Abstract
Three kinds of polypropylene were melt spun using the straight die of 0.45mm diameter with 5mm length in the temperature range of 190 to 350°C at the rate of output 0.765cc/min. Details of the sample are following; Four fractions, ranging in molecular weight from 1.07×104 to 74×104 (I), five thermally degradated polypropylenes having molecular weight of 3.2×104 to 30.6×104 (II), of which the details of the preparation were described in the other paper (Kamide, Inamoto and Ohno; J. Chem. High Polymer, 22, 597 (1965)) and unfractioanted polypropylene (_??_=31.7×104) (III). Maximum draft ratio (MDR) is defined as 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. Relationship between MDR and spinning temperature (at die) (ST) closely depends on molecular weight (MW). Minimum MW having fiber formability is about 3×104 and in this case, the range of temperature suitable for melt spinning (RST) is extremely narrow (190±0.5°C). Although RST becomes wider with increased MW, RST becomes narrower again in the range _??_=40×104. Lower limit of ST, at which the continous melt spinning is possible becomes higher with increased MW. Most of the elongational deformation during the spinning ceases within 20cm. under the die, where the elongatioal viscosity is low. In the more deformed parts, the negligible orientation is observed by the birefringence measurement. The orientation may be attained after solidification and crystallization is completed. Since Poisson ratio of molten polypropylene estimated by using values of the compressibility and the Young's modulus is 0.5, the elongational viscosity at the outlet of the die is calculated as three times the shear rate viscosity (at the die-wall, shear rate is 103 sec-1 in this study), utilizing the results reported (Kamide, Inamoto, Ohno; J. Chem. High Polymer, 22, 529 (1965)) and assuming the apparent activation energy of melt flow of polypropylene as 8kcal/mole. Iso-elongational-viscous state was approximately attained at the optimum spinning temperature. when the temperature of atomosphere near the die is cooled, reduction of spinnability is observed at each spinning temperature, although the optimum spinning temperature does not change as far as the same sample was spun.
