A high flame retardant polypropylene resin for new energy vehicles and preparation method thereof

Abstract

The present invention relates to a high-flame-retardant polypropylene resin for new energy vehicles and a preparation method thereof, belonging to the technical field of polymer materials. The raw materials of the high-flame-retardant polypropylene resin contain polypropylene, maleic anhydride grafted polypropylene, POE grafted acrylic acid, LLDPE grafted maleic anhydride, Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, TPC polyester elastomer, nano-cerium oxide and silicone powder; Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material obtained by coating the surface of nano-boron nitride with Al2O3, then polymerizing ammonium polyphosphate and grafting vinyltrimethoxysilane. The present invention uses POE grafted acrylic acid, LLDPE grafted maleic anhydride, Si-APP@BN, bio-based phytic acid metal chelate, TPC polyester elastomer and other components to synergistically construct a heat-conducting flame-retardant network, breaking through the bottleneck of existing technologies through molecular structure design and process innovation.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a highly flame-retardant polypropylene resin for new energy vehicles and a preparation method thereof. Background Art

[0002] Traditional fuel-powered vehicles primarily rely on engines as their power source, while new energy vehicles rely on batteries to generate electricity to drive the motor. This shift in powertrains presents new safety risks. With the rapid growth of new energy vehicle ownership, their safety is receiving increasing attention, with fire safety being a top priority. During the charging and discharging process, new energy vehicle batteries generate heat due to internal chemical reactions and the thermal effects of the current. A malfunction in the battery management system, or if the battery experiences external impact, overheating, or other abnormalities, thermal runaway can occur. Thermal runaway is an extremely dangerous condition in which the energy within the battery is instantly released, causing the battery to catch fire or even explode. Conventional materials used in vehicle interiors and key components can easily fuel a fire, causing it to spread rapidly and pose a significant threat to the lives and property of drivers and passengers.

[0003] Polypropylene (PP) resin is a widely used material in the automotive industry, offering numerous advantages, including low density, low cost, good processability, and excellent mechanical properties. It is widely used in the manufacture of automotive interior components such as instrument panels, seats, and door panel trims, as well as some exterior components. However, conventional PP resins have poor flame retardancy, with a Limiting Oxygen Index (LOI) typically between 18% and 20%, making them flammable. In a fire, conventional PP products are not only easily ignited but also burn rapidly, releasing large amounts of heat and toxic fumes, severely hindering escape and firefighting efforts.

[0004] To meet the stringent fire safety requirements of new energy vehicles, the development of highly flame-retardant polypropylene resins has become an inevitable trend. Highly flame-retardant polypropylene resins modify the molecular structure of polypropylene by adding appropriate flame retardants, thereby improving its flame retardancy to a certain extent. The application of highly flame-retardant polypropylene resins is of great significance in the new energy vehicle sector. In battery modules, the use of highly flame-retardant polypropylene in components such as the battery casing and module frame can effectively prevent the spread of fire caused by thermal runaway, thereby protecting the battery system. In automotive interiors, the use of highly flame-retardant polypropylene materials can reduce the combustion rate of interior materials in the event of a fire, reduce the production of toxic fumes, and provide more time for drivers and passengers to escape. Furthermore, highly flame-retardant polypropylene resins can also be used in the manufacture of electrical components such as cable ducts and wiring harness sheathing in vehicles, improving the fire safety of electrical systems and ensuring stable operation under complex operating conditions.

[0005] However, at present, polypropylene resin with flame retardant added still has the following problems:

[0006] (1) Degradation of mechanical properties: Although adding flame retardants can improve flame retardancy, it often leads to a decrease in the mechanical properties of polypropylene resin, such as tensile strength, impact strength, and toughness. For example, inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide will make the material brittle when added in high amounts.

[0007] (2) Dispersion problem: Flame retardants are difficult to disperse in the polypropylene matrix and are unevenly dispersed, which will result in good flame retardant effects in some parts and poor flame retardant effects in other parts. It may also cause uneven material properties and affect product quality.

[0008] (3) Balance between heat dissipation and flame retardancy: New energy vehicle batteries and motors generate a lot of heat during operation, requiring good heat dissipation. When flame retardant polypropylene resin is improved, it will affect the heat dissipation performance, causing the battery or motor temperature to be too high, affecting its performance and life.

[0009] With the continuous advancement of new energy vehicle technology, the performance requirements for highly flame-retardant polypropylene resins are also continuously improving. It is necessary to continuously develop safer and more stable highly flame-retardant polypropylene resins to better meet the needs of the booming new energy vehicle industry. Summary of the Invention

[0010] To address the aforementioned issues of decreased mechanical properties, difficulty dispersing, and poor balance between heat dissipation and flame retardancy in existing highly flame-retardant polypropylene resins, the present invention provides a highly flame-retardant polypropylene resin for new energy vehicles and a preparation method thereof. This resin utilizes the synergistic effects of POE grafted onto acrylic acid, LLDPE grafted onto maleic anhydride, Si-APP@BN, bio-based phytic acid metal chelates, and TPC polyester elastomers to construct a multi-scale, synergistically modified structure of a thermally conductive and flame-retardant network. This breakthrough overcomes existing technological bottlenecks through molecular structure design and process innovation. The specific technical solution is as follows:

[0011] A highly flame-retardant polypropylene resin for new energy vehicles comprises the following raw materials in parts by weight: 70 to 80 parts of polypropylene, 5 to 8 parts of maleic anhydride grafted polypropylene, 1 to 2 parts of POE grafted acrylic acid, 1 to 2 parts of LLDPE grafted maleic anhydride, 16 to 20 parts of Si-APP@BN, 8 to 10 parts of bio-based phytic acid metal chelate, 3 to 5 parts of nano-titanium carbide, 8 to 10 parts of TPC polyester elastomer, 1 to 1.5 parts of nano-cerium oxide, and 1.5 to 2 parts of silicone powder. The Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0012] Among the above raw materials, the preparation method of Si-APP@BN includes the following steps:

