Effects of Modified Starch on Morphology, Properties and Biodegradation of Thermoplastic Cassava Starch and Pbat Blown Films for Food Packaging

Abstract

Modified starch enhanced the compatibility and modified the properties of thermoplastic starch (TPS) and polybutylene adipate terephthalate (PBAT) biodegradable films. Native (NS), acetylated (AS), octenyl-succinated (OS) and hydroxypropylated (HS) starch were compounded with PBAT via extrusion. PBAT/TPS (40/60 and 50/50 ratios) blend films were produced by blown-film extrusion and characterized for morphology, crystallinity, thermomechanical properties, mechanical and barrier properties. Topographic and scanning electron micrographs showed diverse dispersion and morphologies of starch granules depending on hydrophobicity that governed interface exposure between incompatible polymers. Hydrophilic starch formed phase separated fibrous-like networks entangled in PBAT at higher TPS ratios. Hydrophobic OS starch improved compatibility and interaction with PBAT, greatly modifying mechanical and barrier properties (82-89%). TPS slightly increased α-relaxation temperature and modified arrangements of aromatic structures in PBAT, involving C-H and C-O bonding, subsequently influencing crystallinity of PBAT and the starch phase. Biodegradation of the blend films was dependent on hydrophilicity of starch, giving the fastest degradation in NS and HS. Findings indicated that hydrophobically modified starch improved compatibility with PBAT for biodegradable packaging, while film properties were highly dependent on the morphology of blend matrices.