Preparation method of high-strength phenolic resin-based composite material

Abstract

The invention discloses a preparation method of a high-strength phenolic resin-based composite material, which comprises the following steps: adding phenol and a formaldehyde solution into a reaction kettle according to a molar ratio of (1: 1.2)-(1: 1.5), heating to 40-50 DEG C, adding a modifier accounting for 2-5% of the mass of phenol and a catalyst accounting for 1-3% of the mass of phenol, stirring to react for 1.5-2.5 hours, heating to 80-90 DEG C, and continuing to react for 0.5-1 hour, performing reduced pressure distillation to remove moisture and unreacted monomers to obtain modified phenolic resin; and putting the reinforcement into plasma treatment equipment, treating for 10-20 minutes at the power of 80-120W in an argon atmosphere, immersing the treated reinforcement into a silane coupling agent solution for 2-4 hours, taking out, and drying for 1-2 hours at the temperature of 80-100 DEG C to obtain the surface-activated reinforcement. According to the preparation method of the high-strength phenolic resin-based composite material, phenolic resin is modified, and a flexible chain segment is introduced into a resin molecular chain, so that the brittleness of the phenolic resin is improved; the reinforcement is subjected to plasma activation-silane coupling agent composite treatment, so that the interface bonding performance between the reinforcement and the matrix is improved.

Description

A method for preparing a high-strength phenolic resin-based composite material Technical Field

[0001] This invention relates to the field of composite material preparation technology, specifically to a method for preparing a high-strength phenolic resin-based composite material. Background Technology

[0002] Phenolic resins possess excellent heat resistance, corrosion resistance, insulation properties, and simple molding processes, making them widely used in the preparation of various composite materials. Phenolic resin-based composite materials are materials composed of phenolic resin as the matrix and various reinforcing agents, combining the excellent properties of both the matrix and the reinforcing agents. They have significant application prospects in aerospace, automotive, electronics, and construction fields.

[0003] However, traditional phenolic resin-based composites suffer from insufficient mechanical strength, particularly low flexural and tensile strength, limiting their application in high-end fields. This is mainly due to the following reasons: First, phenolic resin itself is brittle with rigid molecular chains, making it prone to breakage under stress. Second, the interfacial bonding between the reinforcement and the phenolic resin matrix is ​​poor, with significant interfacial gaps between them, preventing effective stress transfer and causing the composite to easily delaminate at the interface. Third, traditional manufacturing processes often employ one-time curing, resulting in insufficient cross-linking of the resin and numerous internal pores and defects, further reducing the mechanical properties of the composite.

