KINETICS OF MICROSTRUCTURE REARRANGEMENT DURING ANNEALING OF COLD-DRAWN ISOTACTIC POLYPROPYLENE

In the reported experiments, the microstructure of polypropylene, annealed after cold drawing to an oriented state, was examined using density measurements and small- and wide-angle x-ray scattering (SAXS and WAXS) techniques. Data, for isothermal annealing, showed an increase in SAXS intensity, in crystal perfection, and in density over the observed time range, but no change in long spacing during the same period. Long spacing, SAXS intensity, and density were all strongly dependent upon annealing temperature, increasing at higher temperatures. Upon annealing, the elastic modulus and yield strength dropped below the as-drawn values in an immeasurably short time, and did not appear to change thereafter during the time range examined. The kinetics of the microstructural changes are compared qualitatively to the predictions of nucleation and growth theory and of spinodal decomposition. The defects in the microstructure are considered as the ″solute molecules″ of the spinodal model. The experimental results do not agree neatly with either model.