Flame-retardant modified long glass fiber / polypropylene compound and preparation method thereof

Abstract

The invention discloses a flame-retardant modified long glass fiber / polypropylene compound and a preparation method thereof, and relates to the technical field of high-molecular polymers. The preparation method comprises the following steps: adding modified carbon fibers and modified long glass fibers into a synergistic solution, uniformly mixing, drying, adding modified polypropylene particles, uniformly stirring, blending, extruding, cooling with water, and pelletizing to obtain the flame-retardant modified long glass fiber / polypropylene compound. The components such as gamma-aminopropyltriethoxysilane, trihydroxymethyl phosphorus oxide and phytic acid are introduced into the synergistic liquid, so that the flame retardance and thermo-oxidative aging resistance of the flame-retardant modified long glass fiber / polypropylene compound can be effectively improved; the modification process of the carbon fibers and the long glass fibers further improves the flame retardance and thermo-oxidative aging resistance of the flame-retardant modified long glass fiber / polypropylene compound. Therefore, the method has a wider application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly to a flame-retardant modified long glass fiber / polypropylene composite and a preparation method thereof. Background Art

[0002] Fiber-reinforced plastics are currently the most widely used type of polymer matrix composite materials. Long glass fiber-reinforced polypropylene prepared by the melt impregnation technique has the advantages of high strength, low density, good low-temperature toughness, good heat resistance, and small molding shrinkage. However, long glass fiber-reinforced polypropylene composites are more flammable than pure polypropylene. Once ignited in the air, they are prone to produce flaming drips during the combustion process, which can easily spread the flame. Therefore, this limits its application in products such as electronic and electrical appliances, transportation, and office automation.

[0003] At the same time, during the processing, storage, and actual use of long fiber-reinforced polypropylene composites, the action of external environmental factors (such as temperature, humidity, light, etc.) will also cause the matrix molecular weight to decrease, and changes or damage to occur at the fiber or fiber / matrix interface, resulting in a reduction in its mechanical properties. Therefore, in actual applications, the aging phenomenon has always accompanied the entire production and application process of the material. Since the halogen-free flame-retardant long glass fiber-reinforced polypropylene material has excellent mechanical and heat resistance properties and can be used for a long time at a relatively high temperature (greater than 100°C), it is particularly necessary to improve its flame retardancy and resistance to thermal-oxidative aging.

[0004] To solve the above technical problems, the patented technical solution CN114854133B proposes a halogen-free flame-retardant long glass fiber-reinforced polypropylene composite and a preparation method thereof, which are prepared from the following components in parts by weight: 18 - 50 parts of polypropylene, 30 - 35 parts of halogen-free flame-retardant masterbatch, 10 - 40 parts of glass fiber, 1 - 5 parts of polyethylene, 1 - 5 parts of compatibilizer, 0.5 - 2 parts of zeolite, 0.5 - 2 parts of quartz powder, 0.1 - 0.5 parts of cross-linking agent, and 0.5 - 2 parts of processing aid. This invention effectively promotes the high dispersion of glass fiber in the melt pool of the impregnation system by adding spherical quartz powder, so that the polypropylene resin and glass fiber are fully impregnated and combined, further enhancing the mechanical properties of the final composite material. However, the flame retardancy and resistance to thermal-oxidative aging of the flame-retardant modified long glass fiber / polypropylene composites prepared by these existing methods still need to be improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a flame-retardant modified long glass fiber / polypropylene composite and a preparation method thereof, to solve the following technical problems:

[0006] The existing flame-retardant modified long glass fiber / polypropylene composites still have problems with unsatisfactory flame retardancy and resistance to thermal-oxidative aging.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A preparation method of a flame-retardant modified long glass fiber / polypropylene composite, comprising the following steps:

[0009] Add modified carbon fiber and modified long glass fiber to the synergistic solution and mix evenly. After drying, add modified polypropylene particles and stir evenly. Then, through blending, extrusion, water cooling, and pelletizing treatments, a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0010] Preferably, the dosage ratio of the synergistic solution, modified carbon fiber, modified long glass fiber, and modified polypropylene particles after mixing evenly and drying is 20 - 30 g: 8 - 10 g: 30 - 40 g: 100 g;

[0011] During the blending treatment, the temperature is 210 - 230 °C, the rotation speed is 250 - 350 r / min, and the duration is 20 - 30 min.

