There are several benefits of using the supercritical fluid microcellular injection moulding process. The part weight, melt temperature, viscosity, moulding pressure, shrink/warpage, and cooling/cycle time are all significantly reduced. The purpose of this study is to investigate the rheological behaviour of PS melt dissolved SCF of nitrogen during Microcellular Injection Moulding process applied with Gas Counter Pressure (GCP) technology. The application of gas into the mould cavity prior to the melt filling provides a counter force against the melt front advancement, restricting the foaming process during the melt filling stage. A slit cavity is designed to measure the pressure drop of polystyrene mixed with 0.4wt% supercritical nitrogen fluid under different mould temperatures (185°C, 195°C, and 205°C), injection speeds (5, 10, and 15 mm/s) as well as counter pressures (0, 150, 300 bars). It was found that melt viscosity is reduced by up to 30% when GCP is increased from 50 to 150 bar as compared to conventional injection moulding. The non-nucleation mixture melt obtained by using a GCP of 300 bar has 32~49% lower viscosity. In addition, the glass transition temperature, Tg, was found to be reduced from 96 °C to 50 °C when the applied GCP is 300 bar.

In the present study, semi-crystalline polypropylene (PP) and amorphous polystyrene (PS) were adopted as matrix materials. After the exothermic foaming agent azodicarbonamide was added, injection molding was implemented to create samples. The mold flow analysis program Moldex3D was then applied to verify the short-shot results. Three process parameters were adopted, namely injection speed, melt temperature, and mold temperature; three levels were set for each factor in the one-factor-at-a-time experimental design. The macroscopic effects of the factors on the weight, specific weight, and expansion ratios of the samples were investigated to determine foaming efficiency, and their microscopic effects on cell density and diameter were examined using a scanning electron microscope. The process parameters for the exothermic foaming agent were optimized accordingly. Finally, the expansion ratios of the two matrix materials in the optimal process parameter settings were compared. After the experimental database was created, the foaming module of the chemical blowing agents was established by Moldex3D Company. The results indicated that semi-crystalline materials foamed less due to their crystallinity. PP exhibits the highest expansion ratio at low injection speed, a high melt temperature, and a low mold temperature, whereas PS exhibits the highest expansion ratio at high injection speed, a moderate melt temperature, and a low mold temperature.

This study investigated the effect of polycaprolactone (PCL) loading (0.5, 1, and 3 wt%) on the morphology, tensile strength, and thermal properties of microcellular injection molded PP/PCL and PPgMA/PCL composites. We used the filler, PCL, that is micro-material in size. Results showed that 0.5 wt% loading of PCL on foamed PP has the largest tensile strength. However, tensile strength was almost similar to that of PPgMA composites. Tensile strength depends on the filler dispersion in the matrix and cell size present on the foamed composites. Good dispersion resulted in good tensile strength. The elongation decreased on PP but increased on PPgMA composites. The highest degradation temperature for PP/PCL and PPgMA/PCL was noted for 3.0 wt% PCL loading and neat PPgMA respectively. Cell size decreased and cell density increased with the addition of PCL into the PP and PPgMA matrix.

Chitosan is a biodegradable material with good biocompatibility. It can be used in medicine, foodstuff, the chemical industry and heavy metal adsorption. In this study, an exothermic foaming agent (Azodicarbonamide) injection molded was added to polypropylene (PP), maleic anhydride (MA) grafted PP (PPgMA) and Chitosan composites. MA served as a compatibilizer due to the poor bonding between PP and chitosan. This study investigated the effects of the modifier and chitosan loading on the tensile strength, thermal properties and morphology in chemical foam injection-molded PP and PPgMA composites. The results showed that the tensile strength decreased with the addition of chitosan, but Young’s modulus increased with the added chitosan loading. The enhancement was significant for foam injection molding. The cell size decreased and the cell density increased with the addition of chitosan for the PP/PPgMA composites. The thermogravimetric analysis (TGA) results showed that the thermal degradation could be decreased with the addition of chitosan in both the PP and PPgMA composites. The use of foamed chitosan composites will be further investigated in the removal of heavy metal in waste water.