High-flame-retardancy polylactic acid composite material for vehicles and preparation method thereof

Abstract

The invention discloses a high-flame-retardancy polylactic acid composite material for a vehicle and a preparation method of the high-flame-retardancy polylactic acid composite material. The high-flame-retardancy polylactic acid composite material is prepared from the following raw materials: phytic acid Phyt, melamine Mel, polylactic acid PLA and expandable graphite EG. The preparation method comprises the following steps: S1, mixing a phytic acid solution with melamine, heating to form PhytMel, separating out solid PhytMel, and drying to obtain PhytMel fine powder; s2, PLA, PhytMel and EG are dried and evenly mixed, then the premixed raw materials are added into a hopper of an extruder, strip-shaped objects are extruded from a die head, the strip-shaped objects are cut and granulated to the needed size through a granulator, finally, drying is conducted for 5 hours, and the final product is obtained. According to the high-flame-retardancy polylactic acid composite material for the vehicle, excellent flame retardancy, mechanical property, light weight and processability are realized through the environmental protection property of PLA, the flame retardancy and molecular weight protection effect of PhytMel and the carbon layer forming ability of EG, and an innovative and practical solution is provided for green manufacturing of automotive interiors and structural parts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer composites, in particular to a high-flame-retardant polylactic acid composite material for vehicles and a preparation method thereof. BACKGROUND

[0002] In recent years, with the increasing emphasis on environmental protection and sustainable development worldwide, the demand for environmentally friendly materials in the automotive industry continues to grow. As a biodegradable thermoplastic made from renewable resources such as corn starch or sugarcane, polylactic acid (PLA) has gradually attracted attention in the automotive field due to its unique environmental characteristics. Compared with traditional petroleum-based plastics such as polypropylene or polyethylene, PLA reduces dependence on non-renewable fossil fuels in the production process and can naturally degrade under certain conditions, thereby significantly reducing the long-term impact of waste on the environment. In addition, PLA has a lower density of about 1.24 g / cm³, which is lighter than many traditional engineering plastics such as ABS (density about 1.05-1.36 g / cm³), helping to achieve automotive lightweighting, thereby improving fuel efficiency or the range of electric vehicles. PLA also has good processing performance and can be molded through conventional processes such as injection molding and extrusion, making it suitable for manufacturing automotive interior parts such as instrument panels and door panel trim and other non-structural components. These characteristics make PLA a potential choice for the automotive industry to pursue green and low-carbon technology, especially in markets that emphasize sustainable development.

[0003] However, despite the significant advantages of PLA in environmental protection and lightweighting, its widespread application in the automotive industry still faces multiple technical challenges. First, the heat distortion temperature (HDT) of PLA is usually between 55-60°C, which is much lower than the high-temperature environment that automotive parts may face in actual use, such as interior temperatures exceeding 80°C under direct sunlight in summer, which causes PLA to soften or deform easily at high temperatures, limiting its application in high-temperature exposure areas. Second, the automotive industry has strict requirements for material flame retardancy (such as UL94 V-0 standard), and unmodified PLA has poor flame retardant performance, making it difficult to meet the needs of interior materials in terms of fire safety, which poses a major obstacle to its application in passenger safety. In addition, PLA also has insufficient mechanical properties, with low impact strength and elongation at break, and a tensile strength of about 50-70 MPa, making it prone to cracking in vibration or impact environments, and it is difficult to perform load-bearing or high-stress components compared to traditional automotive plastics such as polycarbonate or nylon.

[0004] To overcome the above problems, researchers try to improve the performance of PLA by modification methods such as blending, adding reinforcing agents or flame retardants, etc. For example, by adding glass fibers or nano fillers to enhance mechanical strength, by copolymerization modification to improve heat resistance, or by introducing flame retardants to improve fire performance. However, although traditional halogen-containing flame retardants have significant effect, they will release toxic substances, which is contrary to the environmental protection goal; while the efficiency of bio-based flame retardants is low, which is difficult to meet the strict flame retardant standards of the automotive industry. In addition, the modification process often further increases the cost, limiting the commercial application of PLA. In view of these technical bottlenecks, developing a new composite material that can significantly improve the heat resistance, flame retardance and mechanical properties of PLA while maintaining its environmental protection characteristics has become the focus of current research. SUMMARY

[0005] The purpose of the present application is to provide a high flame-retardant polylactic acid composite material for vehicles and a preparation method thereof, which significantly improves its heat resistance, flame retardance and mechanical properties while maintaining its environmental protection characteristics, so as to meet the requirements of the automotive industry in terms of durability, cost-effectiveness and safety, thereby promoting the wide application of PLA in automobile manufacturing.

[0006] The above technical purpose of the present application is achieved by the following technical scheme: A high flame-retardant polylactic acid composite material for vehicles, which is composed of the following raw materials: phytic acid Phyt, melamine Mel, polylactic acid PLA and expandable graphite EG.

