Triboelectrification of molten linear low-density polyethylene under continuous extrusion

The triboelectrification of molten linear low-density polyethylene under continuous extrusion through brass and stainless steel dies was studied in this work within a temperature range from 180 to 210 °C. The electric charge build-up was only observed during the extrusion through the brass die at all the temperatures studied and is attributed to slip at the die wall, namely, to a dynamic friction between the polymer melt and the die wall. The magnitude of the electric charge in the melt increased along with temperature and was dependent on the flow conditions (shear stress and sliding velocity). The electric charge exhibited a maximum for each studied temperature; the lower the temperature the lower the shear stress at which the maximum appeared. The results in this work suggest that such maxima and the further reduction in the electric charge as the shear stress is increased stem from a decrease of the contribution of slip to the average fluid velocity, because of shear thinning in the melt. Finally, friction curves were monotonic for all the temperatures and shear rates studied.