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

Effects of the sample preparation conditions on the elastic modulus of poly mers were studied for isotactic PP, HDPE, and a series of PP-HDPE blends ob tained 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 r emains virtually unchanged. Variation of the elastic modulus in PP-rich com positions is explained in terms of the mutual synergistic influence of comp onents 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 con ditions as a result of a difference in the elastic moduli and thermal expan sion coefficients between the blend components.