The rheology of PVC - An overview

Three aspects of the rheological behavior of PVC are considered. These are (a) particulate flow which occurs below the true crystalline melting point, (b) true melting flow which occurs at or above the melting point and (c) the flow of PVC compounds. The effect of structural differences, resulting from different polymerization temperatures employed in preparing different molecular weight polymere, on the melt viscosity and flow activation energy is reexamined and new data presented to unconfound the effect of syndiotacticity and molecular weight. The three flow behaviors of PVC is shown to be presented by three distinct flow regions. Because of thermal instability, the true melt flow region is only achieved with difficulty. However, in commercial operations this latter state is seldom, if ever, achieved in rigid formulations. The effect of compounding additives, especially lubricants and plasticizers and the importance of thermal and mastication history on the flow behavior is discussed with reference to the flow mechanism.