Stabilizers

Stabilizers provide protection against degradation caused by heat, oxidation, and solar radiation. Thus, when used in plastic compositions they may be classified as heat (or thermal) stabilizers, antioxidants and UV light stabilizers.

It is the role of heat stabilizers to prevent the polymer from degrading during the short period of high temperature (150℃ to 300℃) processing and to protect the finished plastic article against slow aging over longer periods at service temperatures.

Antioxidants inhibit or retard oxidative degradation at normal or elevated temperatures during processing, storage or service. Most polymers undergo some oxidation degradation, but hydrocarbon polymers are specially susceptible.Antioxidants, therefore, are generally added in small quantities.

Most plastics exhibit varying degrees of degradation upon prolonged outdoor exposure. Polypropylene, poly (vinyl chloride), polyethylene, polyesters, crstalline and high impact polystyrenes, and ABS are particularyly sensitive. Other plastics, particularly poly (methyl methacrylate) and the fluorocarbons, are much more resistant. To arrest or retard polymer degradation caused by the ultraviolet portion of solar radiation, plastic formulations contain UV absorbers. These are compounds such as substituted benzophenones, benzotriazoles and acrylonitriles that selectively absorb harmful radiation and convert it to heat energy.

Pigments such as titanium dioxide and zinc oxide are also used to protect plastics against the harmful effect of ultraviolet radiation.

They function by absorbing some UV radiation, but their ability to reflect radiation (heat as well as light) accounts for much of their effectiveness.In applications where colour is not a requirement, carbon black, which absorb UV light, is widely used as a very effective stabilizer (e.g. in black polyethylene).