Phosphorus-containing side group novolac epoxy resin based on cardanol and flame-retardant cured product thereof

Abstract

A preparation method of the cardanol-based phosphorus-containing side group novolac epoxy resin comprises the following steps: (1) in the presence of a catalyst A, carrying out a stirring reaction on cardanol and an aldehyde compound at 80-110 DEG C for 3-10 h to prepare an intermediate A; (2) stirring the intermediate A and a phosphorus-containing compound at 50-150 DEG C to react for 10-24 hours to prepare an intermediate B; and (3) in the presence of a catalyst B, stirring and reacting the intermediate B and epichlorohydrin at 70-110 DEG C for 2-6 hours, and in the presence of a catalyst C, stirring and reacting at 30-65 DEG C for 1-4 hours to prepare the cardanol-based phosphorus-containing side group novolac epoxy resin. Through a rigid structure on a main chain of the novolac epoxy resin, a phosphorus-containing structure on a side chain of the novolac epoxy resin and an epoxy group, the toughness and flame retardance of an epoxy cured product can be improved on the premise that the thermal stability is not reduced, and the novolac epoxy resin has an extremely good application research prospect.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, specifically to a phosphorus-containing phenolic epoxy resin based on cashew phenol and its flame-retardant cured product. Background Technology

[0002] Epoxy resin is a commonly used thermosetting resin. Its molecular structure contains active epoxy groups, which can undergo cross-linking reactions with various curing agents such as acid anhydrides and amines to form a three-dimensional network structure. While these cured epoxy products possess excellent dielectric properties, low shrinkage, and good adhesion, their high cross-linking density makes them prone to stress cracking and results in poor impact resistance. Furthermore, these materials are highly flammable, releasing large amounts of smoke and toxic gases during combustion, posing significant safety hazards. Therefore, modifying epoxy resins to improve their mechanical and flame-retardant properties has become crucial.

[0003] Cashew nut shell extract (CNSL) is a renewable agricultural byproduct that has attracted widespread attention due to its unique molecular structure and excellent reactivity. The cashew nut shell molecule consists of a rigid aromatic ring and a flexible C-ring. 15 The alkane side chain composition of cashew phenol, possessing a structural characteristic of both rigidity and flexibility, helps improve the mechanical properties of epoxy cured products. Simultaneously, the unsaturated double bonds in the alkyl side chains and the phenolic hydroxyl groups in the cashew phenol structure endow it with good chemical reactivity, making it a promising candidate for development as a multifunctional chemical modifier. Existing research shows that cashew phenol can be chemically modified to prepare flame retardants and toughening agents, but most are additive modifiers, which can easily lead to a decrease in the thermomechanical properties of epoxy cured products. In contrast, reactive flame retardants designed based on the cashew phenol structure can participate in the curing of the epoxy matrix, thereby effectively improving the overall performance of the system. However, research on cashew phenol-based reactive flame retardant modifiers is still relatively limited. Based on this, by introducing epoxy groups at the phenolic hydroxyl positions of the cashew phenol molecule, enabling it to directly participate in the curing of the epoxy matrix, the toughness and flame retardant properties of the cured product can be significantly improved without sacrificing thermomechanical properties. Therefore, designing a reactive phenolic epoxy resin based on cashew phenol for modifying epoxy resin systems has significant research value. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol and its flame-retardant cured product. This invention first synthesizes a phenolic resin using cashew nut shell phenol and aldehyde compounds as raw materials. Then, utilizing the reactivity of the unsaturated alkyl chains on cashew nut shell phenol, a phosphorus-containing compound is introduced to form a phosphorus-containing side-group structure. Subsequently, the phenolic hydroxyl groups in the phenolic resin are epoxidized to obtain the phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol. This resin can not only be used as a matrix resin but also for improving the toughness and flame-retardant properties of epoxy cured products.

[0005] The technical solution of the present invention is as follows: A method for preparing a phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, characterized by comprising the following steps: (1) Under inert gas, cashew phenol, aldehyde compounds and catalyst A are mixed and heated to react, and cashew phenol-based phenolic resin, i.e. intermediate A, is obtained; (2) Under inert gas, intermediate A is reacted with a phosphorus-containing compound by heating to obtain a phenolic resin containing phosphorus side groups, i.e., intermediate B; (3) Under inert gas, intermediate B, epichlorohydrin and catalyst B are mixed, heated and reacted, then cooled, and alkaline catalyst C is added to the system and the reaction is continued for a period of time to obtain the phosphorus-containing side-group phenolic epoxy resin based on cashew phenol.

