Manufacturability of Fine-Celled Cellular Structures in Rotational Foam Molding

Abstract

Any closed-cell polyolefin foam production tends to achieve the highest possible cell size distribution uniformity, cell size reduction, and cell density augmentation. However, 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 results in coarser-celled final cellular structures. Although a fine-celled morphology (cell size<100 [mm] and cell density > 10⁶ [cells/cm³]) in rotationally molded foams has been closely approached, it has not been actually achieved yet, nor has it been ever clarified whether it is actually achievable in rotational foam molding or not. This study 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 nonpressurized polymer melts originating from extrusion melt compounded foamable resins in a pellet form.