Foldable Conductive Cellulose Fiber Networks Modified by Graphene Nanoplatelet-Bio-Based Composites

Truly foldable flexible electronic components require a foldable substrate modified with a conducting material that can retain its electrical conductivity and mechanical integrity even after hard mechanical manipulations and multiple folding events. Here, such a material exploiting the combination of all-biodegradable components (substrate and the polymer matrix) and graphene nanoplatelets is designed and fabricated. A commercially available thermoplastic starch-based polymer (Mater-Bi) and graphene nanoplatelets are simultaneously dispersed in an organic solvent to formulate conductive inks. The inks are spray painted on pure cellulose sheets and hot-pressed into their fiber network after drying. The resultant nanostructured flexible composites display excellent isotropic electrical conductivity, reaching very low sheet resistance value approximate to 10 Omega sq(-1), depending on the relative concentration between the biopolymer and the graphene nanoplatelets. Transmission electron microscopy results indicated that during hot-pressing, graphene nanoplatelets are physically embedded into the cellulose fibers, resulting in high electrical conductivity of the flexible composite. The paper-like flexible conductors can withstand many severe folding events, maintaining their mechanical and electrical properties and showing only a slight decrease of their electrical conductivity with respect to the unfolded counterparts. Unlike conductive paper technologies, the proposed paper-like flexible conductors demonstrate both sides isotropic conductivity due to pressure-induced impregnation.