Incorporation of apricot shell loads into novel highly ductile thermoplastic zein biopolymers through injection molding for food packaging

Abstract This study explores the effect of apricot shell flour (ASF) on the development of biodegradable zein (ZEI) thermoplastic materials plasticized with 25 wt.% of diethylene glycol (DEG). Materials were processed by extrusion and injection molding technologies. Mechanical analysis revealed an outstanding ductility. ZEI-DEG exhibited a strain at break of 57.2%, which was increased to 119.2% with 15% ASF, while impact strength rose from 6.4 to 15.9 kJ/m², confirming a synergistic plasticization effect between DEG and ASF. A decrease in glass transition was observed by dynamic mechanical thermal analysis with the incorporation of ASF, due to the interaction of fatty acids present in ASF with zein. Morphology analysis showed good filler dispersion and good compatibility with the zein matrix. Thermogravimetric analysis (TGA) revealed a slight decrease in thermal stability with ASF, but materials remained stable up to 350 ºC. Materials exhibited a progressive darkening with dark brown colors, providing a wood-like appearance that is potentially attractive for sustainable wood plastic composite applications such as packaging. The properties of these materials were far higher than the traditionally glycerol-plasticized zein materials. Overall, these findings highlight ASF as a promising bio-based filler that enhances flexibility and toughness of thermoplastic zein while maintaining good thermal behavior and creating aesthetically appealing natural composites. These green materials offer significant potential for biodegradable food packaging, furniture, and interior design products.