by the method according to any one of claims 8-13, characterized in that, The composite material includes a matrix on which the modified PBO fiber material of claim 7 is laminated.

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