Preparation and characterization of extruded thermoplastic zein–poly(propylene carbonate) film

Abstract

The novel film mainly composed of zein and poly(propylene carbonate) (PPC) was developed to study its feasibility as an alternative to petroleum-based plastics for food or non-food packaging, in combination with the acetone-pretreatment along with extrusion process using a conical twin-screw extruder. The effects of film formulation (the ratio of corn–zein to PPC, and plasticizer concentration) on physicochemical properties of extruded films were investigated. The results indicate that the addition of PPC with an appropriate concentration could improve the tensile strength and water resistance of the extruded zein–PPC film. In addition, PPC has a minor role in the film transparency and in contrast, the film transparency is highly dependent on the concentration of glycerol. Moreover, different models were used to describe the relationship between the tensile strength and humidity conditions. The Halsey model was identified as an ideal model perfectly fitting the experimental data, suggesting that the tensile strength of zein–PPC film was decreased with increasing equilibrium moisture content (EMC) of films. Scanning electron microscopy (SEM) revealed that the extruded film consisted of a single phase and also, the presence of PPC has a significant impact on the internal and external structures of the films. Furthermore, the results obtained from thermogravimetric analysis (TGA) showed the improved thermal stability of extruded zein–PPC film when compared to either the pure PPC or zein film. In conclusion, zein–PPC film could be considered a promising candidate to replace conventional petroleum-based plastic used in composite for packaging applications.