Shrinkage and warpage of injection-molded parts can be minimized by applying microcellular foaming technology to the injection molding process. However, unlike the conventional injection molding process, the optimal conditions of the microcellular foam injection molding process are elusive because of core differences such as gas injection. Therefore, this study aims to derive process conditions to minimize the shrinkage and warpage of microcellular foam injection-molded parts made of glass fiber reinforced polyamide 6 (PA6/GF). Process factors and levels were first determined, with experiments planned accordingly. We simulated designed experiments using injection molding analysis software, and the results were analyzed using the Taguchi method, analysis of variance (ANOVA), and response surface methodology (RSM), with the ANOVA analysis being ultimately demonstrating the influence of the factors. We derived and verified the optimal combination of process factors and levels for minimizing both shrinkage and warpage using the Taguchi method and RSM. In addition, the mechanical properties and cell morphology of PA6/GF, which change with microcellular foam injection molding, were confirmed.

This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the improvement of this phenomenon according to the glass fiber content (GFC), two factors associated with the reduction of the shrinkage difference and the non-directionalized fiber orientation were set as variables. The shrinkage was measured in the flow direction and transverse direction, and it was confirmed that the shrinkage difference between these two directions is the cause of warpage of GFRP specimens. In addition, by applying the MCP to injection molding, it was confirmed that warpage was improved by reducing the shrinkage difference. To further confirm these results, the effects of cell formation on shrinkage and fiber orientation were investigated using scanning electron microscopy, micro-CT observation, and cell morphology analysis. The micro-CT observations revealed that the fiber orientation was non-directional for the MCP. Moreover, it was determined that the mechanical and thermal properties were improved, based on measurements of the impact strength, tensile strength, flexural strength, and deflection temperature for the MCP.

Wood chips from furniture-manufacturing byproducts, which do not include adhesive or paint in the waste wood, were used for the flouring process and chemical modification of wood flour (WF). After chemical modification, the WF was mixed with polypropylene through extrusion compounding and injection-molding to prepare wood-plastic composite (WPC) injection-molded specimens for the American Society for Testing and Materials. Static contact angle measurements and stereomicroscope observations were performed. In this study, it was confirmed that the impact strength was improved by up to 55.8% and the tensile strength by up to 33.8%. The flexural modulus decreased marginally. As a result of WF chemical modification, the measured contact angle of WPC increased, which means that the wettability of the WPC specimen surface decreased. In addition, it was observed through stereomicroscopy that the whitening of the surface of the WPC specimen improved.

Foaming technology used in the plastic production process makes it possible to reduce costs and lighten the products, which is why this technology is widely used. Foaming technology is generally categorized as involving either a “Chemical Foaming Process” or a “Physical Foaming Process,” the latter also referred to as a “Microcellular Foaming Process” (MCP). In both processes, gas particles dissolved inside a polymer create cells. For the chemical foaming process, chemical blowing agents are mixed with plastic pellets, whereas for MCPs, gas is directly supplied to a polymer melted inside the barrel of an injection molding machine. The cell morphology changes when either the chemical foaming process or the MCP is applied in an injection foaming process. This study aims to compare and analyze the change of the cell morphology in such a case. In particular, Poly Lactic Acid (PLA) is used in the experiment. In this study, the foaming characteristics of a biodegradable material (PLA) and a convectional material – Acrylonitrile Butadiene Styrene (ABS) – are compared and analyzed. The analysis of the experiment results is done based on an analysis of the foaming ratio and a comparison of the cross-section of the cell morphology of specimens under different experimental conditions. For the former, a weight comparison was made, while for the latter, a scanning electron microscope (SEM) was utilized.

In this work, a high-magnification extrusion-foaming technique for biomass-based biodegradable composite materials using water vaporization was examined. Starch was selected as the biomass and polylactic acid was selected as a biodegradable matrix resin. No additional plasticizer or additives were used in this extrusion-foaming process. The foaming ratio was deduced according to the conditions of the extrusion-foaming process to confirm the forming characteristics of the foaming materials. Scanning electron microscopy was performed to examine the morphology of the composite foam. To investigate the potential of the foam cushion as an ecofriendly packing material, we conducted experiments on its static compression and dynamic cushioning properties and examined whether its biodegradability could be controlled by varying the mixing ratio of the materials. Thus, we developed a water-foaming process that is ecofriendly and whose products can be recycled as compost after use.

The shrinkage of reinforced polymer composites in injection molding varies, depending on the properties of the reinforcing agent. Therefore, the study of optimal reinforcement conditions, to minimize shrinkage when talc and glass fibers (GF) (which are commonly used as reinforcements) are incorporated into polypropylene (PP), is required. In this study, we investigated the effect of reinforcement factors, such as reinforcement type, reinforcement content, and reinforcement particle size, on the shrinkage, and optimized these factors to minimize the shrinkage of the PP composites. We measured the shrinkage of injection-molded samples, and, based on the measured values, the optimal conditions were obtained through analysis of variance (ANOVA), the Taguchi method, and regression analysis. It was found that reinforcement type had the largest influence on shrinkage among the three factors, followed by reinforcement content. In contrast, the reinforcement size was not significant, compared to the other two factors. If the reinforcement size was set as an uncontrollable factor, the optimum condition for minimizing directional shrinkage was the incorporation of 20 wt % GF and that for differential shrinkage was the incorporation of 20 wt % talc. In addition, a shrinkage prediction method was proposed, in which two reinforcing agents were incorporated into PP, for the optimization of various dependent variables. The results of this study are expected to provide answers about which reinforcement agent should be selected and incorporated to minimize the shrinkage of PP composites.