[0007] The present application also provides a preparation method of a high flame-retardant polylactic acid composite material for vehicles, comprising the following steps: S1, mix phytic acid solution with melamine according to a specific molar ratio, then heat the mixture to 50-80℃, and use a magnetic stirrer to continuously and uniformly promote the reaction between the phosphate groups of phytic acid and the amine groups of melamine to form phytic acid-melamine salt PhytMel, then naturally cool the mixture to room temperature, separate the solid PhytMel by filtration or centrifugation method, rinse the solid with deionized water about 50mL each time, wash for 2-3 times to remove unreacted raw materials, and finally dry the washed solid in an oven at 60-80℃ for 6-12 hours until the weight is constant to obtain PhytMel fine powder; S2, dry PLA at 80℃ under vacuum for 4-6 hours, dry PhytMel and EG at 60℃ for 4-6 hours, weigh the dried raw materials according to the proportion, mix in a high-speed mixer or a sealed bag for 5-10 minutes to ensure uniformity, then add the pre-mixed raw materials to the hopper of the extruder, melt mix through a twin-screw extruder to uniformly disperse PLA, PhytMel and EG, then extrude a strip from the die, cool in a water bath at 20-25℃, cut and pelletize to the desired size using a pelletizer, and finally dry in a vacuum oven at 60℃ for 5 hours to remove moisture to obtain the final product.

[0008] Further preferably, the magnetic stirrer is continuously stirred for 1-2 hours at a speed of 300-500 rpm in S1.

[0009] Further preferably, the molar ratio of phytic acid to melamine is 1:2.

[0010] Further preferably, the weighing ratio is 75wt% of polylactic acid, 15wt% of phytic acid-melamine salt, and 10wt% of expandable graphite.

[0011] Further preferably, the parameters of the twin-screw extruder are set as follows: feed zone: 160℃, plasticizing zone: 170℃, homogenizing zone: 175℃, die: 170℃, and screw speed: 200rpm.

[0012] In summary, the present application has the following beneficial effects: The present application has the following beneficial effects: The present application has the following beneficial effects:

[0013] Figure 1 is a flow chart for preparing the composite PLA material of the present application. DETAILED DESCRIPTION

[0014] The application will be further described in detail below with reference to the accompanying drawings.

[0015] Example one, a kind of high flame-retardant polylactic acid composite for vehicle, is composed of the following raw materials: phytic acid Phyt, melamine Mel, polylactic acid PLA and expandable graphite EG.

[0016] A kind of preparation method of high flame-retardant polylactic acid composite for vehicle, as shown in Figure 1 The method comprises the following steps: S1, phytic acid solution and melamine are mixed according to a specific molar ratio, the molar ratio of phytic acid to melamine is 1:2, then the mixture is heated to 50-80℃, and a magnetic stirrer is used for continuous stirring for 1-2 hours at a speed of 300-500 rpm, to promote the reaction between the phosphate group of phytic acid and the amine group of melamine to form phytic acid-melamine salt PhytMel, then the mixture is naturally cooled to room temperature, and the solid PhytMel is separated by filtration or centrifugation, and the solid is washed with deionized water about 50 mL each time for 2-3 times to remove unreacted raw materials, and finally the washed solid is dried in an oven at 60-80℃ for 6-12 hours until the weight is constant to obtain PhytMel fine powder; S2, PLA is dried at 80℃ under vacuum for 4-6 hours, and PhytMel and EG are dried at 60℃ for 4-6 hours, the dried raw materials are weighed according to the proportion, mixed in a high-speed mixer or a sealed bag for 5-10 minutes to ensure uniformity, then the pre-mixed raw materials are added to the hopper of an extruder, melted and mixed by a double-screw extruder to uniformly disperse PLA, PhytMel and EG, and then extruded into a strip from a die, cooled in a water bath at 20-25℃, cut and granulated to the required size by a granulator, and finally dried in a vacuum oven at 60℃ for 5 hours to remove moisture to obtain the final product.

[0017] The weighing proportion of each raw material is polylactic acid: 75wt%, phytic acid-melamine salt: 15wt%, and expandable graphite: 10wt%.

[0018] The parameters of the double-screw extruder are set as follows: feeding zone: 160℃, plasticizing zone: 170℃, homogenizing zone: 175℃, die: 170℃, and screw speed: 200 rpm.

[0019] Example two, which is different from example one, is that the proportion of polylactic acid is 85wt%, and the proportion of phytic acid-melamine salt is 15wt%.

[0020] Example three, which is different from example one, is that the proportion of polylactic acid is 85wt%, the proportion of phytic acid-melamine salt is 5wt%, and the proportion of expandable graphite is 10wt%.

