Generally speaking, plastics can be divided into hygroscopic and non-hygroscopic, hygroscopic plastics such as cellulose plastic, plexiglass, nylon, polycarbonate, ABS and polyphenylene ether. Non-hygroscopic plastics such as polyethylene, polypropylene, polystyrene and fluoroplastics.

Hygroscopicity refers to the affinity of plastics for water molecules. For hygroscopic plastics, if the moisture content exceeds a certain limit, the water will become water vapor during processing, which will promote high-temperature hydrolysis of the plastic, foam the melt, reduce viscosity, affect the appearance of automotive plastic parts, and reduce mechanical strength.

Because automotive plastics are a kind of high polymer, the molecular structure of the high polymer determines the physical state of molecular motion. Factors affecting the physical state of polymers include molecular structure, chemical composition, stress, and ambient temperature. With the change of temperature, the thermal motion of molecules presents three different mechanical states, namely the glass state, the highly elastic state and the viscous state, which will change under certain conditions.

Polymers that are glassy at room temperature are often called plastics. Polymers with high elasticity at room temperature are rubber materials. From a practical point of view, the glass transition temperature is the upper limit of the working temperature of plastic materials. If the glass transition temperature is exceeded, the plastic will lose or greatly reduce its mechanical properties. There is basically no high elastic state between the tg and tm of the fully crystalline polymer, and its deformation remains basically unchanged, which is beneficial to expand the application temperature range of the polymer.

When the polymer changes from the molten state to the condensed state, the independent movement of the molecules in the disordered state becomes a phenomenon in which the molecules stop freely moving, obtain a fixed position, and arrange them into a normal model. This phenomenon is called crystallization. The molecular chain that can be arranged stably and orderly is called crystalline. If the molecular chain is not arranged neatly, it is called amorphous.

Crystalline polymers generally have good heat resistance, opacity and mechanical properties. As the intermolecular force increases, the density, rigidity, tensile strength, hardness, heat resistance, solvent resistance, air tightness, and chemical resistance of crystalline plastics increase with the increase in crystallinity. Elasticity, elongation and impact strength decrease. The amorphous part of the automobile plastic parts can increase the toughness and strength of the automobile plastic parts, but it may also cause the performance of the various parts of the automobile plastic parts to be uneven, and even cause the automobile plastic parts to warp and crack.

In order to improve the crystallization tendency of plastics in industry, heat treatment (ie, baking for a period of time) is often used.

It changes from an amorphous phase to a crystalline phase, from an unstable crystal structure to a stable crystal structure, and from fine grains to larger grains. Generally speaking, polymers with simple molecular structure and high symmetry tend to crystallize when changing from high temperature to low temperature.

Automobile plastic parts plastics are harmful in the production process, especially toxic, irritating and corrosive to the human body. Therefore, before repairing plastic parts, the relevant safety requirements should be strictly followed.

(1) During the production process, protect the human body when grinding and cutting plastic parts of automobiles, such as wearing protective clothing, masks, and protective glasses.

(2) Automobile plastic parts will emit toxic and harmful gases during the welding process, so you need to wear masks and protective glasses, and operate in a well-ventilated place. People have to stand in the upper air.

(3) When handling glass fiber and hardener, the fiber hardener may harm human skin. Therefore, it is necessary to wear rubber gloves, long-sleeved clothes, and fasten the collar and cuffs.