Properties of polypropylene‐polyethylene blends

High‐density polyethylene (PE) and isotactic polypropylene (PP) were melt‐blended in the following percentages of PE by weight: O, 10, 33.3, 40, 50, 66.6, 90, and 100. For these blends we obtained data on shear stress vs shear rate; tensile modulus and strength; density; and rates of water‐vapor transmission for films. The shear‐rate/shear‐stress data at 190 and 210°C are well fitted by the Ellis model with a maximum relative error of 5 percent. At 190°C all the mixtures were found to exhibit flow instabilities at high shear rates except the 90 percent and pure PE compositions. These, however, were unstable at 140, 150, and 160°C. The 10, 33.3, 40, 50, and 66.6 percent PE mixtures ruptured at elongations of less than 15 percent at the maximum tensile stress. The maximum tensile strength and modulus pass through maxima at 10 percent PE. Density is given by the equation ρ = 0.9029 + 0.0544 (wt fraction PE). Water‐vapor permeability was measured using wax‐sealed permeability cups, according to ASTM E96‐66. Valid results were obtained for only a few compositions because of faulty seals that could be detected only during careful dismantling of the specimen dishes. Faulty seals could account for the value, about ten times ours, reported in the literature for linear PE.