Effects of kneading conditions on the dispersion of pigments in polyethylene using a continuous kneader

Abstract

The objectives in studying the effects of kneading conditions on the dispersion of pigments in polyethylene using a continuous kneader were to study the effects of the kneading temperature, the rolling temperature, the speed of rotation (twin screw), and the particle size of pigment particles on the pigment dispersion in polyethylene and to determine the suitable kneading conditions. The raw material used in the study were iron oxide (inorganic pigment) and high density polyethylene resin (HDPE). The present study used a fractal analysis method to evaluate the dispersibility of pigment in polyethylene. In addition, evaluation methods to find a simple quantitative index of pigment dispersion have been studied. The experimental results showed that the higher the kneading temperature, the higher the dispersibility of pigment in polyethylene, but at the higher kneading temperature the process becomes more of mixing than dispersion. The dispersibility of pigment increased as the rotational speed of screw increased since a higher speed provided higher intensity of shear stress to break agglomerates of pigment, so that the pigment could disperse better in polyethylene. Pigment of larger particle size was found to disperse better than the smaller one. Finally, the rolling temperature had no effect on the dispersibility of pigment. It only affected the internal structure between the pigment and polyethylene.