Polyethylene Terephthalate

a polyester produced by polycondensation of terephthalic acid or its dimethyl ether with ethylene glycol.

Polyethylene terephthalate is a white, odorless solid with molecular weight 20,000–40,000; the maximum crystallinity of unoriented polyethylene terephthalate is 40–45 percent, and of the oriented variety, 60–65 percent; density, 1.38–1.40 g/cm³(20°C); melting point, 255°-265°C; softening point, 245°-248°C.

Polyethylene terephthalate is insoluble in water and organic solvents and is relatively resistant to dilute acid solutions, such as 70-percent H₂SO₄, 5-percent HCl, or 30-percent CH₃COOH, and to cold solutions of alkalies and bleaching agents, for example, sodium hypochlorite or hydrogen peroxide. It hydrolyzes under the action of alkaline solutions at temperatures above 100°C and, at 200°C, even under the action of water.

Polyethylene terephthalate has high strength and resistance to abrasion and repeated tensile and bending stress, low hygro-scopicity (moisture content, 0.4–0.5 at 20°C and 60 percent relative humidity), and a working temperature range of –60° to 170°C. It is a good dielectric (loss tangent, 0.013–0.015 at 1 megahertz) and is relatively resistant to light, X rays, and γ-rays.

Polyethylene terephthalate is processed mainly into fibers and films, and also into various molded products, such as radio components and chemical equipment. World production of polyethylene terephthalate in 1973 was about 3.5 million tons.