Plasticization of poly(lactic acid) using different molecular weight of poly(ethylene glycol)

Poly (lactic acid) (PLA) has been known as an excellent candidate for developing the future bioplastic due to its biodegradability and competitive price. However, inherent brittleness and low thermal stability of PLA have limited its applications. Considerable studies have been developed to improve the flexibility of PLA, in which blending PLA with various plasticizers has been identified as a cost-effective way to lower glass-transition temperature (T-g) and thus improve its elongation property. In this study, PLA was modified by incorporating poly(ethylene glycol) as a plasticizer with different molecular weights ((M) over bar (w) 400, 1000, and 6000, called respectively as PEG 400, PEG 1000, and PEG 6000) via a solvent-casting blend method. FTIR was used for analyzing the chemical interaction while TGA and DSC measured the thermal behavior of PLA/PEG. The results indicated that the addition of lower (M) over bar (w) (PEG 400 and PEG 1000) could reduce the T-g due to the enhancement of chain mobility of PLA with PEG and so driving into a more amorphous states resulted reduction of melting temperature (T-m) compared to the neat PLA. Further, at a higher (M) over bar (w) of PEG 6000, the longer chain of ethylene glycol, in contrast, resulted a gradual increase in the T-g as well as T-m where the value went back to the point of neat PLA compared to the other lower molecular weight of PLA. This was due to the decrease in polymer miscibility with the increasing of (M) over bar (w). In terms of thermal stability, the addition of PEG exhibited two step degradation behavior while the neat PLA only possessed single step degradation. The presence of PEG could act as a protective barrier layer that could hinder the permeability of the volatile compound and product during decomposition reaction and thus could eventually delay and slower the degradation process. It was observed that the addition of PEG at higher (M) over bar (w) (PEG1000 and PEG 6000) exhibited a higher second degradation temperature up to 380 degrees C.