Effects of processing and degree of fusion on the rheology of PVC

PVC foils made from polymer grades having K‐values of 58 and 68 have been milled at different temperatures and shear conditions on a two‐roll mill. Compression molded foils were also made from the softest grade. The resulting samples have been studied using DSC and rotational dynamic rheometry at temperatures below and above the processing temperatures. DSC confirmed the correlation between the processing temperature and the temperature T b separating endotherm A and B. However, this correlation is only valid for high processing temperatures (≥150°C). Also, if the processing temperature is lowered at the end of the processing, T b will be lower than the maximum processing temperature. In most cases the area of endotherm A increased with increasing processing temperature and shear. From measurements of tan(δ) we find that when measuring at a temperature below the lowest processing temperature, the higher the degree of fusion, the larger is the relative amount of the elastic energy stored. Measuring at a temperature above the highest processing temperatures yields the opposite result. In between there is a transition zone where polymer grades having different M̄ w respond differently to changes in thermomechanical processing history. These and other observations are discussed in terms of the gel‐destruction temperature introduced by Lyngaae‐Jørgensen, the breakdown of the particulate structure, and the creation of a three‐dimensional fusion network held together by ordered and crystalline regions.