EXTRUDED OPEN-CELLED LDPE-BASED FOAMS USING NON-HOMOGENEOUS MELT STRUCTURE
Chul B. Park, Valentina Padareva, Patrick C. Lee, Hani E. Naguib
Microcellular Polymer Manufacturing Laboratory, Dept. of Mech. and Ind. Eng. U of Toronto
Canada

Keywords: open-cell, cross-linking, extrusion

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This paper presents an open-celled foaming extrusion process with low-density polyethylene (LDPE) and LDPE/polystyrene (PS) blends. The basic strategy for achieving a high open-cell content was to induce a hard/soft melt structure with cross-linking and to foam this non-homogeneous melt structure. The hard sections formed by cross-linking assist in maintaining the shape of each cell and the overall foam structure while the soft sections easily open up the cell walls during cell growth. Since too hard a polymer matrix adversely affects cell opening, an optimum amount of cross-linking was observed for cell opening. The effect of the processing temperature on cell opening was also investigated in this study. A large expansion ratio of foam at a low temperature was favorable for cell opening with thin cell walls, but too low a temperature was not desirable because of the increased melt strength. On the other hand, too high a temperature was not desirable either because of the lowered expansion ratio. This optimum processing temperature for cell opening has been experimentally verified at various contents of a cross-linking agent. A high open-cell content up to 99% was successfully achieved at the processing temperature around 110oC using the optimum material composition. The morphologies and volume expansion ratios of open-cell foams were obtained at various processing conditions.