Influence of polymer-particle-interaction on the flow behavior of highly filled plastics

Adding fillers to polymers can lead to highly functional materials and thereby to 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 which has to be overcome by a higher pressure in plastic processing. Besides the amount of filler the flow behavior of highly filled polymers depends on the filler itself and its particle shape. Especially the aspect ratio plays an important role. Another 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. Polylactide (PLA) was used as matrix whereas copper was used as filler material in different amounts up to 30 vol.-%. Copper was chosen because it is available in similar sizes in spherical, platelet or fibrous shape regarding the influence of the aspect ratio. Rheological investigations were done on a plate-plate rheometer while the interactions were investigated using differential scanning calorimetry. The results 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 only a minor interaction between polymer chains and filler surface. This leads to the conclusion that the change in flow behavior is mainly caused by a direct interaction between the particles.