[0013] The nano-boron nitride is placed in the reaction chamber of the ALD equipment, and trimethylaluminum and deionized water are used as pulse raw materials, and the Al2O3 layer is coated on the surface of the nano-boron nitride to obtain material A; according to the mass ratio, material A: ammonium polyphosphate: ammonium sulfate catalyst = (3-5): (1-2): (0.1-0.3), material A, ammonium polyphosphate and ammonium sulfate catalyst are added to the supercritical CO2 reactor, and reacted at 150℃-180℃ and 20MPa-30MPa for 3h-5h, and the ammonium polyphosphate is allowed to react in the material The surface of material A is polymerized to form a gradient coating structure to obtain material B. Material B is placed in a plasma treatment device, and argon is used as the working gas. The treatment is carried out at a frequency of 13MHz to 14MHz and a power of 100W to 150W for 5min to 10min to generate free radicals on the surface of the particles of material A. Vinyltrimethoxysilane is introduced and reacted at 50℃ to 60℃ for 2h to 3h to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, that is, an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0014] In the above-mentioned preparation method of Si-APP@BN, the alternating pulses are to introduce trimethylaluminum and deionized water in alternating pulses at a temperature of 200°C to 220°C and a pressure of 100Pa to 200Pa. Each cycle is: first, a trimethylaluminum pulse is used for 0.1s to 0.3s, with an interval of 10s to 15s, and then a deionized water pulse is used for 0.1s to 0.3s, with an interval of 10s to 15s; a total of 50 to 80 cycles; the thickness of the Al2O3 layer is 2nm to 5nm.

[0015] In the above-mentioned preparation method of Si-APP@BN, the total amount of the material A, ammonium polyphosphate and ammonium sulfate catalyst added is 0.5 kg to 1 kg per liter of reactor volume;

[0016] In the above-mentioned preparation method of Si-APP@BN, the amount of vinyltrimethoxysilane used is 0.5 mL to 1.0 mL of vinyltrimethoxysilane per gram of material B.

[0017] Among the above raw materials, the preparation method of the bio-based phytic acid metal chelate comprises the following steps:

[0018] Phytic acid and zinc sulfate heptahydrate are added to water in a mass ratio of (1-1.5):(2-2.5):(6-8) and mixed evenly. The pH is adjusted to 5-6 and stirred at 50-60°C for 4-6 hours to obtain PA-Zn. The PA-Zn is then filtered, washed, and vacuum-dried to a constant weight to obtain a bio-based phytic acid metal chelate. This is used to promote carbon formation and reduce molten droplets.

[0019] In the above-mentioned method for preparing the bio-based phytic acid metal chelate, the stirring speed is 200 r / min to 300 r / min; and the vacuum drying temperature is 40° C. to 60° C.

[0020] The method for preparing the highly flame-retardant polypropylene resin for new energy vehicles comprises the following steps:

[0021] S1, premixing to form a continuous phase: adding polypropylene and maleic anhydride grafted polypropylene, POE grafted acrylic acid and LLDPE grafted maleic anhydride according to the amount to be used into an internal mixer at 180°C to 185°C, and performing internal mixing to form a continuous phase;

[0022] S2, powder pretreatment: mixing Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, nano-cerium oxide and silicone powder by airflow to obtain a mixture;

[0023] S3, Gradient feeding: Divide the mixture into three equal parts and add them into the internal mixer three times during the internal mixing process, with an interval of 5 minutes to 10 minutes between each addition. After all the materials are added, continue internal mixing for 15 minutes to 25 minutes.

[0024] S4, cross-linking: adding the TPC polyester elastomer to an internal mixer, raising the temperature to 190°C to 195°C, and mixing for 5 minutes to 10 minutes to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining a mixed material;

[0025] S5, reinforcement and molding: adding the mixed material into an injection molding machine for injection molding to obtain a highly flame-retardant polypropylene resin.

[0026] In S1 of the above preparation method, the rotating speed of the banburying is 30 rpm to 40 rpm, and the banburying time is 5 min to 10 min.

[0027] In S3 of the above preparation method, the rotating speed of the banburying is 40 rpm to 50 rpm.

[0028] In S4 of the above preparation method, the rotating speed of the banburying is 30 r / min to 40 r / min.

[0029] In S5 of the above preparation method, the injection molding parameters are: feed temperature 190℃~195℃, discharge temperature 180℃~185℃, injection pressure 80MPa~120MPa, holding pressure 40MPa~60MPa, injection speed 40g / s~60g / s, and cooling rate 6℃ / min~8℃ / min.

[0030] The present invention provides a highly flame-retardant polypropylene resin for new energy vehicles and a preparation method thereof, which has the following beneficial effects:

[0031] 1. Since polypropylene is a non-polar polymer, it has poor compatibility with many polar additives. Maleic anhydride grafted polypropylene introduces polar maleic anhydride groups into the polypropylene molecular chain, enabling it to form a better interface with other polar materials, such as bio-based phytic acid metal chelates, nano-cerium oxide, etc., thereby enhancing the interaction between different components and improving the overall mechanical properties and stability of the material.

[0032] 2. POE (polyolefin elastomer) itself has good flexibility and elasticity. After grafting with acrylic acid, on the one hand, the acrylic group can chemically react or physically entangle with the polypropylene matrix or other additives, enhancing the compatibility with the matrix; on the other hand, the elastomeric structure of POE can absorb energy through its own deformation when the material is impacted, thereby effectively improving the toughness and impact strength of the material.