[0006] Preferably, a phosphorus-containing side-group phenolic epoxy resin based on cashew phenol is prepared by the following steps: (1) Under inert gas, cashew phenol, aldehyde compounds and catalyst A are mixed and heated to 80-110 °C for 3-10 h to obtain cashew phenol-based phenolic resin (intermediate A). (2) Under inert gas, intermediate A and phosphorus-containing compound are heated to 50-150 °C and reacted for 10-24 h to obtain phenolic resin containing phosphorus side groups (intermediate B). (3) Under inert gas, intermediate B, epichlorohydrin and catalyst B are mixed, heated to 70-100 °C, and reacted at a constant temperature for 2-6 h. Then the temperature is lowered to 30-65 °C, and alkaline catalyst C is added to the system. The reaction is continued for 1-4 h, and finally the phosphorus-containing side-group phenolic epoxy resin based on cashew phenol is obtained.

[0007] In a preferred embodiment, in step (1), the aldehyde compound is one or more of formaldehyde, paraformaldehyde, benzaldehyde, 1-naphthaldehyde, and 2-naphthaldehyde; in step (1), the catalyst A is one or more of hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, boron trifluoride ether, phosphoric acid, oxalic acid, and zinc acetate.

[0008] In a preferred embodiment, in step (1), the molar ratio of cashew phenol to aldehyde and catalyst A is 1:(0.5-0.98):(0.1%-5%); the inert gas in step (1) is nitrogen, argon or helium.

[0009] In a preferred embodiment, in step (2), the phosphorus-containing compound is one or more of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diphenylphosphine oxide, diphenyl phosphite, dimethyl phosphite, and diethyl phosphite.

[0010] In a preferred embodiment, in step (2), the molar ratio of cashew phenol to phosphorus-containing compound in intermediate A is 1:0.8-2; and the inert gas in step (2) is nitrogen, argon or helium.

[0011] In a preferred embodiment, in step (3), the catalyst B is one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, and benzyltriethylammonium chloride; and the alkaline catalyst C in step (3) is one or more of sodium hydroxide solution and potassium hydroxide solution.

[0012] In a preferred embodiment, in step (3), the molar ratio of cashew phenol to epichlorohydrin in intermediate B is 1:2-13; the molar ratio of intermediate B to catalyst B in step (3) is 1:0.001-0.03; the mass concentration of the alkaline catalyst C solution in step (3) is 20-50%; the molar ratio of cashew phenol to alkaline catalyst C in intermediate B in step (3) is 1:1.05-1.5; and the inert gas in step (3) is nitrogen, argon, or helium.

[0013] A modified epoxy curing compound based on cashew phenolic resin with phosphorus side groups comprises the following raw materials in parts by weight: 1-10 parts of phosphorus side group phenolic epoxy resin, 90-100 parts of bisphenol A type epoxy resin and 10-35 parts of amine curing agent.

[0014] A method for preparing a phosphorus-containing side-group phenolic epoxy resin-modified epoxy cured product based on cashew phenol, wherein the preparation method is as follows: Preheat 90-100 parts of bisphenol A type epoxy resin at 80-150 ℃, then add 1-10 parts of phosphorus-containing side-group phenolic epoxy resin and stir until completely dissolved. Maintain the temperature for 0.5 h, then cool to 75-100 ℃. Continue to add 10-35 parts of amine curing agent and stir evenly to obtain resin prepolymer. Pour it into a preheated mold and degas in a vacuum oven at 50-100 ℃ for 3-30 min. Place it in an oven for heating and curing at 110 ℃×1 h, 120 ℃×1 h, 140 ℃×2 h, 160 ℃×2 h, and 180 ℃×2 h. After cooling, obtain phosphorus-containing side-group phenolic epoxy resin modified epoxy cured product.

[0015] In a preferred embodiment, the bisphenol A type epoxy resin is one or more of E-51, E-42, and E-44.

[0016] In a preferred embodiment, the amine curing agent is one or more of the following: diaminodiphenylmethane, diaminodiphenyl sulfone, o-phenylenediamine, benzidine, p-phenylenediamine, p-phenylenediamine, m-phenylenediamine, diaminodiphenyl ether, and o-toluidine.

