Polyolefin plastic is a general plastic, which mainly includes polyethylene (PE), polypropylene (PP) and advanced olefin polymers such as POE, EVA and MMA. Polyethylene (PE) is divided into high density polyethylene (HDPE) and low density polyethylene (LDPE). Polyolefin plastics, that is, polymers of olefins, are a kind of polymer materials with the largest output and the most uses. Polyethylene and polypropylene are the most important. Because of its rich raw materials, low price, easy processing and molding, excellent comprehensive performance and other characteristics, it is widely used in real life, and its application in automobiles is becoming more and more important, and there is a trend of gradual expansion.

Polyolefin plastics have the following characteristics:

(1) Low density. The density of polyolefin plastics is usually between 0.83 and 0.96 g/cm3, which is a light material except wood. When the foam is made, its density is even lower, ranging from 0.010 to 0.050g/cm3, while that of steel is 7.8 g/cm3, that of aluminum is 2.7 g/cm3, and that of glass is 2.6 g/cm3. Every 100 kg of plastic can replace 750~850 kg of other materials, which can reduce the self-weight of the car and increase the payload.

(2) Good physical and chemical properties. Good hand feeling, wear resistance, good insulation performance against electricity, heat and sound, high transparency and good air permeability, and can be widely used for manufacturing electrical insulating materials and insulating materials; Good chemical resistance, corrosion resistance to acid, alkali, salt and other chemicals.

(3) Good coloring. Can be made into various colors as required, such as black, gray, white, mahogany and so on.

(4) Good processability. It can be processed into tubes, plates, films and fibers by extrusion, blow molding and injection molding. Complex products can be molded twice, and can be mass-produced by various molding methods, with high production efficiency, low cost and remarkable economic benefits. If calculated by unit volume, the cost of producing plastic products is only110 of non-ferrous metals.

(5) Environmental protection and energy saving. Can be recycled, and is a material which can be widely popularized and conforms to the sustainable development strategy of mankind. Oil can be saved by more than 0.5 L per 1 00 km.

(6) low price. At present, the price of PP in the market is 8 000 yuan /t, while other plastics are generally not lower than 10 000 yuan /t, and the price of some plastic materials even reaches more than 40 000 ~ 50 000 yuan/t.

(7) Disadvantages: large shrinkage, strong water absorption, poor dimensional stability, difficulty in making high-precision products, flammability, large amount of black smoke and toxic gases when burning, and easy aging and deformation after long-term use; But its defects can be reduced by modification.