Synergism of the elastic modulus of poly(propylene)-high-density poly(ethylene) blends

Effects of the sample preparation conditions on the elastic modulus of polymers were studied for isotactic PP, HDPE, and a series of PP-HDPE blends were obtained by dispersing components during their extrusion mixing in the melt, followed by cooling. As the cooling rate increases, the elastic modulus in disordered regions of the individual HDPE samples grows, while that of PP remains virtually unchanged. Variation of the elastic modulus in PP-rich compositions is explained in terms of the mutual synergistic influence of components in the course of their crystallization. It is shown that increase in the modulus is due to the formation of stronger intercrystallite links in the PP phase and in the interphase region. The strengthening is induced by residual stresses arising in the system under the rapid crystallization conditions as a result of a difference in the elastic moduli and thermal expansion coefficients between the blend components.