## 3 Results
While the addition of an ester resin (LF or UG) increased TPS hardness values in 12% (from 17 in neat TPS to 19 for TPS-LF and/or TPS-UG), the materials that contain the other resin additives (GR, CM, and RD) reduced TPS hardness values in 12% (from 17 in neat TPS to values up to 15) (Figure 3d). Although the hardness of polymers do not necessarily provide correlate results with other fundamental properties, since it is an empirical quantity related to the inherent indentation resistance [46], it was observed that the TPS-resin blends showed similar tend than the tensile strength values (Figure 3b). Similarly, [PERSON] et al. (2018) blended PLA with TPS in 70:30 proportion and further added increasing amounts of maleinised linseed oil (from 2 to 8 phr) to increase the compatibility between both biopolymeric matrices, and observed a decrease of Shore D values accompanied by a related decrease on the tensile strength values [28]. Comparing these results with those previously obtained for Mater-Bi(r) NF 866 blended with 10 wt. % of GR and LF, it was observed that GR decreased the Shore D values of Mater-Bi(r) NF 866 (around 8%), but it was maintained in Mater-Bi(r) blended with 10% of LF [5]. These results confirm once again the good miscibility of LF with starch polymeric matrix. The typical stress-strain curves of the materials with the toughness values of each formulation is shown in Figure 4. It was found that the addition of either GR or rosin derivatives significantly reduced the TPS toughness (\(p<0.05\)). The results show that GR has the highest toughness among the studied formulation and that the toughness values present no statistical differences when LF or RD were added (\(p>0.05\)). It is important to notice that TPS-LF presents statistically the same elongation at break and a higher Young's modulus than neat TPS (Figure 3a). Therefore, LF provides the highest strength between the studied materials. The same trend was exhibited by UG, since it is an ester of gum rosin. On the other hand, GR statistically maintains TPS Young's modulus and increases its  
Figure 3: Tensile and hardness properties of TPS and TPS-resin formulations: (**a**) Young modulus, (**b**) Tensile Strength, (**c**) elongation at break and (**d**) Shore D. \(\mathrm{a^{-d}}\) Different letters within the same property show statistically significant differences between formulations (\(p<0.05\)). elongation at break. Thus, TPS-GR would withstand greater tension that neat TPS. The other modified gum rosin additives (CM and RD) exhibit behaviour similar to GR. These results confirm a stiffening and a plasticisation effect produced by LF and GR addition, respectively. The DSC curves of TPS and its TPS-resin formulations with 10 wt. % of GR and rosin derivatives are shown in Figure 5. T\({}_{\text{g}}\) of TPS is dependent on glycerol and water contents and it could be found between 34 \({}^{\circ}\)C and 70 \({}^{\circ}\)C [47; 48]. The studied TPS exhibits the T\({}_{\text{g}}\) at 45.7 \({}^{\circ}\)C. However, the addition of gum rosin and rosin derivatives shifts the glass transition temperature to higher temperatures. For TPS-GR and TPS-RD, T\({}_{\text{g}}\) was found at 56.5 \({}^{\circ}\)C and 58.1 \({}^{\circ}\)C, respectively. Meanwhile for TPS-LF, TPS-CM and TPS-UG it was found between 70 \({}^{\circ}\)C and 80 \({}^{\circ}\)C. These results suggest that the formulations present a stiffening effect since GR and its derivatives increase the T\({}_{\text{g}}\) values, but it was more marked in those formulations blended with UG, CM and LF. The increase on T\({}_{\text{g}}\) values is very interesting for several applications (i.e., a cup for hot beverages and/or lids for hot food). GR and RD possess similar chemical structure (see Figure 1). GR is mainly made up of abietane-type acid while RD is made up of pimarane-type acids and is more stable [49]. Therefore, RD side groups are not modified [49], and its chains can move freely between TPS chains lubricating them [5].