Fotodegradação de termoplásticos semicristalinos.

Abstract

ABSTRACT When polymer products are exposed to the natural weathering, some structural changes occur in the molecules resulting in deterioration in mechanical properties and modification in surface appearance like yellowness and formation of surface cracks. The weatherability of polymer varies widely and depends on a number of factors like the polymer chemical structure and the presence of impurities, plays major role during photodegradation because it controls the initiation step wich ultimately results in chain scission. This work will describe the effects of natural photodegradation on the chemical structure and physical properties of threee types of polyolefins (polypropylene, high density polyethylene and low density polythylene) and two types of polyethylene terephthalate (amorphous and semi-crystalline). Samples were exposed the natural weathering in Campina Grande (PB) for periods of up to 38 weeks. At selected intervals they were analysed for mechanical and thermal properties, melt flow index, extent of chemical degradation and fracture suface. By comparing the results obtained for the three types of polyolefines it was observed that polypropylene was the most sensitive one showing changes in maximum elongation after only three weeks exposure whereas high density polyethylene did not show any sign of chemical degradation even after 38 weeks. On the other hand, low density polyethylene showed and intermediate behaviour and some evidence thet crosslinking reactions was formed during exposure. In the case of polyesters,