The application of melt elasticity measurements to polymer processing

In recent years there has been increasing recognition of the importance of melt elasticity in polymer processing. A new instrument has been developed that determines the elastic properties of polymers in the melt state by measuring both the stress relaxation and strain recovery characteristics as a function of applied rate of strain, temperature, and magnitude of applied strain. Data on several different polymers will be presented together with examples of the significance of melt elasticity in such processing operations as thermoforming, blow molding, and film forming. A material parameter that is very important in the processing of polymers such as polystyrene and poly(methylmethacrylate) is the transition above the glass transition, Tg, referred to as the liquid‐liquid transition, TII. At this transition there is an abrupt change in the elasticity of the melt. Processing above or below this transition produces products with very different end use properties.