[0012] Preferably, the preparation method of the synergistic solution is as follows:

[0013] Step A1: Mix castor oil, polytetrahydrofuran ether diol, isophorone diisocyanate, and dimethylolpropionic acid, then add dibutyltin dilaurate and stir at 80 - 85 °C for 1.5 - 2 h. Then add flame retardant OP550 and polybutylene adipate glycol and stir for 2 - 2.2 h. Then add trimethylolphosphine oxide and acetone and react at 75 - 80 °C for 1 - 1.2 h. After cooling to 40 °C, first add triethylamine and react for 10 - 20 min, then dropwise add γ-aminopropyltriethoxysilane and react for 30 - 40 min. Finally, add deionized water and emulsify at high speed. After vacuum distillation, a composite emulsion is obtained;

[0014] Step A2: Add phytic acid to deionized water, stir evenly, then dropwise add γ-aminopropyltriethoxysilane and stir at 70 - 75 °C for 3 - 4 h. Then add the composite emulsion and stir evenly to obtain the synergistic solution.

[0015] Preferably, the dosage ratio of castor oil, polytetrahydrofuran ether diol, isophorone diisocyanate, dimethylolpropionic acid, dibutyltin dilaurate, flame retardant OP550, polybutylene adipate glycol, trimethylolphosphine oxide, acetone, triethylamine, γ-aminopropyltriethoxysilane, and deionized water in Step A1 is 20 - 30 g: 15 - 20 g: 17 - 25 g: 4 - 5 g: 0.1 - 0.2 g: 6 - 8 g: 6 - 10 g: 4 - 5 g: 40 - 50 g: 2 - 3 g: 1.6 - 2 g: 70 - 100 mL;

[0016] The rotation speed during the high-speed emulsification in Step A1 is 5000 - 8000 r / min, and the emulsification duration is 30 - 40 min;

[0017] In step A2, the dosage ratio of deionized water, phytic acid, γ-aminopropyltriethoxysilane, and composite emulsion is 10 - 20 mL: 10 - 20 g: 4 - 7 g: 120 - 235 g;

[0018] The mass concentration of phytic acid described in step A2 is 70%.

[0019] Preferably, the preparation method of the modified carbon fiber is as follows:

[0020] Step B1: Add carbon fiber to nitric acid solution, reflux at 70 - 80 °C for 3 - 5 h, then rinse with deionized water until neutral, and obtain pretreated carbon fiber after drying;

[0021] Step B2: Add melamine polyphosphate and γ-aminopropyltriethoxysilane to toluene and mix evenly, then add pretreated carbon fiber and stir and react at 80 - 90 °C for 6 - 8 h, and then obtain modified carbon fiber through filtration, washing, and drying processes.

[0022] Preferably, the dosage ratio of the nitric acid solution and carbon fiber described in step B1 is 200 mL: 10 - 15 g;

[0023] The mass concentration in the nitric acid solution described in step B1 is 4% - 6%;

[0024] In step B2, the dosage ratio of toluene, melamine polyphosphate, γ-aminopropyltriethoxysilane, and pretreated carbon fiber is 100 - 150 mL: 3 - 7 g: 2 - 4 g: 8 - 10 g.

[0025] Preferably, the preparation method of the modified long glass fiber is as follows:

[0026] Step C1: Immerse long glass fiber in sodium hydroxide solution at 45 - 55 °C for 1.5 - 2.5 h, then obtain pretreated long glass fiber through washing and drying processes;

[0027] Step C2: Add nano magnesium hydroxide and sodium dodecylbenzenesulfonate to deionized water, then immerse pretreated long glass fiber and perform ultrasonic treatment, and then obtain modified long glass fiber through drying and calcination processes.

[0028] Preferably, the dosage ratio of the long glass fiber and sodium hydroxide solution described in step C1 is 50 - 60 g: 500 mL;

[0029] The mass concentration of the sodium hydroxide solution described in step C1 is 1.5% - 2.5%;

[0030] In step C2, the dosage ratio of deionized water, nano magnesium hydroxide, sodium dodecylbenzenesulfonate, and pretreated long glass fiber is 500 mL: 25 - 40 g: 15 - 25 g: 40 - 50 g;

[0031] In the calcination treatment in step C2, the temperature is 300 - 350 °C and the duration is 1 - 2 h.

[0032] Preferably, the preparation method of the modified polypropylene particles is as follows:

[0033] Step D1: Mix ammonium polyphosphate, pentaerythritol, and melamine to obtain a composite flame retardant;

[0034] Step D2: Add the composite flame retardant, montmorillonite, and maleic anhydride grafted polypropylene to the polypropylene resin and mix evenly at 100 - 120 °C, then blend at 190 - 220 °C at 200 - 300 r / min for 20 - 30 min, and finally obtain modified polypropylene particles through extrusion granulation.

[0035] Preferably, in step D1, the dosage ratio of ammonium polyphosphate, pentaerythritol, and melamine is 9 - 12 g: 6 - 8 g: 3 - 4 g;

[0036] In step D2, the dosage ratio of polypropylene resin, composite flame retardant, montmorillonite, and maleic anhydride grafted polypropylene is 100 g: 10 - 15 g: 3 - 5 g: 2 - 3 g.