[0021] Table 1 compares the performance test results of each example PhytMel is the core flame-retardant component of the composite material of the present application, which is generated by the acid-base reaction between phytic acid and melamine. Phytic acid contains multiple phosphate groups. If directly incorporated into PLA, it may cause degradation of the PLA molecular chain during high-temperature processing due to its strong acidity, resulting in a decrease in molecular weight and thus weakening the tensile strength and toughness of the material. Melamine, as a basic compound, contains multiple amine groups, which react with phytic acid to form a stable PhytMel salt structure, effectively neutralizing the acidity of phytic acid and significantly reducing the degradation of the PLA molecular chain, thus protecting the molecular weight of PLA and maintaining its mechanical properties (e.g., tensile strength up to 45 MPa and elongation at break about 15%). In addition, PhytMel plays a chemical flame-retardant role during combustion, and the phosphate groups of phytic acid promote the formation of a dense carbon layer, isolating oxygen and heat transfer, while melamine decomposes at high temperatures to release nitrogen, diluting combustible gases and reducing the heat release rate HRR and total heat release THR. Compared with traditional halogen-containing flame retardants, PhytMel is derived from renewable plant resources, is non-toxic and environmentally friendly, and significantly improves the ecological friendliness of the material.

[0022] EG, as another key component, further enhances the flame-retardant properties and thermal stability of the composite material. EG rapidly expands at high temperatures to form a porous and dense carbon layer, effectively isolating oxygen and heat, preventing flame spread, and significantly reducing the burning rate and heat release. The physical barrier effect of EG and the chemical flame-retardant mechanism of PhytMel form a synergistic effect, making the flame-retardant properties of the composite material meet the automotive industry standards (such as UL94 V-0). In addition, the expansion properties of EG improve the thermal insulation performance of the material, protecting the structural integrity of automotive parts during a fire. Compared with other inorganic fillers (such as aluminum hydroxide), EG achieves excellent results with a smaller amount and has a small impact on the density of the material, maintaining the lightweight advantage of PLA (density still close to 1.24 g / cm³). The addition of EG also improves the thermal stability of the composite material, increasing the heat distortion temperature (HDT) and enabling it to meet the use requirements of automotive interiors in high-temperature environments.

[0023] The present application significantly improves the flame-retardant properties of PLA to the V-0 level through the synergistic effect of PhytMel and EG, meeting the high safety standards of the automotive industry; improves the carbon residue rate and thermal stability; maintains the hydrolysis resistance and environmental friendliness; and although the mechanical properties are slightly lower than those of pure PLA, they can be optimized through formulation adjustment and are suitable for a variety of scenarios. These characteristics make the present application an ideal high-flame-retardant polylactic acid composite material for automotive use, promoting the widespread application of PLA in automotive manufacturing.

[0024] The embodiments are only used to explain the present application, and are not used to limit the present application, and any modification without creative contribution made by the person skilled in the art according to the embodiments after reading the specification is protected by the patent law as long as it is within the scope of the claims of the present application.

Claims

1. A highly flame-retardant polylactic acid composite material for automobiles, characterized by: It is composed of the following raw materials: phytic acid Phyt, melamine Mel, polylactic acid PLA and expandable graphite EG.

2. The method for preparing a highly flame-retardant polylactic acid composite material for a vehicle according to claim 1, characterized in that: The following steps are involved: S1. Mixing a phytic acid solution and melamine in a specific molar ratio, heating the mixture to 50-80°C, and stirring the mixture evenly with a magnetic stirrer to promote the reaction between the phosphate groups of phytic acid and the amine groups of melamine to form phytic acid-melamine salt PhytMel. Then, naturally cooling the mixture to room temperature, separating solid PhytMel by filtration or centrifugation, and rinsing the solid with deionized water (about 50 mL each time) 2-3 times to remove unreacted raw materials. Finally, drying the washed solid in an oven at 60-80°C for 6-12 hours until the weight is constant to obtain PhytMel fine powder. S2. PLA is dried under vacuum at 80°C for 4-6 hours, while PhytMel and EG are dried at 60°C for 4-6 hours. The dried raw materials are weighed proportionally and mixed in a high-speed mixer or sealed bag for 5-10 minutes to ensure uniformity. The pre-mixed raw materials are then added to the extruder hopper and melt-mixed by a twin-screw extruder to uniformly disperse PLA, PhytMel, and EG. Strips are then extruded from the die, cooled in a water bath at 20-25°C, cut into pellets with a pelletizer to the desired size, and finally dried in a vacuum oven at 60°C for 5 hours to remove moisture to obtain the final product.

3. The method for preparing a highly flame-retardant polylactic acid composite material for a vehicle according to claim 2, wherein: In the S1, a magnetic stirrer is used to continuously stir for 1-2 hours at a rotation speed of 300-500 rpm.

4. The method for preparing a highly flame-retardant polylactic acid composite material for a vehicle according to claim 3, wherein: The molar ratio of phytic acid to melamine is 1:

2.

5. The method for preparing a highly flame-retardant polylactic acid composite material for vehicles according to claim 4, characterized in that: The weighing ratio is polylactic acid: 75wt%, phytic acid-melamine salt: 15wt%, and expandable graphite: 10wt%.

6. The method for preparing a highly flame-retardant polylactic acid composite material for vehicles according to claim 5, characterized in that: The parameters of the twin-screw extruder were set as follows: feeding zone: 160°C, plasticizing zone: 170°C, homogenizing zone: 175°C, die head: 170°C, and screw speed: 200 rpm.

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