Thermoluminescence study of the crystal modifications of polypropylene fibres

Polypropylene fibres with different crystal modifications were investigated using thermoluminescence (TL). Unirradiated, ultraviolet-irradiated and γ-ray-irradiated fibre specimens were studied from room temperature to 200°C. It was found that the glow curves obtained for fibres with both monoclinic and pseudohexagonal modifications have a sharp peak at the melting temperature, but the glow intensities for the fibres with the pseudohexagonal modification were much stronger than for the monoclinic ones. The TL glow peak at the melting temperature for the specimens with the pseudohexagonal modification was found to extend to a temperature as low as 100°C, suggesting that the characteristic molecular motion may occur during the transition of the crystal modifications. In addition, a weak TL peak was detected at about 65°C for the γ-ray-irradiated specimens, which corresponds to the temperature at which polypropylene achieves its maximum crystallization rate constant.