Plastic Industry

Plastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. There are two types of plastics, thermoplastic and thermoset. Thermoplastics, if exposed to heat, will melt in two to seven minutes. Thermosets will keep their shape until they are a charred, smoking mess. Some examples of thermoplastics are grocery bags, piano keys and some automobile parts.

The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their hardness, density, and their ability to resist heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred celsius. While plastics can be made electrically conductive to some extent, they are still no match for metals like copper or aluminum. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, railroad ties, etc.

Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). So-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.

Other plastics emerged in the prewar period, though some would not come into widespread use until after the war. By 1936, American, British, and German companies were producing Polymethyl methacrylate (PMMA), better known as acrylic glass. Although acrylics are now well known for their use in paints and synthetic fibers, such as fake furs, in their bulk form they are actually very hard and more transparent than glass, and are sold as glass replacements under trade names such as "Perspex", "Plexiglas" and "Lucite". These were used to build aircraft canopies during the war, and its main application now is large illuminated signs such as are used in shop fronts or inside large stores, and for the manufacture of vacuum-formed bath-tubs.