Patent ID: 10072105

Abstract:
The present invention relates to a method for the manufacture of polypropylene having a target melt flow rate of from 10 to 200 g/10 min as determined in accordance with ISO 1133 (230° C., 2.16 kg) comprising the sequential steps of i) polymerizing propylene monomer, and optionally one or more alpha olefin co-monomers so as to form a polypropylene having an initial melt flow rate of from 0.5 to 20 g/10 min (ISO 1133, 230° C., 2.16 kg), ii) visbreaking said polypropylene to obtain polypropylene having said target melt flow rate and wherein the ratio of target to initial melt flow rate is more than 1 iii) maintaining the polypropylene obtained from step ii) at an elevated temperature for a time sufficient to reduce the FOG value of the polypropylene as determined in accordance with VDA 278. The method allows the time for FOG reduction to be reduced as compared to polypropylenes that have the same target melt flow rate, yet which have obtained said melt flow rate without the visbreaking step.