Orientation control of cellulose nanofibrils in all-cellulose composites and mechanical properties of the films

In this study, highly oriented all-cellulose composite films were successfully prepared by mechanical drawing of water-swollen cellulose nanofibril/regenerated cellulose composite film, and their mechanical properties were investigated by tensile tests. Cellulose nanofibrils with a uniform width of ~3 nm and length of the order of a few micrometers were prepared via 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation of wood pulp and successive mechanical treatment. The nanofibrils were then dispersed in a cotton/lithium chloride/N, N-dimethylacetamide solution, and all-cellulose composite films were prepared by regenerating the cotton cellulose. The cellulose nanofibrils were individually dispersed and successfully oriented in the film by mechanical drawing, and the orientation parameter of the nanofibrils was as high as 0.80 for a draw ratio of 2.0. Although the Young’s modulus and tensile strength of the films were significantly improved by the mechanical drawing, the reinforcing effect by the oriented cellulose nanofibrils in the present all-cellulose composite were not clear, presumably because the cellulose nanofibrils are less compatible with the cellulose matrix in this study.