## 3 Results  
### Tensile Properties  
Figure 1 shows the tensile strength, modulus of elasticity, and elongation at the breaking point of the studied films stored for one week at 53% RH and 25 \({}^{\circ}\)C. The tensile strength is between 1.98 and 4.0 MPa, the elastic modulus was found between approximately 76 and 127 MPa, and the elongation varied between 16 and 150% for the formulations with essential oil.  
In Figure 1 shows that an increase in the concentration of starch and glycerol influences the films' mechanical properties. Consequently, F1 showed a value significantly higher (\(p<0.05\)) in tensile strength since the other formulations contained oils; these substances could function as a plasticizer of the system, increasing the molecular mobility. Therefore, the TS and EM decrease, and the E increases significantly (\(p<0.05\)) with the oil content. Different authors have reported that the addition of essential oils significantly changes tensile strength (TS) and elongation at break (EB) of films based on starch. For instance, [PERSON] et al., 2019 reported that adding orange essential oil into corn starch films decreased the tensile strength and elongation of the films because the film structure featured discontinuities in the presence of essential oil [23]. On the other hand, [PERSON] et al., 2013 developed cassava starch composite films incorporated with cinnamon essential oil, concluding that cinnamon essential oil significantly decreased TS and increased EB, reducing the interaction of the intermolecular forces between polymer chains [24].  
It is essential to mention that the higher the value of the modulus, the stiffer the material. In this way, the films with essential oil showed similar values, while the control film showed the maximum value in elastic modulus. These values are similar to those reported for films based on corn and wheat starch incorporated with lemon essential oil (lo). The reported results showed that the incorporation of LO caused a decrease in water content, transparency, whiteness index (WI), water vapour permeability (WVP), solubility, and tensile strength properties. In this way, they evaluated that the tensile strength decreased as the essential oil concentration increased and, conversely, the elongation at break increased compared to the control film [25]. This phenomenon could be due, as mentioned above, to an increase in molecular mobility promoted by the oils. This effect is seen in the significantly increase in elongation. Other authors suggest that the decrease in tensile strength can be attributed to the change in polymer-polymer interactions in polymer-oil interactions caused by the addition of essential oils and the mixture of both polymers. These less rigid and more deformable materials can be applied to manufacturing food packaging materials [26]. In general, similar studies highlight that the tensile strength of yarn starch films is better than wheat and corn starch films, which produce weak strength [27]. Possibly it is because the amylose content of yarn starch is higher than in cassava or wheat starch. This fact would be related to a higher crystallinity, increasing the tensile strength and rigidity of the material [28].  
Figure 1: Mean values and standard deviation of the tensile strength (**a**), elastic modulus (**b**), and elongation at a breakpoint (**c**) for the different films stored for one week at 53% RH and 25 \({}^{\circ}\)C. The formulations: 1 (without essential oil), 2 (essential oil of lime), 3 (essential oil of funnel), 4 (essential oil of lavender), 5 (essential oil of lime, funnel and lavender).