Effect of homogenization stirring speed on mechanical and water barrier properties of gallic acid treated zein-oleic acid composite films

In this study, the effect of different homogenization stirring speeds (10,000 rpm, 12,000 rpm, 14,000 rpm, 16,000 rpm, 18,000 rpm and 20,000 rpm) on mechanical and water barrier properties of gallic acid treated zein-oleic acid composite films was investigated. In addition, the effect of low and high homogenization speed on film microstructure with respect to speeds at 10,000 rpm and 20,000 rpm was also investigated. Results showed that homogenization stirring speed significantly (p < 0.05) and diversely affected the mechanical and water barrier properties of the films. A higher tensile strength (TS) of 33.4 MPa was registered in gallic acid treated zein-oleic acid composite containing 2% oleic acid homogenized at 12,000 rpm while the lowest tensile strength of 10.9 MPa was registered in gallic acid treated zein-oleic acid composite containing 2% homogenized at 10,000 rpm. Overall, higher tensile strength values irrespective of film type were observed at homogenization stirring speeds of 12,000 rpm, 16,000 rpm and 18,000 rpm. Lower water vapour permeability values (WVP) were obtained at homogenization stirring speeds of 10,000 rpm, 12, 000 rpm and 16,000 rpm with the lowest value of 0.23 (g mm m (2) h (1) kPa (1)) registered in gallic acid treated sample homogenized at 10,000 rpm. Results further revealed that WVP increased with increasing homogenization stirring speed especially in gallic acid treated zein films suggesting that the film matrix was being weakened as homogenization became more intense. Films produced by low homogenization speeds were characterized by smooth and homogeneous film microstructures as opposed to heterogeneous and coarse microstructures exhibited by films produced using high homogenization speeds. (C) 2016 Published by Elsevier Ltd.