[0037] Advantages of the present invention:

[0038] The present invention provides a flame retardant modified long glass fiber / polypropylene composite and a preparation method thereof. The present invention effectively improves the flame retardancy and thermal-oxidative aging resistance of the flame retardant modified long glass fiber / polypropylene composite through the following methods.

[0039] (1) In the present invention, ammonium polyphosphate, pentaerythritol, and melamine mixed in a specific ratio will act synergistically during combustion to form a more dense, continuous, stable, and ablation-resistant expanded carbon layer, which more effectively blocks heat transfer, absorbs heat and oxygen, prevents the escape of combustible gases, and delays the thermal decomposition process of polypropylene resin and other components, thereby significantly improving the flame retardancy, flame retardant stability, and thermal-oxidative aging resistance of the modified polypropylene particles; and during combustion, the expanded carbon layer will cooperate with the modified carbon fiber and modified long glass fiber to form a more stable fire barrier to prevent flame spread.

[0040] (2) During the pretreatment process of the carbon fiber in the present invention, oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups are introduced onto the carbon fiber surface, making the surface rough, enhancing the interaction between it and substances such as melamine polyphosphate in the subsequent modification, thereby improving the mechanical properties of the composite; the pretreatment can also reduce the agglomeration phenomenon, making the properties of the composite more uniform and stable. During the modification process of the carbon fiber in the present invention, melamine polyphosphate will coat the carbon fiber surface, and γ-aminopropyltriethoxysilane will react with the oxygen-containing functional groups on the carbon fiber surface to form a silanized layer on the carbon fiber surface, further improving the chemical stability of the carbon fiber and its compatibility with other materials, thereby improving the flame retardancy of the entire composite and reducing the combustion rate and heat release of the material.

[0041] (3) During the pretreatment process of the long glass fiber in the present invention, the surface of the long glass fiber can be made cleaner, and the surface can also be made rough through etching, increasing the specific surface area, improving the chemical activity of the long glass fiber surface, and reducing the occurrence of agglomeration phenomenon, thereby making the properties of the composite more uniform and stable. Modifying the long glass fiber in the present invention will make nano magnesium hydroxide evenly adhere to the long glass fiber surface and form a coating layer on the long glass fiber surface, improving the flame retardancy of the long glass fiber. During the subsequent calcination process, the structure of nano magnesium hydroxide is more stable, further enhancing the flame retardant effect of the long glass fiber. At the same time, due to the further improvement of the interfacial bonding between the modified long glass fiber and the polypropylene matrix, and the strengthening effect of nano magnesium hydroxide, the mechanical properties of the composite will also be improved.

[0042] (4) In the present invention, before mixing with the modified polypropylene particles, it is first mixed with the synergistic solution and dried, which will form a coating layer on the surface of the modified carbon fiber and modified long glass fiber, improving the dispersibility of the flame retardant on the fiber surface, enabling the composite to form a more continuous and dense flame retardant barrier during combustion, reducing the flame retardant weak points caused by the agglomeration of the flame retardant and the possibility of the composite producing drips during combustion, and further improving the flame retardancy efficiency. Phytic acid in the synergistic solution can promote the formation of a carbon layer during the combustion process, and the silane coupling agent can form a silicon-oxygen structure with high thermal stability on the material surface. Their combined action with the flame retardant on the fiber surface can more effectively inhibit heat transfer, oxygen supply, and the generation of combustible gases during the combustion process, thereby significantly improving the flame retardancy and thermal-oxidative aging resistance of the final product. And when the fiber wrapped with the synergistic solution is mixed with the modified polypropylene particles, it can better transfer the stress from the matrix (polypropylene) to the fiber, thereby improving the mechanical properties such as the tensile strength and impact strength of the final product.

[0043] Therefore, the flame retardant modified long glass fiber / polypropylene composite prepared by the present invention has more excellent flame retardancy, thermal-oxidative aging resistance, and a broader application prospect. Detailed implementation mode

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0045] The properties and sources of some raw materials in the present invention are as follows:

[0046] The polypropylene resin was purchased from Jiangsu Boquan Biotechnology Co., Ltd., CAS: 86403-32-9; the carbon fiber was purchased from Zhejiang Asia-America Nano Technology Co., Ltd., product number: AM-C-F-1; the long glass fiber was purchased from Haozheng New Materials Technology (Dongguan) Co., Ltd., product number: E5006L Sumitomo; the nano magnesium hydroxide was purchased from Zhejiang Zhitaina Micro New Materials Co., Ltd., CAS: 1309-42-8; the polytetrahydrofuran ether glycol (PTMEG-2000) was purchased from Shandong Suihua Biotechnology Co., Ltd., CAS: 2519-06-1; the flame retardant OP550 was purchased from Shanghai Guangbin Trading Co., Ltd., CAS: 184538-58-7; the phytic acid with a concentration of 70% was purchased from Shanghai Yuanye Biotechnology Co., Ltd., purity: BR.

