Fire-resistant flame-retardant PP composite material for new energy battery shell and preparation method thereof

Abstract

The invention discloses a fire-resistant flame-retardant PP composite material for a new energy battery shell and a preparation method thereof, belongs to the technical field of PP composite materials, and aims to solve the technical problem that the mechanical strength, flame retardance, heat aging resistance and corrosion resistance of the PP composite material in the prior art need to be further improved. The glass fiber reinforced polypropylene composite material specifically comprises the following components in parts by weight: 30-50 parts of polypropylene, 3-8 parts of polypropylene grafted master batch, 20-50 parts of glass fiber, 15-30 parts of a composite flame retardant, 1-3 parts of modified nano zinc oxide, 6-10 parts of a composite reinforcing agent and 1-5 parts of an additive. The polypropylene grafted master batch, the composite flame retardant, the modified nano zinc oxide and the composite reinforcing agent are added into the polypropylene base material, so that the mechanical strength, the flame retardance, the heat aging resistance and the corrosion resistance of the PP composite material are further optimized.

Description

Technical Field

[0001] This invention relates to the field of PP composite material technology, specifically to fire-resistant and flame-retardant PP composite material for new energy battery casings and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in the new energy field, safety issues, especially the risk of "thermal runaway" in large-capacity power lithium batteries, have attracted much attention. The highly active materials inside lithium batteries are prone to violent reactions when heated, short-circuited, squeezed, or overcharged, generating a large amount of heat. If the battery casing cannot effectively block flames and heat, it is very easy to cause safety accidents such as combustion and explosion.

[0003] As a critical protective carrier, the battery casing's flame retardancy and structural stability directly determine the battery's safety performance. Currently, most plastic-cased lithium batteries use polypropylene as the casing material. Although polypropylene has advantages such as heat resistance and electrolyte corrosion resistance, it has a low oxygen index and is easily combustible. When burning, it releases a lot of heat and the flame spreads quickly, making it difficult to cope with the high-temperature flame impact during battery "thermal runaway," thus creating potential safety hazards.

[0004] In existing technologies, the flame retardancy of polypropylene is mostly improved by adding flame retardants, but there are certain drawbacks. When a single flame retardant is mixed with the polypropylene matrix, it is easy to agglomerate, which leads to a decrease in mechanical properties and uneven dispersion of flame retardant components, making it difficult to form an effective barrier. At the same time, traditional modification methods cannot simultaneously achieve comprehensive properties such as high mechanical strength, heat aging resistance, and electrolyte corrosion resistance. Therefore, it is necessary to develop a polypropylene composite material that has both high flame retardancy and high aging and corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a fire-resistant and flame-retardant PP composite material for new energy battery casings and its preparation method, in order to solve the technical problem that the mechanical strength, flame retardancy, heat aging resistance and corrosion resistance of PP composite materials in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a fire-resistant and flame-retardant PP composite material for new energy battery casings, comprising the following components by weight: 30-50 parts polypropylene, 3-8 parts polypropylene grafted masterbatch, 20-50 parts glass fiber, 15-30 parts composite flame retardant, 1-3 parts modified nano zinc oxide, 6-10 parts composite reinforcing agent and 1-5 parts additives. The additives comprise the following components by weight: 0.5-1 parts antioxidant 1010 and 0.5-1 parts hexadecyltrimethylammonium chloride.

[0007] Furthermore, the preparation method of the polypropylene grafted masterbatch is as follows: polypropylene is added to a preheated torsional rheometer, and after mixing at 160-180℃ for 3-5 minutes, styrene is added and mixed for 3-5 minutes, then maleic anhydride is added and mixed for 5-8 minutes, and finally dicumyl peroxide is added and mixed for 10-15 minutes. The material is then discharged to obtain the polypropylene grafted masterbatch; the weight ratio of polypropylene, styrene, maleic anhydride and dicumyl peroxide is 40:0.4-0.5:1-1.2:0.01.

[0008] Reaction principle: At a high temperature of 180℃, polypropylene is first mixed and melted to form a melt. Then, dicumyl peroxide is added and decomposed upon heating to generate strong free radicals. These free radicals capture hydrogen atoms from the polypropylene molecular chain, transforming the polypropylene into excited-state macromolecular free radicals. These macromolecular free radicals first undergo a grafting reaction with the highly active electron donor styrene, and then further undergo an addition reaction with maleic anhydride polar molecules. The mixing and shearing action of the torsion rheometer promotes monomer dispersion and reaction, ultimately generating a polypropylene-grafted styrene-maleic anhydride composite graft copolymer, i.e., polypropylene graft masterbatch.

[0009] Furthermore, the composite flame retardant is prepared by the following steps: A1. Melamine aqueous solution is added dropwise to a reaction vessel containing an aqueous solution of hydroxyethylidene diphosphate, and then formic acid solution is added dropwise to adjust the pH of the solution to 4-5. The reaction is carried out at 80-100℃ for 3-4 hours, and then post-processed to obtain the complex precursor. A2. Add γ-glycidyl etheroxypropyltrimethoxysilane to an aqueous ethanol solution, sonicate hydrolyze for 30-60 min, then add expanded graphite, stir at 50-60℃ for 5-6 h, filter, and dry the product at 60℃ for 12 h to obtain modified expanded graphite. A3. The composite precursor and modified expanded graphite were added to a ball mill and ball-milled for 6 hours to obtain the composite flame retardant.

