Correspondence to:

ABSTRACT Other crystalline polymer pairs have been studied wherein a synergism was found in their mechanical properties. For example, PP/HDPE was studied by Noel and Carley (1975) in a wide range of compositions. They found that very low amounts of HDPE caused a maximum in the tensile modulus and strength of the blends. They concluded that, when the HDPE component is less than 10%, the HDPE acts as a stiffener. In contrast, small amounts of PP were found to make the blend ductile. Stell et al. (1976) studied polymer blends of PS/HDPE in stretched films. These authors found that the mechanical properties of the films (tensile strength and elongation at break) were best when the films were quenched right after hot stretching