Solvent strength and biopolymer blending effects on physicochemical properties of zein-chitosan-polyvinyl alcohol composite films

Abstract

The aim of this research was to optimise and develop edible films made from zein (ZN), chitosan (CS), poly(vinyl alcohol) (PVOH) and poly(ethylene glycol) (PEG400) using Box Behnken Design (BBD). Four factors viz. ZN:CS ratio (w/w) (1:3, 1:1, 3:1), PVOH wt.% (in dry film) (0, 0.25, and 0.5), PEG400 wt% (0.13, 0.21, 0.31) and ethanol (40–80% v/v in water), were investigated. The effects on tensile strength (TS), Young's modulus of elasticity (EM), elongation at break (%EAB), water vapour permeability (WVP), solubility in water (Ws), and optical properties were evaluated. The films were further characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), x-ray diffraction (XRD) and swelling behaviour. SEM micrographs showed that high levels of ZN and PEG400 resulted in rough surfaces with major film defects, but these were minimised at high levels of CS or PVOH. XRD analysis indicated potential interactions through hydrogen bonding between the polar groups of ZN and hydroxyl moieties of PVOH and CS. Stress-strain curves showed that ZN and CS composite films possessed high TS but were brittle. Incorporation of PVOH increased the ductility of the composite films. Optimum films were obtained using ZN/CS/PVOH/PEG400 ratio of 0.35/0.29/0.13/0.23 (wt.%) and 60% ethanol, giving dry state properties of TS, EM, and EAB as 24.21 MPa, 356.62 MPa and 84.23%. respectively. This study demonstrated the influence of critical interactions between solvent features (polarity) and interfacial properties of ZN, CS, PVOH and PEG400. The observed crosslinking behaviour suggested the effectiveness of blending technique in improving the compatibility of biopolymers and overall functionality of edible films.