# Recent Approaches to the Plasticization of Poly(lactic Acid) (PLA) (A Review)
## 6 Conclusions  
The review demonstrates the ways to regulate plasticity and some associated characteristics (such as thermal and thermophysical parameters, rheological behavior, biodegradability, etc.) of PLA-based materials (Table 1). The basic approaches to improve PLA brittleness include copolymerization and blending with flexible polymers, introducing oligomers and low-molecular additives and structural modification. Each approach may provide good plasticity for PLA-based materials, but the application of any of them can be dictated by the final application field, further processing, etc. It can be concluded that an optimal is the application of copolymers obtained via reactive mixing as the additives to PLA and its blends with other polymers. Directed copolymerization of PLA with flexible polymers is also effective but is limited by low product yield and high cost. The use of PLA copolymers is justified not as individual materials but as compatibilizers for mechanical blends of PLA and the corresponding polymer. The introduction of oligomeric and low-molecular plasticizers is the simplest way to modify PLA; however, the effect of such plasticization persists for a short time due to the leaching of additives from the polymer. Among low-molecular additives, essential oils are of greatest interest since they provide not only plasticization but also enhancement in functionality (for instance, antimicrobial activity). Despite the high values of elongation at the breakup of PLA obtained via structural modification, the use of this approach is hindered by the fact that it must be the final stage of the material processing. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Approach** & **Tensile Strength (MPa)** & **Elongation at Breakup (\%)** & **Impact Strength (kj/m\({}^{2}\))** & \(T_{g}\) (\({}^{\circ}\)C)** & **Ref.** \\ \hline Poly(L-lactide)-b-poly(ethylene & & & & & \\ glycol)-b-poly(L-lactide) & 31 & 157 & n.d. & 30 & [33] \\ Multiblock copolymer of & & & & & \\ poly(L-lactide-co-\(\varepsilon\)-caprolactone) & 12 & 57 & n.d. & n.d. & [24] \\ (80/20 (\(w/w\))) (reactive mixing with & & & & & \\ hexamethyle discyanate) & & & & & \\ Poly(L-lactide-co–ethylene-glycidyl & & & & & \\ methacrylate) (95/5 (\(w/w\))) (reactive mixing & 67 & 270 & 6 & 66 & [29] \\ with dicumyl peroxide) & & & & & \\ Poly(L-lactide) and block copolymer of & & & & & \\ poly(L-lactide) and poly(caprolactone) & 47 & 210 & n.d. & 61 & [23] \\ (85/15 (\(w/w\))) & & & & & \\ Poly(lactic acid) and poly(butylene & & & & & \\ adipate-co-terephthalate) blend (85/15 (\(w/w\))) & 24 & 485 & n.d. & 61 & [39] \\ Poly(lactic acid) and poly(butylene succinate & & & & & \\ adipate) blend (80/20 (\(w/w\))) & 47 & 25 & 5 & 59 & [50] \\ Poly(L-lactide) and poly(ethylene glycol) & 32.5 & 140 & n.d. & 50 & [61] \\ \(400\) (90/10 (\(w/w\))) & & & & & \\ Poly(L-lactide) and L-lactic acid oligomer & n.d. & 300 & n.d. & 31 & [89] \\ (75/25 (\(w/w\))) & & & & & \\ Poly(lactic acid) with over oxidized sunflower oil & & & & & \\ (80/20 (\(w/w\))) & 18 & 230 & n.d. & n.d. & [95] \\ Poly(lactic acid) (Bioflex (BF), trade name & & & & & \\ Bio-Flex® F2110) + carvacrol + & 8 & 300 & n.d. & n.d. & [122] \\ montmorillonite (90/5/5 (\(w/w\)/w)) & & & & & \\ Poly(lactic acid) in \(n\)-pentanol (AR grade) & 12.5 & 570 & n.d. & n.d. & [131] \\ (uniaxial stretching) & & & & & \\ Pre-oriented poly(lactic acid) & n.d. & 270 & n.d. & 62 & [140] \\ (uniaxial stretching) & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Analysis of the mechanical characteristics and \(T_{g}\) of PLA-based materials obtained using various approaches to plasticization (n.d.—non-determined). **Author Contributions:** Conceptualization, E.E.M. and K.V.A. ; writing--review and editing, E.E.M. and K.V.A. ; visualization, E.E.M. and K.V.A. ; supervision, E.E.M. and K.V.A. ; project administration, E.E.M. and K.V.A. ; funding acquisition, E.E.M. and K.V.A. All authors have read and agreed to the published version of the manuscript.