## 3 Results
It is seen that the spectra of the formulations are similar to that of neat TPS. This is expected since the resins content is 10 wt. %. [PERSON] and [PERSON] (2015) have reported a similar behaviour when working with starch films blended with chitosan added in 0.37-1.45 wt. % [57]. Further, there are no significant shifts in the characteristic peaks of TPS, which indicates that the interaction with the resins is not strong enough to be detectable with this technique in accordance with [PERSON] et al. (2017) [54]. Nevertheless, two main differences can be observed in the spectra of TPS-resin blend formulations with respect to neat TPS. The first one is referred to the reduction of the -OH group band related with the bound water, found at 3284 cm\({}^{-1}\) and at 1648 cm\({}^{-1}\). A reduction in this peak indicates that when TPS is blended with resins, the -OH groups of TPS have more affinity with resins than with water. Therefore, -OH groups are involved in positives interaction with GR and/or resin derivatives such as hydrogen bonding [57]. The second difference was found in the region between 2000 cm\({}^{-1}\) and 1500 cm\({}^{-1}\) (see zoom in Figure 7). In TPS-CM signals of -C=O stretch of maleic anhydride appeared as low intensity peaks at 1780 cm\({}^{-1}\) and 1850 cm\({}^{-1}\)[58]. In TPS-LF and TPS-UG a low intensity band was found at 1727 cm\({}^{-1}\). This band is representative of the -C=O stretching of the ester group [43]. In TPS-GR and TPS-RD the peak of stretching of the carboxylic group (-C=O) is found at 1692 cm\({}^{-1}\)[5]. Those displacement of carbonyl group band suggest an hydrogen bonding interactions between TPS and the respective resins [5; 59]. Finally, the morphology and microstructure of the cryo-fractured surfaces of TPS as well as the effect the gum rosin presence on the TPS matrix were studied by SEM (Figure 8). No apparent phase separation is observed in the SEM image of the cryo-fractured surfaces of plasticized corn starch with glycerol and water (Figure 8a), confirming the homogeneous dispersion of glycerol and water in corn starch matrix and the successful formation of TPS. Moreover, neat TPS shows a smooth fracture surface typical of TPS with amylose content around 25-30% [52]. No apparent phase separation was observed in TPS-resin blends regardless the resin used, indicating that all resins are well incorporated to the TPS matrix (Figure 8b-f). All TPS-resin blend formulations showed a much rougher behaviour in accordance with the increased stiffening effect. Among al TPS-resin blend formulations, TPS-GR (Figure 8b) and TPS-RD (Figure 8e) show much cracked surface. Moreover, in TPS-GR (Figure 8b), some micro-voids are observed (see inset Figure 8b), which are probably responsible of the reduction of the mechanical resistance of this formulation as reveals the marked reduction of the tensile strength (Figure 3b) and Shore D hardness (Figure 3d). Similarly, TPS-RD (Figure 7e) shows some micro-domains that in some cases shows phase debonding (see inset Figure 8e), with the corresponding reduction of the tensile strength (Figure 3b) as well as Shore D hardness (Figure 3d). Meanwhile, in TPS-CM (Figure 8c), TPS-LF (Figure 8d) and TPS-UG (Figure 8f) formulations, resin particles appear homogeneously dispersed as small spherical domains (see inset Figure 8c for TPS-CM, inset Figure 8d for TPS-LF and inset Figure 8f for TPS-UG). In a previous work, Mater-Bi\({}^{\circledR}\) NF 866 was blended with 10 wt. % of LF and SEM micrographs shows poor interfacial adhesion between the polymeric phases since small domains with empty interface were observed [5]. Thus, the results obtained here suggest that LF possess good miscibility with starchy matrix (see inset Figure 8d). In fact, in a more detailed microscopic analysis somewhat improvement in the miscibility between the amorphous and semi-crystalline phases of thermoplastic starch due to the LF gum rosin derivate addition was observed for the already commented Mater-Bi\({}^{\circledR}\) NF 866 blended with 10 wt. % of LF [37].