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Improving the performance of starch film by engineering the interaction of nanocrystalline cellulose fillers with starch molecules

Abstract

Starch as a renewable and biodegradable polymer, is an essential alternative to synthetic polymers in production of films for food packaging and agricultural mulching applications. The major problem with the plasticized starch is its increased permeability to water vapor and oxygen and its low strength. To improve these properties, nanocrystalline cellulose (NCC), which has the Young’s modulus as high as 134 GPa, has been tried as nanofillers. The major concern in preparation of nanocomposites is the uniform distribution of nanofillers within the starch molecules, which in turn decides their performance characteristics. In this work, we have prepared NCC from microcrystalline cellulose by high pressure homogenization process. Due to high surface energy and hydrophilicity of formed NCC particles, they tend to form aggregates in water. To prevent this, during homogenization, solubilized starch was added as stabilizers. The starch macromolecule stabilized the formed NCC by steric hindrance. The average diameter of nanocellulose prepared without starch was 197.8 ± 4.0 nm (Polydispersity index: 0.239) while that of stabilized by starch was 391.7 ± 36.2 nm (Polydispersity index: 0.458). The increased size corresponds to the coating layer formed by starch molecules. To prepare starch film, soluble starch (4%) having glycerol (2%) as plasticizing agent were gelatinized by stirring in hot plate. For nanocomposite starch film, the nanocellulose was added in varying concentrations (2% and 4%) to starch / glycerol solution and mixed using a high speed mixer for uniform distribution. These solutions were casted on Teflon plates and dried at 50 ºC, overnight. The uniformity of distribution of NCC in the starch film was analyzed by FTIR at multiple locations of the film. Starch stabilized NCC showed comparatively uniform distribution throughout the film surface. The crystalline structure of NCC has profound effect on the performance characteristics of nanocomposites films. So, the percent change in its crystallinity (1α and 1β) is being analyzed during the various steps in processing of the nanocomposites. The water vapor permeability and mechanical strength analysis of films are in progress

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