Extrusion rheology of rigid PVC

Abstract

PVC is a very versatile thermoplastic. Unfortunately, its potentialities often cannot be realized in practice because of the difficulties encountered in processing. For instance, successful extrusion is possible only in a limited range of conditions and with the use of processing aids. If processing temperatures and shear stresses are loo low, or residence times in the screw are too short, one obtains what is sometimes called “insufficient plastification”. This results in products with poor mechanical properties. If, on the other hand, processing temperatures are too high or residence times are too long, degradation of the PVC occurs which again leads to an unsatisfactory product. These restrictions only leave a small range of conditions where rigid PVC can be processed successfully. Even then, it is necessary to add processing aids such as stabilizers to retard the degradation process, and lubricants which are thought to facilitate powder transport and melt flow. In this situation a better insight into the influence of processing conditions and processing aids on the rheological properties of PVC melts and on the mechanical properties of PVC products seems highly desirable.