## 3 Results  
TPS was successfully produced from corn starch plasticised with glycerol and water and then it was further used to prepare TPS-resin blends by melt extrusion using GR and GR derivatives. Both neat TPS as well as each TPS-resin compounding were further processed by injection moulding. Injection moulded samples of TPS-resin blend formulations were successfully obtained without any change in the injection moulding processing parameters with respect to neat TPS. It is known that during the melt-extrusion and injection moulding process, bio-based polymeric matrices can suffer degradation due to the strong shear stresses that act in the viscous molten polymer [22; 41]. In fact, injection moulding parameters (i.e., injection speed, barrel temperature and back pressure) significantly affect the impact strength of the polymeric matrices [42]. Thus, injection moulded polymers for rigid packaging are required for high mechanical performance to overcome the strong shear stresses during processing to successfully obtain injected moulded parts as well as to offer the desired mechanical resistance during service. Thus, tensile tests measurements up-to-rupture as well as Shore D hardness were assayed on injected TPS and TPS-resin blend formulations (Figure 3). Results show that TPS is a brittle polymer with a Young's modulus of 11.93 MPa (Figure 3a), a tensile strength of 2 MPa (Figure 3b) and a strain at break of 63.46% (Figure 3c). Young's modulus of TPS-GR, TPS-CM, TPS-RD and TPS-UG have no statistical differences among them nor with TPS (Figure 3a, \(p>0.05\)). TPS-LF is the only formulation that presents a statistically higher modulus with respect to TPS (\(p<0.05\)), indicating a stiffening effect due to LF addition to the TPS matrix. These results show that LF increased the mechanical properties in the formulation due to a reinforcement effect, which increases the TPS modulus by 55%. This reinforcement effect is because LF increases the cohesion between the starch phases [37]. The ester groups in LF interacted with the starch hydroxyls groups by hydrogen bonding interactions which leads to the compatibilisation of both components [43]. In a previous work we have blended Mater-Bi(r) type bioplastic (Mater-Bi(r) NF 866 which is composed of TPS, polybutylene adipate-co-terephthalalate (PBAT) and poly(\(\varepsilon\)-caprolactone) (PCL) with LF and we observed that 10 wt. % was not able to significantly improve the Young's modulus of the neat polymeric matrix, while it requires higher amounts (i.e.,: 15 wt. %) to significantly increase it [5]. The higher Young's modulus obtained here shows that LF possess good miscibility with starch matrix, being the only resin able to significantly increase the Young's modulus of TPS. In fact, in a more detailed microscopic analysis it was observed that LF not only possess good miscibility with starch phase of Mater-Bi(r) NF 866, but also it was able to increase the miscibility between the semi-crystalline and the amorphous phases of thermoplastic starch (TPS) [37]. The TPS tensile strength (Figure 3b) was significantly reduced when all the additives were incorporated to the polymeric matrix, being TPS-LF and TPS-UG the formulations with the highest tensile strength among the studied samples. Regarding the flexibility of the materials, the results show that the elongation at break significant (Figure 3c, \(p<0.05\)) increased only when unmodified GR was added to the TPS matrix. GR act as a plasticiser as it increased neat TPS elongation at break in 43%. The plasticising effect of gum rosin has been already observed for other bioplastics such as PLA [44], PCL [45] and Mater-Bi(r) NF 866 [5]. Meanwhile, the other gum rosin derivatives produce no significant effect on the elongation at break of neat TPS (Figure 3c, \(p>0.05\)). Hardness properties of TPS and the formulations with GR and rosin derivatives were also measured (Figure 3d). All the formulations presented significant differences with TPS Shore D hardness (\(p<0.05\)).