Stress–strain behavior of polyolefin blends

Abstract

As part of a study on reuse of plastics as blends, the yield tensile strength, elongation at break, and the modulus of melt blends of low-density polyethylene, high-density polyethylene, and polypropylene have been studied over the entire ternary composition range. The modulus and strength are nearly monotonic functions of blend composition. The contribution of the pure components to these properties is roughly additive. The elongation at break is a more complex function of composition in that minima are observed near the center of the triangular composition diagram and on each of the three binary legs. The response is nearly symmetrical along two of the binary legs but is skewed toward high-density polyethylene for blends of high- and low-density polyethylene. The deterioration of elongation produced by blending is much less severe for polyolefins than observed for other blend systems. This, combined with the observed additivity of strength, make polyolefin blends mechanically superior to blends of other plastics found in wastes. This fact is interpreted in terms of compatibility and amorphous phase interactions which are likely for polyolefins. Modification of polyolefin blends by addition of a rubbery copolymer of ethylene and propylene produced large improvements in elongation at break for some compositions.