Plastic is an organic substance, such as wood, paper, wool. It is created with natural resources, mainly coal, common salt, gas and especially oil – of which the world production of plastics absorbs about 4% in a year. Various methods are used to form the polymer chains, giving life to the plastics materials, so as to realize the final product ready for use. In this last case at the plastic materials are joined some additives, namely particular substances that enhance or attenuate their properties, such as dyes; agents with special features such as flame retardants, antioxidants, antistatic, plasticizers; natural or artificial fillers, to increase rigidities and improving the mechanical properties; to obtain a lighter product.
Plastic materials are divided into two main families: thermoplastic and thermosetting. The thermoplastic materials are formed by heat but not changed in structure and, therefore, they can be remodeled using the heat. Thermosetting materials take shape with the heat, which, on the contary, will irreversibly change their chemical structure, so they could not be more softening. Polymers which form plastics, can be in powder, granules, liquids and solutions. The main processes that turn them into final products, using pressure and heat, are:
- CALENDERING which consists to stretch and compress with a machine, formed by heated cylinders, the heated polymer and made plastic, for obtaining sheets of the desired thickness.
- EXTRUSION consists of a continuous transformation of heated plastic material that is pushed by a screw through a nozzle that gives the material the desired shape and that through cooling takes its final shape. This is the procedure more widely used in plastics manufacturing.
- BLOWING process is a procedure through which the molten polymer is subjected to air or steam blow, so to take the form of the mold in which it is fed.
- MOLDING is a technique in which the molten polymer feeds a mold of which, for compression and cooling, it assumes the desired form.
Plastic materials are increasingly applied in many areas such as packaging, construction, furniture, transport, electrical and electronics applications, agriculture, health, sport and leisure.