UNIT IX SECTION 6 SYNTHETIC PLASTICS ARE OUTSTANDING EXAMPLES OF "BETTER THINGS FOR BETTER LIVING" Introduction. A plastic, or resin, is a material that can be molded into some desired shape. In the broadest sense these terms might include such materials as iron or glass, but in actual usage they refer to such natural products as rosin, gums, and amber, and to synthetic organic molding materials. The first synthetic plastics were devised to replace such natural materials as amber, paraffins, tar, bitumens, asphalts, rubber, rosin, glue, shellac, gelatin, waxes, and copals. Thus celluloid was originally devised as a substitute for ivory. Synthetic plastics have opened up many new fields of usefulness in addition to those fields in which they have displaced natural products. Today plastics are replacing natural textile fibers such as silk or wool ; they are replacing metals and wood in automobiles and airplane manufacture. In the building industry their hardness, beauty, and resistance to chemical change recommend them for many architectural purposes, from fireplace mantels to table and counter tops, protective paints and varnishes, molded hardware, and lighting fixtures. Plastics decrease manufacturing costs because they can be molded into shapes which would require many costly operations to obtain from metals. The cast and laminated plastics can be easily turned and machined, are light in weight, strong, and free from the corrosion which is the enemy of metals. Their excellent insulating properties render them invaluable in the manufacture of a wide variety of electrical equipment. The use of plastics has just begun.' will be widely used within the next twenty years in It is safe to predict that plastics the manufacture ' In 1939, 6966 workers pocketed ?9, 839, 935 in wages earned in the production of J77,653,314 worth of synthetic resins. The production of coal-tar resins jumped from 131,568,162 pounds in 1937 to 152,121,989 pounds in 1939. 674
SYNTHETIC PLASTICS 675 of flooring, furniture, prefabricated houses, basins, tubs, ducts, dishes, and tableware. Many of these applications merely await the perfection of manufacturing processes, the lowering of the cost of production, and the development of distributing agencies. The Fourteen or More Different Major Types of Plastics May Be Classified Under Three Main Types. 1. Rigid, thermosetting materials. Phenol-formaldehyde and ureaformaldehyde plastics are examples of those types of synthetic resins which, once hardened by heat, cannot be softened by heating again. 2. Rigid thermoplastics. Examples of rigid plastics which can be softened by heating and re-formed are the cellulose esters and ethers, methyl methacrylate, polystyrene, vinylidene chloride, and polyvinyl esters. 3. Flexible elastic thermoplastics. Examples of flexible thermoplastics are rubber hydrochloride, vinylidene chloride, and the plasticized polyvinyl esters. One might include in this group the plastics especially adapted for the preparation of textile fibers, nylon, and vinyon. Synthetic rubbers and rubber substitutes also belong to this group of plastic materials. Synthetic plastics may also be classified as to their method of preparation ; and from this viewpoint two types may be distinguished, namely, the polymerization and condensation plastics, or resins as they are often called. Polymerization plastics result from the building of large molecules by the interaction of smaller ones of the same kind or of different kinds. In the latter case the product is called a copolymer. Condensation products result from the interaction of two or more different compounds which yield new molecules of an essentially diff^erent type plus water. take place simultaneously. In many instances both types of reactions " Bakelite" Was One of the First Synthetic Plastics. In 1909 an American chemist, Leo H. Baekeland, announced a synthetic plastic which he called "Bakelite" phenolic resinoid. This synthetic resin was produced by heating phenol with formaldehyde in the presence of a catalyst. Today phenolic resinous products in a variety of forms are noted for their strength, chemical resistance, and electrical insulating properties. Phenolic resins may be used in the form of a varnish to protect or insulate metal surfaces. Paper, canvas, and other fabrics may be impregnated with them and then heated under pressure to produce very tough materials, such as radio panels, automobile gears, and heavy-duty bearings. Mixed with wood flour.