Plastics can be classified by chemical structure, namely the molecular units that make up the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking.
Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural. biodegradable, and electrically conductive. plastics can also be classified by various physical properties, such as density, tensile strength, glass transition temperature, and resistance to various chemical products.
Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper[paper?:paper sample maker cutting machine] clips to spaceships. They have already displaced many traditional materials, such as wood, stone, horn and bone, leather. paper, metal, glass, and ceramic, in most of their former uses.
