Mechanical Properties of Oriented Polystyrene Film

Abstract

Cast films of polystyrene were oriented by stretching at temperatures above the softening temperature of the material and then cooled. A factorially designed experiment was carried out in which the amount of stretching, temperature of stretching, time held in the stretched state before cooling, and effect of several cycles of stretching before cooling were investigated as they affect the birefringence, the stress‐strain properties, dynamic modulus and damping, and the softening temperature of polystyrene. The values of many of the mechanical properties are more closely related to the birefringence than to the amount of hot stretching. In general, the value of the stress‐strain properties in the direction of hot stretch, the dynamic modulus, and the birefringence all increase with an increase in the amount of stretching, a decrease in temperature, an increase in rate of cooling after stretching, and a decrease in the number of times the film was stretched before finally cooling. The softening temperature is decreased in direct proportion to the birefringence.Annealed films give higher softening temperatures than films which have been stretched and then allowed to shrink before cooling.