Microcellular injection molding of in-situ modified poly(ethylene terephthalate) with supercritical nitrogen

The microcellular injection molding (commercially known as MuCell) of in-situ polymerization-modified PET (m-PET) was performed using supercritical nitrogen as the physical blowing agent. Based on design of experiment (DOE) matrices, the influence of operating conditions on mechanical properties of molded samples were studied systematically for two kinds of m-PETs, namely, n-m-PET and m-m-PET synthesized using pentaerythritol (PENTA) and pyromellitic dianhydride (PMDA) as modifying monomers, respectively. The optimal conditions for injection molding were obtained by analyzing the signal-to-noise (S/N) ratio of the tensile strength of the molded samples. The specific mechanical properties, especially the impact strength, of the microcellular samples under these conditions increased significantly. Scanning electron microscope (SEM) analyses showed a uniform cell structure in the molded specimens with an average cell size of around 35 urn. The m-m-PET modified with PMDA generated a slightly finer cell structure and a higher cell density than the n-m-PET.