Lactide-derived ester oligomers for highly compatible poly(lactide) plasticizer produced through an eco-friendly process: renewable resources, biodegradation, enhanced flexibility, and elastomeric performance

Abstract

A biodegradable poly(lactide) (PLA) plasticizer system derived from renewable feedstocks was deliberately designed with an ester structure identical to as many repeating units of the PLA matrix as possible for maximized compatibility, using two solvent-free one-pot synthetic routes, resulting in elastomeric performance as well as tunable plasticization. First, hydroxyl-ended lactide oligomers were precisely prepared with target molar mass values of 330–430 g mol⁻¹ by controlled bulk ring opening oligomerization using 1-, 2-, and 3-arm initiators. They were subsequently esterificated with acetic anhydride to produce acetyl-terminated lactide oligomers (ALO) with enhanced thermal stability. T_d,5% was increased by 23–43 °C and efficient biodegradation of 78–55% was achieved. The ALO series was added as plasticizers to PLA from 10 to 50 phr (9–33 wt%), and showed the ability to lower T_g,PLA to approximately 10–20 °C in DSC analysis and complete miscibility with PLA, as confirmed by visible or UV-vis transmittance, and SEM studies. The ALO had little contribution to changes in the PLA structure on SEC traces after the thermo-mixing process. The blends exhibited reasonable migration level, and controllable mechanical characteristics with ductile-to-elastomeric properties (E′ = 889–15 MPa, σ_y = 74–7 MPa, σ_b = 69–9 MPa, and ε_b = 13–658%), when compared to those of PLA. Interesting elastomeric behaviors were observed and then evidenced by stress relaxation moduli (2.4–9.8 MPa) and small residual strains (7–17%) after recovery tests, respectively. These results suggest that the ALO series can be practical “double green” and “dual performance” plasticizers for PLA.