Supercritical CO₂ foaming of radiation crosslinked polypropylene/high-density polyethylene blend: Cell structure and tensile property

A blend of isotactic polypropylene (PP) with high-density polyethylene (HDPE) in different PP/HDPE ratios was irradiated by γ-ray to induce cross-linking and then foamed using supercritical carbon dioxide (scCO₂) as a blowing agent. Radiation effect on the melting point and crystallinity were analyzed in detail. The average cell diameter and cell density were compared for PP/HDPE foams prepared under different conditions. The optimum absorbed dose for the scCO₂ foaming of PP/HDPE in terms of foaming ability and cell structure was 20 kGy. Tensile measurements showed that the elongation at break and tensile strength at break of the crosslinked PP/HDPE foams were higher than the non-crosslinked ones. Of particular interest was the increase in the foaming temperature window from 4 ℃ for pristine PP to 8–12 ℃ for the radiation crosslinked PP/HDPE blends. This implies much easier handling of scCO₂ foaming of crosslinked PP with the addition of HDPE. - Highlights: • HDPE was added to improve the scCO₂ foaming of polypropylene. • Radiation cross-linking was employed to improve the scCO₂ foaming of PP/HDPE blend. • Tensile strength of irradiated PP/HDPE was improved compared to un-treated PP foam. • Larger foaming temperature window (12 ℃) was achieved for scCO₂ foaming of PP/HDPE.