Weather Resistance of Polymeric Materials

the capacity of polymeric materials to withstand the actions of various atmospheric agents (solar radiation, heat, oxygen, moisture, industrial gases, and so on) without significant change in their external form and operational properties (mechanical, dielectric, and others).

The resistance of different types of polymeric materials to the action of specific atmospheric agents varies. Fibers and films are extremely sensitive to the action of solar radiation; opaque plastics, to the action of heat; and resins, to ozone. The change in any operational property of the material during a set time of exposure, or the time of exposure during which there is a definite change in these characteristics (for example, the time before cracks appear, the time before breaking occurs, and so on), serves as a criterion for the weather resistance of polymeric materials. The selection of a characteristic according to which the weather resistance of polymeric materials is judged is determined by the type of material concerned. The weather resistance of paint and varnish coatings is evaluated by the change in their external appearance (sheen, color, or degree of cracking) as well as in their protective properties.

The weather resistance of polymeric materials is determined to a great degree by the intensity of the actions of atmospheric agents, and consequently depends upon the local climate. In evaluating the weather resistance of polymeric materials, therefore, the climatic zone in which the testing was carried out must always be considered. The weather resistance of polymeric materials is frequently determined under laboratory conditions rather than natural conditions by means of speeded-up methods. For this purpose various instruments are utilized—for example, weath-erometers, which simultaneously reproduce the action of various atmospheric agents. The weather resistance of polymeric materials is greatly dependent upon the chemical and physical structure of the polymer, as well as upon its ingredients. Examples of polymeric materials possessing good weather resistance are organosilicon rubbers, poly-acrylic nitrile fibers, plastics with a polyamide base, poly-methyl methacrylate, and cellulose acetate. The weather resistance of polymeric materials may be increased by using various stabilizers of polymeric materials.