Wettability, surface microstructure and mechanical properties of films based on phosphorus oxychloride-treated zein

BACKGROUND: Zein, the predominant protein in corn, has been extensively studied as an alternative packaging material in edible and biodegradable films. However, films made from 100% zein are brittle under normal conditions. The aim of this investigation was to improve the film‐forming properties of zein by chemical phosphorylation. The surface hydrophobicity, surface microstructure and mechanical properties of films based on untreated and phosphorus oxychloride (POCl₃)‐treated zein were evaluated and compared. The effect of POCl₃ treatment on the rheological properties of zein solutions was also studied. RESULTS: POCl₃ treatment, especially at pH 7 and 9, led to an increase in the apparent viscosity of zein solutions. Atomic force microscopy (AFM) analysis showed that the film based on POCl₃‐treated zein at pH 7 had a stone‐like surface microstructure with a higher roughness (R_q) than the untreated zein film. The AFM data may partially account for the phenomenon that this film exhibited high surface hydrophobicity (H₀). POCl₃ treatment diminished the tensile strength (TS) of zein films from 4.83–6.67 to 1.3–2.29 MPa. However, the elongation at break (EAB) of the films at pH 7 and 9 increased from 3.0–4.5% (control film) to 150.1–122.7% (POCl₃‐treated film), indicating the potential application of zein films in wrapping foods or in non‐food industries such as sugar, fruit or troche that need good extension packing materials. CONCLUSION: The data presented suggest that the properties of zein films could be modulated by chemical phosphorylation treatment with POCl₃ at an appropriate pH value. Copyright © 2011 Society of Chemical Industry