Thermal, crystallization, mechanical and decomposition properties of poly(lactic acid) plasticized with poly(ethylene glycol)

In order to modify the brittleness of poly(lactic acid) (PLA), a series of PLA/poly(ethylene glycol) (PEG) blends were prepared by the solution-cast technique using PEG as a plasticizer. The thermal, crystallization, mechanical, and hydrophilic properties of the PLA/PEG blends were compared with those of neat PLA. It is concluded that the PLA/PEG blends change from miscible to partially miscible at the critical PEG content of 10 wt%. Above 10 wt% PEG content, the miscible PLA/PEG blends occur the phase separation, and the PEG component does not co-crystallize with PLA component with PLA and PEG crystallizing separately. The introduction of PEG reduces the intermolecular force and enhances the mobility of PLA chains, thus improving the crystallization capacity and flexibility of PLA. The PLA/PEG blends show plastic fracture behavior, yielding higher elongation and lower modulus values compared with neat PLA. Below 30 wt% PEG content, blending with PEG significantly decreases the modulus and yield stress and increases the fracture strain of PLA with an increase in the PEG content. Whereas above 30 wt% PEG content, the crystallization of PEG component results in an increase in modulus and a corresponding decrease in elongation at break of the blends. The thermal degradation temperature is in the range of 320-330 degrees C for PLA/PEG blends, in comparison with 375 degrees C for neat PLA. At ambient temperature, the desired mechanical properties are achieved by blending PLA with 30 wt% PEG. The PEG plasticizer is compatible with the PLA matrix and has a relatively low migration rate toward the blend surfaces with a low PEG content (30 wt%). J. VINYL ADDIT. TECHNOL., 24:E154-E163, 2018. (c) 2018 Society of Plastics Engineers