Mould Foaming Of Polymers With Supercritical CO₂

This work was aimed at studying mould foaming of polymers including PS, PP and PET using supercritical CO2as the blowing agent. The effects of the processing conditions on the expansion ratio and the microcellular morphology were investigated. The result showed that microcellular PS could be prepared by the molten mould foaming process. The shrink of the foam size and the morphology distortion were caused by cooling contraction. However, they could be weakened by increasing saturation pressure or decreasing foaming temperature. PET could not be foamed under molten state due to its thermal degradation. The experimental results also showed that using high melt strength PP and melt-cooling foaming method could effectively broaden the foaming window of PP. It was easy to prepare the microcellular PP with smaller cells and higher cell density by using the high melt strength PP as the raw material. In order to prepare the flat microcellular PET sheets, the solid mould foaming of PET was adopted. The result showed that the flat microcellular PET sheets could be produced with the foaming temperatures of225～245℃, saturation pressures of10～16MPa and saturation time of10min by using the two-dimensional foaming method. Meanwhile, the cells size was significantly decreased.