Free radical mechanism for reactive processing of polymers in the presence of organoclay/peroxide nanoreactors: Grafting maleic anhydride onto polypropylene

Abstract

PP-graft-MA is a common PP compatibilizer, produced via reactive extrusion using peroxides as initiator, which causes severe molar mass reduction. To control PP degradation and increase maleic anhydride grafting, Shi and coworkers (2006), proposed the use of nanoreactors. In this paper we propose a complete new reactive mechanism involving nanoreactors during PP-graft-MA reactive processing. The samples were prepared via melt mixing using nanoreactors with different organoclay: peroxide ratios (oMMT:DCP). Organic MMT showed to absorb not more than 16 wt% of DCP, i.e., diffusional controlled release of alkoxy radical will not be observed at o-MMT:DCP ratios < 5:1. The presence of o-MMT tend to increase MA homopolymerization, which consumes the initiator, interfering with the grafting of succinic groups onto the PP backbone, due to increased hindrance of oligo (MA) formed, thereby reducing degradation of the PP chain. Thus, the use of nanoreactors promotes MA homopolymerization rather than grafting as previously proposed in the literature.