[0010] Reaction principle: The phosphate group of hydroxyethylidene diphosphate undergoes a condensation reaction with the amino group of melamine at pH 4-5 to form a phosphorus-nitrogen-containing complex precursor. Then, a silane coupling agent is ultrasonically hydrolyzed in an ethanol aqueous solution to generate an active intermediate containing silanol groups. Subsequently, it undergoes a condensation reaction with the hydroxyl groups on the surface of expanded graphite, thereby modifying the surface of expanded graphite through covalent bonds and improving its compatibility. Finally, the mechanical force of ball milling is used to fully mix and tightly bind the complex precursor with the modified expanded graphite, ultimately forming a composite flame retardant that combines phosphorus-nitrogen flame retardant elements and a modified expanded graphite structure.

[0011] Further, in step A1, the ratio of the aqueous solution of hydroxyethylidene diphosphate to the aqueous solution of melamine is 5-7 mL:50 mL, the mass fraction of hydroxyethylidene diphosphate in the aqueous solution is 60%, the mass fraction of melamine in the aqueous solution is 5%, and the concentration of the formic acid solution is 0.1 mol / L. The post-treatment operation includes: filtering after the reaction, washing the product with deionized water 3-5 times, and drying in a vacuum drying oven at 80°C for 8 hours; in step A2, the ratio of the aqueous solution of γ-glycidyl etheroxypropyltrimethoxysilane, aqueous ethanol solution, and expanded graphite is 0.5 g:100 mL:8-10 g, and the aqueous ethanol solution is composed of anhydrous ethanol and deionized water in a volume ratio of 19:1; in step A3, the weight ratio of the composite precursor and the modified expanded graphite is 7-14 g:9 g.

[0012] Further, the preparation method of the modified nano zinc oxide is as follows: sodium hydroxide solution is added dropwise to an ethanol aqueous solution until the solution pH is 8-9, stirred for 3-5 min, then n-octyltriethoxysilane is added, the temperature is raised to 30-40℃ and stirred for 30-60 min, then nano zinc oxide is added, ultrasonically dispersed for 30-60 min, the temperature is further raised to 70-80℃, stirred and refluxed for 3-4 h, after the reaction is completed, centrifuged, washed 3-4 times with anhydrous ethanol, the precipitate is placed in a vacuum drying oven and dried at 60℃ for 6 h to obtain modified nano zinc oxide; the ratio of the amount of ethanol aqueous solution, n-octyltriethoxysilane and nano zinc oxide is 20-30 mL:0.02 g:2 g, the ethanol aqueous solution is composed of anhydrous ethanol and deionized water in a volume ratio of 9:1, and the concentration of the sodium hydroxide solution is 0.1 mol / L.

[0013] Reaction principle: In an ethanol-water solution, sodium hydroxide is used to adjust the pH to 8-9 to provide an alkaline environment, promoting the hydrolysis of the ethoxy group of n-octyltriethoxysilane to generate an active intermediate containing silanol groups. Subsequently, nano-zinc oxide is added, and under reflux conditions at 70-80℃, the silanol groups generated by the hydrolysis of silane undergo a condensation reaction with the hydroxyl groups on the surface of nano-zinc oxide. The n-octyltriethoxysilane is grafted onto the surface of nano-zinc oxide through covalent bonds Si-O-Zn. Ultrasonic dispersion is used to promote uniform mixing, and unreacted impurities are removed by centrifugation and washing. After vacuum drying, modified nano-zinc oxide with surface-grafted silane coupling agent is obtained.

[0014] Furthermore, the composite reinforcing agent is prepared by the following steps: B1. Add Tris buffer to deionized water and slowly add dilute hydrochloric acid to adjust the pH of the solution to 8.5. Then add dopamine hydrochloride and stir for 15-20 min. Add hexagonal boron nitride powder and stir for 5-10 min. Then sonicate for 30-60 min. Finally, let it stand at 20-30℃ for 24 h and then perform post-treatment to obtain polydopamine-modified hexagonal boron nitride. B2. Polydopamine-modified hexagonal boron nitride is added to a reaction vessel containing anhydrous ethanol and ultrasonically dispersed at 20-30℃ for 20-30 min. Then, propyltriethoxysilane triisocyanate is added and the temperature is raised to 50-60℃ for 2-3 h. Next, deionized water is added and the reaction is carried out for 5-10 min. Finally, Al2O3 powder is added and stirred at 60-70℃ for 6-8 h. After post-treatment, the composite reinforcing agent is obtained.

[0015] Reaction principle: In a weakly alkaline Tris buffer solution at pH 8.5, dopamine hydrochloride undergoes oxidative self-polymerization to form polydopamine. The active groups, such as catechol contained in polydopamine, are adsorbed onto the surface of hexagonal boron nitride, resulting in polydopamine-modified hexagonal boron nitride. Then, after dispersing the polydopamine-modified hexagonal boron nitride in anhydrous ethanol, propyltriethoxysilane triisocyanate is added. First, the isocyanate groups react with the amino groups on the surface of polydopamine. Subsequently, deionized water is added to hydrolyze the ethoxy groups of the silane into silanol groups. Finally, the silanol groups undergo a condensation reaction with the hydroxyl groups on the surface of the added Al2O3 powder. Through the bridging effect of the silane coupling agent, the polydopamine-modified hexagonal boron nitride and Al2O3 are composited, forming a composite reinforcing agent.

