Development of novel zein-cellulose nanocomposite films

Zein is a hydrophobic biopolymer, which naturally forms biodegradable films. These films are rigid, brittle, and lack good mechanical and barrier properties for packaging applications. This study aims at improving the mechanical and barrier properties of zein films by the development of zein-cellulose nanocomposites. A ‘nanocomposite’ is a mixture of polymer matrix, which forms the continuous phase and the filler (having at least one dimension less than 100nm), which forms the dispersed phase. Zein-cellulose nanocomposites have zein as the matrix and cellulose as the filler. Nano-sized cellulose was prepared using wet-media milling machine and mass ratios of 1%, 3%, 5% and 10% of both, naked (not stabilized) nano-cellulose and GA - stabilized nano-cellulose were used in the film formulation. Tributyl citrate (TBC) was used as the plasticizer. The films were prepared using solvent-cast technique and characterized to test their mechanical and barrier properties. The controls were pure zein films and films with only plasticizer. Texture Analysis showed that filler loading of 5% was most effective in increasing the elongation-at-break to about 16 to 20 times of the controls. However, the tensile strength did not change. Water vapor permeability of the nanocomposites was minimum at 1% by wt. of naked cellulose (~4 times less than control) or at 5% by wt. of stabilized cellulose (~6 times less than control). Water absorption results showed that the rate of water uptake decreased as the filler loading increased. DSC and FTIR suggested that there is no interaction between the zein and the nano-cellulose in the films. The AFM results showed that the films’ surface is flat, but the thickness of the films increased with filler loading. Therefore, incorporation of nano-cellulose improved the flexibility and water barrier properties of the films. Gum Arabic, which was used as a stabilizer for nano-cellulose, seemed to have aided the even distribution of cellulose in the zein matrix. Thus, these films can be a good starting point to further study the arrangement of cellulose within the zein matrix and test its potential applications on food systems and as edible films.M.S.Includes bibliographical referencesby Seema Lakshmana Ra