Dependence of mechanical properties in polyolefin blends on shear and thermal history

Variously dispersed two‐component blends of linear polyethylene and a thermoplastic rubber were subjected to different thermal histories after compression molding and their properties were evaluated. It has been shown that ultimate properties of the blends are not defined by the composition, but vary greatly with degree of dispersion and thermal history. Stronger materials failing in a ductile manner were produced under shock cool conditions and in, finely‐dispersed blends. Brittle failures and weaker materials were favored by annealing procedures and in blends subjected to brief and/or lowshear dispersion procedures. Time and temperature dependent changes in properties of blends prepared under standard conditions have been observed and activation energies for the aging process calculated. Data interpretation was based on a hypothesis of domain morphology in the blends, and on the existence of “tie molecules” which help to determine the cohesive strength of domain boundaries.