Compatibility evaluation and mechanical properties of isotactic polypropylene/high density polyethylene (iPP/HDPE) blends

In present work, the rheological and morphological investigations in conjunction with the crystallization behavior analysis were carried out for clarifying the compatibility of isotactic polypropylene/high density polyethylene (iPP/HDPE) blends with different mass ratios. The results of rheology and SEM characterization showed that the iPP-rich blends possess higher interfacial interaction than the HDPE-rich blends originating from the first crystallized iPP with larger volume contraction as well as similar melt flow rates of iPP and HDPE, giving rise to positive deviation of viscoelasticity and smaller size of the dispersed phase. Based on the characterization of crystallization behavior by using DSC, POM and WAXD, it was concluded that, although the iPP and HDPE in the blend crystallize separately without the formation of co-crystals, there is still some interaction between them, which is reflected in the melting temperature depression of iPP and HDPE components, the destruction of the morphology of iPP spherulites, as well as the mutual effect on crystal growth. This could be ascribed to partial compatibility of iPP and HDPE. Moreover, advantageous interfacial interaction for the iPP-rich blends is favorable for effective stress transfer from matrix to dispersed phase, leading to better mechanical properties of the iPP-rich blends in contrast to those of pure iPP. On the contrary, the negative deviation of viscoelasticity and mechanical properties of the HDPE-rich blends could be attributed to the poor interfacial interaction between phases.