3.8. Thermal characteristics
The thermal behavior of the native and OEO-included biocomposite films was examined using DSC. Fig. 5 shows the typical DSC thermogram of films with or without essential oil. Two endothermic peaks were detected for all films. The first endothermic peak that occurs over the temperature range of 108–114◦C may be assigned to the overlapping of different phenomena e.g., evaporation, melting and recrystallization of small and/or imperfect gelatin crystallites, and corporation of the glass transition of -amino acid blocks in the polypeptide chain (Denavi et al., 2009; Rivero et al.,2010), while the second peak in the range of 240–263◦C being associated with the thermal degradation of polymers. The second endothermic peaks, represent the polymer degradation, for control and 0.4% (w/v) OEO-containing films which have appeared at 261–263◦C, while these peaks have shifted to lower temperature at 244–240◦C for 0.8 and 1.2% (w/v) OEO, respectively (Fig. 5).This shift may be described by the plasticizing action of oil, which increases the free volume within the polymer network and thesegmental mobility of the polymer chains (Sobral et al., 2001). Sim-ilar results have been found by Aliheidari et al. (2013) in sodiumcaseinate-based films containing Matricaria recutita essential oil.