[0016] Further, in step B1, the ratio of Tris buffer, deionized water, dopamine hydrochloride, and hexagonal boron nitride powder is 0.4-0.5g:300mL:0.7-0.8g:2-3g, and the concentration of dilute hydrochloric acid is 0.1mol / L. The post-treatment is as follows: after the reaction, the product is filtered and washed with deionized water until the filtrate becomes colorless. The product is then transferred to a vacuum drying oven and dried at 60°C for 24 hours. In step B2, the ratio of polydopamine-modified hexagonal boron nitride, anhydrous ethanol, propyltriethoxysilane triisocyanate, deionized water, and Al2O3 powder is 2-3g:100mL:0.5g:8mL:1g. The post-treatment is as follows: after the reaction, the product is centrifuged and then transferred to a vacuum drying oven and dried at 60°C for 24 hours.

[0017] This invention also proposes a method for preparing fire-resistant and flame-retardant PP composite material for new energy battery casings, comprising the following steps: adding polypropylene and polypropylene grafted masterbatch to a mixer and stirring at 60-80℃ for 2-5 minutes, then adding additives and stirring for 2-3 minutes, followed by adding glass fiber, modified nano zinc oxide and composite reinforcing agent, and continuing to stir for 5-8 minutes, and finally adding composite flame retardant and stirring for 3-5 minutes, then transferring to a twin-screw extruder, melt-blending for 3-5 minutes, and then extruding and granulating to obtain the PP composite material.

[0018] Furthermore, the twin-screw extruder has six temperature zones set from the feed end toward the die head, with temperatures of 170°C, 180°C, 185°C, 190°C, 190°C, and 190°C respectively, and the spindle speed of the twin-screw extruder is 40 r / min.

[0019] The present invention has the following beneficial effects: In the composite flame retardant of this invention, the phosphorus-nitrogen structure formed by the reaction of hydroxyethylidene diphosphate and melamine can synergistically inhibit the combustion reaction through gas-phase flame retardancy and condensed-phase flame retardancy. The expanded graphite modified with silane coupling agent can rapidly expand at high temperatures to form a dense carbon layer, physically blocking the transfer of heat and oxygen. The introduction of silane coupling agent also improves the compatibility between expanded graphite and PP matrix, avoiding flame retardant failure caused by agglomeration. Glass fiber, as an inorganic high-temperature resistant fiber, has excellent structural stability at high temperatures. Together with the phosphorus-nitrogen structure and modified expanded graphite in the composite flame retardant, it forms a triple flame retardant system of "chemical flame inhibition - physical barrier - structural support". At the same time, the polypropylene grafted masterbatch improves the interfacial bonding between the flame retardant and the matrix, ensuring uniform dispersion of flame retardant components and reducing the risk of localized combustion. The dual effects of phosphorus-nitrogen chemical flame retardancy and expanded graphite physical barrier, combined with the dispersion effect of interface optimization, enable the composite material to achieve a vertical burning rating of V-0, significantly improving its fire resistance and flame retardant performance.

[0020] In the polypropylene grafted masterbatch of this invention, the polar groups of maleic anhydride and the regulating effect of styrene can form a strong interfacial bond with the composite reinforcing agent, modified nano zinc oxide and other polar fillers, reducing interfacial voids. In the composite reinforcing agent, dopamine hydrochloride modified hexagonal boron nitride combines with a silane coupling agent. The silanol groups at the hydrolysis site of the silane coupling agent undergo a condensation reaction with the hydroxyl groups on the surface of alumina, achieving a tight composite of rigid particles. Glass fiber itself has high tensile strength and flexural rigidity, forming a "fiber-rigid particle" dual support structure with the composite reinforcing agent. The layered structure of hexagonal boron nitride and the high rigidity of alumina synergistically provide mechanical support. Moreover, the modified reinforcing agent is uniformly dispersed in the PP matrix, avoiding agglomeration stress concentration. In addition, the modified nano zinc oxide is tightly bonded to the matrix through silane grafting, filling microscopic voids and further improving structural integrity. The above synergistic effects improve the hardness, tensile strength and flexural strength of the composite material, and comprehensively optimize mechanical properties.

[0021] In the composite reinforcing agent of this invention, the inorganic fillers hexagonal boron nitride and alumina have excellent thermal conductivity, which can quickly dissipate heat to delay thermo-oxidative aging. The high-temperature resistance of glass fiber can reduce the thermal shrinkage of the material at high temperatures. Combined with the excellent thermal conductivity of the composite reinforcing agent, heat is quickly dissipated to delay thermo-oxidative aging. At the same time, the interfacial bonding strengthened by the polypropylene graft masterbatch reduces structural cracking caused by thermal stress and delays the aging process. The nano-zinc oxide modified by silane coupling agent is bonded to the matrix through covalent bonds, eliminating interfacial voids and blocking the alkali solution penetration channels. In the composite reinforcing agent, the silane-modified alumina and polydopamine-modified hexagonal boron nitride have excellent chemical stability, and the layered structure forms a physical barrier, which can also prevent the alkali solution from directly contacting the matrix. In addition, the interfacial reinforcement effect of the polypropylene graft masterbatch further avoids material failure caused by alkali solution intrusion along the interface. Multiple synergies enable the material to maintain a high level of hardness, tensile strength and flexural strength after heat aging and alkali immersion, and significantly improve the heat aging resistance and alkali corrosion resistance. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0023] In this application, the polypropylene is selected from Shanghai Qiaowei Chemical Technology Co., Ltd., with an effective ingredient content of 90% and a grade of K7926. In this application, the glass fiber is selected from Laiwu Jingkai Engineering Materials Co., Ltd., with an effective component content of 96% and a thickness of 0.15mm; In this application, the expanded graphite is selected from Hebei Hengguang Mineral Products Co., Ltd., with a particle size of 80 mesh and an expansion degree of 300. In this application, the nano zinc oxide is selected from Nangong Dinghong Metal Materials Co., Ltd., with an effective component content of 99.9%, grade DH-ZnO, and particle size of 300 mesh; In this application, the hexagonal boron nitride is selected from Zhengzhou Lizuan Superhard Materials Products Co., Ltd., with CAS number 1043-11-5, particle size of 2000 mesh, and grade 001; In this application, Al2O3 is selected from Nangong Dinghong Metal Materials Co., Ltd., with CAS number Al2O3, particle size of 1µm, and grade Al2O3 powder.

