Preparation and characteristics of zein/ethyl cellulose composite coating applied in aqueous system

Zein and ethyl cellulose (EC) were used as raw materials to prepare a composite coating applied in aqueous systems with mechanical properties, water stability, water solubility (including room-temperature (RT)/high-temperature and neutral/acidic conditions), and oil resistance as evaluation index. Results showed the most suitable conditions were mass ratio of zein/EC at 1:9, 93 % (v/v) aqueous ethanol, oleic acid as the plasticizer with the amount of 0.3 g/g, and curing temperature at 70 °C. Under these conditions, the tensile strength of composite coating was 4.61 MPa and elongation at break was 21.60 % after 4 weeks of soaking in water. Oil seepage was not observed within 1 week. The water solubility of coating in neutral water was 5.13 % at RT for 24 h, and 3.79 % at 80 °C for 2 min; in acidic water (pH = 4) was 4.54 % at RT for 24 h, and 5.44 % at 80 °C for 2 min. SEM results showed swelling occurred in zein coating after soaking, presenting micropores in soaked zein coating; zein microparticles in composite coating partially broke down and fell off after soaking. Water contact angle results revealed surface hydrophobicity by the following order: EC coating > composite coating > zein coating. FTIR results showed composite coating was physically compounding by hydrophobic interactions and hydrogen bonds.