Effect of friction on the microstructure of compacted solid additive blends for polymers

The present study is concerned with the characterization of the heat generation during the pelletizing process that produces a shell/core pellet structure. Shell formation contributes to the mechanical durability of compacted pelletized additive blends and alleviates health and environmental issues by handling powder additives. A model system comprised of erucamide (low melting point component) and silica was selected for the investigation. The thermal conductivity of the model system was investigated as a function of the erucamide content. The frictional heat generated during the pelletizing process was studied by conducting tribological experiments. The results show that thermal conductivity behaves according to the rule of mixtures. Frictional heat was correlated to the depth of the shell formation examined by Scanning Electron Microscopy after testing. Temperature distributions using semi-infinite solid approximation with constant surface temperature show that the inside boundary of the shell microstructure is almost always above 70 °C. Differential Scanning Calorimetry experiments show that erucamide, the low-melting component, has an onset of melting at temperatures around 70 °C, well below its melting point (83 °C). This suggests that frictional heating generated at the surface raises temperature until onset of melting of erucamide takes place which leads to the formation of a shell/core microstructure.