Thermostable and Impermeable “Nano-Barrier Walls” Constructed by Poly(lactic acid) Stereocomplex Crystal Decorated Graphene Oxide Nanosheets

Abstract

In contrast to the relatively clear understanding of epitaxial crystallization induced by one-dimensional nanofillers, the underlying interfacial interactions between polymer crystals and two-dimensional graphene oxide (GO) nanosheets are something of a mystery. Here, the GO-assisted formation of poly(lactic acid) (PLA) stereocomplex crystals (SCs) is disclosed from the quantitative structural analysis to the direct morphological observations at multiscale and the interaction mechanism at the molecular level. It is unexpected to observe that the edges of GO featuring rich grooves and ultralow thickness were ready to induce a layer of ordered lamellae, in clear contrast to the random growth of lamellae on the basal planes. The origin of GO-induced crystallization was appraised from the interaction point of view as indicated by the evident red-shift of a set of functional groups in the Fourier transform infrared spectroscopy spectra. More importantly, the GO nanosheets, albeit presented at an extremely low content (0.05 wt %), decorated by the preferred formation of SCs enabled the simultaneous enhancement of gas barrier properties and resistance to heat distortion. Specifically, the unique combination of greatly improved heat deformation temperature (HDT) and low oxygen permeability coefficient (PO2) for the composite crystallized at 165 °C was demonstrated (146.5 °C and 0.95 × 10–15 cm3 cm cm–2 s–1 Pa–1), outperforming pure PLA with an increment of 75% and a decrease of 77% in HDT and PO2, respectively. The proposed methodology affords elucidation of well-tailored thermal and barrier properties, which may motivate further extension of this rational design to other material combinations.