Thermoplastics refers to plastics that melt after heating, can flow to the mold after cooling, and then melt after heating; heating and cooling can be used to produce reversible changes (liquid ←→solid), yes The so-called physical change.
General-purpose thermoplastics have continuous use temperatures below 100°C. Polyethylene, polyvinyl chloride, polypropylene, and polystyrene are also called the four general-purpose plastics. Thermoplastic plastics are divided into hydrocarbons, vinyls with polar genes, engineering, cellulose and other types. It becomes soft when heated, and becomes hard when cooled. It can be repeatedly softened and hardened and maintain a certain shape. It is soluble in certain solvents and has the properties of being meltable and soluble. Thermoplastics have excellent electrical insulation, especially polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), polypropylene (PP) have extremely low dielectric constant and dielectric loss. For high frequency and high voltage insulation materials.
Thermoplastics are easy to mold and process, but have low heat resistance and are easy to creep. The degree of creep varies with load, environmental temperature, solvent, and humidity.
In order to overcome these weaknesses of thermoplastics and meet the needs of applications in the fields of space technology and new energy development, all countries are developing heat-resistant resins that can be melt-formed. Composite materials using them as matrix resins have higher mechanical properties and chemical resistance, can be thermoformed and welded, and have better interlaminar shear strength than epoxy resins.