EFFECT OF DRAWING DIFFERENT MFI POLYPROPYLENE FILAMENTS ON A GRADIENT HEATER

Abstract

High-modulus and high-tenacity polypropylene fibres were prepared by drawing as-spun filaments on a heater with a temperature gradient. The results on two different MFI PP show that the fibre properties are significantly affected by the temperature profiles at the final stage of drawing on a gradient heater. High crystal perfection and crystallinity at very high draw ratios have been obtained for the gradient drawn fibres. The gradient drawn filaments showed superior mechanical properties when compared to filaments drawn over a constant temperature heater. Fibres with an initial modulus of 16.4 GPa and tenacity of 875 MPa were obtained in the process. The molecular weight of the parent material significantly influenced the mechanical properties of the material. High molecular-weight (low MFI - Melt Flow Index) materials are characterised by comparatively lower modulus but higher tenacity values. High draw ratios were possible for the higher MFI samples, leading to more orientation and modulus.