Read the following text, divide it into logical parts, and entitle them.

Date: 2015-10-07; view: 906.

PLASTICS

But for plastics man wouldn't have had an endless variety of products such as threads, sheets, tubes, moulded objects, etc. It is known that plastics are organic substances which are made synthetically by polymerization. The ancestor of synthetic plastics is celluloid. If the properties of celluloid had been perfect, it could have been the basis for a new industry. But celluloid has certain disadvantage - its flammability. More than that, it is necessary that the material of this kind be readily moulded, which was not the case with celluloid. Thus it was not until the discovery of bakelite in 1907 that the real foundation of the synthetic plastics industry was laid. Plastics consisting of long-chain molecules, they can be softened by heat and moulded into a desired shape. It is known that these plastics are thermoplastic. Plastics which are having cross-linked polymeric chains are of much greater rigidity and cannot be softened. They are called thermosetting. It is essential that the terms thermoplastic and thermosetting be also applied to the resins from which plastics are made, the resin being the principal agent incorporated in plastics. It may be natural, like cellulose, but it is most generally synthetic. It is also known that the resin is a binder. There are some other substances added to the plastics without which it would not be possible to synthesize these wonderful materials. Because it is necessary that plastics should enhance such properties as hardness, resistance to shock, or resistance to abrasion, filters are added. Examples of filters are: asbestos, glass fibres, and wood flour. It is required that plasticizers be also included in the formulation. Hadn't antioxidants been added, chemical stability and long life of plastics wouldn't have been possible. It was suggested that catalysts should be added to assist the final cure (final formation of the product). Furthermore, if it were not for stabilizers, plastics would not be protected against sunlight, heat and other destructive factors. The procedure which is used to shape plastics into a final form depends on their properties. Some plastics may be injection moulded. Other plastics must be compression moulded, it means that after they are filled into the mould they must be subjected to pressure. Certain plastics are simply cast into their final shape.