Impact-resistant polypropylene compositions having improved whitening resistance

Abstract

Disclosed are polypropylene compositions having high impact resistance at low temperatures, and improved whitening resistance. They comprise: (a) 60-90 parts by weight of polypropylene with an isotacticity index >90; and (b) 10-40 parts by weight of an ethylene/butene-1 polymeric mixture containing 50-95% by weight of polymerized ethylene, and consisting essentially of: 20-95% by weight of a crystalline fraction (I) with crystallinity of the polyethylene type, that is insoluble in xylene at 23.degree. C.; and 5-80% by weight of an ethylene/butene-1 amorphous copolymeric fraction (II), that is soluble in xylene at 23.degree. C., and contains 40-70% by weight of ethylene; and in which the weight ratio between total polymerized ethylene and the amorphous fraction (II) is 0.6-8. Such compositions are obtained by polymerization processes comprising the step of homopolymerizing propylene to stereoregular polymer, and a subsequent step of copolymerizing ethylene/butene-1 mixtures, said steps being effected by Ziegler-Natta stereospecific catalysts, which include a titanium compound carried on a magnesium halide in the active form.

Dependencies are inferred from the claim text.