In this paper, a study on the batch processing and characterization of microcellular foamed high-density polyethylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 109 cells/cm3 and fully grown cells smaller than 10 µm. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming. (citation # 293)

In this study, processing-structure relationships in expanded polystyrene (EPS) made using near-critical carbon dioxide as a physical blowing agent were investigated. In order to investigate the relationship between structure and properties of EPS it was necessary to be able to make samples with a wide range of controlled structures. For this reason, a systematic investigation of the relationship between processing conditions and structure was performed based on a statistical experimental design. Regression analysis was conducted on the data and expressions were developed to quantify the relationships between structural parameters and processing conditions. The samples were saturated with carbon dioxide at relatively high pressure and ambient temperature and the saturated specimens were expanded at elevated temperatures. The importance of the individual processing parameters was determined. Statistical analysis of data showed that foaming time was the most important factor determining foam density, whereas saturation pressure was the most important factor determining cell size and cell density. By controlling the foaming conditions, EPS samples having the same densities and different cell sizes were produced. (citation # 52)