High-flame-retardant polypropylene resin for new energy automobile and preparation method of high-flame-retardant polypropylene resin

Abstract

The invention relates to high-flame-retardant polypropylene resin for a new energy automobile and a preparation method of the high-flame-retardant polypropylene resin, and belongs to the technical field of high polymer materials. The high-flame-retardant polypropylene resin is prepared from the following raw materials: polypropylene, maleic anhydride grafted polypropylene, POE grafted acrylic acid, LLDPE grafted maleic anhydride, Si-APP (at) BN, a bio-based phytic acid metal chelate, nano titanium carbide, a TPC polyester elastomer, nano cerium oxide and silicone powder. Si-APP (at) BN is an organic silicon modified ammonium polyphosphate (at) boron nitride core-shell structure material obtained by coating the surface of nano boron nitride with Al2O3, then polymerizing ammonium polyphosphate and grafting vinyl trimethoxy silane. The POE grafted acrylic acid, the LLDPE grafted maleic anhydride, the Si-APP coated BN, the bio-based phytic acid metal chelate, the TPC polyester elastomer and other components have a synergistic effect, a heat conduction-flame retardant network is constructed, and the bottleneck of the prior art is broken through through molecular structure design and process innovation.

Description

Technical Field

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

[0002] Traditional fuel vehicles mainly use engines as power sources, while new energy vehicles rely on battery packs to provide electricity to drive the motor. This change in the power system has brought new safety hazards. With the rapid growth of the number of new energy vehicles, their safety issues have received more and more attention, among which fire safety is the top priority. During the charging and discharging process, the batteries of new energy vehicles are prone to generate heat due to internal chemical reactions and the thermal effect of current. Once the battery management system fails, or the battery is subjected to abnormal conditions such as external impact and overheating, thermal runaway may occur. Thermal runaway is an extremely dangerous state. The energy inside the battery will be released instantly, causing the battery to catch fire or even explode. If ordinary materials are used for the interior and key components of the car, it is very easy to support combustion when a fire occurs, causing the fire to spread rapidly, posing a huge threat to the life safety and property of the driver and passengers.

[0003] Polypropylene (PP) resin is a material widely used in the automotive industry, with many advantages such as low density, low cost, good processing performance, and excellent mechanical properties. It is widely used in the manufacture of automotive interior parts, such as dashboards, seats, door panel interiors, etc., as well as some external parts. However, the flame retardant properties of ordinary polypropylene resin are poor, and the limiting oxygen index (LOI) is usually between 18% and 20%, which is a flammable material. In a fire environment, ordinary polypropylene products are not only easily ignited, but also burn quickly, releasing a large amount of heat and toxic smoke, seriously hindering the escape of personnel and fire rescue work.

[0004] In order to meet the strict requirements of new energy vehicles for fire safety, the development of high flame retardant polypropylene resin has become an inevitable trend. High flame retardant polypropylene resin modifies the molecular structure of polypropylene by adding suitable flame retardants, thereby improving its flame retardant properties to a certain extent. In the field of new energy vehicles, the application of high flame retardant polypropylene resin is of great significance. In terms of battery modules, the use of high flame retardant polypropylene to make battery shells and battery module frames and other components can effectively prevent the spread of fire caused by battery thermal runaway and protect the safety of the battery system. In automotive interiors, the use of high flame retardant polypropylene materials can reduce the burning speed of interior materials when a fire occurs, reduce the generation of toxic smoke, and buy more escape time for drivers and passengers. In addition, high flame retardant polypropylene resin can also be used to manufacture electrical components such as cable ducts and wiring harness sheaths of automobiles to improve the fire safety of electrical systems and ensure the stable operation of vehicles under complex working conditions.

[0005] However, at present, polypropylene resin with added flame retardant 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, toughness, etc. 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. Uneven dispersion 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, which requires good heat dissipation. When flame retardant polypropylene resin improves its flame retardancy, 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 high flame retardant polypropylene resins are also continuously improving. It is necessary to continuously develop safer and more stable high flame retardant polypropylene resins to better meet the needs of the booming new energy vehicle industry. Summary of the invention

[0010] Aiming at the above problems of decreased mechanical properties, difficult dispersion, 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, which 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 multi-scale synergistic modified structure of a thermal conductive-flame retardant network, and breaks through the bottleneck of existing technologies through molecular structure design and process innovation. Its specific technical scheme is as follows:

[0011] A highly flame-retardant polypropylene resin for new energy vehicles, comprising 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 comprises the following steps:

