[Technical Post] Application of several modified bio-based plastics in automobiles
Since the 21st century, with the rapid development of the automobile industry, environmental problems such as lack of petroleum resources and air pollution have become increasingly prominent. In 2017, my country's automobile sales were close to 29 million vehicles. Increasing the proportion of applications in the automotive industry has become an important development direction for the automotive industry. Plastics are used in many parts of automobiles, such as door panels, pillars, bumpers, instrument panels and other decorative parts, accounting for about 10% of the vehicle mass. According to the forecast of China Association of Automobile Manufacturers, the amount and proportion of plastics in automobiles will be further increased, and attention must be paid to the treatment of automobile plastic waste in the future .
Bio-based plastics have the characteristics of degradability, environmental protection in production and processing, wide source of raw materials, low odor, and low volatile organic compound (VOC) content. They have great application potential in the automotive industry. However, due to the high cost and poor heat resistance of degradable plastics ､Uncontrollable degradability and other defects limit its application in the automotive industry, so it must be modified. In recent years, according to the needs of the automobile market, the world's large automobile manufacturers and material suppliers have increased their investment in the research and development of bio-based degradable plastics to develop auto parts with degradable properties .
Mercedes-Benz, Audi, Toyota, BMW and other auto manufacturers have released models that use bio-based degradable plastics to prepare auto parts. Domestic degradable plastics are rarely used in the automotive industry. Xinda Group has carried out research on advanced technologies for automotive lightweighting and sustainable development by filling bio-based degradable materials, low-density materials and composite materials. After the car is scrapped, the plastic parts can be completely degraded. At present, bio-based degradable plastics that are widely used in the automotive industry include polylactic acid (PLA), polyhydroxyalkanoate (PHAs), polybutylene succinate (PBS), etc. These materials are relatively developed at home and abroad. High, some have reached the scale of industrialization. The following summarizes the research achievements and development of bio-based degradable plastics at home and abroad.
1 Application of PLA in the automotive industry
Because PLA materials are generally amorphous and have poor mechanical properties and heat resistance, the application of PLA in the automotive field is limited . It needs to be modified by polymer materials before it can be used. . Japan's Toyota's Raum model uses kenaf fiber/PLA composite material to make spare tire cover, and polypropylene (PP)/PLA modified material to make auto door panels and side trim panels. Japan's Toray Company has also developed PLA fibers suitable for the manufacture of interior parts such as automotive door panels, seats, and ceilings . The German company Rochling and Corbion have jointly developed PLA and glass fiber or wood fiber composite materials, which are used in automotive functional components and interior parts. American RTP Company has developed glass fiber (GF)/PLA composite products, which are used in automotive air shrouds, sun hoods, sub-bumpers, side guards and other parts . The EU ECOplast project has developed a bio-based plastic made from PLA and nanoclay, which is specially used for the production of auto parts.
The domestic research on the application of PLA in the automotive industry is relatively late, but the promotion is rapid. Lvcheng Biomaterials Technology Co., Ltd. has launched a high-strength and high-toughness PLA composite material, which has been used in automotive air intake grilles, triangular window frames and other parts. Kumho Sunli Company has successfully developed polycarbonate (PC)/PLA, which has good mechanical properties and can be degraded and recycled, and is used in automotive interior parts . Yan Jingdan et al.  analyzed and verified the feasibility of PLA used in the manufacture of auto parts, and demonstrated that modified PLA can meet the use requirements of general automotive interior parts. Tang Shaojun of Chery Automobile Company  modified PLA by filling mineral powder (talcum powder, calcium carbonate) and increasing the amount of toughening agent, which improved the heat resistance and impact resistance, and was used in the manufacture of auto parts. Ding Weiliang  used PP/PLA blending modification to prepare interior and exterior trim parts such as automobile shift covers, which has the advantages of low molding temperature, high strength, low odor, and good dimensional stability. Chen Xuesi et al.  used bio-based macromolecules to toughen and modify PLA, by controlling the optical purity of poly-L-lactic acid, improving the crystallinity of the product, and achieving the effect of improving heat resistance, and further using inorganic or natural fiber reinforcement to prepare PLA. Composite materials, endowed with higher heat resistance and mechanical properties, are used in automobile bumpers, dashboard panels, door panels and interior parts of high-speed rail. LEI et al.  prepared flame retardant PLA nanocomposites by blending organic montmorillonite (OMMT) and aluminum phosphinate (AlPi). The PLA/AlPi/OMMT system not only has excellent flame retardant properties, but also has With good thermal stability and mechanical properties, it can be used in automotive trims that require high flame retardant properties. Zhou Yinghui et al.  used glass/ceramic microbeads filled with glass fibers to prepare PLA composites, which have good heat resistance and mechanical properties, low density, and have broad application prospects in automotive lightweighting.
The application of PLA in automobiles started early in foreign countries, and the technology is relatively mature. The application of modified PLA in the automotive field is relatively advanced. With the improvement of domestic environmental protection awareness, the research, development and application of modified PLA for automobiles has begun to increase. , Currently mainly used in automotive decorative parts, with the development of plastic modification technology, the application of PLA in the automotive field will be more extensive.
2 Application of PHAs in the automotive industry
PHAs not only have the mechanical properties of traditional polymer materials, but also have excellent degradability and biocompatibility. Commonly used poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate and 3-hydroxybutyrate Valerate copolymer (PHBV), poly-3-hydroxybutyrate and 3-hydroxyhexanoate copolymer (PHBH), etc. With the continuous development and optimization of the synthesis and modification methods of PHAs, the price of PHAs will gradually decrease, which is very attractive to the automotive industry. According to PHAs producers Kaneka and Telles, 30% of PHAs will be used in the automotive field in the next two years.
