In the spinning of polypropylene the “smectic” phase generally appears in the as spun fibres obtained from high fluidity polypropylene (for example Mw = 118000) at 200°C and more. The amount of the “smectic” form decreases as the draw down ratio increases. At 200°C and for a draw ratio of 40 the “smectic” form is about 70% of the crystalline phase. At 200°C and for a draw ratio of to 130 or higher, only the monoclinic form is observed. At 180°C, and whatever is the draw ratio, only the monoclinic form is observed. For high-molecular - weight polypropylene (for example Mw = 320000) the “smectic” form has never been observed whatever is the spinning temperature within the range 220–260°C. The fibres with high amount of smectic phase show low orientation factors, whereas the fibres having only monoclinic form show the highest orientation factors. These results, compared with elongational behaviour of the polypropylene, suggest that the smectic form appears in the fibres as the elongation rate on the spinning line is lower than the relaxation rate of polypropylene chains.