[0033] Third, LLDPE (linear low-density polyethylene) exhibits excellent flexibility and processing properties. After grafting with maleic anhydride, the polarity of maleic anhydride improves compatibility with other ingredients. Simultaneously, it synergizes with the grafted acrylic acid on POE to form a flexible network structure within the polypropylene matrix, further enhancing the material's toughness and impact resistance, while also improving its tensile properties.

[0034] Fourth, in POE-grafted acrylic acid, the elastic chain segments of POE can undergo significant deformation when the material is impacted, absorbing a large amount of impact energy through their own flexibility. At the same time, the grafted acrylic acid groups can form chemical bonds or strong physical interactions with the polypropylene matrix or other additives, enhancing the bonding strength with the matrix and making the toughening effect more stable. LLDPE-grafted maleic anhydride also has a flexible molecular chain structure and can play a similar energy absorption role within the material. Moreover, the grafted maleic anhydride groups interact differently with the acrylic acid groups in POE-grafted acrylic acid and the polypropylene matrix. The combination of the two forms a more complex and effective toughening network structure within the material, realizing a dual toughening mechanism and significantly improving the material's toughness and impact resistance.

[0035] POE-grafted acrylic acid and LLDPE-grafted maleic anhydride each improve compatibility with the polypropylene matrix and other additives through the grafted polar groups. POE-grafted acrylic acid primarily exhibits better compatibility with certain highly polar additives, while LLDPE-grafted maleic anhydride excels in compatibility with other non-polar or weakly polar components. Their combined use can encompass a wide range of components of varying polarity within the material system, comprehensively optimizing the compatibility of the entire system, reducing phase separation, and improving the uniformity and stability of material properties. In particular, they can enhance the compatibility of Si-APP@BN, bio-based phytic acid metal chelates, and other ingredients, resulting in a more uniform and dense product structure and, consequently, improved performance across various performance indicators.

[0036] Fifth, TPC polyester elastomers form a stable network structure through crosslinking, primarily improving the material's strength, hardness, and heat resistance, enabling it to maintain excellent shape and performance stability under high temperatures and stress. POE grafted acrylic acid and LLDPE grafted maleic anhydride focus on enhancing the material's toughness and impact resistance, making it less susceptible to breakage when subjected to external forces. The combined use of these three agents achieves a better balance between key properties such as strength, toughness, and heat resistance, meeting the multifaceted performance requirements of new energy vehicles. During the crosslinking process, the active groups on the TPC polyester elastomer's molecular chains not only react with the polypropylene matrix but also interact with certain groups on the POE grafted acrylic acid and LLDPE grafted maleic anhydride, further strengthening the interfacial bonding between the different phases. While improving the material's toughness, the POE grafted acrylic acid and LLDPE grafted maleic anhydride also provide more reactive sites and a better dispersion environment for crosslinking the TPC polyester elastomer, promoting the uniform formation of the crosslinked network. This synergistic effect further stabilizes the material's internal structure, enabling it to better resist external forces and temperature fluctuations, thereby enhancing its overall performance.

[0037] 6. Ammonium polyphosphate (APP) decomposes under heat to produce phosphoric acid, metaphosphoric acid, etc. These substances can promote the dehydration and carbonization of polymers such as polypropylene, forming a dense carbon layer. This carbon layer can isolate oxygen and heat, preventing further combustion. Boron nitride (BN) has good thermal stability and thermal insulation properties. When the material burns, it can block heat transfer to a certain extent, delay the thermal decomposition of the material, and synergize with ammonium polyphosphate to enhance the flame retardant effect. Nano-scale boron nitride has high strength and modulus. After surface modification to form Si-APP@BN, it is evenly dispersed in the material, can bear part of the load, and play a role in enhancing the mechanical properties of the material. The surface properties of Si-APP@BN modified with silicone are improved, making it more dispersible in the polypropylene matrix, so that its flame retardant and reinforcing effects can be more effectively exerted.

[0038] Si-APP@BN combines the high strength, high modulus, and thermal stability of nano-boron nitride, the flame retardancy and char-forming properties of ammonium polyphosphate, and the interfacial modification and toughening properties of silicone. These synergistic functions not only enhance the material's flame retardancy but also positively impact its mechanical properties, thermal stability, and processing performance. Compared to nano-boron nitride alone, this provides a more comprehensive performance improvement.

[0039] 7. The bio-based phytic acid metal chelate formed by phytic acid and metal ions can catalyze the carbonization reaction of polymers such as polypropylene when heated, forming a more stable and dense carbon layer. At the same time, it can reduce the phenomenon of melt dripping during the material combustion process. Melt dripping not only spreads flames but also reduces the flame retardancy of the material. Reducing melt dripping can effectively improve the flame retardancy of the material.

[0040] 8. During the crosslinking process, the active groups on the TPC polyester elastomer molecular chains chemically react with the polypropylene matrix or other additives, forming a three-dimensional network structure. This network restricts the movement of the molecular chains, improving the material's strength, hardness, and heat resistance. At the same time, the inherent elastic properties of the TPC polyester elastomer maintain a certain degree of flexibility, preventing the material from becoming too brittle due to crosslinking.

[0041] 9. Nano-cerium oxide has excellent antioxidant properties, capturing free radicals generated during material processing and use, inhibiting the oxidative degradation of polymers like polypropylene. This extends the material's service life and maintains the stability of its mechanical and other properties. Furthermore, the nano-size effect of nano-cerium oxide can influence the material's crystallization behavior, further optimizing its performance.

