Plastic deformation of polypropylene VII. Long period as function of temperature and rate of drawing

Polypropylene fibers prepared by quenching in ice-water were drawn at 25, 80, 120, and 140°C to a draw ratio between 6 and 8 at draw rates 0.05, 0.5, 5, and 50 cm/min. The long period increases almost linearly with the draw rate for drawing at 25°C and decreases for drawing at higher temperatures. The effect in the latter cases is an annealing effect. As a consequence of the shorter exposure of the drawn fibers to the high temperature at higher draw rate, the long-period growth proceeds for a shorter time and hence results in a smaller increase of long period. At 25°C, however, the long-period growth is negligible. The increase of long period with draw rate is the consequence of higher adiabatic heating as calculated from the energy input during the plastic deformation which transforms the spherulitic into the fibrous structure. One concludes that the long period established during this transformation depends on the maximum temperature reached in the micronecking zone and not on the macroscopically observed temperature of the sample in the neck.