Micromechanical studies on binary and ternary blends of polyethylene, polypropylene, and polyamide 66: Influence of the compatibilizer

The microhardness H of PE/PP/PA blends prepared by one-Step and two-step mixing processes was determined. The microhardness of the blends was markedly affected by the composition. Results reveal that the presence of compatibilizers induces a remarkable decrease in the H of the blends. It is shown that the large deviation of H from the additivity law of the single components is mainly due to the depression of the crystal hardness values of polymer crystals. However, the decrease in crystallinity of the individual components in each blend also has to be considered. Comparison of experimental and calculated H data and analysis of DSC results in all the blends suggest that the surface free energy of the crystals increases as a consequence of the blending process. Results are discussed in light ofthe changes occurring in the defective boundary surface of the crystals. Finally, a linear relationship between the hardness H and the yield stress σ y , as well as between H and the Young's modulus E, are found. The deviation of the H/ σ y and the H/E ratios from the theoretical predictions are discussed in the light of the strain rate used and the compatibilizer effects on the blend structural properties.