[0042] 10. Gradient feeding in three steps with interval mixing can avoid uneven dispersion caused by adding too much powder at once. After each addition, the powder is gradually dispersed into the continuous phase under the stirring action of the internal mixer, basically achieving initial dispersion. When the next addition is made, the newly added powder continues to disperse in the initially dispersed system. This cycle is repeated until all powders are highly evenly dispersed in the continuous phase.

[0043] Reinforcement and molding: During the injection molding process, due to the flow of the material in the mold and the shear force it is subjected to, some polymer chains will be oriented along the flow direction. These oriented polymer chains partially crystallize to form a microfiber structure, which improves the mechanical properties of the material. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to specific implementation cases, but the present invention is not limited to these embodiments.

[0045] Example 1

[0046] A highly flame-retardant polypropylene resin for new energy vehicles comprises the following raw materials in parts by weight: 75 parts of polypropylene, 6.5 parts of maleic anhydride-grafted polypropylene, 1.5 parts of POE-grafted acrylic acid, 1.5 parts of LLDPE-grafted maleic anhydride, 18 parts of Si-APP@BN, 9 parts of bio-based phytic acid metal chelate, 4 parts of nano-titanium carbide, 9 parts of TPC polyester elastomer, 1.2 parts of nano-cerium oxide, and 1.8 parts of silicone powder. The Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0047] Among the above raw materials, the preparation method of Si-APP@BN includes the following steps:

[0048] The nano-boron nitride was placed in the reaction chamber of the ALD equipment, and trimethylaluminum and deionized water were used as pulse raw materials. At a temperature of 210°C and a pressure of 150Pa, trimethylaluminum and deionized water were pulsed alternately. Each cycle was: first, trimethylaluminum was pulsed for 0.2s, followed by an interval of 12s, and then deionized water was pulsed for 0.2s, followed by an interval of 12s. A total of 65 cycles were performed. The surface of the nano-boron nitride was coated with an Al2O3 layer with a thickness in the range of 2nm to 5nm to obtain material A. According to the mass ratio of material A: ammonium polyphosphate: ammonium sulfate catalyst = 4:1.5:0.2, material A, ammonium polyphosphate and ammonium sulfate catalyst were added to a supercritical CO2 reactor with a total amount of 0.8kg added per liter of reactor volume. The reaction was carried out at 165°C and 25MPa for 4h to allow ammonium polyphosphate to polymerize on the surface of material A to form a gradient coating structure to obtain material B. Material B was placed in a plasma treatment equipment, and argon was used as the working gas. The material A was treated at a frequency of z and a power of 130W for 8 minutes to generate free radicals on the particle surface. Vinyltrimethoxysilane was introduced, with 0.8mL of vinyltrimethoxysilane added per gram of material B, and the reaction was carried out at 55°C for 2.5 hours to allow the organosiloxane to attach to the particle surface, thereby obtaining Si-APP@BN, i.e., organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0049] Among the above raw materials, the preparation method of the bio-based phytic acid metal chelate comprises the following steps:

[0050] Phytic acid and zinc sulfate heptahydrate were added to water in a mass ratio of phytic acid: zinc sulfate heptahydrate: water = 1.2:2.3:7, mixed evenly, and the pH adjusted to 5.5. The mixture was stirred at 55°C and 250 rpm for 5 hours to obtain PA-Zn. The mixture was then filtered, washed, and vacuum-dried at 50°C to constant weight to obtain a bio-based phytic acid metal chelate. This was used to promote carbon formation and reduce molten droplets.

[0051] The method for preparing the highly flame-retardant polypropylene resin for new energy vehicles comprises the following steps:

[0052] S1, premixing to form a continuous phase: adding polypropylene and maleic anhydride grafted polypropylene, POE grafted acrylic acid, and LLDPE grafted maleic anhydride according to the amount to be used into an internal mixer at 182°C, and mixing at 35 / min for 8 min to form a continuous phase;

[0053] S2, powder pretreatment: mixing Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, nano-cerium oxide and silicone powder by airflow to obtain a mixture;

[0054] S3, gradient feeding: Divide the mixture into three equal parts and add them into the internal mixer three times during the internal mixing process at a speed of 45 / min, with an interval of 8 minutes between each addition. After all the additions are completed, continue internal mixing at a speed of 45 / min for 20 minutes;

[0055] S4, cross-linking: adding TPC polyester elastomer to an internal mixer, heating to 192°C, and mixing at a speed of 35 / min for 8 minutes to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining a mixed material;

[0056] S5, reinforcement and molding: adding the mixed material to an injection molding machine for injection molding. The injection molding parameters are as follows: feed temperature 192° C., discharge temperature 183° C., injection pressure 100 MPa, holding pressure 50 MPa, injection speed 50 g / s, and cooling rate 7° C. / min; obtaining a highly flame-retardant polypropylene resin.

[0057] Example 2

[0058] A highly flame-retardant polypropylene resin for new energy vehicles comprises the following raw materials in parts by weight: 70 parts of polypropylene, 5 parts of maleic anhydride-grafted polypropylene, 1 part of POE-grafted acrylic acid, 1 part of LLDPE-grafted maleic anhydride, 16 parts of Si-APP@BN, 8 parts of bio-based phytic acid metal chelate, 3 parts of nano-titanium carbide, 8 parts of TPC polyester elastomer, 1 part of nano-cerium oxide, and 1.5 parts of silicone powder. The Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0059] Among the above raw materials, the preparation method of Si-APP@BN includes the following steps:

