FECHINE, G. J. M.; http://lattes.cnpq.br/8109533360196619; FECHINE, Guilhermino José Macêdo.
Resumen:
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,