[0004] To improve the strength of phenolic resin-based composites, various improvement schemes have been proposed in the prior art. For example, adding rubber elastomers to phenolic resin for toughening modification can improve the brittleness of the resin, but it will lead to a decrease in the heat resistance of the composite material. Another example is to perform surface coating treatment on the reinforcement to improve its compatibility with the matrix, but the coating process is complex, costly, and the coating is prone to peeling off. Yet another example is to use a hot-pressing-sintering composite process, which can reduce the porosity inside the composite material, but the process conditions are harsh, the energy consumption is high, and it is not conducive to industrial production. Therefore, developing a simple, cost-effective preparation method that can significantly improve the mechanical strength of phenolic resin-based composites is of great practical significance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-strength phenolic resin-based composite materials, so as to solve the problems of insufficient mechanical strength and complex preparation process of phenolic resin-based composite materials in the prior art mentioned above.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a high-strength phenolic resin-based composite material, comprising the following steps: (1) Modification preparation of phenolic resin: Phenol and formaldehyde solution are added to a reaction vessel at a molar ratio of 1:1.2-1:1.5, heated to 40-50℃, and modifier accounting for 2-5% of the mass of phenol and catalyst accounting for 1-3% are added. The mixture is stirred and reacted for 1.5-2.5h, and then heated to 80-90℃ and reacted for another 0.5-1h. Water and unreacted monomers are removed by vacuum distillation to obtain modified phenolic resin; (2) Surface activation treatment of the reinforcement: The reinforcement is placed in a plasma treatment device, and under an argon atmosphere, the power is 80-120W, and the treatment time is 10-20min. The treated reinforcement is immersed in a silane coupling agent solution for 2-4 hours, then removed and dried at 80-100℃ for 1-2 hours to obtain a surface-activated reinforcement. The reinforcement is then surface-activated using plasma treatment. Under an argon atmosphere, high-energy particles in the plasma bombard the reinforcement surface, removing oil, impurities, and oxide layers. Simultaneously, active groups such as hydroxyl and carboxyl groups are introduced onto the reinforcement surface, increasing its surface roughness and surface energy. During the subsequent silane coupling agent immersion treatment, the alkoxy groups in the silane coupling agent molecules undergo hydrolysis and condensation reactions with the hydroxyl groups on the reinforcement surface, forming strong chemical bonds. Meanwhile, the active groups at the other end of the silane coupling agent molecules react with the modified phenolic resin molecular chains, thereby enhancing the surface roughness and surface energy of the reinforcement. A stable interfacial bonding layer is constructed between the reinforcement and the matrix, which significantly improves the interfacial bonding performance between the two, ensuring that the stress can be effectively transferred between the matrix and the reinforcement when under stress, and avoiding interfacial peeling damage; (3) Composite molding of composite materials: The modified phenolic resin prepared in step (1) and the surface activated reinforcement obtained in step (2) are mixed at a mass ratio of 1:0.8-1:1.2, added to a high-speed mixer, and mixed at 100-120℃ for 20-30 min to obtain a mixture; the mixture is placed in a mold, pre-cured at 120-130℃ and 5-8MPa for 30-40 min, and then heated to 160-180℃ and 12-15MPa for hot-press curing for 1.5-2.5 h, and controlled The mass ratio of modified phenolic resin to reinforcement is in the range of 1:0.8-1:1.2, which can ensure that the reinforcement has a suitable content in the matrix, so that the reinforcement can be fully exerted and the resin cannot completely wrap the reinforcement due to excessive reinforcement content, resulting in interface defects; (4) Post-treatment: Take the cured composite material out of the mold and put it in the oven. Perform post-curing treatment at 180-200℃ for 2-3 hours. After cooling to room temperature, a high-strength phenolic resin-based composite material is obtained. Post-curing treatment can make the cross-linking reaction of modified phenolic resin more complete, further improve the cross-linking network structure of resin, reduce the residual stress and unreacted active groups inside the composite material, thereby improving the mechanical strength and dimensional stability of the composite material.

[0007] Preferably, the modifier in step (1) is one or a mixture of two of cashew nut shell oil and tung oil in any proportion. Cashew nut shell oil or tung oil is selected as the modifier. Its molecular structure contains active groups such as unsaturated double bonds and hydroxyl groups, which can cross-link with the phenolic resin molecular chain and introduce flexible segments into the resin molecular chain, thereby improving the brittleness of the phenolic resin and increasing its toughness and mechanical strength. At the same time, controlling the molar ratio of phenol to formaldehyde in the range of 1:1.2-1:1.5 can ensure that the resin has a suitable degree of cross-linking and avoid the resin brittleness due to excessive cross-linking or the resin strength due to insufficient cross-linking. The catalyst is one of oxalic acid and p-toluenesulfonic acid. The addition of the catalyst can accelerate the condensation reaction of phenol and formaldehyde and improve the reaction efficiency. Oxalic acid or p-toluenesulfonic acid is selected as the catalyst. The catalytic effect is mild and will not cause the reaction to be too violent. The vacuum distillation step can effectively remove the water and unreacted phenol and formaldehyde monomers generated during the reaction, reduce impurities in the modified phenolic resin, and improve the purity and performance of the resin.

[0008] Preferably, the formaldehyde solution in step (1) has a mass fraction of 37-40%, the pressure of vacuum distillation is 0.06-0.08 MPa, and the temperature is 100-110℃. Under these conditions, moisture and unreacted monomers can be fully volatilized without causing excessive cross-linking or decomposition of the modified phenolic resin.

[0009] Preferably, the reinforcement in step (2) is one of carbon fiber, glass fiber, and basalt fiber. The length of the reinforcement is 5-15 mm and the diameter is 5-10 μm. The reinforcement of this size can be uniformly dispersed in the matrix and give full play to its reinforcing effect. The above-mentioned reinforcement has the characteristics of high strength and high modulus, which can further improve the mechanical properties of the composite material.

