Rigid amorphous fraction caused by particle-polymer-interaction in highly filled plastics

Adding fillers to polymers allows highly functional materials and thereby properties like electrical conductivity that are not achievable by polymers themselves. But higher amounts of fillers cause an increase in viscosity and thus a change in flow behavior which in turn induces difficulties in plastic processing. Above a certain value (percolation threshold), there is a flow restriction. An important factor is the combination of the polymer and the filler and whether there are any interactions between each other. By differing the amorphous phase of polymers into a rigid amorphous and a mobile amorphous fraction, predictions about interactions are possible. The objective is the generation of such a flow restriction and the combined investigation of a polymer-particle-interaction. Polypropylene (PP) was used as matrix whereas minerals were used as filler materials in different amounts up to 40 vol.-%. SiO2 was chosen because it is available in different spherical sizes. Rheological investigations show that a higher aspect ratio leads to a faster increase in viscosity achieving the rheological threshold. As a result of the caloric investigations, the highly filled plastics show no interaction between polymer chains and filler surface. This leads to the conclusion that the change in flow behavior is mainly caused by direct interaction between the particles.