Combined effect of the nature of the filler and the compatibilizer on the weld line properties of filled blends

The mutual effect of the nature of the filler and the compatibilizer on the properties of a ternary blend based on polypropylene (PP) polyamide-6 (PA) and an inorganic phase is investigated. Low aspect ratio irregular shaped CaCO3 and high aspect ratio plate-like talc are selected as inorganic phases. The effect of different filler levels on the morphology of the weld line region and the region far from the weld line are studied while special attention is paid to both uncompatibilized and compatibilized PPPA blends with maleic anhydride grafted polypropylene (MA-g-PP). It is observed from scanning electron microscopy (SEM) studies that plate-like talc reduces the elongated domain size in the weld line region much more effectively than low aspect ratio CaCO3 for uncompatibilized filled blends. Although both filler are selectively wetted by the dispersed PA phase, the morphology homogenization in the weld line region is found to be related to the ability of the filler to reduce the elongated domain size by increasing the viscosity of dispersed phase rather than the shape of the filler. The selective wetting of talc particles by the PA phase seems to be beneficial in increasing weld line strength by increasing the viscosity of the PA dispersed phase with respect to filler content much faster than CaCO3. However, the additional compatibilization effect causes much finer, homogeneous spherical PA/ CaCO3 domains dispersed within the PP matrix compared to plate-like PA/talc domains, which are highly oriented at the weld line. For that reason, the shape of the filler is of predominant importance to achieve homogeneous morphology in the weld line region. Compared to uncompatibilized filled blends, low aspect ratio irregular shaped CaCO3 yields better weld line strength with respect to all filler levels. For compatibilized PPPA filled blends, the shape of the filler is of supreme significance in order to achieve better mechanical properties especially where weld line properties are concerned.