[0060] The nano-boron nitride was placed in the reaction chamber of the ALD equipment, and trimethylaluminum and deionized water were used as pulse raw materials. At a temperature of 200°C and a pressure of 100Pa, trimethylaluminum and deionized water were pulsed alternately. Each cycle was as follows: first, trimethylaluminum was pulsed for 0.1s, followed by an interval of 10s, and then deionized water was pulsed for 0.1s, followed by an interval of 10s. The cycle was repeated 50 times in total. The surface of the nano-boron nitride was coated with an Al2O3 layer with a thickness ranging from 2nm to 5nm to obtain material A. According to the mass ratio of material A: ammonium polyphosphate: ammonium sulfate catalyst = 3:1:0.1, material A, ammonium polyphosphate and ammonium sulfate catalyst were added to a supercritical CO2 reactor, and the total The amount is 0.5 kg per liter of reactor volume, and the reaction is carried out at 150°C and 20 MPa for 3 hours to allow ammonium polyphosphate to polymerize on the surface of material A to form a gradient coating structure to obtain material B. Material B is placed in a plasma treatment equipment, and argon is used as the working gas. The treatment is carried out at a frequency of 13 MHz and a power of 100 W for 5 minutes to generate free radicals on the particle surface of material A; vinyltrimethoxysilane is introduced, and 0.5 mL of vinyltrimethoxysilane is introduced per gram of material B. The reaction is carried out at 50°C for 2 hours to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, that is, organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0061] Among the above raw materials, the preparation method of the bio-based phytic acid metal chelate comprises the following steps:

[0062] Phytic acid and zinc sulfate heptahydrate were added to water in a mass ratio of 1:2:6 (phytic acid: zinc sulfate heptahydrate: water). The mixture was mixed evenly, and the pH was adjusted to 5. The mixture was stirred at 50°C and 200 rpm for 4 hours to obtain PA-Zn. The mixture was then filtered, washed, and vacuum-dried at 40°C to a constant weight to obtain a bio-based phytic acid metal chelate. This was used to promote carbon formation and reduce molten droplets.

[0063] The method for preparing the highly flame-retardant polypropylene resin for new energy vehicles comprises the following steps:

[0064] S1, premixing to form a continuous phase: adding polypropylene and maleic anhydride grafted polypropylene, POE grafted acrylic acid, and LLDPE grafted maleic anhydride according to the amount to be used into an internal mixer at 180°C, and mixing at 30 r / min for 5 min to form a continuous phase;

[0065] S2, powder pretreatment: mixing Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, nano-cerium oxide and silicone powder by airflow to obtain a mixture;

[0066] S3, gradient feeding: Divide the mixture into three equal parts and add them into the internal mixer three times during the internal mixing process at 40 r / min, with an interval of 5 minutes between each addition. After all the additions are completed, continue internal mixing at 40 r / min for 15 minutes;

[0067] S4, cross-linking: adding the TPC polyester elastomer to an internal mixer, heating to 190°C, and mixing at 30 r / min for 5 min to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining a mixed material;

[0068] S5, reinforcement and molding: adding the mixed material to an injection molding machine for injection molding. The injection molding parameters are: feed temperature 190° C., discharge temperature 180° C., injection pressure 80 MPa, holding pressure 40 MPa, injection speed 40 g / s, and cooling rate 6° C. / min; obtaining a highly flame-retardant polypropylene resin.

[0069] Example 3

[0070] A highly flame-retardant polypropylene resin for new energy vehicles comprises the following raw materials in parts by weight: 80 parts of polypropylene, 8 parts of maleic anhydride grafted polypropylene, 2 parts of POE grafted acrylic acid, 2 parts of LLDPE grafted maleic anhydride, 20 parts of Si-APP@BN, 10 parts of bio-based phytic acid metal chelate, 5 parts of nano-titanium carbide, 10 parts of TPC polyester elastomer, 1.5 parts of nano-cerium oxide, and 2 parts of silicone powder. The Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0071] Among the above raw materials, the preparation method of Si-APP@BN includes the following steps:

[0072] The nano-boron nitride was placed in the reaction chamber of the ALD equipment, and trimethylaluminum and deionized water were used as pulse raw materials. At a temperature of 220°C and a pressure of 200Pa, trimethylaluminum and deionized water were pulsed alternately. Each cycle was as follows: first, trimethylaluminum was pulsed for 0.3s, followed by a 15s interval, and then deionized water was pulsed for 0.3s, followed by a 15s interval. The cycle was repeated 80 times in total. The surface of the nano-boron nitride was coated with an Al2O3 layer with a thickness ranging from 2nm to 5nm to obtain material A. According to the mass ratio of material A: ammonium polyphosphate: ammonium sulfate catalyst = 5:2:0.3, material A, ammonium polyphosphate and ammonium sulfate catalyst were added to a supercritical CO2 reactor, and the reaction mixture was added. A total amount of 1 kg is added per liter of reactor volume, and the reaction is carried out at 180°C and 30 MPa for 5 hours to allow ammonium polyphosphate to polymerize on the surface of material A to form a gradient coating structure to obtain material B. Material B is placed in a plasma treatment equipment, and argon is used as the working gas. The treatment is carried out at a frequency of 14 MHz and a power of 150 W for 10 minutes to generate free radicals on the particle surface of material A; vinyltrimethoxysilane is introduced, and 1.0 mL of vinyltrimethoxysilane is introduced per gram of material B. The reaction is carried out at 60°C for 3 hours to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, that is, organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0073] Among the above raw materials, the preparation method of the bio-based phytic acid metal chelate comprises the following steps:

[0074] Phytic acid and zinc sulfate heptahydrate were added to water in a mass ratio of phytic acid: zinc sulfate heptahydrate: water = 1.5:2.5:8, mixed evenly, and the pH adjusted to 6. The mixture was stirred at 60°C and 300 rpm for 6 hours to obtain PA-Zn. The mixture was then filtered, washed, and vacuum-dried at 60°C to constant weight to obtain a bio-based phytic acid metal chelate. This was used to promote carbon formation and reduce molten droplets.