[0047] Example 1: A preparation method of a flame-retardant modified long glass fiber / polypropylene composite is as follows:

[0048] S1: Mix 9 g of ammonium polyphosphate, 6 g of pentaerythritol, and 3 g of melamine evenly to obtain a composite flame retardant;

[0049] S2: Add 10 g of the composite flame retardant, 3 g of montmorillonite, and 2 g of maleic anhydride-grafted polypropylene to 100 g of polypropylene resin, then mix at 300 r / min for 10 min at 100 °C, add it to a twin-screw extruder and blend at 200 r / min for 20 min at 190 °C, and finally perform extrusion granulation to obtain modified polypropylene particles;

[0050] S3: Add 10 g of carbon fiber to 200 mL of a 4% nitric acid solution by mass, reflux at 70 °C for 3 h, then rinse with deionized water until neutral, and dry to obtain pretreated carbon fiber;

[0051] S4: Add 3 g of melamine polyphosphate and 2 g of γ-aminopropyltriethoxysilane to 100 mL of toluene and mix evenly, then add 8 g of pretreated carbon fiber, stir and react at 80 °C for 6 h, filter, wash alternately with toluene and ethanol 3 times, and vacuum dry at 80 °C for 6 h to obtain modified carbon fiber;

[0052] S5: Soak 50 g of long glass fibers in 500 mL of a sodium hydroxide solution with a mass fraction of 1.5% at 45 °C for 1.5 h, then rinse with deionized water until neutral, and then dry at 80 °C for 6 h to obtain pretreated long glass fibers;

[0053] S6: Add 25 g of nano-magnesium hydroxide and 15 g of sodium dodecylbenzenesulfonate to 500 mL of deionized water, then immerse 40 g of pretreated long glass fibers and ultrasonically treat for 30 min, then dry at 80 °C for 3 h, and finally calcine at 300 °C for 1 h to obtain modified long glass fibers;

[0054] S7: Mix and stir 20 g of castor oil, 15 g of polytetrahydrofuran ether diol, 17 g of isophorone diisocyanate, and 4 g of dimethylolpropionic acid for 10 min, then add 0.1 g of dibutyltin dilaurate and stir at 80 °C for 1.5 h, then add 6 g of flame retardant OP550 and 6 g of polybutylene adipate diol and stir at 80 °C for 2 h, then add 4 g of trimethylolphosphine oxide, 40 g of acetone and react at 75 °C for 1 h, wait until cooled to 40 °C, add 2 g of triethylamine and react for 10 min, then slowly dropwise add 1.6 g of γ-aminopropyltriethoxysilane and react at 40 °C for 30 min, and finally add 70 mL of deionized water and emulsify at 5000 r / min for 30 min, and carry out vacuum distillation at a vacuum degree of -0.08 MPa and a temperature of 40 °C for 1.5 h to obtain a composite emulsion;

[0055] S8: Add 10 - 20 g of phytic acid with a concentration of 70% to 10 mL of deionized water, stir evenly, then drop in 4 g of γ-aminopropyltriethoxysilane and stir at 70 °C for 3 h, then add 120 g of the composite emulsion and stir evenly to obtain a synergistic solution;

[0056] S9: Add 8 g of modified carbon fibers and 30 g of modified long glass fibers to 20 g of the synergistic solution and mix evenly, dry at 80 °C, then add 100 g of modified polypropylene particles and stir at 80 °C for 8 min, then at 210 °C, blend at 250 r / min for 20 min, and then carry out extrusion, water cooling, and pelletizing to obtain a flame retardant modified long glass fiber / polypropylene composite.