[0017] The beneficial technical effects of this invention are as follows: This invention provides a phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, which is used for flame retardant and toughening modification of epoxy resin.

[0018] This invention utilizes cashew nut shellac and aldehyde monomers to synthesize phenolic resins, then uses unsaturated olefins on the side groups and phosphorus-containing compounds to construct phosphorus-containing phenolic resins. Furthermore, epoxidation modification of the phenolic hydroxyl groups constructs a cashew nut shellac-based phenolic epoxy resin with phosphorus-containing side groups. This improves its compatibility with epoxy groups and enhances the crosslinking density of the system through the ring-opening reaction of carboxyl groups with epoxy. First, the synergistic effect of phosphorus and phenolic resin improves the flame retardant properties of the epoxy cured product. Second, by controlling the rigidity and flexibility of the cashew nut shellac, phosphorus compounds, and aldehyde compounds, toughness can be improved without reducing mechanical properties. The cashew nut shellac-based phosphorus-containing side-group phenolic epoxy resin imparts excellent thermal stability to the modified epoxy cured product, showing great promise for applications in industrial fields requiring high heat resistance, flame retardancy, and mechanical properties. Detailed Implementation

[0019] Example 1 A phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, the preparation method of which is as follows: Step 1: Mix 300 g of cashew phenol and 2 g of oxalic acid in a 1 L four-necked flask, protect with N2, heat to 90 °C, and then slowly add 67 g of 38% formaldehyde aqueous solution to the above reaction mixture over 1 h. After the addition is complete, continue stirring for 6 h. After the reaction is complete, wash the reaction product repeatedly with hot water and then dry it by vacuum distillation to obtain intermediate A.

[0020] Step 2: Place 160 g of intermediate A and 102 g of DOPO in a 1 L four-necked flask, mechanically stir, protect with N2, heat to 130 ℃, and stir at a constant temperature for 4 h. After the reaction is complete, wash the product in hot water three times, and finally dry to obtain intermediate B.

[0021] Step 3: Add 100 g of intermediate B, 150 g of epichlorohydrin, and 1 g of tetrabutylammonium bromide to a four-necked flask and mechanically stir. Under N2 protection, heat to 90 °C and maintain this temperature with stirring for 3 h. Then cool to 60 °C and slowly add 30 g of 40% NaOH solution dropwise over 2 h, continuing the reaction for another 3 h. After the reaction is complete, wash the reaction solution with water until neutral, and recover the epichlorohydrin by vacuum distillation to obtain a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol.

[0022] NMR analysis of the product revealed characteristic peaks of the aromatic ring represented by cashew phenol and DOPO at chemical shifts of 6.5–8.0 ppm; characteristic peaks of the methyl and methylene groups on cashew phenol at chemical shifts of 0.8–2.1 ppm; a characteristic peak of the methylene group connecting the benzene ring at chemical shifts of 3.5–4.0 ppm; and two proton signal peaks at chemical shifts of 2.5–2.8 ppm, attributed to the epoxy groups. Furthermore, the number-average molecular weight of the phenolic epoxy resin was determined by GPC to be 4430, and the epoxy value determined by the epoxide acetone method was 0.46 mol / 100 g. Its general chemical formula is:

[0023] The epoxy resin composition containing the phosphorus-containing side-group phenolic epoxy of this embodiment is prepared by the following method: Preheat 90 parts of E51 epoxy resin at 150 °C, then add 10 parts of phosphorus-containing side-group phenolic epoxy and stir until homogeneous. Continue stirring at a constant temperature for 0.5 h. Cool down to 90 °C, then add 25 parts of diaminodiphenylmethane and stir until homogeneous. Pour the mixture into a preheated mold and degas in a vacuum oven at 50 °C for 20 min. Place the mold in an oven for staged heating, curing at 110 °C × 1 h, 120 °C × 1 h, 140 °C × 2 h, 160 °C × 2 h, and 180 °C × 2 h. After cooling, the phosphorus-containing side-group phenolic epoxy modified epoxy cured product is obtained.

[0024] Example 2 A phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, the preparation method of which is as follows: Step 1: Mix 300 g of cashew phenol and 1 g of hydrochloric acid in a 1 L four-necked flask, protect with N2, heat to 90 °C, and then add 28 g of paraformaldehyde to the above reaction mixture in two portions over 1 h. After the addition is complete, continue stirring for 3 h. After the reaction is complete, wash the reaction product repeatedly with hot water and then dry it by vacuum distillation to obtain intermediate A.

