Factors affecting the heptane solubility of polypropylene polymers and yarns

摘要

AbstractThe heptane solubility of polypropylene yarns prepared under a variety of experimental conditions from several molecular weight ranges of polymers has been examined. The heptane solubilities of the yarns have been found to vary over a wide range, depending upon the conditions of extrusion during fiber formation and the subsequent degree of orientation of the fibers. The solubility of the yarns increases with higher spinning temperatures presumably as a function of the formation of low molecular weight soluble fractions formed as a result of thermal degradation. A reduction in the solubility occurs as the yarns are oriented either during the winding operation or by subsequent drawing. The reduced solubility has been explained on the basis of increased molecular alignment thereby promoting increased crystallinity as well as the possible entrapment of normally soluble atactic polymer. The fact that the polymer solubility can be decreased by bringing the polymer to a higher state of crystallinity has been shown by annealing studies. The solubilities of the original polymers, therefore, exhibit little correlation with the yarns produced from them. The solubilities of the annealed polymers, however, more closely approach the values obtained for the highly oriented yarns.