[0010] Preferably, the mass fraction of the silane coupling agent solution in step (2) is 1-3%, and the solvent is a mixed solution of ethanol and water with a volume ratio of ethanol to water of 3:1. This concentration of silane coupling agent solution can ensure that the coupling agent forms a uniform adsorption layer on the surface of the reinforcement, while avoiding the aggregation of coupling agent molecules due to excessive concentration.

[0011] Preferably, in step (3), the stirring speed of the high-speed mixer is 1500-2000 r / min, the mold preheating temperature is 100-110℃, and the mixing time is 20-30 min. This allows the reinforcement to be evenly dispersed in the modified phenolic resin, avoiding reinforcement agglomeration. The step-by-step curing process is adopted. First, pre-curing is carried out at a lower temperature and pressure, which allows the modified phenolic resin to slowly cross-link and initially form a blank with a certain strength. This avoids internal stress caused by uneven resin shrinkage due to rapid curing. Then, hot-press curing is carried out at a higher temperature and pressure, which can promote the full cross-linking reaction of the resin. At the same time, the pores inside the composite material are compacted, reducing internal defects and further improving the density and mechanical strength of the composite material. The mold preheating temperature is controlled at 100-110℃, which can avoid a sudden drop in temperature when the mixed material comes into contact with the cold mold, which would cause the resin viscosity to suddenly increase and affect the material's fluidity and molding effect.

[0012] Preferably, the heating rate of the oven in step (4) is 5-10℃ / min, which can prevent the composite material from generating thermal stress due to a sudden temperature rise, which could lead to cracks in the material.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) The preparation method of the high-strength phenolic resin-based composite material, by modifying the phenolic resin and introducing flexible segments into the resin molecular chain, effectively improves the brittleness of the phenolic resin and improves the toughness and mechanical properties of the resin itself; at the same time, the plasma activation-silane coupling agent composite treatment of the reinforcement significantly improves the interfacial bonding performance between the reinforcement and the matrix, ensures the effective transmission of stress, and thus greatly improves the mechanical strength of the composite material; (2) The preparation method of the high-strength phenolic resin-based composite material adopts a step-by-step curing-hot pressing molding composite preparation process, first pre-curing to form a blank, and then hot pressing to promote the full curing of the resin. Crosslinking and post-curing treatment are carried out to improve the crosslinking network, which effectively reduces the pores and defects inside the composite material, reduces residual stress, and further improves the density and mechanical property stability of the composite material; (3) The preparation method of this high-strength phenolic resin-based composite material is simple and controllable, the raw materials are readily available, the production cost is moderate, and no complicated equipment and harsh process conditions are required, making it suitable for large-scale industrial production; (4) The high-strength phenolic resin-based composite material prepared by this method not only has high mechanical strength, but also good heat resistance and corrosion resistance, and has a wide range of applications, which can meet the requirements of high-end fields such as aerospace and automobile manufacturing. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] This invention provides a method for preparing a high-strength phenolic resin-based composite material, which is described in detail below.

[0016] Example 1: A method for preparing a high-strength phenolic resin-based composite material, comprising the following steps: (1) Modification preparation of phenolic resin: Phenol and formaldehyde solution with a mass fraction of 37% are added to a reaction vessel at a molar ratio of 1:1.2, the temperature is raised to 40°C, cashew shell oil accounting for 2% of the mass of phenol and oxalic acid accounting for 1% are added, the mixture is stirred and reacted for 1.5h, then the temperature is raised to 80°C and the reaction continues for 0.5h, and the water and unreacted monomers are removed by vacuum distillation at a pressure of 0.06MPa and a temperature of 100°C. Modified phenolic resin was obtained; (2) Surface activation treatment of the reinforcement: Carbon fibers with a length of 5 mm and a diameter of 5 μm were placed in a plasma treatment device, and under an argon atmosphere, the power was 80 W and the treatment time was 10 min. Then the treated carbon fibers were immersed in a 1% silane coupling agent solution (the solvent was a mixed solution of ethanol and water, and the volume ratio of ethanol to water was 3:1) for 2 h. After being taken out, they were dried at 80 °C for 1 h to obtain surface-activated carbon fibers; (3) Composite molding of composite materials: The modified phenolic resin prepared in step (1) and the surface activated carbon fiber obtained in step (2) are mixed at a mass ratio of 1:0.8 and added to a high-speed mixer. The mixture is mixed for 20 minutes at a speed of 1500 r / min and a temperature of 100℃ to obtain a mixture. The mixture is placed in a mold preheated to 100℃ and pre-cured at 120℃ and a pressure of 5MPa for 30 minutes. Then, it is heated to 160℃ and hot-pressed for 1.5 hours at a pressure of 12MPa. (4) Post-treatment: The cured composite material is taken out of the mold and placed in an oven. The temperature is raised to 180℃ at a heating rate of 5℃ / min and post-cured for 2 hours. After cooling to room temperature, a high-strength phenolic resin-based composite material is obtained. The performance of the composite material prepared in this embodiment is tested. The results show that the bending strength is 285MPa, the tensile strength is 162MPa, the heat distortion temperature is 225℃, and the mass loss rate after soaking in 5% hydrochloric acid solution for 72 hours is 0.8%.

