Rheological analysis of polyvinyl butyral near the glass transition temperature

In many polymer manufacturing operations, the material is processed near th e glass transition temperature (T-g). Examples are thermoforming, blow mold ing, film blowing, hot embossing, forging, plastic welding, and de-airing i n safety glass lamination. In these processes, solid-like behaviors such as strain hardening and yielding play important roles. These material propert ies cause the material to flow (or deform) in a way that substantially diff ers from a polymer melt. In order to understand the flow behavior near the T-g, polyvinyl butyral (PVB), a rubbery polymer used in safety glass lamina tion, was studied in this work. The flow properties of the polymer above th e T-g were characterized by using both shear and elongational rheometers, a nd a tensile tester. The measured flow properties were described by a visco elastic constitutive model.