Enhancing the inter-fiber bonding properties of cellulosic fibers by increasing different fiber charges

Cellulosic fiber has been increasingly used in many fields. The fiber charge, including the surface charge and inner charge, affects the properties of cellulosic fiber and fiber-based materials significantly. In this study, the cellulosic fiber was subjected to different treatments, including 2,2,6,6-tetramethyl-piperidine-1-oxyl radical-mediated oxidation, carboxymethyl cellulose attachment and mechanical refining, to alter the fiber charge selectively. The effects of the fiber surface charge and inner charge on fiber performances and inter-fiber bonding strength for improving the high-value application of cellulosic fibers, respectively, were discussed. The results showed that the performances of cellulosic fiber can be improved with the increase of either surface or inner fiber charges, including the increased water retention value, flexibility and inter-fiber bonding strength, but with slightly decreased drainability. An increasing bulk fiber charge showed more significant enhancement of the inter-fiber bonding strength than only an increase of the fiber surface charge on cellulosic fiber. This was because the fiber inner charge contributed to the increase of fiber flexibility and deformability, which could benefit the inter-fiber bonding indirectly. As a consequence, the bulk fiber charge enhancement was better for tensile strength improvement of handsheets (fiber-based material) than only fiber surface charge enhancement. Increasing both the surface charge and inner charge improved the tensile strength effectively with less change of the bulky fiber network than the refining treatment.