Fabrication And Characterization Of Crosslinked Cellulose Nanocrystals Re-Enforced Bipolymeric Films For Preservation Of Leafy Vegetables

Abstract

Biodegradable polymer films are increasingly being used as alternate packaging material due to the less environmental and health burden compared to synthetic plastics. Biobased films are also attractive candidates for packaging fresh food such as vegetables and fruits as they possess high moisture retention capacity and maintain desirable sufficient moist surface around the fresh food. Due to the high hydrophilicity of biobased or biodegradable polymers, the practical application of biobased polymer films in food packaging is challenging as their large hydrophilic groups on surface and in between polymer chains can absorb excess moisture which may lead to polymer chain disentanglement and dissolution as excess water can disrupt the weak physical forces (intermolecular hydrogen bonding) holding the individual polymer chains together in the film. The objective of the work is to perform film post treatment techniques in reducing the number of free hydrophilic groups on the surface of the film as well as dehydrate the film using chemical crosslinking and thermal treatment respectively. In this work, a simple packaging film was fabricated by solution casting method using polyvinyl alcohol (PVA), chitosan, citric acid as cross linker and cellulose nanocrystals (CNC) in varied amounts, as fillers to enhance mechanical strength. The films were characterized using tensile machine, Fourier Transformed Infra-red spectroscopy, thermal analysis, moisture absorption studies, film dissolution, film permeability studies and X-ray diffraction analysis. Varying the amount of CNC affected the thermal stability of the films, wherein increased amounts improved thermal properties. TGA studies showed that T max (temperature where highest mass loss occurs) in E3 (398°C) increased to 404 °C in E12 with increased amounts of CNC. Acylation with acetic anhydride, heat treatment of films at 100°C and a combination of both treatments improved film stability in water. Swelling degree observed after 15 minutes of immersion of films in distilled water were at their barest minimum in all films subjected to any of the treatments. The films significantly decreased the rate of browning of fresh lettuce, keeping its fresh green colour for approximately eleven days before signs of browning set in. This was in contrast to fresh lettuce packaged with poly ethylene films which turn brown after three to four days. The fabricated films may serve as active packaging system for extending the shelf life of fresh lettuce, and potentially other vegetables and fruits in the food distribution chain.