Influence of PP types on migration of zinc from nano-ZnO/PP composite films

Polypropylene nanocomposites have great potential applications in food packaging and the evaluation of the migration of nanoparticles is important for the food safety. Three types of polypropylene (homopolymer of polypropylene, PPH; blockcopolymer of polypropylene, PPB; random copolymer of polypropylene, PPR) nanocomposite films with or without coupling agent were tested in 3% acetic acid as food simulant. The migration amount of zinc was quantified by inductively coupled plasma atomic emission spectroscopy. The surface morphology and crystallinity were explored by field emission scanning electron microscopy, atomic force microscopy, and differential scanning calorimetry, respectively. The results showed that the incorporation of titanate coupling agent could inhibit ZnO-NPs migration from the films since titanate coupling agent could improve the interface between ZnO-NPs and PP molecular chain segment. Furthermore, the migration rate of zinc was dependent on the degree of crystallinity ( X c ) of PP and their order of the maximum migration rate was PPH, PPB and PPR. The notable phase separation could be observed from the morphology of nano-ZnO/PPH, while ZnO-NPs could be well dispersed in the PPR matrix. Thus, ZnO-NPs restricted the molecular chain segment of PPH and reduced its X c from 88.6% to 73.2%. The results demonstrated that titanate coupling agent and PPR could inhibit the migration of ZnO-NPs significantly.