Plastic has a variety of other materials do not have a variety of advantages, especially based on the cost and energy saving aspects. The density of plastic is usually between 0.83 and 2.2g/cm3, it is a lighter material except wood, when it is made into foam, its density can be as low as between 0.01 and 0.05g/cm3, while steel is 7.8g/cm3 and aluminum is 2.7g/cm3, which are higher than plastic.
Plastic molding and processing performance is excellent, the complex shape of the product can be a molding, can use a variety of molding methods for mass production, high production efficiency, low cost, the same quality of the parts, using plastic manufacturing costs only for steel or aluminum 1/2 ~ 2/3.
So by the automotive industry a large number of adoptions, especially with the outbreak of the three oil crises and the increasing depletion of petroleum resources, the car to reduce the weight and reduce energy consumption requirements are increasingly increasing, coupled with the requirements of ride comfort, safety, aesthetics, the amount of automotive plastic parts are increasing year by year.
According to their behavior when heated and whether or not they have repeated molding processability, plastics can be classified into two categories: thermoplastics and thermosets. The former can be melted when heated, and can be molded and processed in various ways, and solidified when cooled. Re-heat and can melt, processing, that is, with a number of repeated processing. The latter by heat melting molding at the same time, the curing reaction, the formation of three-dimensional mesh structure, and then heat does not melt, in the solvent is not dissolved, when the temperature exceeds the decomposition temperature will be decomposed and destroyed, does not have repeatability.
Thermoplastics can be divided into general-purpose plastics and engineering plastics according to heat resistance, mechanical properties and cost, market size. Engineering plastics refers to long-term heat-resistant temperature of more than 100 ℃, tensile strength of more than 50MPa, flexural modulus of more than 2000MPa, good rigidity, creep, with self-lubricating properties, can be used as a substitute for metal as a structural material of a class of thermoplastics.
Engineering plastics can be divided into general engineering plastics and high-performance engineering plastics. High-performance engineering plastics long-term heat-resistant temperature of more than 150 ℃. By a monomer polymerization of plastics called homopolymers, such as PP. By two or more monomers copolymerized polymer compounds called copolymers, such as ABS (acrylonitrile-butadiene-styrene copolymer), E / P (ethylene-propylene copolymer), EPDM (EPDM).
Homopolymer resins have molecular chains similar to the structure shown below：
The copolymer resin has a molecular chain similar to the structure illustrated below:
Industry is also often used by two or more plastics and plastics or plastics and rubber to form a macroscopic non-phase, microscopic phase separation of multi-component multiphase materials, usually called polymer copolymer or polymer alloys, such as PC / ABS, ABS / PVC and so on.