Effect of graphene oxide addition on the characteristics of nanocomposite films made of graphene oxide and nanocellulose obtained from recycled pulp

Films consisting of 6,6,2,2-tetramethylpiperidine-N-oxyl (TEMPO) oxidized cellulose nanofibers (TOCNFs) prepared from recycled pulp and graphene oxide (GO) were produced by the solution molding method. Electrical conductivity titration and FTIR spectra showed that recycled fibers and cellulose nanofibers were successfully oxidized and the number of carboxyl groups increased. Mechanical properties, thermal stability, crystallinity index, and morphological structure of the nanocomposite films of TOCNFs and GO were characterised by tensile strength tests, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Tensile strength of films made of TOCNFs with 1.5% GO was 61% higher than those without GO, while tensile strength TOCNF films with 3% GO decreased by 2%. The values did not differ statistically from the non-amended TOCNF. Addition of up to 3% GO did not markedly affect thermal stability of nanocomposite films. Recycled pulp had 83% crystallinity, while the crystallinity index of TEMPO-oxidized cellulose nanofibers decreased to 65.5%. SEM observations showed that TOCNFs and small amounts of GO formed nanocomposite films with a homogeneous structure. This research provides an approach for effective utilization of recycled pulp as a feedstock for cellulose nanofibers and TOCNFs/GO nanocomposite films.