Natural weathering of polypropylene films. II. Ultimate properties and exposure time

Changes in the ultimate properties brought about by outdoor weathering during the rainy season of polypropylene (PP) films were studied. The results obtained showed that the draw ratio λd, tensile stress σb, breaking ratio λb, breaking factor (BF), work draw Ud, and work for rupture Ur all increased with increase in outdoor exposure time, attaining a maximum at about 240-h exposure time, before decreasing with further increases in exposure time. On the other hand, the draw ratio δs remained practically constant up to about 100-h exposure time. The changes in the former set of properties were corroborated by the changes in the apparent crystallinity of the PP samples. In addition, it was shown that a 504-h exposure time was not enough to reduce the properties to damaging levels.