[0057] Example 2: A method for preparing a flame retardant modified long glass fiber / polypropylene composite is as follows:

[0058] S1: Mix 10.5 g of ammonium polyphosphate, 7 g of pentaerythritol, and 3.5 g of melamine evenly to obtain a composite flame retardant;

[0059] S2: Add 12.5 g of a composite flame retardant, 4 g of montmorillonite, and 2.5 g of maleic anhydride-grafted polypropylene to 100 g of polypropylene resin. Then mix at 350 r / min for 13 min at 110°C, add the mixture to a twin-screw extruder, and blend at 250 r / min for 25 min at 200°C. Finally, perform extrusion granulation to obtain modified polypropylene particles;

[0060] S3: Add 12.5 g of carbon fiber to 200 mL of a 5% nitric acid solution by mass fraction. Reflux at 75°C for 4 h, then rinse with deionized water until neutral, and dry to obtain pretreated carbon fiber;

[0061] S4: Add 5 g of melamine polyphosphate and 3 g of γ-aminopropyltriethoxysilane to 125 mL of toluene and mix evenly. Then add 9 g of pretreated carbon fiber, stir and react at 85°C for 7 h, filter, wash alternately with toluene and ethanol 4 times, and vacuum dry at 85°C for 7 h to obtain modified carbon fiber;

[0062] S5: Immerse 55 g of long glass fiber in 500 mL of a 2% sodium hydroxide solution by mass fraction at 50°C for 2 h, then rinse with deionized water until neutral, and dry at 85°C for 7 h to obtain pretreated long glass fiber;

[0063] S6: Add 32.5 g of nano magnesium hydroxide and 20 g of sodium dodecylbenzenesulfonate to 500 mL of deionized water, then immerse 45 g of pretreated long glass fiber and perform ultrasonic treatment for 35 min, dry at 85°C for 4 h, and finally calcine at 330°C for 1.5 h to obtain modified long glass fiber;

[0064] S7: Mix 25 g of castor oil, 18 g of polytetrahydrofuran ether diol, 22.5 g of isophorone diisocyanate, and 4.5 g of dimethylolpropionic acid and stir for 15 min. Then add 0.15 g of dibutyltin dilaurate and stir at 83°C for 1.8 h. Then add 7 g of flame retardant OP550 and 8 g of polybutylene adipate diol and stir at 83°C for 2.1 h. Then add 4.5 g of trimethylolphosphine oxide, 45 g of acetone, and react at 78°C for 1.1 h. After cooling to 40°C, add 2.5 g of triethylamine and react for 15 min. Then slowly dropwise add 1.8 g of γ-aminopropyltriethoxysilane and react at 40°C for 35 min. Finally, add 85 mL of deionized water and emulsify at 6500 r / min for 35 min. Perform vacuum distillation at a vacuum degree of -0.09 MPa and a temperature of 45°C for 2 h to obtain a composite emulsion;

[0065] S8: Add 15 g of phytic acid with a concentration of 70% to 15 mL of deionized water. After stirring evenly, drop in 5.5 g of γ-aminopropyltriethoxysilane and stir at 73 °C for 3.5 h. Then add 177.5 g of the composite emulsion and stir evenly to obtain the synergistic solution;

[0066] S9: Add 9 g of modified carbon fiber and 35 g of modified long glass fiber to 25 g of the synergistic solution and mix evenly. After drying at 80 °C, add 100 g of modified polypropylene particles and stir at 90 °C for 10 min. Then, at 220 °C, blend at 300 r / min for 25 min, and then perform extrusion, water cooling, and pelletizing treatments to obtain the flame-retardant modified long glass fiber / polypropylene composite.

[0067] Example 3: A preparation method of a flame-retardant modified long glass fiber / polypropylene composite is as follows:

[0068] S1: Mix 12 g of ammonium polyphosphate, 8 g of pentaerythritol, and 4 g of melamine evenly to obtain the composite flame retardant;

[0069] S2: Add 15 g of the composite flame retardant, 5 g of montmorillonite, and 3 g of maleic anhydride-grafted polypropylene to 100 g of polypropylene resin. Then mix at 120 °C and 400 r / min for 15 min, add it to a twin-screw extruder, and blend at 220 °C and 300 r / min for 30 min. Finally, perform extrusion granulation treatment to obtain the modified polypropylene particles;

[0070] S3: Add 15 g of carbon fiber to 200 mL of a 6% nitric acid solution by mass fraction, reflux at 80 °C for 5 h, then rinse with deionized water until neutral, and dry to obtain the pretreated carbon fiber;

[0071] S4: Add 7 g of melamine polyphosphate and 4 g of γ-aminopropyltriethoxysilane to 150 mL of toluene and mix evenly. Then add 10 g of the pretreated carbon fiber, stir and react at 90 °C for 8 h, filter, wash alternately with toluene and ethanol 5 times, and vacuum dry at 90 °C for 8 h to obtain the modified carbon fiber;

[0072] S5: Immerse 60 g of long glass fiber in 500 mL of a 2.5% sodium hydroxide solution by mass fraction at 55 °C for 2.5 h, then rinse with deionized water until neutral, and dry at 90 °C for 8 h to obtain the pretreated long glass fiber;

