Effect of ionic liquid on chain segment motion and charge detrapping in poly(L-lactide)/ionic liquid composites

The effect of ionic liquid on the chain segment motion and charge detrapping in poly(l-lactide) (PLA)/ionic liquid (IL) composites has been investigated by means of thermally stimulated depolarization current (TSDC), scanning electron microscopy, and differential scanning calorimetry. There are four current peaks (namely, alpha, rho(1), rho(2), and rho(3) peaks, respectively) in TSDC spectra of PLA and PLA/IL composites. The alpha peak corresponds to the glass transition, the rho(1) peak is attributed to space charge trapped in the amorphous phase, the rho(2) peak is originated from space charge trapped in the interphase that includes PLA/IL interface and crystalline/amorphous interface of PLA, and the rho(3) peak is originated from space charge trapped in the crystalline phase. With the increase of IL content from 0 to 5phr, rho(2) and rho(3) peaks gradually merge into one single peak. By analyzing the characteristic parameters of these peaks, it is found that IL can accelerate the mobility of chain segments and increase structural defects in PLA/IL composites. In addition, IL decreases the stability of trapped charge in both amorphous and crystalline phases, but not affecting the stability of trapped charge in interphase.