Effects of cold-drawing and heat-setting on the structure and properties of medium speed spun polypropylene filaments

Effects of cold-drawing and heat-setting on some aspects of mechanical properties and structural parameters of polypropylene filaments spun at 3500 m/min are examined. Similar to the yam produced at low speeds, drawing changes the structure and properties of the filaments. Heat-setting increases the compactness and uniformity of micro-fibrilar structure of the filaments. Crystalline fraction as determined by the change in density and molecular orientation as measured by birefringence increase with the increase in draw ratio. True strength does not change considerably, but nominal strength increases and the breaking-extension decreases with draw ratio and heatsetting treatment. The temperature of the onset of melting as indicated by DSC examination does not effect considerably by drawing and heat-setting. The increase of crystalline fraction as measured by density is not in accordance with the results of the crystalline fraction measurement by X-ray diffraction. The trend in increase of crystallinity determined by DSC agrees with the increase of crystalline fraction determined by density.