Photostabilizers BT - Polypropylene: An A-Z reference

Abstract

The outdoor performance of polymers depends largely on their photooxidative (combined action of ultraviolet (UV)-light and oxygen) stability, although generally the overall effect is that of a combined photo- and thermal-oxidation of the polymer. Commercial polypropylene (PP) is highly sensitive to UV light and its photostabilization is essential for outdoor and indoor end-use applications. The shorter wavelength of the sun’s radiation does not reach the surface of the earth and, in most locations, there is little incident radiation below 285 nm. It is the incident UV-part of the sun’s radiation, in the region 290-400 nm, which is mainly responsible for the light-induced polymer oxidation (photooxidation). Saturated hydrocarbon polymers (e.g.‘pure’ PP) are intrinsically transparent to the incident sun spectrum and should not be affected by the solar radiation. Commercial PP, however, absorbs weakly at wavelengths above 285 nm and its sensitivity to sunlight is a consequence of lightabsorbing impurities, particularly oxygen-containing species, and trace levels of metals and other species present arising from production processes, i.e. polymer manufacture, melt processing and fabrication. These impurities sensitize and accelerate PP photooxidative degradation under service conditions involving exposure to light (outdoors and indoors) resulting in discoloration, gradual loss of mechanical properties and ultimate embrittlement of polymer artifact with adverse economic and, possibly, health consequences. Fortunately, the vulnerability of PP to the deleterious effects of their outdoor service environment can be greatly controlled, and the outdoor performance can be markedly improved, by appropriate choice of photostabilizers used either separately or in synergistic combinations. Indeed, the largest market for photostabilizers is in polyolefins and in particular in PP.