Study of Foaming Morphology in Microcellular Injection Molded TPU/MWCNT Composites under Gas Counter Pressure

Due to the global environmental issues, microcellular injection molding (MuCell) process with the advantages of the energy saving, environmentally friendly and light weighting has become more and more popular in industry. In order to improve the common defects of uneven cell size and cell rupture in MuCell, this study aims to ameliorate the issues of excessively large open-cell structure and density reduction caused by cell rupture in MuCell with thermoplastic polyurethane (TPU). TPU 1185A supplied by BASF was selected as the material, to which multi-walled carbon nanotubes (MWCNT) were added and a gas counter pressure (GCP) control was applied, subsequently. The cell structure change was observed via scanning electron microscope (SEM). The results showed that adding nanotubes to TPU can increase the viscosity of the polymer melt and lower the average cell size, which will significantly reduce the number of cells with a diameter greater than 100 μm. With the GCP technique employed, the overall cell size was further reduced as well as the number of cells with a diameter greater than 100 μm, and the cell density was further increased.