[0073] S6: Add 40 g of nano magnesium hydroxide and 25 g of sodium dodecylbenzenesulfonate to 500 mL of deionized water, then immerse 50 g of the pretreated long glass fiber and perform ultrasonic treatment for 40 min, dry at 90 °C for 5 h, and finally calcine at 350 °C for 2 h to obtain the modified long glass fiber;

[0074] S7: Mix 30 g of castor oil, 20 g of polytetrahydrofuran ether diol, 25 g of isophorone diisocyanate, and 5 g of dimethylolpropionic acid and stir for 20 min. Then add 0.2 g of dibutyltin dilaurate and stir at 85 °C for 2 h. Next, add 8 g of flame retardant OP550 and 10 g of polybutylene adipate glycol and stir at 85 °C for 2.2 h. Then add 5 g of trimethylolphosphine oxide, 50 g of acetone, and react at 80 °C for 1.2 h. After cooling to 40 °C, add 3 g of triethylamine and react for 20 min. Then slowly dropwise add 2 g of γ-aminopropyltriethoxysilane and react at 40 °C for 40 min. Finally, add 100 mL of deionized water and emulsify at 8000 r / min for 40 min. After vacuum distillation at -0.1 MPa and 50 °C for 2.5 h, a composite emulsion is obtained;

[0075] S8: Add 20 g of 70% phytic acid to 20 mL of deionized water, stir evenly, then dropwise add 7 g of γ-aminopropyltriethoxysilane and stir at 75 °C for 4 h. Then add 235 g of the composite emulsion and stir evenly to obtain a synergistic solution;

[0076] S9: Add 10 g of modified carbon fiber and 40 g of modified long glass fiber to 30 g of the synergistic solution and mix evenly. After drying at 80 °C, add 100 g of modified polypropylene particles and stir at 100 °C for 12 min. Then, at 230 °C, blend at 350 r / min for 30 min, and then perform extrusion, water cooling, and pelletizing to obtain a flame retardant modified long glass fiber / polypropylene composite.

[0077] Comparative Example 1:

[0078] Compared with Example 1, in this comparative example, only the "9 g of ammonium polyphosphate, 6 g of pentaerythritol, 3 g of melamine" added in the preparation process of the composite flame retardant is replaced with "3 g of ammonium polyphosphate, 3 g of pentaerythritol, 12 g of melamine", and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally a flame retardant modified long glass fiber / polypropylene composite is obtained.

[0079] Comparative Example 2:

[0080] Compared with Example 1, in this comparative example, only the "pretreated carbon fiber" added in the preparation process of the modified carbon fiber in S4 is replaced with "carbon fiber", and the rest of the steps and parameters are the same. This comparative example will not be repeated here, and finally a flame retardant modified long glass fiber / polypropylene composite is obtained.

[0081] Comparative Example 3:

[0082] This comparative example is the same as Example 1 except that in S6, the "pretreated long glass fiber" added during the preparation of the modified long glass fiber is replaced with "long glass fiber", and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0083] Comparative Example 4:

[0084] This comparative example is the same as Example 1 except that in S6, the calcination at 300 °C for 1 h is not carried out during the preparation of the modified long glass fiber, and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0085] Comparative Example 5:

[0086] This comparative example is the same as Example 1 except that in S9, the "adding 8 g of modified carbon fiber, 30 g of modified long glass fiber into 20 g of synergistic solution and mixing evenly, drying at 80 °C, then adding 100 g of modified polypropylene particles and stirring at 80 °C for 8 min" during the preparation of the flame-retardant modified long glass fiber / polypropylene composite is replaced with "mixing 8 g of modified carbon fiber and 30 g of modified long glass fiber evenly, drying at 80 °C, then adding 100 g of modified polypropylene particles and stirring at 80 °C for 8 min", and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0087] Comparative Example 6:

[0088] This comparative example is the same as Example 1 except that in S9, the "modified carbon fiber" added during the preparation of the flame-retardant modified long glass fiber / polypropylene composite is replaced with "pretreated carbon fiber", and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0089] Comparative Example 7:

[0090] This comparative example is the same as Example 1 except that in S9, the "modified long glass fiber" added during the preparation of the flame-retardant modified long glass fiber / polypropylene composite is replaced with "pretreated long glass fiber", and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0091] Comparative Example 8:

[0092] This comparative example is the same as Example 1 except that in S9, the "modified polypropylene particles" added during the preparation of the flame-retardant modified long glass fiber / polypropylene composite is replaced with "polypropylene resin", and the remaining steps and parameters are the same. This comparative example will not be repeated here, and finally a flame-retardant modified long glass fiber / polypropylene composite is obtained.

