In this study, we developed a foaming control system using the Gas Counter Pressure (GCP) combined with mold temperature control during the microcellular injection molding (MuCell) process and investigated its influence on the parts' surface quality and foams structures. The results revealed that under GCP control alone when GCP is greater than 10 MPa, part surface roughness for transparent polystyrene (PS) improved by 90%. When GCP increased, the skin thickness also increased, the weight reduction decreased and the average cell size reduced to about 30 lm. For black PS parts, when GCP is greater than 10 MPa, the part gloss reaches the same value as that molded by conventional injection molding. By increasing gas holding time, the cell density decreased and the cell size distribution became more uniform. The increase in amount of supercritical fluid foaming agent also increased the cell density. Applying mold temperature control alone with temperature in the range of 90-120 C (near T g ), the surface roughness improved by 65%. Increasing mold temperature decreased the skin thickness; however, the cell size distribution became significantly nonuniform. It was found that thin skin, small and uniform cell size as well as good surface quality can be achieved efficiently by simultaneous combining of GCP and mold temperature control. The proposed innovative approach may lead to a significant improvement and a more broad application for MuCell process.
This study investigated the influence of montmorillonite (MMT) content on the mechanical/thermal properties of microcellular injection-molded polylactide (PLA)/ clay nanocomposites. Carbon dioxide was the blowing agent. The PLA/MMT nanocomposites were prepared by twin screw extrusion. The results showed that as MMT content is increased, tensile strength, impact strength, and cell density decrease. This is caused by the speed degradation of PLA due to the addition of MMT. MMT decreases the crystallization temperature but increases the decomposition temperature of the nanocomposites. The XRD results showed that the layer spacing of the clay increases as MMT content increases. TEM pictures showed that the MMT is well dispersed within the PLA matrix.
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