Stabilizer of Polymer Plastics

any one of the substances that inhibit the aging of polymers. Stabilizers are subdivided into antioxidants, heat stabilizers, antiozone agents, ultraviolet absorbers, and antirads.

Antioxidants increase the resistance of polymers to the action of atmospheric oxygen by inhibiting thermal oxidative destruction. The most important antioxidant stabilizers include derivatives of secondary aromatic amines (for example, phenyl-β-naphthylamine), hydroquinolines (for example, 6-ethoxy-l,2-dihydro-2,2,4-trimethylquinoline), phenols and bisphenols (for example, 2,6-di-tert-butyl-4-methylphenol), and aryl phosphites (for example, tri-(p-nonylphenyl)-phoshite).

Heat stabilizers, which inhibit the destruction of heat-resistant polymers, include metal oxides and certain organometallic compounds. Antiozone agents, which protect polymers against atmospheric ozone, can act through various mechanisms. Thus, chemical antiozone agents, such as derivatives of p-phenyl-enediamine and tributylthiourea, react with, for example, ozone and the products of the ozonolysis of polymers. Physical antiozone agents, mainly mixtures of solid, crystalline paraffin hydrocarbons, migrate to the surface of the polymer to form a barrier against the reaction of the polymer with ozone.

Ultraviolet absorbers (light stabilizers) are substances capable of absorbing ultraviolet light (for example, carbon black) or of inhibiting the photooxidative destruction caused by the concurrent action of light and oxygen (derivatives of benzophenone, esters of salicylic acid). Properties of antirads, that is, of substances that inhibit radiation-induced aging, are possessed by certain aromatic hydrocarbons (for example, naphthalene and anthracene), secondary aromatic amines, and derivatives of p-phenylenediamine.

The substances used as stabilizers of polymer plastics must satisfy several requirements. They must disperse well in polymers and, as a rule (excepting antiozone agents), not migrate to the surface of the polymer. Low volatility is required, and the substances must not affect the processing operations of polymers or the specific properties of items made from polymers. Stabilizers introduced into white or colored materials must not alter the color of these materials. The content of stabilizer in polymers usually ranges from 0.1 to 3.0 percent. With the use of more than one stabilizer (usually 2–3), an effect known as synergism is observed; here, the separate stabilizers act to increase one another’s effectiveness.