Strain recovery of post-yield compressed semicrystalline poly(butylene terephthalate)

Cubic specimens of a semicrystalline poly(butylene terephthalate) (PBT) have been compressed up to post-yield deformation levels with a fast (3.0 x 10(-2) s(-1)) and a slow (1.5 x 10(-4) s(-1)) Strain rate at three different temperatures (25 degrees C, 45 degrees C, and 100 degrees C, i.e. below, close and above the glass transition temperature of the material, T-g, respectively). Differently from literature results reported for amorphous polymers, semicrystalline PBT shows that, after a post-yield deformation, recovery occurs also at temperatures higher than T-g, and that an irreversible deformation, epsilon(irr), is set in the material. The irreversible strain component has been evaluated as the residual deformation after a thermal treatment of 1 It at 180 degrees C. After unloading, isothermal strain recovery has been monitored for time periods of I h at various temperatures. From the obtained data, strain recovery master curves have been constructed by a time-temperature superposition scheme. The features of the recovery process for the various deformation conditions have been analysed. In particular, it appears that specimens deformed below T-g show a lower irreversible component, whereas, when deformed above T-g, they display a higher irreversible deformation and a slower recovery process. Moreover, the effect of deformation rate appears particularly marked for samples deformed above T-g. (c) 2006 Elsevier Ltd. All rights reserved.