[0025] Step 2: 170 g of intermediate A and 96 g of diphenylphosphine oxide were placed in a 1 L four-necked flask, mechanically stirred, protected with N2, heated to 120 ℃, and stirred at a constant temperature for 6 h. After the reaction was completed, the product was washed three times in hot water and finally dried to obtain intermediate B.

[0026] Step 3: Add 100 g of intermediate B, 150 g of epichlorohydrin, and 1 g of tetrabutylammonium chloride to a four-necked flask and mechanically stir. Under N2 protection, heat to 85 °C and maintain the temperature with stirring for 3.5 h. Then cool to 55 °C and slowly add 30 g of 40% NaOH solution dropwise over 2 h, continuing the reaction for another 3 h. After the reaction is complete, wash the reaction solution with water until neutral, and recover epichlorohydrin by vacuum distillation to obtain a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol.

[0027] NMR analysis of the product revealed characteristic peaks of the aromatic ring represented by cashew phenol and diphenylphosphine oxide at chemical shifts of 6.5–7.5 ppm; characteristic peaks of the methyl and methylene groups on cashew phenol at chemical shifts of 0.8–2.0 ppm; a characteristic peak of the methylene group connecting the benzene ring at chemical shifts of 3.6–4.1 ppm; and two proton signal peaks at chemical shifts of 2.55–2.85 ppm, attributed to the epoxy groups. Furthermore, the number-average molecular weight of the phenolic epoxy resin was determined by GPC to be 4167, and the epoxy value determined by the epoxide acetone method was 0.48 mol / 100 g. Its general chemical formula is:

[0028] The epoxy resin composition containing the phosphorus-containing side-group phenolic epoxy of this embodiment is prepared by the following method: Preheat 90 parts of E51 epoxy resin at 150 °C, then add 10 parts of phosphorus-containing side-group phenolic epoxy and stir until homogeneous. Continue stirring at a constant temperature for 0.5 h. Cool down to 90 °C, then add 25.5 parts of diaminodiphenylmethane and stir until homogeneous. Pour the mixture into a preheated mold and degas in a vacuum oven at 50 °C for 20 min. Place the mold in an oven for staged heating, curing at 110 °C × 1 h, 120 °C × 1 h, 140 °C × 2 h, 160 °C × 2 h, and 180 °C × 2 h. After cooling, the phosphorus-containing side-group phenolic epoxy modified epoxy cured product is obtained.

[0029] Example 3 A phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, the preparation method of which is as follows: Step 1: Mix 300 g of cashew phenol and 0.5 g of p-toluenesulfonic acid in a 1 L four-necked flask, protect with N2, heat to 90 °C, and then slowly add 90 g of benzaldehyde to the above reaction mixture over 1 h. After the addition is complete, continue stirring for 4 h. After the reaction is complete, wash the reaction product repeatedly with hot water and then dry it by vacuum distillation to obtain intermediate A.

[0030] Step 2: Place 180 g of intermediate A and 105 g of diphenyl phosphite in a 1 L four-necked flask, mechanically stir, protect with N2, heat to 130 ℃, and stir at a constant temperature for 4 h. After the reaction is complete, wash the product in hot water three times, and finally dry to obtain intermediate B.

[0031] Step 3: Add 100 g of intermediate B, 150 g of epichlorohydrin, and 1 g of tetramethylammonium chloride to a four-necked flask and mechanically stir. Under N2 protection, heat to 90 °C and maintain this temperature with stirring for 3 h. Then cool to 60 °C and slowly add 37 g of 45% KOH solution dropwise over 1 h, continuing the reaction for another 3 h. After the reaction is complete, wash the reaction solution with water until neutral, and recover the epichlorohydrin by vacuum distillation to obtain a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol.

