Supercritical CO2 foaming of pressure-induced-flow processed linear polypropylene

Abstract Linear polypropylene is very difficult to foam due to its low melt strength and high crystallinity. Pressure-induced flow (PIF) has been demonstrated to be able to improve the foamability of linear PP under a very high pressure. In this study, we report a systematic evaluation to optimize PP foaming process using supercritical CO 2 . PP was firstly processed by means of PIF at optimized conditions. For CO 2 foaming of PP, the effect of foaming pressure and saturation time was investigated in detail. A threshold foaming pressure of 13.8 MPa was found to be needed to achieve low-density foams. Comparing to commercially available EPP and high melt strength PP foams, the PIF PP foams possess much higher compressive strength and thermal stability at lower densities.