Document Abstract
ANTEC Papers: 2003
Manufacturability Of Fine-Celled Cellular Structures In Rotational Foam Molding
Chul Park, Donglai Xu, Remon Pop-Iliev
The control of the cell size of rotationally foam molded cellular structures formed on the base of a chemical blowing agent (CBA) might be often aggravated by some inherent limitations that are unique to the rotational molding process which yield coarser-celled final cellular structures. Since a fine-celled morphology in rotationally molded foams has been closely approached, but has not been actually achieved yet, it is hypothesized that the retention of fine-celled foam morphologies in rotational foam molding is being precluded by the fact that the CBA-blown bubbles having cell sizes less than 100 microns shrink and ultimately dissolve in the non-pressurized viscous polymer melt before the time at which its temperature can be reduced to the point of crystallization. However, it has never been clarified in a scientific manner whether a fine-celled morphology is actually achievable in rotational foam molding or not. This paper attempts to provide an answer to this fundamental question by focusing on the understanding of the mechanisms governing the formation, growth, shrinkage, and collapse of CBA-blown bubbles in non-pressurized polymer melts originating from extrusion melt compounded foamable resins in a pellet form. A detailed theoretical model involving diffusion, surface tension, and viscoelastic effects has been developed to simulate the bubble lifespan in rotational foam molding and investigate its effect on the cell morphologies of the final foams. It has been found that the preferred fine-celled bubbles seldom reach the solidification stage of the inherently lengthy rotational molding cycle because of their significantly shorter lifespan.