Graphene Oxide Technology to Advance the Performance of Poly(lactic acid) Materials

Abstract: In the past two decades, a burgeoning biorefinery concept has grown in concert with the materials science, contributing to the rise of biobased materials that respect environment and are versatile for various applications. An excellent example is poly(lactic acid) (PLA) that exhibits high strength and desirable degradability. Unfortunately, PLA suffers from poor mechanical ductility and toughness, and low resistance to heat and water/gas permeation. In order to promote the performance of PLA and thus to broaden the application areas, this study brings to light the morphological and structural specificities for fabrication of high-performance PLA films. The proposed strategy hinges on innovative uses of graphene oxide (GO) nanostructures, giving the possibility to simultaneously tailor the crystalline morphology, mechanical and barrier properties, and degradation behavior for PLA.While recognizing the GO-enabled function in controlling the crystalline morphology of racemic PLA, the nucleation mechanism induced by GO nanosheets was elucidated as a first step. In addition to the observation of random lamellae induced by the basal planes of GO nanosheets, it was of particular interest to reveal that the ultrathin edges of nanosheets were ready to trigger the ordered alignment of PLA lamellae. The high nucleation activity of GO was further employed to preferentially accelerate the stereocomplex crystallization of PLA, which subsequently suppressed the development of homo-crystals by generation of spatial hindrance. As a result of the decoration of GO nanosheets with sterecomplex crystals, an impressive combination of barrier and thermal properties, and mechanical strength and ductility was achieved for the racemic PLA/GO composites.As a parallel approach, the morphology and structure of GO were tailored to enhance PLA-GO interactions and to improve GO dispersion: (1) few-layer nanosheets were firmly immobilized onto microsized starch particles by hydrogen bonding, permitting the creation of strong and active nanointerfaces in PLA biocomposites that enhanced interfacial interactions and facilitated filler dispersion; (2) the planar dimensionality of GO was shrunk to quasi-zero, conferring the generation of higher density of oxygen functional groups and enhanced interactions with PLA matrix, and resulting in higher nucleation activity and accelerated hydrolytic degradation.In addition to the fundamental insights into the PLA-GO interaction mechanisms, the methodologies proposed here can shape new routes to high-performance PLA materials with promising potential in a diversity of applications.