Gamma polymorph and branching formation as inductors of resistance to electron beam irradiation in metallocene isotactic polypropylene

The influence of a wide dose range of electron beam (EB) irradiation is analyzed on films obtained from metallocene isotactic polypropylene (iPP) under two different thermal processing conditions. A greater irradiation resistance is observed in those films with content in gamma crystallites higher than in alpha monoclinic entities in terms of melting temperature variation with irradiation. This change is on the order of 0.5 degrees C per 100 kGy in slowly crystallized films while a value of 1.5 degrees C per 100 kGy is found in quenched specimens. On the other hand, dual studies on films and pellets have proved that branching takes place in this metallocene iPP. The scission processes that occur during irradiation cannot account by themselves for the observed changes in molecular weight distribution as demonstrated by simulation. The observed changes in the theological behaviour of the irradiated iPP corroborate that increasing degrees of branching are generated by the irradiation Process. (C) 2010 Elsevier Ltd. All rights reserved.