1938: Plastics

The number and variety of synthetic plastics have been augmented considerably during the past year or two. New synthetic raw materials and a better understanding of the processes involved in the formation of synthetic plastics have led to the manufacture of a variety of products suitable for a wide range of industrial applications:

Cellulose Plastics.

Cellulose-acetate products have increased rapidly in importance. Their strength and resiliency have led to their adoption in the automotive industry for steering wheels, dashboards, body fitments, etc. Ethyl cellulose, recently introduced, should be used to a greater extent in the future because of its surprising toughness at below-zero temperatures.

Phenolic Plastics.

These are still the most widely used of the synthetic resin plastics. Their unusual property of hardening with heat, good electrical characteristics, strength, and chemical resistance have resulted in continually broadening their field of usefulness. Most striking of all developments has been the increase in the size of moldings; as, for example, radio cases and cabinets, clock cases, business-machine housings, and the like. Outstanding also has been the increased use of cast-phenolic plastics for innumerable decorative purposes.

Urea Plastics.

Urea plastics are extensively used for light colored plastic moldings. In both molded and laminated form, these have become of wide service as a new medium for the expression of the decorator's art, and as such are used for lighting fixtures, paneling, display signs, etc.

Vinyl Plastics.

Vinyl resins have become of increased importance. Polyvinyl acetate is a component of cements, gumming tapes, etc., and is used as an intermediate in the preparation of the vinyl acetals, the best known of which is the vinyl butyryl plastic used in safety glass. This new laminated glass is highly resistant to rupture at low temperatures.

Polyvinyl chloride and the copolymers of polyvinyl chloride and acetate are useful for wire-coating compositions, paper, and can coatings; the last having achieved considerable volume as providing satisfactory linings for beer cans.

Other vinyl resins of importance are the polyacrylate and polymethacrylate plastics, which can be produced as tough water-white materials, more transparent than glass. These have only recently been introduced; and already they have replaced glass in certain applications; for example, in aeroplane cockpit enclosures.

Styrene was one of the earliest synthetic organic compounds, but it is only recently that polystyrene plastics have become of wide usefulness. Being transparent, water-white, highly water-resistant, and possessing superior electrical properties, these plastics have been employed in widely diversified fields, ranging from the merely decorative to superior films for condenser wrappings, and to chemically resistant closures for acid and alkali containers.

Alkyd Plastics.

These materials, prepared from polyhydric alcohols and polybasic acids, have been employed extensively in lacquers, paints, and varnishes, rather than in the plastic field. Near relatives of these materials — namely, the polyamide-polybasic acid plastics — have only recently been introduced as new chemical fibers which surpass silk in elasticity, strength, and water-resistance. These new polyamide plastics were first introduced as synthetic toothbrush bristles.

Sulphur Olefine Plastics.

These rubber-like plastics, prepared by the condensation of ethylene chloride and polysulfides — have proved of considerable value for the manufacture of oil-and-grease-resistant moldings suitable for gaskets, packings, etc.

The widespread adoption of injection molding, particularly for the fabrication of thermoplastic materials, has been a great stimulus to the plastic industry. Essentially, this process involves squirting a heated plastic material through an orifice into a chilled mold, where it is cooled sufficiently to become rigid. This method of molding has effected a number of economies, due to the shorter molding cycle employed and the automatic loading and injection features permitted.

The growing importance of the plastics industry is best indicated by the fact that, in the ten-year period 1927-36, the annual domestic output of plastics, exclusive of cellulose plastics, increased from 10,000,000 to more than 160,000,000 pounds. This is even more remarkable when it is remembered that during seven of those years business in general was in the throes of a world-wide depression.