At present, there are few reports on the application of PHAs in the automotive industry, mainly in the form of textiles, such as car mats. According to its application form, in the future, it will be modified in terms of low VOC, low odor, antistatic, flame retardant, surface modification and mechanical properties improvement, and further promote the application of PHAs in the automotive industry . In recent years, with the continuous development and application of nanotechnology, PHAs are modified by using the unique surface effects and quantum scale effects of nanomaterials to improve their physical properties or impart some unique properties . Yu Houyong et al.  used cellulose nanocrystals to graft to modify PHBV; DAITX et al.  used nano-montmorillonite melt composite to modify PHBV; VIDHATE et al.  added multi-walled carbon nanotube (MWCNT) melt composite method. The preparation of PHBV/MWCNT nanocomposites modified PHAs can significantly improve the thermal properties, physical properties and electrical properties of PHAs; it has been reported that nano-TiO2 can make PHAs have antibacterial and anti-ultraviolet functions, and nano-SiO2 can improve the thermal properties and electrical properties of PHAs. mechanical properties.
 studied the effects of different surface modifiers on the mechanical properties and water resistance of PHAs. After adding 4% polyisocyanate (pMDI) by mass, the ultimate strength and modulus of PHB and wood flour composites were significantly improved. Adding surface modifiers to fiber reinforced composites can improve the lubricity of reinforced fibers and thus enhance the reinforcement effect. The highly reactive isocyanate groups in pMDI can also react with hydroxyl groups on wood fibers to reduce the surface energy. , the lubricity is improved, thereby improving the water resistance and mechanical properties of PHAs .
These modifications are all conducive to promoting the application of PHAs in the automotive industry. Although there are few application cases of PHAs in the automotive industry at present, with the continuous deepening of their development and modification research, the modified PHAs will be widely used in the automotive industry.
3 Application of PBS in the automotive industry
PBS is mainly composed of succinic acid and butanediol. At present, PBS is mainly used in packaging materials, agricultural film products, textiles, medical products and other fields. According to the forecast of statistical agencies, about 10% of the global PBS will be used in the automotive industry, which is a market worthy of attention .
PBS has excellent degradability, good processability and dyeability, but it also has problems such as low melt strength, poor mechanical properties and heat resistance. Modification by copolymerization, blending, and composite with nanomaterials can greatly improve the comprehensive performance of PBS, broaden the application field, and even replace polyethylene terephthalate and polypropylene .
At present, the degradation performance of degradable plastics is uncontrollable, and the short service life in automobiles is the bottleneck restricting its popularization and application. Shi Kehui of Zhengzhou University  modified PBS by adjusting the molecular end groups. Maleic anhydride (MA) and epichlorohydrin (ECH) were used as end-capping agents, and different proportions of PBS were added during the polymerization of PBS. The modified PBS material was prepared by chemical reaction with different end-capping agents during banburying and extrusion in an extruder. The degradation properties, thermal degradation process and mechanism of the products before and after modification were studied. The results showed that PBS The degradation rate of the polymer is greatly affected by the relative molecular weight of the polymer, end-capping groups, processing technology and other factors.
Wen Tao of Hunan University of Technology  prepared PLA/PBS/zinc oxide (ZnO) nanocomposite materials, and prepared high-performance low-density PLA/PBS/ZnO microporous plastics by supercritical CO2 foaming method, and analyzed and tested the composite materials. The mechanical properties, degradation properties and rheological properties of the material have broad application prospects in the field of automotive lightweighting.
The use of natural fiber reinforced PBS to prepare composite materials and use in the automotive industry is also a hot field. Xu Xiaoling et al.  studied a number of properties of bamboo fiber acylation-modified PBS composites, and the results showed that the optimal proportion of the blended modified materials had good compatibility between the components, which was conducive to the crystallization of the composites and improved the performance of the composites. Heat resistance and physical properties. Faurecia and Mitsubishi Chemical Co., Ltd., using natural fiber/PBS composite technology, have launched a PBS material, which is applied to interior parts such as automotive door trims, instrument panels, air ducts, consoles and door panel inserts in . At present, the application of PBS in automobiles is still relatively small, but there are many researches on modification. Nanomaterial modification and flame retardant modification will further expand its application in the automobile industry.
Biodegradable plastics have very broad application prospects due to their green, environmentally friendly and rich sources, but they also have some shortcomings. First, there is a single type of material, insufficient production capacity, and the processing technology is still immature; second, the material cost is high, and the comprehensive performance is poor, making it difficult to fully replace petroleum-based plastics; third, bio-based plastics are mainly used in packaging materials, tableware, agriculture, etc. In the low-end field, the application in the field of automotive electronics needs to be broken through; fourth, the domestic environmental protection concept is immature, the national policy support is small, and the cost problem prevents many companies from investing more in research and development, the market share is low, and the company is basically in a state of loss. And vicious circle; Fifth, the degradable characteristics of bio-based plastics lead to poor thermal stability, mechanical properties will decrease under high temperature conditions, and the problem of uncontrollable service life and degradation is difficult.
Therefore, the future development direction of bio-based degradable plastics in the automotive industry is to develop low-cost, high-performance bio-based materials; the second is to develop bio-based composite materials that meet the application performance requirements of the automotive industry, popularize applications and expand market scale; three Bio-based fibers or inorganic long fibers are used to modify bio-based degradable plastics to further improve the comprehensive properties of bio-based plastics and promote their application in the automotive field.