LOW-TEMPERATURE PROPERTIES OF HARD ELASTIC POLYPROPYLENE FIBERS

The temperature dependence of hard elastic polypropylene fibre was studied in the temperature range -140-degrees-C to 20-degrees-C. The third yield point was found on the stress-strain curve below the glass transition temperature, as were the first and second yield points. The yield behaviours for the first and third points depended strongly on the temperature and changed remarkably at the glass transition temperature. The first, second and third yield behaviours were associated with, respectively, the initial deformation of the total stacked lamellar structure, the onset of unfolding of the lamellar crystal, and the deformation of the amorphous chains between lamellae after the lamellar separation.