[0024] Example 1 This embodiment provides a fire-resistant and flame-retardant PP composite material for new energy battery casings and its preparation method, including the following steps: S1. Preparation of polypropylene grafting masterbatch Weigh 40g of polypropylene and add it to a preheated torsional rheometer. After mixing at 160℃ for 3 minutes, add 0.4g of styrene and mix for 3 minutes. Then add 1g of maleic anhydride and mix for 5 minutes. Finally, add 0.01g of dicumyl peroxide and continue mixing for 10 minutes. Discharge the material to obtain polypropylene grafted masterbatch.

[0025] S2, Preparation of composite flame retardants Weigh out 95 mL of anhydrous ethanol and 5 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out: Add 50 mL of 5% melamine aqueous solution to a reaction vessel containing 5 mL of 60% hydroxyethylidene diphosphate aqueous solution, then add 0.1 mol / L formic acid solution to adjust the pH of the solution to 4, react at 80℃ for 3 h, filter after the reaction, wash the product 3 times with deionized water, and dry in a vacuum drying oven at 80℃ for 8 h to obtain the complex precursor; Weigh 0.5g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to 100mL of ethanol aqueous solution. Sonicate hydrolyze for 30min, then add 8g of expanded graphite. Stir at 50℃ for 5h and filter. Dry the product at 60℃ for 12h to obtain modified expanded graphite. Weigh out 7g of the composite precursor and 9g of modified expanded graphite and add them to a ball mill and ball mill for 6 hours to obtain the composite flame retardant.

[0026] S3, Preparation of modified nano zinc oxide Weigh out 90 mL of anhydrous ethanol and 10 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out 20 mL of ethanol-water solution, add 0.1 mol / L sodium hydroxide solution dropwise until the pH of the solution is 8, stir for 3 min, then add 0.02 g of n-octyltriethoxysilane, heat to 30 °C and stir for 30 min, then add 2 g of nano zinc oxide, sonicate for 30 min, continue to heat to 70 °C, stir and reflux for 3 h, after the reaction is complete, centrifuge, wash 3 times with anhydrous ethanol, put the precipitate into a vacuum drying oven and dry at 60 °C for 6 h to obtain modified nano zinc oxide.

[0027] S4. Preparation of composite reinforcing agent Weigh 4g of Tris buffer and add it to 3000mL of deionized water. Slowly add 0.1mol / L dilute hydrochloric acid to adjust the pH of the solution to 8.5. Then add 7g of dopamine hydrochloride and stir for 15min. Then add 20g of hexagonal boron nitride powder and stir for 5min. Then sonicate for 30min. Finally, let it stand at 20℃ for 24h. After the reaction is complete, filter the product and wash it with deionized water until the filtrate becomes colorless. Transfer the product to a vacuum drying oven and dry it at 60℃ for 24h to obtain polydopamine modified hexagonal boron nitride. Weigh 20g of polydopamine-modified hexagonal boron nitride and add it to a reaction vessel containing 1000mL of anhydrous ethanol. Disperse the mixture ultrasonically at 20℃ for 20min. Then add 5g of propyltriethoxysilane triisocyanate and heat to 50℃ for 2h. Next, add 80mL of deionized water and react for 5min. Finally, add 10g of Al2O3 powder and stir at 60℃ for 6h. After the reaction is complete, centrifuge the product and transfer it to a vacuum drying oven to dry at 60℃ for 24h to obtain the composite reinforcing agent.

[0028] S5. Preparation of PP composite materials Weigh out 0.5 parts of antioxidant 1010 and 0.5 parts of hexadecyltrimethylammonium chloride by weight, mix them evenly, and obtain the additive. Weigh out 30 parts by weight of polypropylene and 3 parts by weight of polypropylene grafted masterbatch and add them to a mixer. Stir at 60°C for 2 minutes. Then add 1 part of additive and stir for 2 minutes. Next, add 20 parts of glass fiber, 1 part of modified nano zinc oxide and 6 parts of composite reinforcing agent and continue stirring for 5 minutes. Finally, add 15 parts of composite flame retardant and stir for 3 minutes. Transfer the mixture to a twin-screw extruder. Set the temperatures of the six temperature zones set from the feed end to the die head of the twin-screw extruder to 170°C, 180°C, 185°C, 190°C, 190°C and 190°C respectively. Adjust the spindle speed of the twin-screw extruder to 40 r / min. After melt blending for 3 minutes, extrude and granulate to obtain the PP composite material.

[0029] Example 2 This embodiment provides a fire-resistant and flame-retardant PP composite material for new energy battery casings and its preparation method, including the following steps: S1. Preparation of polypropylene grafting masterbatch Weigh 40g of polypropylene and add it to a preheated torsional rheometer. After mixing at 170℃ for 4 minutes, add 0.4g of styrene and mix for 4 minutes. Then add 1.1g of maleic anhydride and mix for 6 minutes. Finally, add 0.01g of dicumyl peroxide and continue mixing for 10 minutes. Discharge the material to obtain polypropylene graft masterbatch.

