THE EFFECTS OF STRESS, ENVIRONMENT AND POLYMER VARIABLES ON THE DURABILITIES OF ORIENTED POLYPROPYLENE TAPES

The combined roles of temperature, applied stress, relative humidity and exposure time have been investigated with respect to the degradation and changes in properties of a selection of oriented polypropylene tapes. Tapes were studied, having a range of average molecular weights and antioxidant types and one commercial sample contained carbon black. After ageing under ambient and elevated temperatures (90-130 degrees C) and selected loads, for periods up to and including their failure, tapes were analysed for changes in tensile physico-chemical and thermal analytical property changes. Results are explained in terms of oxidative scission of polymer chains, which caused subsequent physical structural reorganisation. While application of low and medium stresses had little effect on these changes, stresses above 10% breaking stress seriously enhanced physico-chemical deterioration and shortened the times-to-failure, The effects of relative humidity were similar to those of increased temperature in that rates of degradation were enhanced. The presence of carbon black reduced stress sensitivity of tapes to degradation when loaded below 10% stress levels, and improved creep resistance, but showed poorer ageing performance at higher stress levels.