**3.3 Effect of plasticizers added simultaneously into biobased films**

When the plasticizers having both hydroxyl and carboxyl groups were simultaneously added into the biobased films, their physicomechanical properties were better than those of plasticizers with only hydroxyl group-containing agents. Yoon et al. reported that as the additives containing both hydroxyl and carboxyl groups were simultaneously added into the formulation, the TS and %E were enhanced compared to the glycerol, having only hydroxyl groups. For instance, %E of the glycerol-succinic acid–added films increased, while only succinic acid–added film showed inadequate potential. The usage of the plasticizer composed of both hydroxyl and carboxyl groups could enhance the flexibility and strength. Moreover, the degree of swelling and solubility values of the comalic acid-/tartaric acid-added films were higher than those of coglycerol-/succinic acid-added films. [6]. This was because the hydroxyl (-OH) group number of malic acid-tartaric acid (7 hydroxyl number) was higher (i.e., having a more hydrophilic character) than glycerolsuccinic acid mixture (5 hydroxyl number). %E of the glycerol or sorbitol-succinic acid–added films increased, while %E of succinic acid–added film decreased with increasing amount of additives. Nevertheless, TS of glycerol or sorbitol-succinic acid–added films decreased, while TS of succinic acid–added film diminished with increasing content of additive. The results of TS and %E mentioned above showed that using cohydroxyl/carboxyl group as a functional group increased physicochemical and mechanical properties of films [30]. Eventually, when the plasticizers having both hydroxyl and carboxyl groups were used simultaneously, TS and %E of the films were found to be better than the films containing plasticizer having only the hydroxyl group [7].
