Relationships among migration properties, molecular structure and catalytic process of isotactic copolymers of propene

Abstract

Isotactic polypropylene-based (iPP) materials find large applications for the food packaging. In this article the structure, thermal and mechanical properties of some commercial grades of ethylene/propene copolymers produced by heterogeneous Ziegler-Natta (ZN) catalysis, have been characterized. These grades can be potentially used for manufacturing food containers. However, despite the desired performances in terms of mechanical and optical properties, we found that the samples exceed the overall migration limit set by the EU Directive into isooctane, used as fatty food simulant. The migrating species are highly defective copolymer chains with low molecular mass and high ethylene content. The migration is intrinsically related to the presence of fractions generated by the heterogeneous multisite surface of the ZN catalysts. A simple chemical route to allow the iPP-based materials to fall within the overall migration limit is proposed.