Principal Correlation of PVC Melt Elongational Properties with Foam Cell Morphology

A lab-scale method developed in this work offers new possibilities to polymer foam manufacturers to significantly reduce the number of experiments required on production extruders to optimise PVC foam formulations. Rheotens elongation experiments were applied to analyse PVC foam formulations without a blowing agent with regard to their melt elongational properties such as melt strength and elongation at break. The uni-axial state of deformation represented by these experiments offers an approximation of the melt behaviour in a multi-axial deformation such as foam extrusion. The evaluated foam formulations were foamed on an extruder under identical processing conditions and the resulting cell morphologies were investigated by Scanning Electron Microscopy. Image analysis of the obtained SEM-images confirmed a principal correlation between the melt elongational properties and the foam cell morphology. It appears, that the PVC melt strength mainly influences the mean cell size and the cell size distribution. In addition, the fraction of open cells is decreasing with increasing melt strength.