History dependence of stress coupled transport in polymer fibres and ribbons

The equilibrium moisture content of polymer samples under stress was determined by measuring linear mass density by determining the vibrational time delay of transverse wave pulses travelling down the length of a stretched fibre or ribbon. For a poly(ether imide) under high applied stress (49 MPa) the resulting enhanced sorption of moisture appeared to result in increasing values of equilibrium moisture content with each cycle. On heat treatment of the sample this effect was reversed. An effect was not clearly evident at lower stress levels (12 MPa). The effect of repeated moisture sorption under stress in bisphenol A polycarbonate samples was to reduce the moisture sorption; this effect was observed only at the lower stress levels. Heat treatment of the material restored the equilibrium moisture content after first raising it to a value higher than that in the as-received sample.