[0032] NMR analysis of the product revealed characteristic peaks of the aromatic ring represented by cashew phenol and diphenyl phosphite at chemical shifts of 6.5–7.5 ppm; characteristic peaks of the methyl and methylene groups on cashew phenol at chemical shifts of 0.8–2.0 ppm; a characteristic peak of the methine group attached to the benzene ring at chemical shifts of 3.4–3.9 ppm; and two proton signal peaks at chemical shifts of 2.50–2.8 ppm, attributed to the epoxy groups. Furthermore, the number-average molecular weight of the phenolic epoxy resin was determined by GPC to be 4156, and the epoxy value determined by the epoxide acetone method was 0.48 mol / 100 g. Its general chemical formula is:

[0033] The epoxy resin composition containing the phosphorus-containing side-group phenolic epoxy of this embodiment is prepared by the following method: Preheat 90 parts of E51 epoxy resin at 150 °C, then add 10 parts of phosphorus-containing side-group phenolic epoxy and stir until homogeneous. Continue stirring at a constant temperature for 0.5 h. Cool down to 90 °C, then add 25.5 parts of diaminodiphenylmethane and stir until homogeneous. Pour the mixture into a preheated mold and degas in a vacuum oven at 50 °C for 20 min. Place the mold in an oven for staged heating, curing at 110 °C × 1 h, 120 °C × 1 h, 140 °C × 2 h, 160 °C × 2 h, and 180 °C × 2 h. After cooling, the phosphorus-containing side-group phenolic epoxy modified epoxy cured product is obtained.

[0034] Example 4 A phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, the preparation method of which is as follows: Step 1: Mix 300 g of cashew phenol and 3 g of zinc acetate in a 1 L four-necked flask, protect with N2, heat to 90 °C, and then add 132 g of 1-naphthaldehyde to the above reaction mixture in two portions over 1 h. After the addition is complete, continue stirring for 8 h. After the reaction is complete, wash the reaction product repeatedly with hot water and then dry it by vacuum distillation to obtain intermediate A.

[0035] Step 2: Place 180 g of intermediate A and 49.5 g of dimethyl phosphite in a 1 L four-necked flask, mechanically stir, protect with N2, heat to 125 ℃, and stir at a constant temperature for 5 h. After the reaction is complete, wash the product in hot water three times, and finally dry to obtain intermediate B.

[0036] Step 3: Add 100 g of intermediate B, 150 g of epichlorohydrin, and 1 g of benzyltriethylammonium chloride to a four-necked flask and mechanically stir. Under N2 protection, heat to 90 °C and maintain the temperature with stirring for 3 h. Then cool to 60 °C and slowly add 45 g of 40% KOH solution dropwise over 1 h, continuing the reaction for another 3 h. After the reaction is complete, wash the reaction solution with water until neutral, and recover epichlorohydrin by vacuum distillation to obtain a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol.

[0037] NMR analysis of the product revealed characteristic peaks of the aromatic ring represented by cashew phenol and 1-naphthaldehyde at chemical shifts of 6.5–8.5 ppm; characteristic peaks of methyl and methylene groups on cashew phenol at chemical shifts of 0.8–2.0 ppm; characteristic peaks of methine groups connecting to the benzene ring and methyl groups represented by dimethyl phosphite at chemical shifts of 3.5–4.5 ppm; and two proton signal peaks at chemical shifts of 2.55–2.75 ppm, attributed to the epoxy groups. Furthermore, the number-average molecular weight of the phenolic epoxy resin was determined by GPC to be 4248, and the epoxy value determined by the epoxide acetone method was 0.49 mol / 100 g. Its general chemical formula is:

[0038] The epoxy resin composition containing the phosphorus-containing side-group phenolic epoxy of this embodiment is prepared by the following method: Preheat 90 parts of E51 epoxy resin at 150 °C, then add 10 parts of phosphorus-containing side-group phenolic epoxy and stir until homogeneous. Continue stirring at a constant temperature for 0.5 h. Cool down to 90 °C, then add 25.7 parts of diaminodiphenylmethane and stir until homogeneous. Pour the mixture into a preheated mold and degas in a vacuum oven at 50 °C for 20 min. Place the mold in an oven for staged heating, curing at 110 °C × 1 h, 120 °C × 1 h, 140 °C × 2 h, 160 °C × 2 h, and 180 °C × 2 h. After cooling, the phosphorus-containing side-group phenolic epoxy modified epoxy cured product is obtained.

[0039] Example 5 A phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, the preparation method of which is as follows: Step 1: Mix 300 g of cashew phenol and 1.5 g of boron trifluoride diethyl ether in a 1 L four-necked flask, protect with N2, heat to 90 °C, and then add 132 g of 2-naphthaldehyde to the above reaction mixture in two portions over 1 h. After the addition is complete, continue stirring for 6 h. After the reaction is complete, wash the reaction product repeatedly with hot water and then dry it by vacuum distillation to obtain intermediate A.

