Process for transforming polypropylene into a crystal modification of high transparency and articles resulting from said process

摘要

The invention relates to a process for producing polypropylene articles comprising a high relative content of the orthorhombic gamma-crystal modification by applying four consecutive process steps, namely (a) heating a polypropylene composition comprising a propylene random copolymer and an alpha-crystal nucleating agent to form a melt, (b) shearing said melt at a high apparent shear rate, (c) shaping said melt into an article, and (d) cooling said melt in a specific range of cooling rate to obtain polypropylene articles of high transparency