Process for the preparation of compositions of poly propylene impact resistant having improved re-consistency bleaching

摘要

Polypropylene compositions having a high impact resistance at low temperatures and an improved whitening resistance, comprising :… A) 60-90 parts by weight of polypropylene with an isotacticity index 90;… B) 10-40 parts by weight of an ethylene/butene-1 polymeric mixture containing 50-95% by weight of ethylene consisting of:… - 20-95% parts by weight of a crystalline fraction (I) with crystallinity of the polyethylene type, insoluble in xylene at room temperature;… - 5-80% parts by weight of an ethylene/butene-1 amorphous copolymeric fraction (II), soluble in xylene at 23 DEG C, containing 40-70% by weight of ethylene;… and in which the weight ratio between the total polymerized ethylene and the amorphous fraction (II) ranges from 0.6 to 8. …??Such compositions are obtained through polymerization processes comprising at least a step for homopolymerizing propylene to stereoregular polymer and a subsequent step for copolymerizing ethylene/butene-1 mixtures in the presence of Ziegler-Natta stereospecific catalysts, which include a titanium compound carried on a magnesium halide in the active form.