Influence of displacement rate, stress orientation and stress history on birefringence properties of polyvinylidene chloride

Abstract

Understanding stress or strain distribution or birefringence properties is important for proper industrial application of polymer films. For example, it is very important to control the stress and birefringence distribution in polymer films that are used for liquid crystal displays of PCs or smart phones, etc. for their performance improvement. As another example, it is very important to understand the stress distribution in packaging polymer films for reliability management of the package because the forming accuracy depends on the stress distribution in the films. Photoelastic analysis is suitable to understand stress, strain distribution and birefringence properties on polymer films; however, understanding of the stress-optical or strain-optical coefficients of the polymer is indispensable when using the analyzing method. In this study, the influence of displacement rate, stress orientation and stress history on birefringence properties is measured for polyvinylidene chloride (PVDC) at room temperature as an example of semi-crystalline polymer films. The stress-optical coefficient of PVDC depends on the displacement rate, stress orientation and stress history. On the other hand, the strain-optical coefficient of PVDC is approximately independent of them. These phenomena are explained by the result from the viscosity, polymer chain orientation and strain-induced crystallization in PVDC. There is potential given that strain-optical coefficients for semi-crystalline rubbery polymers are approximately independent of the displacement rate, stress orientation and stress history on some conditions because of the mechanism of the phenomenon.