Geraniol-Initiated Lactide Oligomers for Plasticizing Polylactide

In order to improve the ductility of polylactic acid (PLA), a fully biobased lactide oligomer, GLO4 was synthesized through the polymerization of l-lactide initiated by geraniol. GLO4 exhibits better comprehensive effect than commercial tributyl acetyl citrate on PLA, increasing the ductility with good durability. By incorporating 20 wt % GLO4, the glass transition temperature of PLA reduces to 31 °C. The elongation at break of PLA increases remarkably to the range of 271.4–514.5%, with 10–20 wt % loading. The effect of chain length (repeating lactic acid units ≈ 4, 12, 24) on the plasticization efficiency of geraniol-initiated lactide oligomers (GLOs) was studied. The possible mechanism was analyzed by molecular dynamics simulation. It was determined that the plasticization efficiency decreased with the increasing chain length of GLOs, which could be explained by the gradually strengthened interactions between the oligomers and PLA chains. All oligomers show good miscibility with PLA through the appearance and morphology analysis. Grafting based on the double bonds of geranyl groups was tried by adding dicumyl peroxide to repair the mechanical properties of PLA, but the geranyl groups were stable. The migration rates of oligomers were low (<1 wt %) in water, n-hexane, and 70 °C surroundings. The transparency and ductility of all plasticized PLA blends can be maintained after 90 days, indicating good durability. The result of this study adds a new choice to the environmentally friendly plasticizers for PLA and may be helpful for the further development of sustainable additives for PLA.