Extruded Open-Celled LDPE-Based Foams Using Non-Homogeneous Melt Structure

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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 crosslinking and to foam this non-homogeneous melt structure. The hard sections formed by crosslinking 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 would adversely affect cell opening, an optimum amount of crosslinking 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. This optimum processing temperature for cell opening was experimentally verified at various crosslinking agent contents. Blending with a small amount of PS turned out to be effective for cell opening; it yielded a higher cell density, which caused thinner cell wall thickness. Optimizing the material compositions and processing temperature successfully achieved a high open-cell content up to 99%.