[0013] Place the nano-boron nitride into the reaction chamber of the ALD equipment, use trimethylaluminum and deionized water as pulse raw materials, alternately pulse, and coat the surface of the nano-boron nitride with Al 2 O 3 layer 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 supercritical CO 2 The reactor is reacted at 150°C to 180°C and 20MPa to 30MPa for 3h to 5h 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 device, argon is used as a working gas, and the device is treated 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 A; vinyltrimethoxysilane is introduced and reacted at 50°C to 60°C for 2h to 3h to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, i.e., organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

[0014] In the above-mentioned preparation method of Si-APP@BN, the alternating pulse is to alternately pulse trimethylaluminum and deionized water at a temperature of 200°C to 220°C and a pressure of 100Pa to 200Pa, and each cycle is: first use trimethylaluminum to pulse for 0.1s to 0.3s, with an interval of 10s to 15s, and then use deionized water to pulse for 0.1s to 0.3s, with an interval of 10s to 15s; a total of 50 to 80 cycles; the Al 2 O 3 The layer thickness 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 0.5kg to 1kg per liter of reactor volume;

[0016] In the above-mentioned preparation method of Si-APP@BN, the amount of vinyltrimethoxysilane used is 0.5mL to 1.0mL 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] 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, stirred at 50-60°C for 4-6 hours to obtain PA-Zn, filtered, washed, and vacuum dried to constant weight to obtain bio-based phytic acid metal chelate. It is used to promote carbonization and reduce 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 above-mentioned method for preparing a 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 to an internal mixer at 180°C to 185°C according to the amount used, 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 mixed material into three equal parts, add them into the mixer three times during the internal mixing process, with an interval of 5min to 10min each time; after all the materials are added, continue internal mixing for 15min to 25min;

[0024] S4, cross-linking: adding the TPC polyester elastomer to an internal mixer, heating to 190°C to 195°C, and internally mixing for 5min to 10min to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining an internally 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 r / min to 40 r / min, 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 r / min to 50 r / min.

[0028] In S4 of the above preparation method, the rotation 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°C ~ 195°C, discharge temperature 180°C ~ 185°C, injection pressure 80MPa ~ 120MPa, holding pressure 40MPa ~ 60MPa, injection speed 40g / s ~ 60g / s, cooling speed 6°C / min ~ 8°C / min.

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

[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 to enhance 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] 3. LLDPE (linear low-density polyethylene) has good flexibility and processing performance. After grafting with maleic anhydride, the polarity of maleic anhydride is also used to improve the compatibility with other ingredients. At the same time, it works synergistically with POE grafted with acrylic acid to form a flexible network structure in the polypropylene matrix, further improving the toughness and impact resistance of the material, and also has a certain effect on improving the tensile properties of the material.

[0034] Fourth, in POE grafted acrylic acid, the elastic chain segment of POE can undergo a large deformation when the material is impacted, and absorb a large amount of impact energy through its own flexibility; at the same time, the grafted acrylic acid group can form chemical bonds or strong physical interactions with the polypropylene matrix or other additives, enhancing the bonding force with the matrix and making the toughening effect more stable. LLDPE grafted maleic anhydride also has a flexible molecular chain structure, which can play a similar energy absorption role inside the material. Moreover, there are different ways of interaction between its grafted maleic anhydride group and the acrylic acid group in POE grafted acrylic acid and the polypropylene matrix. The two are used together to form a more complex and effective toughening network structure inside the material, realizing a dual toughening mechanism, which significantly improves the toughness and impact resistance of the material.

[0035] POE grafted acrylic acid and LLDPE grafted maleic anhydride improve the compatibility with the polypropylene matrix and other additives through the grafted polar groups. POE grafted acrylic acid has better compatibility with certain additives with strong polarity, while LLDPE grafted maleic anhydride performs well in compatibility with other non-polar or weakly polar components. The combination of the two can cover various components of different polarities in the material system, comprehensively optimize the compatibility of the entire system, reduce phase separation, and improve the uniformity and stability of material performance. In particular, it can improve the compatibility of Si-APP@BN, bio-based phytic acid metal chelates and other components, making the product structure more uniform and dense, thereby improving various indicators.

