Effects of Chitosan/ Nanoclay Bentonite on the Mechanical Properties, Water Permeability and Microstructure of Nanocomposite Film

Biopolymer-based films such as chitosan have been studied widely due to their biodegradability and biocompatibility. Chitosan has a great potential for a wide range of food applications but its’ hydrophilic character, and consequently its poor mechanical properties in the moist condition, limits its application (1, 2). Composite films have received much attention, because of their extraordinary possibility to improve the properties of films. One of the promising ways to modify biopolymer properties in terms of physicomechanical properties, inherent water sensitivity, and their relatively lower stiffness and strength, is to make hybrid films using biopolymers and nano-sized fillers known as nanocomposite films. In this research, the effect of bentonite nanoclay/chitosan ratio on the water vapor permeability (WVP), mechanical properties, and surface microstructure of the chitosan nanocomposite films was evaluated.

In this research, chitosan biopolymer aqueous solution with two concentration (2, and 3% w/v) and bentonite nanoclay solutions with two clay compositions (1 and 3% based on chitosan) were prepared, separately. The chitosan solution was then slowly added to the clay suspension at 55oC. The nanocomposite films were prepared using the solvent-casting method. The films based on 2 and 3% chitosan were considered as unfilled control samples. The water vapour permeability (WVP), tensile strength (TS), elongation at break (E), and microstructures of the films were investigated.

The results show that at identical concentrations of chitosan the amount of bentonite nanoclay affect the WVP and tensile strength (TS) of chitosan films, significantly (p<0.01). By adding 1% nanoclay bentonite to polymer matrix, the value of TS strength of nanocomposite film increased to approximately 0.66 (2% chitosan) and 0.35 MPa (3% chitosan). Moreover, the elongation value decreased to 8.8% and 6.47% in the nanocomposite films based on 2 and 3% chitosan, respectively. Further increase in clay content to 3 wt%, the WVP, elongation and TS of nanocomposites film decreased for chitosan 2 wt%. According to the SEM micrograph, non-homogeneous structure was found for 3% clay-chitosan nanocomposite in comparision to 1% nanoclay loaded chitosan nanocomposite in full agreement to the decrease in TS value observed. With increase the percentage of nanoclay bentonite to 3%, the pore spaces of film increased and consequently the TS exhibited decreased

According to the findings of this research, interactions between nanoclay and chitosan in nanoclay-chitosan nanocomposite have led to the formation of a new material with enhanced mechanical, morphological, and WVP properties than the pure chitosan. Finally, in 1% nanoclay concentration, the water vapor permeability, elongation, tensile strength, and also consistency of the microstructure films were significantly modified in compare of pure chitosan