[0017] Example 2: A method for preparing a high-strength phenolic resin-based composite material, comprising the following steps: (1) Preparation of modified phenolic resin: Phenol and formaldehyde solution with a mass fraction of 38% are added to a reaction vessel at a molar ratio of 1:1.3, the temperature is raised to 45°C, tung oil accounting for 3% of the mass of phenol and p-toluenesulfonic acid accounting for 2% are added, the mixture is stirred and reacted for 2 hours, and then the temperature is raised to 85°C and the reaction continues for 0.7 hours. The water and unreacted monomers are removed by vacuum distillation at a pressure of 0.07 MPa and a temperature of 105°C to obtain the modified phenolic resin. (2) Surface activation treatment of the reinforcement: Glass fibers with a length of 10 mm and a diameter of 8 μm are placed in a plasma treatment device. Under an argon atmosphere, the power is 100 W and the treatment time is 15 min. Then, the treated glass fibers are immersed in a 2% silane coupling agent solution (the solvent is a mixed solution of ethanol and water, and the volume ratio of ethanol to water is 3:1) for 3 h. After being taken out, they are dried at 90 °C for 1.5 h to obtain surface activated glass fibers. (3) Composite molding of composite material: The modified phenolic resin prepared in step (1) and the surface activated glass fiber obtained in step (2) are mixed at a mass ratio of 1:1 and added to a high-speed mixer. The mixture is mixed for 25 minutes at a speed of 1800 r / min and a temperature of 110℃ to obtain a mixture. The mixture is placed in a mold preheated to 105℃ and pre-cured at 125℃ and a pressure of 6MPa for 35 minutes. Then, it is heated to 170℃ and hot-pressed for 2 hours at a pressure of 13MPa. (4) Post-treatment: The cured composite material is taken out of the mold and placed in an oven. The temperature is raised to 190℃ at a heating rate of 8℃ / min and post-cured for 2.5 hours. After cooling to room temperature, a high-strength phenolic resin-based composite material is obtained. The performance of the composite material prepared in this embodiment is tested. The results show that the bending strength is 305MPa, the tensile strength is 172MPa, the heat distortion temperature is 238℃, and the mass loss rate after soaking in 5% sodium hydroxide solution for 72 hours is 0.7%.

[0018] Example 3: A method for preparing a high-strength phenolic resin-based composite material, comprising the following steps: (1) Modification preparation of phenolic resin: Phenol and formaldehyde solution with a mass fraction of 40% are added to a reaction vessel at a molar ratio of 1:1.5, the temperature is raised to 50°C, and a mixed modifier of cashew shell oil and tung oil (mass ratio of the two is 1:1) accounting for 5% of the mass of phenol and 3% of oxalic acid are added. The mixture is stirred and reacted for 2.5 h, and then the temperature is raised to 90°C and the reaction is continued for 1 h. The resin is removed by vacuum distillation at a pressure of 0.08 MPa and a temperature of 110°C. (2) Surface activation treatment of the reinforcement: Basalt fibers with a length of 15 mm and a diameter of 10 μm were placed in a plasma treatment device. Under an argon atmosphere, the power was 120 W and the treatment time was 20 min. Then, the treated basalt fibers were immersed in a 3% silane coupling agent solution (the solvent was a mixture of ethanol and water, with a volume ratio of ethanol to water of 3:1) for 4 h. After being taken out, they were dried at 100 °C for 2 h to obtain the surface activation treatment. (3) Composite molding of the composite material: The modified phenolic resin prepared in step (1) and the surface-activated basalt fiber obtained in step (2) are mixed at a mass ratio of 1:1.2 and added to a high-speed mixer. The mixture is mixed for 30 minutes at a speed of 2000 r / min and a temperature of 120℃ to obtain a mixture. The mixture is placed in a mold preheated to 110℃ and pre-cured at 130℃ and a pressure of 8MPa for 40 minutes. Then the temperature is raised to 180℃ and the pressure is 15MPa for heating. (3) Curing: Press and cure for 2.5h; (4) Post-treatment: Take the cured composite material out of the mold and put it into the oven. Heat it to 200℃ at a heating rate of 10℃ / min and perform post-curing treatment for 3h. After cooling to room temperature, a high-strength phenolic resin-based composite material is obtained. The performance of the composite material prepared in this embodiment was tested. The results showed that the bending strength was 318MPa, the tensile strength was 178MPa, the heat distortion temperature was 245℃, and the mass loss rate after soaking in 5% hydrochloric acid solution for 72h was 0.6%.

