Relationship between morphology and deformation mechanisms of polyolefins

Abstract

AbstractThe birefringence changes produced by stretching, polyethylene, polypropylene and polybutene were examined. It was found that the strain optical coefficient at low elongation for polypropylene and polybutene depends upon storage time at room temperature for quenched samples, changing sign from an initial positive value to a negative value. The change is similar to that observed upon changing temperature with polypropylene. At high elongation, the strain optical coefficient becomes positive in all cases. The change for polypropylene cannot be due to increased crystallization and does not correlate with changes in infrared spectra, x‐ray diffraction, NMR, or light scattering. X‐ray diffraction does reveal a difference in the crystal orientation mechanism for the fresh and aged sample.For the fresh sample, the c‐crystal axis tends to orient in the stretching direction, while for the aged sample, the b‐axis orients in this manner. With polybutene, the time dependence of the strain‐optical coefficient correlates with the transition in crystal structure observable by x‐ray diffraction and infrared spectra. It is proposed that the changes are related to the amount of recrystallization or crystal deformation accompanying spherulite deformation upon stretching. A simple theory of these effects is presented which contains a parameter expressing this degree of change in internal structure. It is proposed that this parameter varies with time and temperature.