Rheological behaviour of polypropylene blends utilized in foaming process

Abstract

Morphological structure of polypropylene foams represented by the size of the bubbles and bubbles density is significantly affected by rheological properties of the source materials. Various blends of high molecular weight and high melt strength polypropylenes were prepared in a twin screw extruder, and subsequently foamed. Their shear flow behavior as well as strain hardening during elongation were found to be the factors of a key importance in foaming process optimization. In addition, pressure dependent shear flow behavior of the tested materials was determined using capillary rheometer modified with backpressure chamber, and obtained dependencies of shear viscosity on pressure conditions were analyzed in order to further tailor blend compositions regarding their following use in foaming processes. It has been demonstrated that foam morphology might be controlled not only through degree of bubble coalescence and nucleation rate by the help of optimizing of material components ratio, but also via setting the proper processing conditions.