[0093] Comparative Example 9:

[0094] In this comparative example, compared with Example 1, only the step of "adding 8 g of modified carbon fiber, 30 g of modified long glass fiber into 20 g of synergistic liquid, mixing evenly, drying at 80°C, then adding 100 g of modified polypropylene particles and stirring at 80°C for 8 min" in the preparation process of the flame-retardant modified long glass fiber / polypropylene composite in S9 was replaced with "adding 8 g of modified carbon fiber, 30 g of modified long glass fiber, 100 g of modified polypropylene particles into 20 g of synergistic liquid and stirring at 80°C for 8 min". The rest of the steps and parameters are the same, and this comparative example will not be repeated here. Finally, a flame-retardant modified long glass fiber / polypropylene composite was obtained.

[0095] Performance testing:

[0096] The flame-retardant modified long glass fiber / polypropylene composites prepared in Examples 1 - 3 and Comparative Examples 1 - 9 were respectively added to an injection molding machine (the temperature of the injection molding machine was set at 170°C, the injection pressure was 100 MPa, the injection time was 15 s, and the holding pressure time was 8 s) for injection molding. Then the samples were vulcanized at 5 Mpa and 120°C for 2 h. Flame-retardant modified long glass fiber / polypropylene composite samples (with a thickness of 3 mm) corresponding to Examples 1 - 3 and Comparative Examples 1 - 9 were prepared according to this method.

[0097] Determination of limiting oxygen index:

[0098] Referring to the standard of GB / T 2406.2 - 2009 "Plastics - Determination of burning behavior by oxygen index - Part 2: Ambient - temperature test", the limiting oxygen index (%) of the flame-retardant modified long glass fiber / polypropylene composite samples prepared in Examples 1 - 3 and Comparative Examples 1 - 9 was tested. The test results are shown in Table 1.

[0099] Flame - retardant test:

[0100] Referring to the UL94 standard, the vertical burning test was carried out on the flame-retardant modified long glass fiber / polypropylene composite samples prepared in Examples 1 - 3 and Comparative Examples 1 - 9. The test results are shown in Table 1.

[0101] Determination of tensile strength:

[0102] Referring to the standard of GB / T 1040.2 - 2022 "Plastics - Determination of tensile properties - Part 2: Test conditions for moulding and extrusion plastics", the tensile strength (MPa) of the flame-retardant modified long glass fiber / polypropylene composite samples prepared in Examples 1 - 3 and Comparative Examples 1 - 9 before and after aging at 150°C for 480 h was measured at a rate of 1 mm / min. The test results are shown in Table 1.

[0103] Determination of impact strength

[0104] Referring to the standard of GB / T 1843-2020 "Determination of Izod impact strength of plastics", the impact strength (kJ·m -2 ) of the flame-retardant modified long glass fiber / polypropylene composite samples prepared in Examples 1-3 and Comparative Examples 1-9 before and after 480 h of aging at 150 °C was tested, and the test results are shown in Table 1.

[0105] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-9

[0106]

[0107]

[0108] Data analysis:

[0109] As can be seen from Table 1, the flame-retardant modified long glass fiber / polypropylene composite prepared in the present invention has a high limiting oxygen index, flame retardancy, tensile strength, impact strength, tensile strength retention rate, and impact strength retention rate, that is, the present invention has higher flame retardant ability, mechanical properties, and thermal oxygen aging resistance ability.

[0110] The above has described in detail one embodiment of the present invention, but the content described is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the present invention application shall still fall within the scope covered by the patent of the present invention.

Claims

1. A preparation method of a flame-retardant modified long glass fiber / polypropylene composite, characterized in that, It includes the following steps: Add modified carbon fiber and modified long glass fiber into the synergistic solution and mix evenly. After drying, add modified polypropylene particles and stir evenly. Then, through blending, extrusion, water cooling, and pelletizing processes, a flame-retardant modified long glass fiber / polypropylene composite is obtained.

2. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 1, wherein, The dosage ratio of the synergistic solution, modified carbon fiber, modified long glass fiber, and modified polypropylene particles after mixing evenly and drying is 20 - 30 g : 8 - 10 g : 30 - 40 g : 100 g; During the blending process, the temperature is 210 - 230 °C, the rotation speed is 250 - 350 r / min, and the duration is 20 - 30 min.

3. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 1, characterized in that, The preparation method of the synergistic solution is as follows: Step A1: Mix castor oil, polytetrahydrofuran ether glycol, isophorone diisocyanate, and dimethylolpropionic acid, then add dibutyltin dilaurate and stir at 80 - 85 °C for 1.5 - 2 h. After that, add flame retardant OP550 and poly(butylene adipate) glycol and stir for 2 - 2.2 h. Then, add trimethylolphosphine oxide and acetone and react at 75 - 80 °C for 1 - 1.2 h. After cooling to 40 °C, first add triethylamine and react for 10 - 20 min, then dropwise add γ-aminopropyltriethoxysilane and react for 30 - 40 min. Finally, add deionized water and emulsify at high speed. After vacuum distillation, a composite emulsion is obtained; Step A2: Add phytic acid to deionized water, stir evenly, then dropwise add γ-aminopropyltriethoxysilane and stir at 70 - 75 °C for 3 - 4 h. After that, add the composite emulsion and stir evenly to obtain the synergistic solution.

4. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 3, wherein, The dosage ratio of castor oil, polytetrahydrofuran ether glycol, isophorone diisocyanate, dimethylolpropionic acid, dibutyltin dilaurate, flame retardant OP550, poly(butylene adipate) glycol, trimethylolphosphine oxide, acetone, triethylamine, γ-aminopropyltriethoxysilane, and deionized water in Step A1 is 20 - 30 g : 15 - 20 g : 17 - 25 g : 4 - 5 g : 0.1 - 0.2 g : 6 - 8 g : 6 - 10 g : 4 - 5 g : 40 - 50 g : 2 - 3 g : 1.6 - 2 g : 70 - 100 mL; The rotation speed during high-speed emulsification in Step A1 is 5000 - 8000 r / min, and the emulsification duration is 30 - 40 min; The dosage ratio of deionized water, phytic acid, γ-aminopropyltriethoxysilane, and the composite emulsion in Step A2 is 10 - 20 mL : 10 - 20 g : 4 - 7 g : 120 - 235 g; The mass concentration of phytic acid in Step A2 is 70%.

5. The preparation method of the flame retardant modified long glass fiber / polypropylene composite according to claim 1, characterized in that, The preparation method of the modified carbon fiber is as follows: Step B1: Add carbon fiber to nitric acid solution and reflux at 70 - 80 °C for 3 - 5 h. After that, rinse with deionized water until neutral, and dry to obtain pretreated carbon fiber; Step B2: Add melamine polyphosphate and γ-aminopropyltriethoxysilane to toluene and mix evenly. Then, add the pretreated carbon fiber and stir and react at 80 - 90 °C for 6 - 8 h. After filtration, washing, and drying, the modified carbon fiber is obtained.

6. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 5, wherein, The dosage ratio of the nitric acid solution and carbon fiber in Step B1 is 200 mL : 10 - 15 g; The mass concentration of the nitric acid solution described in step B1 is 4% - 6%; The dosage ratio of toluene, melamine polyphosphate, γ-aminopropyltriethoxysilane, and pretreated carbon fiber described in step B2 is 100 - 150 mL: 3 - 7 g: 2 - 4 g: 8 - 10 g.

7. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 1, characterized in that, The preparation method of the modified long glass fiber is as follows: Step C1: Immerse the long glass fiber in a sodium hydroxide solution at 45 - 55 °C for 1.5 - 2.5 h, then wash and dry it to obtain pretreated long glass fiber; Step C2: Add nano magnesium hydroxide and sodium dodecylbenzenesulfonate to deionized water, then immerse the pretreated long glass fiber and perform ultrasonic treatment, and then dry and calcine it to obtain modified long glass fiber.

8. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 7, characterized in that, The dosage ratio of the long glass fiber and the sodium hydroxide solution described in step C1 is 50 - 60 g: 500 mL; The mass concentration of the sodium hydroxide solution described in step C1 is 1.5% - 2.5%; The dosage ratio of deionized water, nano magnesium hydroxide, sodium dodecylbenzenesulfonate, and pretreated long glass fiber described in step C2 is 500 mL: 25 - 40 g: 15 - 25 g: 40 - 50 g; The temperature during the calcination treatment in step C2 is 300 - 350 °C, and the duration is 1 - 2 h.

9. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 1, characterized in that, The preparation method of the modified polypropylene particles is as follows: Step D1: Mix ammonium polyphosphate, pentaerythritol, and melamine to obtain a composite flame retardant; Step D2: Add the composite flame retardant, montmorillonite, and maleic anhydride grafted polypropylene to the polypropylene resin and mix them evenly at 100 - 120 °C, then blend them at 190 - 220 °C at 200 - 300 r / min for 20 - 30 min, and finally perform extrusion granulation to obtain modified polypropylene particles.

10. The preparation method of the flame-retardant modified long glass fiber / polypropylene composite according to claim 9, characterized in that, The dosage ratio of ammonium polyphosphate, pentaerythritol, and melamine described in step D1 is 9 - 12 g: 6 - 8 g: 3 - 4 g; The dosage ratio of the polypropylene resin, composite flame retardant, montmorillonite, and maleic anhydride grafted polypropylene described in step D2 is 100 g: 10 - 15 g: 3 - 5 g: 2 - 3 g.

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