[0030] S2, Preparation of composite flame retardants Weigh out 95 mL of anhydrous ethanol and 5 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out: Add 50 mL of 5% melamine aqueous solution to a reaction vessel containing 6 mL of 60% hydroxyethylidene diphosphate aqueous solution, then add 0.1 mol / L formic acid solution to adjust the pH of the solution to 4, react at 90℃ for 3.5 h, filter after the reaction is complete, wash the product 4 times with deionized water, and dry in a vacuum drying oven at 80℃ for 8 h to obtain the complex precursor; Weigh 0.5g of γ-glycidyl oxypropyltrimethoxysilane and add it to 100mL of ethanol aqueous solution. Sonicate hydrolyze for 40min, then add 9g of expanded graphite. Stir at 50℃ for 5.5h and filter. Dry the product at 60℃ for 12h to obtain modified expanded graphite. Weigh out 10g of the composite precursor and 9g of modified expanded graphite and add them to a ball mill and ball mill for 6 hours to obtain the composite flame retardant.

[0031] S3, Preparation of modified nano zinc oxide Weigh out 90 mL of anhydrous ethanol and 10 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out 25 mL of ethanol-water solution, add 0.1 mol / L sodium hydroxide solution dropwise until the solution pH is 8, stir for 4 min, then add 0.02 g of n-octyltriethoxysilane, heat to 30 °C and stir for 40 min, then add 2 g of nano zinc oxide, sonicate for 40 min, continue heating to 70 °C, stir and reflux for 3.5 h, after the reaction is complete, centrifuge, wash 3 times with anhydrous ethanol, put the precipitate into a vacuum drying oven and dry at 60 °C for 6 h to obtain modified nano zinc oxide.

[0032] S4. Preparation of composite reinforcing agent Weigh 4g of Tris buffer and add it to 3000mL of deionized water. Slowly add 0.1mol / L dilute hydrochloric acid to adjust the pH of the solution to 8.5. Then add 7g of dopamine hydrochloride and stir for 15 min. Add 25g of hexagonal boron nitride powder and stir for 5 min. Then sonicate for 40 min. Finally, let it stand at 25℃ for 24 h. After the reaction is complete, filter the product and wash it with deionized water until the filtrate becomes colorless. Transfer the product to a vacuum drying oven and dry it at 60℃ for 24 h to obtain polydopamine-modified hexagonal boron nitride. Weigh 25g of polydopamine-modified hexagonal boron nitride and add it to a reaction vessel containing 1000mL of anhydrous ethanol. Disperse the mixture ultrasonically at 25℃ for 25min. Then add 5g of propyltriethoxysilane triisocyanate and heat to 55℃ for 2.5h. Next, add 80mL of deionized water and react for 5min. Finally, add 10g of Al2O3 powder and stir at 65℃ for 7h. After the reaction is complete, centrifuge the product and transfer it to a vacuum drying oven to dry at 60℃ for 24h to obtain the composite reinforcing agent.

[0033] S5. Preparation of PP composite materials Weigh out 0.8 parts by weight of antioxidant 1010 and 0.8 parts by weight of hexadecyltrimethylammonium chloride, mix them evenly, and obtain the additive. Weigh out 40 parts by weight of polypropylene and 5 parts by weight of polypropylene grafted masterbatch and add them to a mixer. Stir at 70°C for 3 minutes. Then add 3 parts of additives and stir for 2 minutes. Next, add 35 parts of glass fiber, 2 parts of modified nano zinc oxide and 8 parts of composite reinforcing agent and continue stirring for 6 minutes. Finally, add 22 parts of composite flame retardant and stir for 4 minutes. Transfer the mixture to a twin-screw extruder. Set the temperatures of the six temperature zones set from the feed end to the die head of the twin-screw extruder to 170°C, 180°C, 185°C, 190°C, 190°C and 190°C respectively. Adjust the spindle speed of the twin-screw extruder to 40 r / min. After melt blending for 4 minutes, extrude and granulate to obtain the PP composite material.

[0034] Example 3 This embodiment provides a fire-resistant and flame-retardant PP composite material for new energy battery casings and its preparation method, including the following steps: S1. Preparation of polypropylene grafting masterbatch Weigh 40g of polypropylene and add it to a preheated torsional rheometer. After mixing at 180℃ for 5 minutes, add 0.5g of styrene and mix for 5 minutes. Then add 1.2g of maleic anhydride and mix for 8 minutes. Finally, add 0.01g of dicumyl peroxide and continue mixing for 15 minutes. Discharge the material to obtain polypropylene grafted masterbatch.

[0035] S2, Preparation of composite flame retardants Weigh out 95 mL of anhydrous ethanol and 5 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out: Add 50 mL of 5% melamine aqueous solution to a reaction vessel containing 7 mL of 60% hydroxyethylidene diphosphate aqueous solution, then add 0.1 mol / L formic acid solution to adjust the pH of the solution to 5, react at 100℃ for 4 h, filter after the reaction, wash the product 5 times with deionized water, and dry in a vacuum drying oven at 80℃ for 8 h to obtain the complex precursor; Weigh 0.5g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to 100mL of ethanol aqueous solution. Sonicate hydrolyze for 60min, then add 10g of expanded graphite. Stir at 60℃ for 6h and filter. Dry the product at 60℃ for 12h to obtain modified expanded graphite. Weigh out 14g of the composite precursor and 9g of modified expanded graphite and add them to a ball mill and ball mill for 6 hours to obtain the composite flame retardant.