[0040] Step 2: Place 180 g of intermediate A and 62 g of diethyl phosphite in a 1 L four-necked flask, mechanically stir, protect with N2, heat to 120 ℃, and stir at a constant temperature for 6 h. After the reaction is complete, wash the product in hot water three times, and finally dry to obtain intermediate B.

[0041] Step 3: Add 100 g of intermediate B, 150 g of epichlorohydrin, and 1 g of tetrabutylammonium bromide to a four-necked flask and mechanically stir. Under N2 protection, heat to 90 °C and maintain the temperature with stirring for 3 h. Then cool to 60 °C and slowly add 45 g of 40% KOH solution dropwise over 1 h, continuing the reaction for another 3 h. After the reaction is complete, wash the reaction solution with water until neutral, and recover the epichlorohydrin by vacuum distillation to obtain a phosphorus-containing side-group phenolic epoxy resin based on cashew nut shell phenol.

[0042] NMR analysis of the product revealed characteristic peaks of the aromatic rings represented by cashew phenol and 2-naphthaldehyde at chemical shifts of 6.5–8.0 ppm; characteristic peaks of the methyl and methylene groups on cashew phenol at chemical shifts of 0.8–2.0 ppm; characteristic peaks of the methylene group connecting the benzene ring and the methylene group in diethyl phosphite at chemical shifts of 3.5–4.5 ppm; and two proton signal peaks at chemical shifts of 2.55–2.8 ppm, attributed to the epoxy groups. Furthermore, the number-average molecular weight of the phenolic epoxy resin was determined to be 4320 by GPC, and the epoxy value was 0.48 mol / 100 g by the epoxide acetone method. Its general chemical formula is:

[0043] The epoxy resin composition containing the phosphorus-containing side-group phenolic epoxy of this embodiment is prepared by the following method: Preheat 90 parts of E51 epoxy resin at 150 °C, then add 10 parts of phosphorus-containing side-group phenolic epoxy and stir until homogeneous. Continue stirring at a constant temperature for 0.5 h. Cool down to 90 °C, then add 25.5 parts of diaminodiphenylmethane and stir until homogeneous. Pour the mixture into a preheated mold and degas in a vacuum oven at 50 °C for 20 min. Place the mold in an oven for staged heating, curing at 110 °C × 1 h, 120 °C × 1 h, 140 °C × 2 h, 160 °C × 2 h, and 180 °C × 2 h. After cooling, the phosphorus-containing side-group phenolic epoxy modified epoxy cured product is obtained.

[0044] Comparative Example 1 The preparation method of pure epoxy cured product is as follows: 79.5 parts of E51 epoxy resin are preheated at 90 °C, and then 20.5 parts of diaminodiphenylmethane are added and stirred evenly to obtain resin prepolymer; it is poured into a preheated mold and degassed in a vacuum oven at 60 °C for 0.5 h; it is then placed in a forced-air drying oven for staged heating, and cured according to the curing program of 110 °C×1 h, 120 °C×1 h, 140 °C×2 h, 160 °C×2 h, and 180 °C×2 h; after cooling, the cured product of pure epoxy resin can be obtained.

[0045] Example 6 Performance Testing of Epoxy Cured Products The epoxy cured products prepared in Examples 1-5 and Comparative Example 1 were subjected to relevant performance tests. The thermal decomposition temperature was tested under a nitrogen atmosphere at a heating rate of 10 °C / min. T g The determination was performed using DMA, and the sample size was 60×13×4 mm. 3 The heating rate was 3 ℃ / min; the impact strength was determined according to GB / T-1843-2008; the bending strength was determined according to GB / T-9341-2000, and the performance test results are shown in Table 1.

[0046] Table 1

[0047] As shown in Table 1, compared with Comparative Example 1, the thermal properties, mechanical properties, and flame retardant properties of Examples 1-5 show that, since the phosphorus-containing structure on the phosphorus-containing side group of the cashew phenol-based phenolic epoxy resin exists on the side group of the phenolic epoxy resin, its modified cured product has excellent thermal stability. Secondly, the phenolic epoxy resin gives the modifier better compatibility with the epoxy matrix and increases the crosslinking density of the cured product, which is beneficial to improving the mechanical properties.