[0036] 5. TPC polyester elastomer forms a stable network structure through cross-linking, which mainly improves the strength, hardness and heat resistance of the material, so that the material can maintain good shape and performance stability under high temperature and stress conditions. POE grafted acrylic acid and LLDPE grafted maleic anhydride focus on enhancing the toughness and impact resistance of the material, so that the material is not easy to break when subjected to external force. The three are used in combination to achieve a better balance between the key properties of the material such as strength, toughness, and heat resistance, and meet the requirements of new energy vehicles for the multi-faceted performance of the material. During the cross-linking process of TPC polyester elastomer, the active groups on its molecular chain not only react with the polypropylene matrix, but also interact with certain groups on POE grafted acrylic acid and LLDPE grafted maleic anhydride, further enhancing the interfacial bonding force between different phases. While improving the toughness of the material, POE grafted acrylic acid and LLDPE grafted maleic anhydride also provide more reaction sites and a better dispersion environment for the cross-linking of TPC polyester elastomer, promoting the uniform formation of the cross-linking network. This mutual synergy makes the internal structure of the material more stable, and when subjected to external forces, temperature changes, etc., it can better cooperate to resist and improve the overall performance of the material.

[0037] 6. Ammonium polyphosphate (APP) will produce phosphoric acid, metaphosphoric acid, etc. when it is decomposed by heat. These substances can promote the dehydration and carbonization of polymers such as polypropylene to form a dense carbon layer. This carbon layer can isolate oxygen and heat, preventing further combustion. Boron nitride (BN) has good thermal stability and heat 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-level 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 it can more effectively play its flame retardant and reinforcing role.

[0038] Si-APP@BN combines the high strength, high modulus, and thermal stability of nano-boron nitride, the flame retardant carbonization of ammonium polyphosphate, and the interface modification and toughening of silicone. These functions work together to not only improve the flame retardant properties of the material, but also have a positive impact on the mechanical properties, thermal stability, and processing properties of the material. Compared with single nano-boron nitride, it can bring more comprehensive performance improvements to the material.

[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 droplet phenomenon of the material during the combustion process. The droplet will not only spread the flame, but also reduce the flame retardant performance of the material. Reducing the droplet can effectively improve the flame retardant grade of the material.

[0040] 8. During the cross-linking process, the active groups on the molecular chain of TPC polyester elastomer react chemically with the polypropylene matrix or other additives to form a three-dimensional network structure. This network structure restricts the movement of the molecular chain and improves the strength, hardness and heat resistance of the material. At the same time, the elastic properties of TPC polyester elastomer itself can maintain the flexibility of the material to a certain extent, preventing the material from becoming too brittle and hard due to cross-linking.

[0041] 9. Nano-cerium oxide has good antioxidant properties, can capture free radicals generated during the processing and use of materials, and inhibit the oxidative degradation reaction of polymers such as polypropylene. This can extend the service life of the material and maintain the stability of the mechanical properties and other properties of the material. In addition, the nano-size effect of nano-cerium oxide can also affect the crystallization behavior of the material, further optimizing the material performance.

[0042] 10. Gradient feeding in three times and intermittent mixing can avoid the problem of uneven dispersion caused by adding too much powder at one time. After each addition of powder, under the stirring action of the internal mixer, the powder gradually disperses into the continuous phase, and basically achieves preliminary dispersion. When feeding the next time, the newly added powder continues to disperse in the system that has been preliminarily dispersed, and this is repeated, so that various powders can reach a highly uniform dispersion state 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 is further described below in conjunction with 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, comprising 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 comprises 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. The cycle was repeated 65 times in total. The surface of the nano-boron nitride was coated with Al2O3 in a thickness of 2nm to 5nm. 2 O 3 layer to obtain material A; according to the mass ratio, material A: ammonium polyphosphate: ammonium sulfate catalyst = 4:1.5:0.2, material A, ammonium polyphosphate and ammonium sulfate catalyst are added to supercritical CO 2 A total of 0.8 kg of material A was added to the reactor per liter of reactor volume, and the reaction was carried out at 165° C. and 25 MPa for 4 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 was placed in a plasma treatment device, and argon was used as the working gas. The material was treated at a frequency of 13.5 MHz and a power of 130 W for 8 minutes to generate free radicals on the particle surface of material A. Vinyl trimethoxy silane was introduced, and 0.8 mL of vinyl trimethoxy silane was introduced per gram of material B. The reaction was carried out at 55° C. for 2.5 hours to allow the organosiloxane to be attached to the particle surface to obtain 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] According to the mass ratio of phytic acid: zinc sulfate heptahydrate: water = 1.2:2.3:7, phytic acid and zinc sulfate heptahydrate are added to water, mixed evenly, the pH value is adjusted to 5.5, stirred at 55°C and 250r / min for 5h to obtain PA-Zn, filtered, washed, and vacuum dried at 50°C to constant weight to obtain bio-based phytic acid metal chelate, which is used to promote carbonization and reduce droplets.

