To design a more efficient plasticizer for PLA based on PEG derivative, the miscibility enhancement of PLA/PLAx-PEGy-PLAx blends were investigated by both atomistic and mesoscale simulations. Flory-Huggins interaction parameters (χ ij ) of PLAx-PEGy-PLAx blends, with PLA block fractions = 0.1–0.5, were calculated using molecular dynamic (MD) simulation to determine the miscibility of PLA/PLAx-PEGy-PLAx blends and compared with PLA/PEG blends (Takhulee et al. J Polym Res 24:8, 2017). Based on the calculated χ ij and radial distribution functions, PLA/PLAx-PEGy-PLAx showed better miscibility compared to PLA/PEG. The values of χ ij for PLA/PLAx-PEGy-PLAx blends are always lower than those for PLA/PEG blends at the same PEG composition. For PLA/PLAx-PEGy-PLAx blends, χ ij increased as a function of PLA block fractions. Mesoscale properties of PLA/ PLAx-PEGy-PLAx blends were then determined using dissipative particle dynamic (DPD) simulation. Smaller PEG domain in PLA/PLAx-PEGy-PLAx blends was observed, compared to that in PLA/PEG blend. Miscibility behavior of PLA/PLAx-PEGy-PLAx blends was investigated by experiments at selected conditions based on the simulation results. By differential scanning calorimetry measurements, acceleration of the crystallization of PLA matrix by blending PLAx-PEGy-PLAx was observed. Although PLA/PEG 70/30 (wt/wt) blend was phase separated when slowly cooled from the melt, due to the crystallization of PEG component, this phenomenon was not observed in PLA/PLAx-PEGy-PLAx blends. The melting temperature (T m ) depression of PLA/PLAx-PEGy-PLAx blends was also more pronounced. From dynamic mechanical analysis, the storage (G′) and loss moduli (G′′) curves in terminal region were determined. The slope of G′ curves for PLA/PEG 75/25 and 70/30 (wt/wt) was less than 2 while this deviation was found only at 70/30 (wt/wt) for PLA/PLAx-PEGy-PLAx. These results indicate that PLAx-PEGy-PLAx is better miscible with PLA.
Journal of Polymer Research – Springer Journals
Published: Oct 4, 2017
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