[0036] S3, Preparation of modified nano zinc oxide Weigh out 90 mL of anhydrous ethanol and 10 mL of deionized water, mix them thoroughly to obtain an ethanol-water solution; Weigh out 30 mL of ethanol aqueous solution, add 0.1 mol / L sodium hydroxide solution dropwise until the solution pH is 9, stir for 5 min, then add 0.02 g of n-octyltriethoxysilane, heat to 40 °C and stir for 60 min, then add 2 g of nano zinc oxide, sonicate for 60 min, continue to heat to 80 °C, stir and reflux for 4 h, after the reaction is complete, centrifuge, wash 4 times with anhydrous ethanol, put the precipitate into a vacuum drying oven and dry at 60 °C for 6 h to obtain modified nano zinc oxide.

[0037] S4. Preparation of composite reinforcing agent Weigh 5g of Tris buffer and add it to 3000mL of deionized water. Slowly add 0.1mol / L dilute hydrochloric acid to adjust the pH of the solution to 8.5. Then add 8g of dopamine hydrochloride and stir for 20min. Add 30g of hexagonal boron nitride powder and stir for 10min. Then sonicate for 60min. Finally, let it stand at 30℃ for 24h. After the reaction is complete, filter the product and wash it with deionized water until the filtrate becomes colorless. Transfer the product to a vacuum drying oven and dry it at 60℃ for 24h to obtain polydopamine-modified hexagonal boron nitride. Weigh 30g of polydopamine-modified hexagonal boron nitride and add it to a reaction vessel containing 1000mL of anhydrous ethanol. Disperse the mixture ultrasonically at 30℃ for 30min. Then add 5g of propyltriethoxysilane triisocyanate and heat to 60℃ for 3h. Next, add 80mL of deionized water and react for 10min. Finally, add 10g of Al2O3 powder and stir at 70℃ for 8h. After the reaction is complete, centrifuge the product and transfer it to a vacuum drying oven to dry at 60℃ for 24h to obtain the composite reinforcing agent.

[0038] S5. Preparation of PP composite materials Weigh out 1 part of antioxidant 1010 and 1 part of hexadecyltrimethylammonium chloride by weight, mix them evenly, and obtain the additive; Weigh out 50 parts by weight of polypropylene and 8 parts by weight of polypropylene grafted masterbatch and add them to a mixer. Stir at 80°C for 5 minutes. Then add 5 parts of additives and stir for 3 minutes. Next, add 50 parts of glass fiber, 3 parts of modified nano zinc oxide and 10 parts of composite reinforcing agent and continue stirring for 8 minutes. Finally, add 30 parts of composite flame retardant and stir for 5 minutes. Transfer the mixture to a twin-screw extruder. Set the temperatures of the six temperature zones set from the feed end to the die head of the twin-screw extruder to 170°C, 180°C, 185°C, 190°C, 190°C and 190°C respectively. Adjust the spindle speed of the twin-screw extruder to 40 r / min. After melt blending for 5 minutes, extrude and granulate to obtain the PP composite material.

[0039] Comparative Example 1 The difference between this comparative example and Example 3 is that step S1 is omitted and polypropylene grafting masterbatch is not added in step S5.

[0040] Comparative Example 2 The difference between this comparative example and Example 3 is that step S2 is omitted and no composite flame retardant is added in step S5.

[0041] Comparative Example 3 The difference between this comparative example and Example 3 is that step S3 is omitted, and the modified nano zinc oxide in step S5 is replaced with nano zinc oxide in step S3.

[0042] Comparative Example 4 The difference between this comparative example and Example 3 is that step S4 is omitted, and the composite reinforcing agent in step S5 is replaced by boron nitride and aluminum oxide from step S4.