[0051] The above-mentioned method for preparing a 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 a speed of 35 / min for 8min 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: the mixed material is divided into three equal parts, and added into the internal mixer three times during the internal mixing process at a speed of 45 / min, with an interval of 8 minutes each time; after all the additions are completed, the internal mixing is continued 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 internal 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 an internal mixing material;

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

[0057] Example 2

[0058] A highly flame-retardant polypropylene resin for new energy vehicles, comprising 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 comprises the following steps:

[0060] Place nano-boron nitride in the reaction chamber of the ALD equipment, use trimethylaluminum and deionized water as pulse raw materials, and alternately pulse trimethylaluminum and deionized water at a temperature of 200°C and a pressure of 100Pa. Each cycle is as follows: first use trimethylaluminum to pulse for 0.1s, then use deionized water to pulse for 0.1s, then use deionized water to pulse for 10s; a total of 50 cycles; the surface of the nano-boron nitride is coated with Al2O3 in a thickness of 2nm to 5nm. 2 O3 layer to obtain material A; according to the mass ratio, material A: ammonium polyphosphate: ammonium sulfate catalyst = 3:1:0.1, material A, ammonium polyphosphate and ammonium sulfate catalyst are added to supercritical CO 2 A total of 0.5 kg of material A was added to the reactor, and the reaction was 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 was placed in a plasma treatment device, and argon was used as the working gas. The material was treated 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. Vinyl trimethoxy silane was introduced, and 0.5 mL of vinyl trimethoxy silane was introduced per gram of material B. The reaction was carried out at 50° C. for 2 hours to allow the organosiloxane to be attached to the particle surface to obtain Si-APP@BN, i.e., 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] According to the mass ratio of phytic acid: zinc sulfate heptahydrate: water = 1:2:6, phytic acid and zinc sulfate heptahydrate are added to water, mixed evenly, the pH value is adjusted to 5, stirred at 50°C and 200r / min for 4h to obtain PA-Zn, filtered, washed, and vacuum dried at 40°C to constant weight to obtain bio-based phytic acid metal chelate, which is used to promote carbonization and reduce droplets.

[0063] The above-mentioned method for preparing a 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 a speed of 30r / min for 5min 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, add them into the internal mixer three times during the internal mixing process at a speed of 40r / min, with an interval of 5min each time; after all the additions are completed, continue the internal mixing at a speed of 40r / min for 15min;

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

[0068] S5, reinforcement and molding: adding the mixed material into an injection molding machine for injection molding, wherein 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, cooling speed 6° C. / min; obtaining a highly flame-retardant polypropylene resin.

[0069] Example 3

[0070] A highly flame-retardant polypropylene resin for new energy vehicles, comprising 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 comprises the following steps:

[0072] Place nano-boron nitride in the reaction chamber of the ALD equipment, use trimethylaluminum and deionized water as pulse raw materials, and alternately pulse trimethylaluminum and deionized water at a temperature of 220°C and a pressure of 200Pa. Each cycle is: first pulse trimethylaluminum for 0.3s, then pulse deionized water for 0.3s, then pulse deionized water for 15s; a total of 80 cycles; the surface of the nano-boron nitride is coated with Al2O3 in a thickness of 2nm to 5nm. 2 O 3 layer to obtain material A; according to the mass ratio, material A: ammonium polyphosphate: ammonium sulfate catalyst = 5:2:0.3, material A, ammonium polyphosphate and ammonium sulfate catalyst are added to supercritical CO 2 A total of 1 kg was added to the reactor per liter of reactor volume, and the reaction was 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 was placed in a plasma treatment device, and argon was used as the working gas. The plasma treatment was 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. Vinyl trimethoxy silane was introduced, and 1.0 mL of vinyl trimethoxy silane was introduced per gram of material B. The reaction was 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] According to the mass ratio of phytic acid: zinc sulfate heptahydrate: water = 1.5:2.5:8, phytic acid and zinc sulfate heptahydrate are added to water, mixed evenly, the pH value is adjusted to 6, stirred at 60°C and 300r / min for 6h to obtain PA-Zn, filtered, washed, and vacuum dried at 60°C to constant weight to obtain bio-based phytic acid metal chelate, which is used to promote carbonization and reduce droplets.