[0075] The method for preparing the highly flame-retardant polypropylene resin for new energy vehicles comprises the following steps:

[0076] S1, premixing to form a continuous phase: adding polypropylene and maleic anhydride grafted polypropylene, POE grafted acrylic acid, and LLDPE grafted maleic anhydride according to the amount to be used into an internal mixer at 185°C, and mixing at 40 / min for 10 minutes to form a continuous phase;

[0077] S2, powder pretreatment: mixing Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, nano-cerium oxide and silicone powder by airflow to obtain a mixture;

[0078] S3, gradient feeding: Divide the mixture into three equal parts and add them into the internal mixer three times during the internal mixing process at 50 / min, with an interval of 10 minutes between each addition. After all the additions are completed, continue internal mixing at 50 / min for 25 minutes;

[0079] S4, cross-linking: adding the TPC polyester elastomer to an internal mixer, heating to 195°C, and mixing at a speed of 40 / min for 10 min to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining a mixed material;

[0080] S5, reinforcement and molding: adding the mixed material to an injection molding machine for injection molding. The injection molding parameters are: feed temperature 195° C., discharge temperature 185° C., injection pressure 120 MPa, holding pressure 60 MPa, injection speed 60 g / s, and cooling rate 8° C. / min; obtaining a highly flame-retardant polypropylene resin.

[0081] In the above embodiments: the polypropylene model is PP F401 raw material particles, which are sourced from Yangzi Petrochemical. The maleic anhydride grafted polypropylene model is ZJ-900P, which is sourced from Guangzhou Zhongjie Chemical Technology Co., Ltd., with a grafting rate of 1.4%. The POE grafted acrylic acid model is R1120, which is sourced from Coase Chemical Co., Ltd. The LL DPE grafted maleic anhydride model is W1L, which is sourced from Coase Chemical Co., Ltd. Nano-titanium carbide is sourced from Nanjing Hongde Nanomaterials Co., Ltd. TPC polyester elastomer is Hytrel 21UV TPC polyester elastomer concentrated masterbatch, which is sourced from Dongguan Longyue Plastic Raw Materials Co., Ltd. Nano-cerium oxide is sourced from Shanghai Naio Nano Technology Co., Ltd. Silicone powder is organosilicon spherical silicone powder TY-390, with an average particle size of 5 μm, sourced from Guangzhou Yifeng Chemical Technology Co., Ltd. Nano-boron nitride is sourced from Henan Shengyang Chemical Co., Ltd. Trimethylaluminum is sourced from Apex (Shanghai) Gas Co., Ltd. Ammonium polyphosphate is sourced from Shandong Yunding Chemical Co., Ltd., with a degree of polymerization ≥1000. The ammonium sulfate catalyst was sourced from Lianyungang Guansu Industrial Co., Ltd., with a purity exceeding 99%. Vinyltrimethoxysilane, a silane coupling agent KH171, was sourced from Shandong Sodium Magnesium New Materials Co., Ltd. Phytic acid was sourced from Zhejiang Fuxuan Biotechnology Co., Ltd. Zinc sulfate heptahydrate was sourced from Jinan Luya Biotechnology Co., Ltd.

[0082] In the above embodiments, the pH value is adjusted by using an acid regulator or an alkaline regulator, the acid regulator is a 1 mol / L hydrochloric acid solution, and the alkaline regulator is a 1 mol / L sodium hydroxide solution.

[0083] Comparative Example 1

[0084] No POE grafted acrylic acid was added to the highly flame-retardant polypropylene resin; other parameters and methods were the same as in Example 1.

[0085] Comparative Example 2

[0086] No LLDPE-grafted maleic anhydride was added to the highly flame-retardant polypropylene resin; other parameters and methods were the same as in Example 1.

[0087] Comparative Example 3

[0088] No POE grafted acrylic acid and no LLDPE grafted maleic anhydride were added to the highly flame-retardant polypropylene resin; other parameters and methods were the same as in Example 1.

[0089] Comparative Example 4

[0090] Si-APP@BN is replaced by material B (a product of ammonium polyphosphate polymerized on the surface of material A), that is, vinyltrimethoxysilane is missing; other parameters and methods are the same as in Example 1.

[0091] Comparative Example 5

[0092] Si-APP@BN is replaced by material A (nano-boron nitride surface coated with Al2O3 layer), that is, ammonium polyphosphate and vinyltrimethoxysilane are missing; other parameters and methods are the same as in Example 1.

[0093] Comparative Example 6

[0094] Si-APP@BN is replaced by nano-boron nitride, that is, the nano-boron nitride remains unchanged; other parameters and methods are the same as in Example 1.

[0095] Comparative Example 7

[0096] In the highly flame-retardant polypropylene resin, the bio-based phytic acid metal chelate was not added, and the bio-based phytic acid metal chelate was replaced by polypropylene; other parameters and methods were the same as in Example 1.

[0097] Comparative Example 8

[0098] In the highly flame-retardant polypropylene resin, 2 parts of the bio-based phytic acid metal chelate were added (reduced amount), and the remainder of the bio-based phytic acid metal chelate was replaced by polypropylene; other parameters and methods were the same as in Example 1.

[0099] Comparative Example 9

[0100] In the highly flame-retardant polypropylene resin, TPC polyester elastomer, POE grafted acrylic acid, and LLDP E grafted maleic anhydride were not added, and TPC polyester elastomer was replaced by polypropylene; other parameters and methods were the same as in Example 1.

[0101] The properties of the highly flame-retardant polypropylene resins prepared in the above examples and comparative examples were tested.

