Green and facile synthesis of tetrahydrogeraniol-initiated lactide oligomers for plasticizing polylactide

To develop a sustainable and compatible plasticizer for polylactide (PLA), lactide oligomers (LOs) with full biocarbon were synthesized through bulk ring-opening polymerization, initiated by tetrahydrogeraniol. The effects of lactic acid chain length (4, 12, 24 theoretical repeating units) and terminal group (tetrahydrogeranyl and ethyl) on plasticization efficiency were studied. It was determined that the plasticization efficiency decreased with the increase in repeating units and the decrease in terminal alkyl chain length, which could be explained by the strengthened interactions. The LOs have good compatibility with PLA, which can be seen from the high transparent appearance of PLA blends, no phase separation in morphology, one glass transition temperature, low migration rate (<1 % in water, n-hexane and 70 °C) and good durability (performance can be maintained more than 90 days). Tetrahydrogeraniol-initiated lactide oligomer with 4 repeating lactic acid units (TLO4) exhibits higher plasticization efficiency and better durability than commercial acetyl-tri-n-butyl citrate. The elongation at break of the PLA blend is remarkably increased by adding 10 wt% TLO4 (323.9 %) and can further reach 453.1 % (20 wt% loading), with a low glass transition temperature at 32 °C. The crystallization ability of PLA was enhanced by a small amount of LOs, without a noticeable increase in crystallization rate. The molecular dynamics simulation was used to help understand the plasticization mechanism of LOs. 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.