Effect of pigmentation on the microstructure and properties of rotationally molded polyethylene

Rotational molding of plastics has experienced growth rates of about 12% pe r annum over the past decade. As a result, ever more demands are being plac ed on the quality of the moldings in terms of dimensional control and mecha nical properties. With most molding methods for plastics, the use of pigmen ts can have a significant effect on the quality of the product. This is par ticularly true for rotational molding because there are no stresses to assi st with dispersion of the pigment, and the slow cooling rates encourage cla ssic spherulite formation. This paper investigates the use of nucleating an d non-nucleating pigments in a rotational molding grade of polyethylene. We demonstrate that the amount of work done on the plastic prior to molding a ffects the microstructure and the mechanical properties of the end product, often in a positive manner. Turbo-blending of pigments is shown to be prob lematic, particularly if the pigment is of the nucleating type. The amount of pigment used has little effect on strength but reduces toughness dramati cally. (C) 1998 Kluwer Academic Publishers.