[0043] Performance testing: The PP composite materials prepared in Examples 1-3 and Comparative Examples 1-5 were added to a twin-screw extruder. The six temperature zones set in the twin-screw extruder from the feed end toward the die head were controlled to be 170°C, 180°C, 185°C, 190°C, 190°C and 190°C respectively. After the PP composite material was completely melted, it was extruded into a mold. After cooling and demolding, it was placed in a vacuum dryer and vacuum dried at 80°C for 2 hours to obtain a new energy battery shell sample. The vertical flammability rating of the test sample was determined in accordance with the standard GB / T 2408-2021 "Determination of flammability of plastics - Horizontal and Vertical Methods". The tensile strength of the test sample was determined in accordance with the standard GB / T 1040.1-2018 "Determination of tensile properties of plastics - Part 1: General". The bending strength of the test sample was determined in accordance with the standard GB / T 9341-2008 "Determination of Flexural Properties of Plastics"; The hardness of the test sample was determined according to standard GB / T 3398.2-2008 "Determination of Hardness of Plastics - Part 2: Rockwell Hardness". The specific test results are shown in Table 1 below: Table 1 - Basic Performance Test Data of the Samples The hardness, tensile strength, and flexural strength of the test samples were determined by placing them in a heat aging chamber according to standard SH / T 1542-2023 "Determination of thermal oxidative stability of polypropylene and propylene copolymers in air - heat aging chamber method". The specific test results are shown in Table 2 below: Table 2 - Aging Performance Test Data of Samples The hardness, tensile strength, and flexural strength of the test samples after immersion in a 0.1% alkali solution were determined according to standard GB / T 11547-2008 "Determination of Resistance of Plastics to Liquid Chemical Reagents". The specific test results are shown in Table 3 below: Table 3 - Data on alkali resistance of the samples Data Analysis: In Table 1, because composite flame retardants were added in Examples 1-3, the phosphorus-nitrogen structure synergistically inhibited the combustion reaction through gaseous and condensed phase flame retardancy. The modified expanded graphite formed a dense carbon layer at high temperature to block heat and oxygen. At the same time, the polypropylene grafted masterbatch improved the interfacial bonding between the flame retardant and the matrix, ensuring uniform dispersion of the flame retardant components and reducing the risk of local combustion. Therefore, the vertical combustion rating reached V-0. However, Comparative Example 1 did not add polypropylene grafted masterbatch, resulting in uneven dispersion of the flame retardant and poor interfacial bonding, which easily led to the formation of local combustion channels, causing the rating to drop to V-2. Comparative Example 2 did not add composite flame retardants, lacking the dual effects of phosphorus-nitrogen chemical flame retardancy and expanded graphite physical barrier, resulting in a vertical combustion rating of only V-2. The Rockwell hardness of Examples 1-3 was 76-78, tensile strength was 51-53 MPa, and flexural strength was 62-65 MPa, all higher than those of Comparative Examples 1-4. This is because the maleic anhydride polar groups of the polypropylene grafted masterbatch in these examples, along with the styrene regulating effect, enhanced the interfacial bonding with the composite reinforcing agent and modified nano-zinc oxide, reducing interfacial voids. The polydopamine-modified hexagonal boron nitride in the composite reinforcing agent was tightly bonded to alumina. The layered structure of hexagonal boron nitride and the high rigidity of alumina synergistically provided mechanical support, and the uniform dispersion without agglomeration or stress concentration, along with the silane grafting filling of microscopic voids, resulted in a comprehensive improvement in mechanical properties. In contrast, Comparative Example 4, lacking a composite reinforcing agent and directly using unmodified boron nitride and alumina, had poor filler dispersion and weak interfacial bonding, leading to the lowest hardness, tensile strength, and flexural strength. Comparative Example 1, lacking polypropylene grafted masterbatch, had more interfacial voids, resulting in decreased mechanical properties. In Table 2, the hardness of Examples 1-3 after heat aging was 65-70, the tensile strength was 44-48 MPa, and the flexural strength was 53-59 MPa, all higher than those of Comparative Examples 1-4. This is because the hexagonal boron nitride and alumina of the composite reinforcing agent in the examples have excellent thermal conductivity, which can quickly dissipate heat and delay thermo-oxidative aging. The interface bonding strengthened by the polypropylene graft masterbatch reduces structural cracking caused by thermal stress, so the performance retention rate after heat aging is high. However, Comparative Example 3 uses unmodified nano zinc oxide, which has gaps at the interface with the matrix. During the heat aging process, thermal stress easily leads to interface cracking, accelerating the performance decline. Therefore, the tensile strength after heat aging is only 38 MPa and the flexural strength is 47 MPa. Comparative Example 2 does not add composite flame retardant, lacks the heat dissipation effect of inorganic fillers, and has poor interface bonding. The performance declines significantly after heat aging, with a tensile strength of 39 MPa and a flexural strength of 48 MPa. In Table 3, the hardness of Examples 1-3 after alkali immersion was 67-72, the tensile strength was 45-49 MPa, and the flexural strength was 55-60 MPa, all significantly higher than those of Comparative Examples 1-4. This is because the silane coupling agent-modified nano-zinc oxide in these examples binds to the matrix through covalent bonds, eliminating interfacial voids and blocking the alkali penetration channels. The alumina and polydopamine-modified hexagonal boron nitride in the composite reinforcing agent exhibit excellent chemical stability, and their layered structure forms a physical barrier, preventing direct contact between the alkali solution and the matrix. The polypropylene grafted masterbatch... The interface reinforcement further prevents the alkali solution from penetrating along the interface, thus resulting in excellent alkali corrosion resistance. However, Comparative Example 4, due to the use of unmodified boron nitride and alumina, has a weak bond between the filler and the matrix interface, allowing alkali solution to easily penetrate through the interface voids, leading to a significant decrease in performance after immersion, with a tensile strength of 38 MPa and a flexural strength of 46 MPa. Comparative Example 3, due to the use of unmodified nano zinc oxide, has voids at the interface, allowing alkali solution to easily penetrate and cause interface peeling, resulting in a tensile strength of only 40 MPa and a flexural strength of 49 MPa, which are lower than those of the examples.

[0044] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A fire-resistant and flame-retardant PP composite material for new energy battery casings, characterized in that, It comprises the following components by weight: 30-50 parts polypropylene, 3-8 parts polypropylene grafted masterbatch, 20-50 parts glass fiber, 15-30 parts composite flame retardant, 1-3 parts modified nano zinc oxide, 6-10 parts composite reinforcing agent and 1-5 parts additives. The additives comprise the following components by weight: 0.5-1 parts antioxidant 1010 and 0.5-1 parts hexadecyltrimethylammonium chloride.

2. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 1, characterized in that, The preparation method of the polypropylene grafting masterbatch is as follows: polypropylene is added to a preheated torsional rheometer and mixed at 160-180℃ for 3-5 minutes. Then, styrene is added and mixed for 3-5 minutes. Then, maleic anhydride is added and mixed for 5-8 minutes. Finally, dicumyl peroxide is added and mixed for 10-15 minutes. The mixture is then discharged to obtain the polypropylene grafting masterbatch. The weight ratio of polypropylene, styrene, maleic anhydride and dicumyl peroxide is 40:0.4-0.5:1-1.2:0.

01.

3. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 1, characterized in that, The composite flame retardant is prepared by the following steps: A1. Melamine aqueous solution is added dropwise to a reaction vessel containing an aqueous solution of hydroxyethylidene diphosphate, and then formic acid solution is added dropwise to adjust the pH of the solution to 4-5. The reaction is carried out at 80-100℃ for 3-4 hours, and then post-processed to obtain the complex precursor. A2. Add γ-glycidyl etheroxypropyltrimethoxysilane to an aqueous ethanol solution, sonicate hydrolyze for 30-60 min, then add expanded graphite, stir at 50-60℃ for 5-6 h, filter, and dry the product at 60℃ for 12 h to obtain modified expanded graphite. A3. The composite precursor and modified expanded graphite were added to a ball mill and ball-milled for 6 hours to obtain the composite flame retardant.

4. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 3, characterized in that, In step A1, the ratio of the aqueous solution of hydroxyethylidene diphosphate to the aqueous solution of melamine is 5-7 mL:50 mL, the mass fraction of hydroxyethylidene diphosphate in the aqueous solution is 60%, the mass fraction of melamine in the aqueous solution is 5%, and the concentration of the formic acid solution is 0.1 mol / L. The post-treatment operation includes: filtering after the reaction, washing the product with deionized water 3-5 times, and drying in a vacuum drying oven at 80°C for 8 hours. In step A2, the ratio of the aqueous solution of γ-glycidyl etheroxypropyltrimethoxysilane, aqueous ethanol solution, and expanded graphite is 0.5 g:100 mL:8-10 g, and the aqueous ethanol solution is composed of anhydrous ethanol and deionized water in a volume ratio of 19:

1. In step A3, the weight ratio of the composite precursor and the modified expanded graphite is 7-14 g:9 g.

5. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 1, characterized in that, The modified nano zinc oxide is prepared as follows: sodium hydroxide solution is added dropwise to an ethanol aqueous solution until the solution pH is 8-9. After stirring for 3-5 min, n-octyltriethoxysilane is added. The temperature is raised to 30-40℃ and stirred for 30-60 min. Then, nano zinc oxide is added and ultrasonically dispersed for 30-60 min. The temperature is further raised to 70-80℃ and stirred under reflux for 3-4 h. After the reaction is completed, the mixture is centrifuged and washed 3-4 times with anhydrous ethanol. The precipitate is placed in a vacuum drying oven and dried at 60℃ for 6 h to obtain modified nano zinc oxide. The ratio of the amount of the ethanol aqueous solution, n-octyltriethoxysilane and nano zinc oxide is 20-30 mL: 0.02 g: 2 g. The ethanol aqueous solution is composed of anhydrous ethanol and deionized water in a volume ratio of 9:

1. The concentration of the sodium hydroxide solution is 0.1 mol / L.

6. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 1, characterized in that, The composite reinforcing agent is prepared by the following steps: B1. Add Tris buffer to deionized water and slowly add dilute hydrochloric acid to adjust the pH of the solution to 8.

5. Then add dopamine hydrochloride and stir for 15-20 min. Add hexagonal boron nitride powder and stir for 5-10 min. Then sonicate for 30-60 min. Finally, let it stand at 20-30℃ for 24 h and then perform post-treatment to obtain polydopamine-modified hexagonal boron nitride. B2. Polydopamine-modified hexagonal boron nitride is added to a reaction vessel containing anhydrous ethanol and ultrasonically dispersed at 20-30℃ for 20-30 min. Then, propyltriethoxysilane triisocyanate is added and the temperature is raised to 50-60℃ for 2-3 h. Next, deionized water is added and the reaction is carried out for 5-10 min. Finally, Al2O3 powder is added and stirred at 60-70℃ for 6-8 h. After post-treatment, the composite reinforcing agent is obtained.

7. The fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 6, characterized in that, In step B1, the ratio of Tris buffer, deionized water, dopamine hydrochloride, and hexagonal boron nitride powder is 0.4-0.5g:300mL:0.7-0.8g:2-3g, and the concentration of dilute hydrochloric acid is 0.1mol / L. The post-treatment is as follows: after the reaction, the product is filtered and washed with deionized water until the filtrate becomes colorless. The product is then transferred to a vacuum drying oven and dried at 60°C for 24 hours. In step B2, the ratio of polydopamine-modified hexagonal boron nitride, anhydrous ethanol, propyltriethoxysilane triisocyanate, deionized water, and Al2O3 powder is 2-3g:100mL:0.5g:8mL:1g. The post-treatment is as follows: after the reaction, the product is centrifuged and then transferred to a vacuum drying oven and dried at 60°C for 24 hours.

8. The method for preparing fire-resistant and flame-retardant PP composite material for new energy battery casings according to any one of claims 1-7, characterized in that, The process includes the following steps: adding polypropylene and polypropylene grafted masterbatch into a mixer and stirring at 60-80℃ for 2-5 minutes, then adding additives and stirring for 2-3 minutes, followed by adding glass fiber, modified nano zinc oxide and composite reinforcing agent, and continuing to stir for 5-8 minutes, and finally adding composite flame retardant and stirring for 3-5 minutes, then transferring to a twin-screw extruder, melt blending for 3-5 minutes, and then extruding and granulating to obtain PP composite material.

9. The preparation method of the fire-resistant and flame-retardant PP composite material for new energy battery casings according to claim 8, characterized in that, The twin-screw extruder has six temperature zones set from the feed end toward the die head, with temperatures of 170℃, 180℃, 185℃, 190℃, 190℃, and 190℃ respectively. The spindle speed of the twin-screw extruder is 40 r / min.

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