plastics based on proteins of animal or plant origin. The principal raw material for protein plastics is the milk protein casein, but the proteins in corn kernels, peanuts, and soybeans are also used. In addition to proteins, these plastics contain plasticizers, dyes, and fillers (for obtaining opaque objects). The most widespread protein plastic is galalith. In order to make it, the casein is pulverized by rollers and mixed with dyes (0.6–1.5 percent of the weight of casein) and plasticizers (1.3 percent dimethylaniline and 1.4 percent diphenylamine); the mixture is then shaped in a cylinder press at temperatures of 50°-100° C and pressures of 10–20 meganewtons (MN) per sq m (100–200 kilograms-force [kgf] per sq cm). The product, which is obtained in the form of rods, strips, tubes, or round objects (button blanks), is hardened (tanned) in a 3–5 percent water solution of formaldehyde and then dried with hot air (50° C). The hardening process makes protein plastics resistant in aggressive media, improves their mechanical strength, and reduces hygroscopicity.
Depending on their composition, protein plastics with a wide range of properties are obtained—for instance, a tensile strength of 70–105 MN/m2 (700–1,050 kgf/cm2), a bending strength of 50–120 MN/m2 (500–1,200 kgf/cm2), and water absorption of 7–14 percent. They are resistant to the action of organic solvents and solutions of weak acids, are decomposed by strong acids and alkaline solutions, and lend themselves well to mechanical processing. Protein plastics are used principally in the manufacture of buttons and buckles (galalith) and also in the production of durable and lustrous films for packaging food products. The output of these plastics both in the USSR and abroad is being curtailed because of the new synthetic materials derived from nonfoodstuffs.