[0019] Comparative Example: Phenolic resin-based composite materials were prepared using a traditional method. The specific steps were as follows: unmodified phenolic resin and untreated glass fiber were mixed at a mass ratio of 1:1, placed in a mold, and cured once at 160°C and 13MPa for 2 hours. After cooling to room temperature, the composite material was obtained. Performance tests were performed, and the results showed that the flexural strength was 210MPa, the tensile strength was 115MPa, the heat distortion temperature was 200°C, and the mass loss rate after immersion in 5% sodium hydroxide solution for 72 hours was 1.5%.

[0020] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0021] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength phenolic resin-based composite material, characterized in that, Includes the following steps: (1) Preparation of modified phenolic resin: Phenol and formaldehyde solution are added to the reaction vessel at a molar ratio of 1:1.2-1:1.5, heated to 40-50℃, and 2-5% modifier and 1-3% catalyst are added according to the mass of phenol. The mixture is stirred and reacted for 1.5-2.5h, and then heated to 80-90℃ and reacted for another 0.5-1h. The water and unreacted monomers are removed by vacuum distillation to obtain modified phenolic resin; (2) Surface activation treatment of the reinforcement: The reinforcement is placed in a plasma treatment device, under an argon atmosphere, with a power of 80-120W and a treatment time of 10-20min. The treated reinforcement is then immersed in a silane coupling agent solution for 2-4h. After removal, it is dried at 80-100℃ for 1-2h to obtain surface activated reinforcement. (3) Composite molding of composite material: The modified phenolic resin prepared in step (1) and the surface activated reinforcement obtained in step (2) are mixed at a mass ratio of 1:0.8-1:1.2 and added to a high-speed mixer. The mixture is mixed at 100-120℃ for 20-30 min to obtain a mixture. The mixture is placed in a mold and pre-cured at 120-130℃ and 5-8MPa for 30-40 min. Then, the temperature is raised to 160-180℃ and the pressure is 12-15MPa for hot-press curing for 1.5-2.5 h. (4) Post-treatment: The cured composite material is taken out of the mold and placed in an oven. It is post-cured at 180-200℃ for 2-3 h. After cooling to room temperature, a high-strength phenolic resin-based composite material is obtained.

2. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: The modifier mentioned in step (1) is one or two of cashew nut shell oil and tung oil mixed in any proportion, and the catalyst is one of oxalic acid and p-toluenesulfonic acid.

3. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: The formaldehyde solution in step (1) has a mass fraction of 37-40%, the pressure of vacuum distillation is 0.06-0.08 MPa, and the temperature is 100-110℃.

4. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: The reinforcement in step (2) is one of carbon fiber, glass fiber, or basalt fiber, and the length of the reinforcement is 5-15 mm and the diameter is 5-10 μm.

5. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: The mass fraction of the silane coupling agent solution in step (2) is 1-3%, and the solvent is a mixed solution of ethanol and water with a volume ratio of ethanol to water of 3:

1.

6. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: In step (3), the stirring speed of the high-speed mixer is 1500-2000 r / min, and the mold preheating temperature is 100-110℃.

7. The method for preparing a high-strength phenolic resin-based composite material according to claim 1, characterized in that: In step (4), the heating rate of the oven is 5-10℃ / min.