The impact of flow induced changes of polymers density on rheological measurements

The influence of real density of polymers in molten state on the rheological values is presented. The investigations were performed by means of extrusion rheometer, using a rheological dye with exchangeable channel with various length and diameter ratio (LID). The materials used in the experiments were low density polyethylene (PE-LD), middle density polyethylene (PE-MD) and the blend of PE-LD with PE-MD in 1:1 ratio, for which p-v-T diagrams were determined. Based on p-v-T measurements the real specific volume and the density of the molten polymer in defined processing conditions (p, 7), were found (Fig. 4). Density was used for determination of the real mass flow ratio. A significant influence of the channel LID ratio on changes of density was stated (Fig. 5, Table 1). The dependence of changes of density values on the type of polymer used was confirmed.