During the microcellular foaming extrusion process, the cell density in the foam could be increased by shear effects due to improved shear energy, which contributes to the free energy for bubble nucleation. However, the cells might also be deformed when the shear stress is high. In order to increase the cell density without destroying the cell structure, mechanical vibration induced by electromagnetic field is introduced into the foaming process. A novel electromagnetic dynamic foaming simulator has been designed to investigate the effects of vibration amplitude and frequency on cell density and cell morphology of foam samples during the dynamic foaming process for polystyrene (PS) microcellular plastics when using supercritical carbon dioxide (ScCO₂)as a blowing agent. Optimal foaming temperature, gas mixing time, and appropriate shear rate are also investigated when using the dynamic foaming simulator. It was found that excessive shear effects in the stable foaming process will stretch the cells in the direction of shear stress and decrease the cell density. However, when the vibration is introduced into the foaming process at optimal foaming temperature and appropriate gas mixing time, the cell diameter can be decreased and cell density can be increased at a lower shear rate, while the cells can maintain the spherical shape, since the total shear energy is increased, but the shear stress in the direction of the melt flow is not sharply increased.

Morphological evolution under shear, during different injection processes, is an important issue in the phase morphology control, electrical conductivity, and physical properties of immiscible polymer blends. In the current work, conductive nanocomposites were produced through three different injection-molding methods, namely, conventional injection molding, multi-flow vibration injection molding (MFVIM), and pressure vibration injection molding (PVIM). Carbon nanotubes in the polyamide (PA) phase and the morphology of the PA phase were controlled by various injection methods. For MFVIM, multi-flows provided consistently stable shear forces, and mechanical properties were considerably improved after the application of high shear stress. Shear forces improved electrical property along the flow direction by forming an oriented conductive path. However, shear does not always promote the formation of conductive paths. Oscillatory shear stress from a vibration system of PVIM can tear a conductive path, thereby reducing electrical conductivity by six orders of magnitude. Although unstable high shear forces can greatly improve mechanical properties compared with the conventional injection molding (CIM) sample, oscillatory shear stress increases the dispersion of the PA phase. These interesting results provide insights into the production of nanocomposites with high mechanical properties and suitable electrical conductivity by efficient injection molding.