## 2 Results
### Direct Functionalization of PLA Backbone: Towards PLA-Based Graft Copolymers
#### 2.2.1 PLA-\(g\)-Maleic Anhydride (PLA-\(g\)-MA)
With the addition of PLA-\(g\)-MA, the mechanical properties of the material were significantly improved. It was found that a 3% PLA-\(g\)-MA was the best compatibilizer composition to achieve the best performance of the material [44]. The reverse reaction of a maleic anhydride on NR (NR-MA), followed by reaction on PLA in a radical medium, was also performed with similar results regarding mechanical properties [46; 47]. However, in this case, the proposed mechanism does not involve a reaction on the PLA backbone but only the alcohol chain end, which reacts on the backbone of NR-MA (Figure 10). PLA-\(g\)-Polyester  
Other degradable and flexible polyesters are now being developed on an industrial scale, such as polybutylene adipate-co-terephthalalate (PBAT), polybutylene succinate (PBS) or poly \(\epsilon-\)caprolactone (PCL); the first two examples are derived from renewable resources. Blends of PLA with these polyesters are good candidates for improving the brittleness and toughness of PLA while maintaining the biodegradability of the blends. Unfortunately, these blends are largely incompatible, especially with PBAT, due to its structure, which contains aromatic rings [48]. As with PLA/NR blends, PLA-\(g\)-MA was used as a reactive compatibilizer whose possible reaction of the alcohol chain end of PBAT with the grafted anhydride is shown in Figure 11.  
Typically, the reaction is carried out in a co-rotating twin screw extruder at a temperature between 160 and 180 \({}^{\circ}\)C and a screw speed of 25-100 rpm [49; 50]. Effective grafting of PBAT was demonstrated by a drastic increase in the molecular mass of the copolymer, from 10 kDa to ca. 20 kDa. The mechanical properties of the PLA/PBAT blend were only slightly improved despite the incorporation of PLA-\(g\)-MA. However, the improvement of the interfacial adhesion between PLA and PBAT was evidenced by SEM micrographs. A very limited compatibility effect of the addition of PLA-\(g\)-MA in PLA/PBAT/TiO\({}_{2}\) blends was also observed, with TiO\({}_{2}\) acting as a nucleating agent [51]. The addition of CaCO\({}_{3}\) to PLA/PBAT/PLA-\(g\)-MA blends resulted in an increase in Young's modulus [52]. Figure 10: Proposed mechanism for the grafting of NR-MA on PLA (from [PERSON] et al. [47], copyright Wiley-VCH GmbH. Reproduced with permission). [PERSON] et al. studied PLA and PBS blends in the presence of PLA-\(g\)-MA or toluene diisocyanate (TDI) as compatibilizers [53]. They showed that TDI is a more effective compatibilizer than PLA-\(g\)-MA for PLA/PBS blend films, their failure mode changed from brittle to ductile due to the improved compatibility. The effect of PLA-\(g\)-MA was also studied on PLA/PBAT/thermoplastic starch (TPS) ternary blend films. The thermal stability, tensile properties and compatibility of the PLA, PBAT, and TPS blends were slightly improved with the addition of the compatibilizer [54]. In the case of PLA/PCL with non-compatible blends, a reaction of MA with PCL is more likely to occur between the anhydride and OH groups on the PCL chain ends. As in the case of PBAT, it is the terminal alcohol of the PCL that reacts with the grafted anhydride of the PLA chain (Figure 12A) [55]. According to the authors, the compatibility effect of PLA-\(g\)-MA was shown by SEM micrographs (Figure 12B) and by a significant increase in the elongation at break of the material, from 7% in PLA or in a mixture of PLA and PCL to 53% in a compatibilized blend. Figure 11: Possible reaction between PLA-\(g\)-MA and PBAT (from [PERSON] et al. [50], copyright Elsevier, reproduced with permission). Figure 12: (**A**) Proposed reaction scheme between PLA-\(g\)-MA and PCL (**B**) SEM micrographs of PLA/PCL blends (**a**) without and (**b**) with 10% PLA-\(g\)-MA (adapted from [PERSON] et al. [55], copyright Springer, reproduced with permission).