An efficient plasticization method for poly(lactic acid) using combination of liquid-state and solid-state plasticizers

A combined use of solid plasticizer [poly(ethylene glycol), PEG] with a nominal M-w of 2000g/mol and liquid plasticizer (epoxidized soybean oil, ESO) for plasticizing poly(lactic acid) (PLA) is proposed in this study. This plasticization method brought an obvious improvement in the melting flowability of the modified PLA, which has been verified by a lower balance torque during blending and a four times increase in the melt flow index compared to neat PLA. Meanwhile, the brittleness of this glassy polymer was also improved significantly; all composites with different contents of combined plasticizers displayed an obvious yield stage and toughness fracture surfaces. The mechanisms of the plasticizing effects were investigated by polarizing optical microscopy and scanning electron microscopy. The PLA/ESO/PEG blends formed a complex reinforcement structure. ESO existed as tiny droplets and uniformly dispersed in the PLA spherulites, and strip-shaped PEG accumulated along the boundaries of interspherulites. The combined use of these two plasticizers, a liquid one and a solid one, had an excellent effect on plasticizing PLA, not only on melt flowability but also on mechanical properties. Thus, the application areas for PLA could be further expanded, such as melt blowing and melt extrusion. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46669.