[0075] The above-mentioned method for preparing a 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 a speed of 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, add them into the internal mixer three times during the internal mixing process at a speed of 50 / min, with an interval of 10 minutes each time; after all the additions are completed, continue the internal mixing at a speed of 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 into an injection molding machine for injection molding, wherein the injection molding parameters are: feed temperature 195°C, discharge temperature 185°C, injection pressure 120MPa, holding pressure 60MPa, injection speed 60g / s, cooling speed 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 model of POE grafted acrylic acid is R1120, which is sourced from Coais Chemical Co., Ltd. The model of LL DPE grafted with maleic anhydride is W1L, which is sourced from Coais Chemical Co., Ltd. Nano titanium carbide is sourced from Nanjing Hongde Nano Materials 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. Trimethyl aluminum is sourced from Apeco (Shanghai) Gas Co., Ltd. Ammonium polyphosphate is sourced from Shandong Yunding Chemical Co., Ltd., with a degree of polymerization ≥1000. The ammonium sulfate catalyst comes from Lianyungang Guansu Industrial Co., Ltd., with a purity of more than 99%. Vinyl trimethoxysilane is a silane coupling agent KH171, which comes from Shandong Sodium Magnesium New Materials Co., Ltd. Phytic acid comes from Zhejiang Fuxuan Biotechnology Co., Ltd. Zinc sulfate heptahydrate comes from Jinan Luya Biotechnology Co., Ltd.

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

[0083] Comparative Example 1

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

[0085] Comparative Example 2

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

[0087] Comparative Example 3

[0088] In the highly flame-retardant polypropylene resin, POE grafted acrylic acid and LLDPE grafted maleic anhydride are not added at the same time; other parameters and methods are the same as in Example 1.

[0089] Comparative Example 4

[0090] Si-APP@BN is replaced by material B (the 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 Al 2 O 3 layer), i.e., 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, no bio-based phytic acid metal chelate is added, and the bio-based phytic acid metal chelate is replaced by polypropylene; other parameters and methods are the same as in Example 1.

[0097] Comparative Example 8

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

[0099] Comparative Example 9

[0100] In the highly flame-retardant polypropylene resin, no TPC polyester elastomer, POE grafted acrylic acid and LLDP E grafted maleic anhydride are added, and TPC polyester elastomer is replaced by polypropylene; other parameters and methods are the same as in Example 1.

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

[0102] 1. Tensile strength: According to GB / T 1040.2 "Determination of tensile properties of plastics Part 2: Test conditions for molded and extruded plastics", dumbbell-shaped standard specimens (thickness 2mm) were prepared and tested using a universal material testing machine. The tensile speed was set to 50mm / min and the temperature was 23°C. The test results are shown in Table 1 below.

[0103] 2. Impact strength: The test is carried out in accordance with GB / T 1843 "Determination of Izod Beam Impact Strength of Plastics". The sample size is strictly processed to 80mm×10mm×4mm. The test is carried out using an Izod beam impact tester at a temperature of 23°C. The test results are shown in Table 1 below.

[0104] 3. Flame retardant performance (UL-94 vertical burning test): A sample with a size of 125mm×13mm×3mm is firmly fixed on a special test frame so that it is in a vertical state. Using a UL-94 vertical burning test machine, a Bunsen burner flame is applied to the bottom of the sample for 10s. During these 10s, the flame height is maintained at 20±2mm and the temperature is stabilized at 1000±50℃. During the burning process, carefully observe and record the burning time of the sample, whether there is dripping, and whether the dripping ignites the absorbent cotton. The test results are shown in Table 1 below.

[0105] 4. Thermal conductivity: The laser flash method is used to measure the thermal conductivity of the material using the LFA457 laser thermal conductivity instrument. First, the high flame retardant polypropylene resin is processed into a disc sample with a diameter of 12.7 mm and a thickness of 3 mm. The sample is placed on the sample stage of the instrument, and a high-energy laser pulse is used to instantly heat one side of the sample. The high-precision infrared detector on the other side of the instrument quickly captures the change in the temperature of the back of the sample over time. The test temperature is set to 25°C. By measuring the thermal diffusivity and combining the material's specific heat capacity and density and other parameters, the thermal conductivity of the material is calculated using a specific calculation formula. 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 higher tensile strength, impact strength, high flame retardant properties 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 high 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 at the same time, the microstructure inside the material becomes more rigid, the synergistic effect between 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, the thermal conductivity is reduced.

