3.5. Thermal stability
TGA thermograms showing thermal degradation behavior of CH films with or without CEO and CWO are shown in Fig. 2.The films’ corresponding degradation temperatures (Td), weight loss (w) and residue are presented in Table 2. The control CH film generally exhibited three main stages of weight loss. Previous studies have also shown that the thermal degradation of CH films follows a three step weight loss [48]. However, five main stages of weight loss were observed in films incorporated with both CEO and CWO. The first weight loss (w1= 5.90–9.18%),observed at an approximate temperature (Td1) of 100–122◦C, is generally due to the evaporation of residual water and the aceticacid in the film. It was found that CH films incorporated with CEO had lower weight loss than those containing CWO. This is mainly attributed to the lower amount of water in films incorporated with CEO, which could be partially explained by the more hydrophobic nature of the main components of this essential oil.The weight loss (w2= 15.00–20.30%) in the second stage, which corresponds to the degradation of lower molecular weight fractions or structurally bound water in the film network, occurred at 258–286◦C. For the third stage of weight loss, w3 of 21.76–33.22%and Td3of 334–342.48◦C were observed for all film samples, possibly associated with a complex process including the dehydration of the sacch aride rings, depolymerisation and decomposition of the acetylated and deacetylated units of the polymers. A higher thermal degradation temperature of the second and third stages was observed in films incorporated with both CEO and CWO compared with the control film. Our results indicated that both essential oils at a level of 20% did not improve the matrix’s thermal degradation. However, it was found that when the essential oil content reached 30%, CH films began thermal degradation at lower temperatures.The higher thermal stability of the films with essential oils could be associated with the interaction between the CH and oil, which might delay the thermal degradation of the composite films. The fourth stage of weight loss (w4of 6.38–11.83%) was obtained for films incorporated with each of the two essential oils. Nevertheless,