BEHAVIOUR OF ELONGATION OF POLYPROPYLENE FILMS UNDER SEVERAL TEMPERATURES

Abstract

Microscopic observation and measurement of stress-strain relation are done under several temperaturec for polypropylene films classified by size of spherulites with which the films are consisted. The results are as follows:(1) Breaking sections of films of large spherulite and moderate spherulite are the boundary between spheruites at 20°C, while films of small ones have no boundary such as large and moderate ones have.(2) Their values of elastic moduli are lowered as temperature increases.(3) Films of large and moderate spherulites show step-wise reduction of stress against strain after passed the point of maximum stress (yield stress) above 60°C while films of small ones show almost constant stress against strain after passed the point of maximum stress. The step-wise reduction of stress may correspond with such mechanisms of elongation observed by the microscope as making holes in the partially elongated areas of film.(4) The film of small spherulites has the greatest values of yield stress and strain at the selected temperatures.