[0102] I. Tensile Strength: Testing was conducted in accordance with GB / T 1040.2, "Plastics—Determination of Tensile Properties—Part 2: Test Conditions for Molded and Extruded Plastics." Dumbbell-shaped standard specimens (2 mm thick) were prepared and tested using a universal testing machine at a tensile speed of 50 mm / min and a temperature of 23°C. The test results are shown in Table 1 below.

[0103] Impact strength: Tested in accordance with GB / T 1843, "Plastics—Determination of Izod Impact Strength," using a cantilever beam impact tester with specimen dimensions of 80 mm × 10 mm × 4 mm at 23°C. The results are shown in Table 1 below.

[0104] III. Flame Retardancy (UL-94 Vertical Burning Test): A specimen measuring 125mm x 13mm x 3mm was securely fixed in a vertical position on a dedicated test stand. Using a UL-94 vertical burning tester, a Bunsen burner flame was applied to the bottom of the specimen for 10 seconds. During this 10-second period, the flame height was maintained at 20±2mm and the temperature was stabilized at 1000±50°C. During the burning process, the burning time, any dripping, and whether any dripping ignited the cotton wool were carefully observed and recorded. The test results are shown in Table 1 below.

[0105] Thermal Conductivity: Measured using the laser flash method using an LFA457 laser thermal conductivity meter. Highly flame-retardant polypropylene resin was first processed into a 12.7mm diameter, 3mm thick disc sample. This sample was placed on the instrument's sample stage. A high-energy laser pulse instantaneously heated one side of the sample. A high-precision infrared detector on the other side of the instrument rapidly captured the temperature change over time on the back of the sample. The test temperature was set at 25°C. The thermal conductivity of the material was calculated using a specific formula by measuring the thermal diffusivity and combining it with parameters such as the material's specific heat capacity and density. The test results are shown in Table 1 below.

[0106] Table 1 Test data results

[0107]

[0108] From the above test results, it can be seen that the high flame retardant polypropylene resin products of Examples 1 to 3 have high tensile strength, impact strength, high flame retardant performance and good thermal conductivity.

[0109] From the results of Comparative Examples 1, 2, and 3, it can be seen that POE grafted acrylic acid and LLDPE grafted maleic anhydride play a major role in toughening and improving compatibility in the highly flame-retardant polypropylene resin system. In Comparative Example 1, POE grafted acrylic acid is not added, and the flexible connection between the material molecules is reduced, resulting in a decrease in tensile strength and impact strength. Comparative Example 2 does not add LLDPE grafted maleic anhydride, which also reduces the intermolecular force and flexibility of the material, and reduces the tensile strength and impact strength. Comparative Example 3 does not add both, and the microstructure inside the material becomes more rigid, the synergistic effect between the molecules is weakened, and the tensile strength and impact strength are greatly reduced. Since POE grafted acrylic acid and LLDPE grafted maleic anhydride are not the main flame retardant and thermal conductive components in the system, they have little effect on the flame retardant properties and thermal conductivity of the material, so the flame retardant grade is still V-0. Since POE grafted acrylic acid and LLDPE grafted maleic anhydride affect the compatibility and component uniformity of the system, it affects the thermal conductivity.

[0110] From the results of Comparative Example 4, it can be seen that the lack of vinyltrimethoxysilane makes it impossible to form a complete Si-AP P@BN core-shell structure. After the organosiloxane is grafted to the particle surface, it can promote the formation of a dense carbon layer when the material burns, effectively blocking the transfer of heat and oxygen, and improving the flame retardant properties of the material. After the lack of vinyltrimethoxysilane, it is difficult for the material to form such an effective barrier layer when burning, and the flame retardant grade is reduced. From the perspective of thermal conductivity, the complete core-shell structure optimizes the heat transfer path inside the material. The lack of organosiloxane grafting results in an incomplete structure, which affects the heat transfer efficiency and reduces the thermal conductivity.

[0111] From the results of Comparative Example 5, it can be seen that only the surface of nano-boron nitride is coated with an Al2O3 layer, and ammonium polyphosphate and vinyltrimethoxysilane are missing. Ammonium polyphosphate decomposes when heated to produce substances such as phosphoric acid, which promotes the carbonization of the material and is one of the main flame retardant ingredients. After the ammonium polyphosphate is missing, the flame retardant effect of the material is greatly reduced, and the flame retardant grade is further reduced. In terms of thermal conduction, in the complete Si-APP@BN core-shell structure, the synergistic effect of ammonium polyphosphate and organosiloxane helps to build a good heat conduction channel. After the two components are missing, the heat conduction channel inside the material is destroyed and the thermal conductivity decreases.

[0112] From the results of Comparative Example 6, it can be seen that the use of unmodified nano-boron nitride, without a series of modification treatments, cannot exert a synergistic flame retardant effect. During the flame retardant process, the modified Si-APP@BN core-shell structure works together through a variety of flame retardant mechanisms, including gas phase flame retardant, condensed phase flame retardant, etc., while the flame retardant effect of unmodified nano-boron nitride is very poor when acting alone, and can only reach HB level. From the perspective of thermal conductivity, the modified structure can optimize the heat conduction path inside the material to a certain extent. The unmodified nano-boron nitride cannot effectively transfer heat in the material system, resulting in a decrease in the overall thermal conductivity.

[0113] The results of Comparative Examples 7 and 8 show that the primary function of bio-based phytic acid metal chelates in highly flame-retardant polypropylene resins is to promote charring and reduce dripping. In Comparative Example 7, omitting the bio-based phytic acid metal chelate facilitates dripping, while in Comparative Example 8, adding a reduced amount results in reduced charring during combustion. Insufficient charring prevents the material from forming an effective barrier to prevent the spread of combustion, resulting in a decrease in flame retardancy. This is because the bio-based phytic acid metal chelate primarily affects flame retardancy in the material system.