[0048] Furthermore, the rational control of the rigid structure and flexible chains in the phenolic epoxy resin structure significantly improves the impact resistance of the cured epoxy. In terms of flame retardancy, the synergistic modification achieved through the rational construction of the phenolic structure and the phosphorus-containing moiety further enhances the flame retardant properties of the cured epoxy. The above data indicate that the cashew phenol-based phosphorus-containing side-group phenolic epoxy resin used in this application, as a modifier, can significantly improve the flame retardant properties and toughness of the cured epoxy without reducing its thermal properties, demonstrating excellent application research prospects.

Claims

1. A method for preparing a phosphorus-containing side-group phenolic epoxy resin based on cashew phenol, characterized in that, Includes the following steps: (1) Under inert gas, cashew phenol, aldehyde compounds and catalyst A are mixed and heated to react, and cashew phenol-based phenolic resin, i.e. intermediate A, is obtained. (2) Under inert gas, intermediate A is reacted with a phosphorus-containing compound by heating to obtain a phenolic resin containing phosphorus side groups, i.e., intermediate B; (3) Under inert gas, intermediate B, epichlorohydrin and catalyst B are mixed, heated and reacted, then cooled, and alkaline catalyst C is added to the system and the reaction is continued for a period of time to obtain the phosphorus-containing side-group phenolic epoxy resin based on cashew phenol.

2. The method for preparing phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (1), the aldehyde compound is one or more of formaldehyde, paraformaldehyde, benzaldehyde, 1-naphthaldehyde, and 2-naphthaldehyde; in step (1), the catalyst A is one or more of hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, boron trifluoride ether, phosphoric acid, oxalic acid, and zinc acetate.

3. The method for preparing the phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (1), the molar ratio of cashew phenol to aldehyde compound is 1:(0.5-0.98), and the amount of catalyst A added is 0.1%-5%; the inert gas in step (1) is nitrogen, argon or helium.

4. The method for preparing the phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (2), the phosphorus-containing compound is one or more of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine oxide, diphenyl phosphite, dimethyl phosphite, and diethyl phosphite.

5. The method for preparing the phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (2), the molar ratio of cashew phenol to phosphorus-containing compound in intermediate A is 1:0.8-2; the inert gas in step (2) is nitrogen, argon or helium.

6. The method for preparing the phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (3), the catalyst B is one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, and benzyltriethylammonium chloride; the alkaline catalyst C in step (3) is one or more of sodium hydroxide solution and potassium hydroxide solution.

7. The method for preparing phosphorus-containing side-group phenolic epoxy resin according to claim 1, characterized in that, In step (3), the molar ratio of cashew phenol to epichlorohydrin in intermediate B is 1:2-13; the molar ratio of intermediate B to catalyst B in step (3) is 1:0.001-0.03; the mass concentration of alkaline catalyst C solution in step (3) is 20-50%; the molar ratio of cashew phenol to alkaline catalyst C in intermediate B in step (3) is 1:1.05-1.5; the inert gas in step (3) is nitrogen, argon or helium.

8. The application of the phosphorus-containing side-group phenolic epoxy resin prepared by the preparation method according to any one of claims 1 to 7 as an epoxy resin modifier.

9. A method for preparing a phosphorus-containing side-group phenolic epoxy resin-modified epoxy cured product based on cashew phenol, characterized in that, Preheat 90-100 parts of bisphenol A type epoxy resin at 80-150 ℃, then add 1-10 parts of phosphorus-containing side-group phenolic epoxy resin and stir until completely dissolved. Maintain the temperature for 0.5 h, then cool to 75-100 ℃. Continue to add 10-35 parts of amine curing agent and stir evenly to obtain resin prepolymer. Pour it into a preheated mold and degas in a vacuum oven at 50-100 ℃ for 3-30 min. Place it in an oven for heating and curing at 110 ℃×1 h, 120 ℃×1 h, 140 ℃×2 h, 160 ℃×2 h, and 180 ℃×2 h. After cooling, obtain a phosphorus-containing side-group phenolic epoxy resin modified epoxy cured product based on cashew phenol.

10. The preparation method according to claim 9, characterized in that, The two-component epoxy resin is one or more of bisphenol A type epoxy resins E-51, E-42, and E-44; the amine curing agent is one or more of diaminodiphenylmethane, diaminodiphenyl sulfone, o-phenylenediamine, benzidine, p-phenylenediamine, p-phenylenediamine, m-phenylenediamine, diaminodiphenyl ether, and o-toluidine.

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