[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 surface of the particles, 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 level 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 Al 2 O 3 layer, lacking ammonium polyphosphate and vinyltrimethoxysilane. 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. Without ammonium polyphosphate, 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 thermal conduction channel. Without these two components, the thermal conduction channel inside the material is destroyed and the thermal conductivity decreases.

[0112] It can be seen from the results of Comparative Example 6 that the use of unmodified nano-boron nitride, without a series of modification treatments, cannot exert a synergistic flame retardant effect. In 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, and the unmodified nano-boron nitride cannot effectively transfer heat in the material system, resulting in a decrease in overall thermal conductivity.

[0113] From the results of Comparative Examples 7 and 8, it can be seen that the main function of bio-based phytic acid metal chelates in highly flame-retardant polypropylene resin is to promote carbonization and reduce droplets. In Comparative Example 7, no bio-based phytic acid metal chelates were added, which was easy to drop; in Comparative Example 8, the reduced amount of addition will lead to a decrease in the amount of carbonization when the material is burned. Insufficient carbonization makes it impossible for the material to form an effective barrier layer to prevent the spread of combustion, and the flame retardant grade decreases. Because bio-based phytic acid metal chelates mainly affect flame retardant properties in the material system.

[0114] From the results of Comparative Example 9, it can be seen that the main function of TPC polyester elastomer in the material is to enhance toughness. In Comparative Example 9, TPC polyester elastomer, POE grafted acrylic acid and LLDPE grafted maleic anhydride are not added, and the material loses the toughening effect of the elastomer. When subjected to impact load, the stress concentration inside the material cannot be effectively dispersed, resulting in a significant decrease in impact strength. Because TPC polyester elastomer is not the main flame retardant and thermal conductive component, its absence has little effect on the flame retardant grade 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.

2. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 1, characterized in that: The preparation method of Si-APP@BN comprises the following steps: Place nano-boron nitride into the reaction chamber of the ALD equipment, use trimethylaluminum and deionized water as pulse raw materials, alternately pulse, and coat the surface of the nano-boron nitride with an Al2O3 layer to obtain material A; according to the mass ratio, material A: ammonium polyphosphate: ammonium sulfate catalyst = (3-5): (1-2): (0.1-0.3), add material A, ammonium polyphosphate and ammonium sulfate catalyst into a supercritical CO2 reactor, react at 150°C-180°C and 20MPa-30MPa for 3h-5h, and allow the ammonium polyphosphate to react in the material The surface of A is polymerized to form a gradient coating structure to obtain material B, and material B is placed in a plasma treatment device, and argon is used as the working gas. The material is treated 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 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, organosilicon-modified ammonium polyphosphate@boron nitride core-shell structure material.

3. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 2, characterized in that: The alternating pulses are performed at a temperature of 200°C to 220°C and a pressure of 100Pa to 200Pa, and trimethylaluminum and deionized water are introduced in alternating pulses. Each cycle is as follows: first, trimethylaluminum is pulsed for 0.1s to 0.3s, with an interval of 10s to 15s, and then deionized water is pulsed for 0.1s to 0.3s, with 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.

4. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 2, characterized in that: The total amount of material A, ammonium polyphosphate and ammonium sulfate catalyst added is 0.5kg to 1kg per liter of reactor volume.

5. A highly flame-retardant polypropylene resin for new energy vehicles according to claim 2, characterized in that: The amount of the vinyl trimethoxy silane used is 0.5 mL to 1.0 mL of vinyl trimethoxy silane per gram of material B.

6. A 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 into 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, which is then filtered, washed, and vacuum dried to constant weight to obtain a bio-based phytic acid metal chelate.

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

8. A method for preparing a highly flame-retardant polypropylene resin for new energy vehicles, for preparing a 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 to an internal mixer at 180°C to 185°C according to the amount used, 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 mixed material into three equal parts, add them into the mixer three times during the internal mixing process, with an interval of 5min to 10min each time; after all the materials are added, continue the internal mixing for 15min to 25min; S4, cross-linking: adding the TPC polyester elastomer to an internal mixer, heating to 190°C to 195°C, and internally mixing for 5min to 10min to cross-link the TPC polyester elastomer and the matrix to form a stable network structure, thereby obtaining 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.

9. The method for preparing a highly flame-retardant polypropylene resin for new energy vehicles according to claim 8, characterized in that: 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.

10. The method for preparing a highly flame-retardant polypropylene resin for new energy vehicles according to claim 8, characterized in that: 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.

Images