Biodegradable biopolymer–graphene nanocomposites

Graphene’s invention has catalyzed many new material applications in different fields. It has been used in combination with different biopolymers to design nanocomposites with improved mechanical, thermal, electrical, as well as, gas-, and water vapor-barrier properties. This review focuses on the chemistry and synthesis of graphene oxide (GO) and sheds some light on the different ecological pathways available for graphene oxide synthesis and reduction. The major pathways for graphene incorporation into biopolymers include (1) solution intercalation, (2) melt intercalation, and (3) in situ polymerization. The fabrication, application, and mechanisms of bonding between biodegradable biopolymers, like poly (lactic acid), cellulose, starch, chitosan, alginates, polyamides, and other biodegradable materials, with different forms of graphene including graphene oxide (GO), reduced graphene oxide (RGO), graphene nanoplatelets (GNP), etc., are the focus of this review. The paper has been organized according to different methods of incorporating graphene derivatives into biopolymers, in order to highlight the mechanisms for chemical bonding-physical changes that biopolymers and graphene nanofillers undergo during the method of preparation and the impact of chemical changes on end use properties. The information has been assembled, so that new conclusions can be drawn from the available data. The mechanism of enhancement of functional properties is evaluated using techniques including fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the synergy resulting from the use of different spectroscopic techniques is discussed beyond what the individual authors have been able to interpret often from a few techniques. Effectiveness of solvents used and reaction conditions have also been focused, in order to offer mechanistic understanding for the improvement of mechanical properties. The new observations and findings by comparing all relevant literature will help the reader to look at the whole spectrum of available methods and materials, in addition to focusing on the original biopolymer–graphene work.