Factors influencing the dispersion of organic pigments in polyethylene upon using a continuous twin-screw kneader

Abstract

The present work studied the factors influencing dispersion of organic pigments in polyethylene upon using a continuous twin-screw kneader, namely, the kneading temperature, the rotational speed of twin-screw, the feed rate and the premix time, including determination of suitable kneading condition, by applying the fractal concept to evaluation of the dispersion state. The raw materials used in the study were two organic pigments, carbon black and quinacridone violet pigment, and high density polyethylene resin (HDPE). In addition, effects of the kneading conditions on the tensile properties of HDPE kneaded with either pigment were also investigated. It was found that the dispersibility of either pigment increased as the kneading temperature and the rotational speed increased, and that the higher the feed rate was. The lower the dispersion state of the pigment became. The premix time, upwards of 10 minutes of primary mixing had insignificant influence on the kneading result. As for the effect of the kneading temperature on the tensile properties of polyethylene with pigment, it was found that as the kneading temperature and the rotational speed of screw increased, the kneaded HDPE turned harder and more brittle. especially at kneading temperatures above 220℃Incidentally, comparison between the carbon black and quinacridone violet pigments revealed that the carbon black pigment, which had a smaller size (approximately one-sixth of that of quinacridone violet) and less polarity, provided more uniform dispersion state and better properties of the polymer blend.