Bionanocomposites based on a covalent network of chitosan and edge functionalized graphene layers

Graphene has outstanding thermal, mechanical and electronic properties. Bionanocomposites are an emerging class of materials, designed with the aim of achieving advanced structural and functional properties by using biobased polymers. As biopolymer, a great interest is for chitosan (CS), poly (N-acetyl-D-glucosamine), a copolymer of linked 2-acetamido-2-deoxy-D-glucopyranose and 2-amino-2-deoxy-D-glucopyranose. Graphene and graphene related materials are increasingly used for the preparation of bionanocomposites. In this study, a high surface area graphite was edge functionalized with hydroxyl groups (G-OH) through the reaction with KOH. G-CHO, with 4.5 mmol/g of functional group, was prepared from G-OH by means of the Reimer-Tieman reaction. Carbon papers and aerogels were prepared from chitosan and graphene layers with aldehydic edge functional groups (G-CHO) able to form chemical bonds with chitosan and thus to form a crosslinked network. Characterization of the graphitic materials was performed with elemental analysis, titration, X-ray analysis and Raman spectroscopy. CS and G-CHO were mixed with mortar and pestle and carbon papers and aerogels were obtained from a stable acidic water suspension through casting and liophilization, respectively. This work demonstrates that carbon papers and aerogels can be prepared without adopting the traditional oxidation-reduction procedure, avoiding harsh reaction conditions, dangerous and toxic reagents, solvents and catalysts and paves the way for selective modification of graphene layers, exploiting the reactivity of aromatic rings.