Impacts of cellulose nanofibril and physical aging on the enthalpy relaxation behavior and dynamic mechanical thermal properties of Poly(lactic acid) composite films

Abstract

We herein report the influences of cellulose nanofibril (CNF) and physical aging on the enthalpy relaxation behavior, thermal transition, and dynamic mechanical properties of eco-friendly poly(lactic acid) (PLA) composite films with 0.5–7.0 wt% CNF loadings, which were fabricated by using a facile masterbatch-based melt-compounding process. For the purpose, melt-quenched neat PLA and PLA/CNF composite films were aged physically at 45 °C for different times. The FT-IR spectra revealed that specific hydrogen-bonding interactions exist between the carboxyl groups of PLA matrix and the hydroxyl groups of CNF fillers, and that the interactions are strengthened by the physical aging. Accordingly, the increments of the peak temperature (Tp) and area (ΔHrelax) of the endothermic enthalpy relaxation at the glass transition temperature region with the aging time were suppressed significantly for the composite films with higher CNF contents, unlike the neat PLA film. In addition, the characteristic relaxation time of PLA/CNF composite films was highly enhanced, indicating the improved enthalpy relaxation and dimensional stability. This result is associated with the fact that the CNF fillers restrict the segmental mobility of PLA chains in the composite films during the physical aging at the glassy state, which was supported by the dynamic mechanical thermal data.