Plastics are organic materials based on synthetic or natural high-molecular compounds (polymers). Extremely wide use was made of plastics based on synthetic polymers.
Polymers are classified in various ways, depending on their properties and application. The most common is the following classification: division into thermoplastics, thermosets and elastomers.
Glass transition temperature - the temperature at which the polymer passes on cooling from a highly elastic or viscous-flow to a glassy state, is one of the main characteristics of polymers.
Thermoplastics (thermoplastic plastics) are materials that can be re-processed when heated. They are fluid when heated above the melting point. The processing of thermoplastics in products is not accompanied by an irreversible chemical reaction, i.e. They are suitable for recycling (molding). Thermoplastic plastics are often called injection molded, since they are processed into parts (products) mainly by injection molding or extrusion. Thermoplastics in their solid state can be processed by cutting. In the plastic state, their shape can be changed by bending, drawing and blowing.
Reaktoplasty (thermosetting plastics) are materials in which irreversible chemical and phase changes occur during heating. In this case, the molecules of the thermoset material form a three-dimensional cross-linked network, and the structure thus formed is not flowable upon reheating, i.e. the material can not be re-processed.
Elastomers are materials that have high elastic properties in the range of operation. Elastomer is an elastic material that can be stretched to a size many times greater than its initial length and return to its original size when the load is lifted. Unlike thermoplastics, elastomers have low glass transition temperatures.
Injection molding is the technological process of processing plastics, non-ferrous metals and other materials by injection of their melt under pressure into a mold with subsequent cooling.
Extrusion is a technological process for obtaining products from polymeric materials (rubber compounds, plastics, starch-containing and protein-containing mixtures) by forcing the melt of material through a forming hole in the extruder.
Household polymers have average physico-chemical properties and relatively low quality. They are used for manufacturing inexpensive industrial consumer goods and packaging. The quality of products, to some extent, is compensated by large volumes of production. Examples of such polymers are polyethylene, polypropylene, polystyrene. In recent years, ways of significantly improving the mechanical and thermal properties of some polymers have been found, which makes it possible to translate them into engineering polymers.
Engineering polymers are characterized by increased strength and heat resistance, and, correspondingly, several times more expensive than household materials. They are used to create products that require durability, wear resistance, low combustibility and are capable of withstanding cyclic loads. Engineering plastics include polycarbonates, ABS plastics, polyesters and other thermo- and thermosetting plastics.
Special polymers are materials of the highest quality. They are characterized by very high strength and heat resistance, as well as a set of special properties (for example, electromagnetic). They are more expensive than ordinary engineering materials and their production volumes are much less. Such materials are used at high temperatures, under heavy loads, in electrical engineering and electronics, etc. Examples include liquid crystalline polymers, as well as composite and modified materials obtained from other engineering plastics.