Studying of the effect of nanoclay and citric acid on the physical and antioxidant properties of Thyme extract loaded starch-CMC active film

In this research, the starch-carboxymethyl cellulose (2:1 ratio) active films containing Thyme extract (5% wt.) were prepared. In order to improve of film properties, nanoclay (montmorillonit = MMT) (1, 3 and 5% wt) and citric acid (0, 5 and 10% wt) were used as nano-reinforcing and crosslinking agents, respectively. Measuring of the mechanical and water vapour barrier properties of the films revealed that the addition of Thyme extract caused to weakening of ultimate tensile strength and increasing of water vapor permeability and moisture uptake. Citric acid also had positive effect on tensile strenght and barrier properties. Among the all additives, Thyme extract and MMT had the highest effect on color properties and caused to decrease lightness and increase yellowness index. According to the results of differential scanning calorimetry (DSC), active film containing 5% MMT and 10% acid citric had the highest melting temperature (229.7 °C). Also, by addition of acid citric and MMT, the antioxidant activity of active film was decreased due to the decreasing of diffusion coefficient for extract. Results indicated that there was a synergistic effect between citric acid and MMT in order to improving of physical properties of active films and simultaneous addition of these two additives cause to decrease the adverse effect of Thyme extract on functional properties of starch-CMC active film.