Migration, aggregations and thermal degradation behaviors of TiO2 and ZnO incorporated PBAT/TPS nanocomposite blown films

Abstract

Metal oxides including titanium dioxide (TiO2) and zinc oxide (ZnO) enhanced the properties and functional performance of biodegradable plastic food packaging. Effects of TiO2 and ZnO nanofillers (1-5%) on bioplastic packaging microstructural changes were investigated for infrared absorption, thermal stability and migration behavior in distilled water, 10% ethanol and 3% acetic acid. Nanoparticles were compounded with thermoplastic starch (TPS) before blending with polybutylene adipate-co-terephthalate (PBAT), and converted into nanocomposite films via blown-film extrusion. Microstructural analysis indicated that addition of TiO2 and ZnO enhanced disruption of starch granules, increasing the amorphous starch portion. Energy dispersive X-ray analysis (EDX) exhibited higher aggregations of TiO2 particles than ZnO, coincident with higher degree of hydrogen bonding between ZnO and TPS phase. Strong interaction between ZnO and polymers also modified degradation temperatures (Td) of both PBAT and TPS phase in PBAT/TPS blend films. TiO2 gave identical Td but higher residual mass depending on nanocomposite amounts that modified the amorphous-crystalline fraction. Films with ZnO had higher migration levels, particularly in acid simulant due to high dissolution of ZnO particles, analyzed by inductively coupled plasma mass spectrometry. Release of titanium was strongly dependent on simulant types, showing maximum at 3-4% TiO2 followed by a sharp drop at higher TiO2 levels. Films containing ZnO showed higher migration levels, indicating that films containing TiO2 were more inert. Migration levels of titanium and zinc metals from TiO2 and ZnO incorporated PBAT/TPS blown films were influenced by alteration of the matrix structure due to simulant penetrations, interaction and adhesion forces between metals and polymers and favorable dissolution of the metal into simulants. Interaction between simulant-polymer and simulant-metal oxide particles further modified film matrices and enhanced release. The films showed promise for use in aqueous surroundings for food applications.