Abstract: The crystallization half-time and mold cycle time of high density (>0.935 g/cm.sup.3) polyethylene are reduced and the impact energy is improved by blending two linear ethylene polymers differing in density by 0.015 to 0.150 g/cm.sup.3, to achieve a density similar to a single high density polyethylene. Both polymer components and resulting blend have a melt flow ratio (MFR) of less than 35 which indicates a relatively narrow molecular weight distribution. Articles are formed which do not show the severe warpage experienced with conventional nucleating agents, and which exhibit impact properties superior to a similar single high density polyethylene copolymer.

Abstract: Shrinkage following injection molding of linear low density polyethylene, e.g. copolymers of ethylene and butene, is reduced by intimately blending high pressure low density polyethylene in minor amounts, e.g. 3 to 50 weight percent of the polymers.