In situ simultaneous measurement of stress, retardation, and three-dimensional refractive indexes during biaxial stretching experiments under various preheating times

Abstract

Abstract An evaluation method for the stretchability of a biaxially oriented film during the stretching process was recently developed using an in situ measurement test machine. Stress, retardation, three-dimensional refractive indexes, light-scattering image, and birefringence distribution of films could be obtained in a short time. This stretching test machine was applied to examine the film stretchability of both semicrystalline polymers, such as polypropylene, and noncrystalline polymers, such as polystyrene, under various preheating times. From the measurements, the stress of semicrystalline polymers increased with increasing preheating times before stretching the film. However, the stress of noncrystalline polymers did not increase with increasing preheating times. This means that semicrystalline polymer is required to set up an optimum stretching condition of the preheating time for a satisfactory biaxially oriented film. Furthermore, the birefringence distribution and thickness uniformity of the stretched film were measured simultaneously. It was found that the stretchability of polypropylene and polystyrene films could be evaluated with a small piece of the sample using the biaxial stretching test machine.