Design and fabrication of expandable cavity injection mold for open cell microcellular foam

Abstract

Microcellular injection molding (MIM) of thermoplastics is a challenging molding process compared to conventional injection molding (IM) process because of its narrow processing window. As far as microcellular molding of open-celled foam is concerned, it is much more difficult because of extremely narrow processing window for open-cell foam and transient nature of melt temperature and pressure inside cavity during the molding process. However, it is expected that molding of open-celled microcellular foam may open many new areas such as tissue engineering, drug delivery, reverse osmosis, dialysis membranes, and fuel cell. The production cost may also be reduced manifolds. In present work a novel expandable cavity mold (EC mold) was designed and fabricated. EC mold has some nonconventional features like pneumatically actuated gate seal, mechanism for cavity expansion, and arrangement for cyclic heating-cooling of core and cavity blocks. In present study polylactic acid (PLA), a biodegradable polymer, was used and expandable cavity molding (EC molding) variables, namely, cavity expansion rare (mm/s), cavity expansion distance (mm), and cavity expansion-compression-expansion (ECE) profile mode, were studied. The results confirm molding of PLA foams with very high cell density and impinged structure. The micrographs and open-cell ratio confirm the formation of PLA foam with ~40% open-cell content.