[0114] The results of Comparative Example 9 show that the primary function of TPC polyester elastomer in the material is to enhance toughness. Without the addition of TPC polyester elastomer, POE grafted with acrylic acid, and LLDPE grafted with maleic anhydride in Comparative Example 9, the material loses the elastomer's toughening effect. When subjected to impact loads, internal stress concentration within the material cannot be effectively dissipated, resulting in a significant decrease in impact strength. Because TPC polyester elastomer is not a primary flame retardant or thermally conductive component, its absence has little impact on the flame retardancy rating and thermal conductivity.

Claims

1. A highly flame-retardant polypropylene resin for new energy vehicles, characterized in that: The highly flame-retardant polypropylene resin comprises the following raw materials in parts by weight: 70 to 80 parts of polypropylene, 5 to 8 parts of maleic anhydride grafted polypropylene, 1 to 2 parts of POE grafted acrylic acid, 1 to 2 parts of LLDPE grafted maleic anhydride, 16 to 20 parts of Si-APP@BN, 8 to 10 parts of bio-based phytic acid metal chelate, 3 to 5 parts of nano-titanium carbide, 8 to 10 parts of TPC polyester elastomer, 1 to 1.5 parts of nano-cerium oxide, and 1.5 to 2 parts of silicone powder; the Si-APP@BN is an organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material; The preparation method of Si-APP@BN comprises the following steps: placing nano-boron nitride into a reaction chamber of an ALD device, using trimethylaluminum and deionized water as pulse raw materials, performing alternating pulses, and coating the surface of the nano-boron nitride with an Al2O3 layer to obtain material A; adding material A, ammonium polyphosphate, and ammonium sulfate catalyst into a supercritical CO2 reactor in a mass ratio of (3-5): (1-2): (0.1-0.3), and reacting at 150°C to 180°C and 20MPa to 30MPa for 3h to 5h, allowing ammonium polyphosphate to polymerize on the surface of material A to form a gradient coating structure to obtain material B, and placing material B into a plasma treatment equipment, using argon as the working gas, and treating at a frequency of 13MHz to 14MHz and a power of 100W to 150W for 5min to 10min to generate free radicals on the particle surface of material B; introducing vinyltrimethoxysilane, and reacting at 50℃ to 60℃ for 2h to 3h to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, that is, organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

2. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The alternating pulses are performed at a temperature of 200°C to 220°C and a pressure of 100Pa to 200Pa, with trimethylaluminum and deionized water being introduced in alternating pulses. Each cycle is as follows: first, a trimethylaluminum pulse is applied for 0.1s to 0.3s, followed by an interval of 10s to 15s, and then a deionized water pulse is applied for 0.1s to 0.3s, followed by an interval of 10s to 15s; a total of 50 to 80 cycles are performed; and the thickness of the Al2O3 layer is 2nm to 5nm.

3. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The total amount of material A, ammonium polyphosphate and ammonium sulfate catalyst added is 0.5 kg to 1 kg per liter of reactor volume.

4. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The amount of vinyltrimethoxysilane used is 0.5 mL to 1.0 mL of vinyltrimethoxysilane per gram of material B.

5. The highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The preparation method of the bio-based phytic acid metal chelate comprises the following steps: According to the mass ratio of phytic acid: zinc sulfate heptahydrate: water = (1-1.5): (2-2.5): (6-8), phytic acid and zinc sulfate heptahydrate are added to water, mixed evenly, the pH value is adjusted to 5-6, and the reaction is stirred at 50-60°C for 4-6 hours to obtain PA-Zn. The PA-Zn is filtered, washed, and vacuum-dried to constant weight to obtain a bio-based phytic acid metal chelate.

6. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 5, characterized in that: The stirring speed is 200 r / min to 300 r / min; the vacuum drying temperature is 40° C. to 60° C.

7. A method for preparing a highly flame-retardant polypropylene resin for new energy vehicles, for preparing the highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The preparation method comprises the following steps: S1, premixing to form a continuous phase: adding polypropylene and maleic anhydride grafted polypropylene, POE grafted acrylic acid and LLDPE grafted maleic anhydride according to the amount to be used into an internal mixer at 180°C to 185°C, and performing internal mixing to form a continuous phase; S2, powder pretreatment: mixing Si-APP@BN, bio-based phytic acid metal chelate, nano-titanium carbide, nano-cerium oxide and silicone powder by airflow to obtain a mixture; S3, Gradient feeding: Divide the mixture into three equal parts and add them into the internal mixer three times during the internal mixing process, with an interval of 5 minutes to 10 minutes between each addition. After all the materials are added, continue internal mixing for 15 minutes to 25 minutes. S4, cross-linking: adding TPC polyester elastomer to an internal mixer, heating to 190°C to 195°C, and internally mixing for 5 minutes to 10 minutes to obtain an internally mixed material; S5, reinforcement and molding: adding the mixed material into an injection molding machine for injection molding to obtain a highly flame-retardant polypropylene resin.

8. The method for preparing a highly flame-retardant polypropylene resin for new energy vehicles according to claim 7, wherein: In S1, the speed of the banburying is 30 r / min to 40 r / min, and the banburying time is 5 min to 10 min; in S3, the speed of the banburying is 40 r / min to 50 r / min; in S4, the speed of the banburying is 30 r / min to 40 r / min.

9. The method for preparing a highly flame-retardant polypropylene resin for new energy vehicles according to claim 7, wherein: In S5, the injection molding parameters are: feed temperature 190°C to 195°C, discharge temperature 180°C to 185°C, injection pressure 80MPa to 120MPa, holding pressure 40MPa to 60MPa, injection speed 40g / s to 60g / s, and cooling speed 6°C / min to 8°C / min.

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