Abstract
The authors have examined the effect of stress on the thermal-ageing behaviours of polypropylene tapes and filaments which have different degrees of orientation. Two polymer samples which contained stabilisers of different efficiencies were extruded into tapes and filaments and then subjected to draw ratios of 4 : 1 and 8 : 1. These products were oven-aged at temperatures in the range 90–130°C and simultaneously stressed at levels up to 15% of respective breaking loads.
Effects of over-ageing were monitored by studying the tensile properties. For the more highly stabilised samples, little effect of either stress or draw ratio was noted. However, the less efficiently stabilised samples had durabilities which reduced with increasing initial draw ratio and applied stress. This latter observation identified important consequences for the long-term stability of polypropylene products used under load.