EFFECTS OF MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION ON FIBER SPINNABILITY OF POLYPROPYLENE

Abstract

This paper is concerned with the effects of melecular weight distribution (MWD) on fiber spinnability of polypropylene. Five kinds of polypropylene were melt-spun using the straight die of 1.00mm diameter with 5mm length in temperature range of 190_??_350°C at the rate of output 0.765cc/min. Details of the sample are following: Three blends (I) having nearly same viscosityaverage molecular weight _??_=1.8×105, ranging in breadth of MWD represented by the ratio of weight-to number-average molecular weight _??_ from 1.2 to 2.0 which were prepared from fractions by mixing in solution, a whole polymer (II) having _??_=3.2×105 and _??_=3_??_4, whole polymer (_??_=1.97×105) (III) from which about 10% of the lower and higher molecular weight portions were removed, respectively, a fraction (IV) having _??_=2.5×105, a fraction (V) added as much as 10% of lower molecular weight fraction (_??_=2.4×104) to (IV). According to the method described in the preceeding paper (Kamide, Inamoto; This journal, 23, 79 (1967)), maximum draft ratio (MDR), i.e. the ratio of the linear velocity at the die-wall to that at the winding wall, at which the continuous melt spinning becomes abruptly impossible, was determined as the parameter of spinnability. Spinning temperature, at which MDR>103 holds, increases with _??_ On the other hand breadth in the range of the spinning temperature corresponding to MDR>103 is independent of _??_. The optimum temperature of melt spinning (OST) is defined as the temperature at which MDR reaches maximum. OST is found to be a kind of material parameter depending on molecular weight and MWD and independent of the spinning conditions. (MDR)max of (I) is qualitatively identical with that of (IV), however, (MDR)max of (II) is by far smaller in comparison with (I) and (IV). Removal of both lower and higher molecular weight portions from the whole polymer makes (MDR)max larger and addition of lower molecular weight portion to fraction makes (MDR)max smaller. (MDR)max of the former ((IV)) is almost the same as that of (I) and (MDR)max of the latter ((V)) is almost the same as that of (II). It became evident from the experimental results described above that the contamination of the lower molecular weight portion which has no spinnability if it were melt-spun by itself is remarkably responsible for the spinnability of polypropylene.