Further understanding the influence of fiber surface and internal charges on the interfiber bonding capability and resulting paper strength

Lignocellulosic fibers, which are abundant and biodegradable, have shown great application potential in many fields. The fiber charge, which characterizes the amount of acidic groups in lignocellulosic fiber, can have an important effect on the fiber performance during papermaking, ultimately affecting the architecture of fibrous matrices. In this study, carboxylic acid groups were installed using 2,2,6,6-tetramethyl-piperidine-1-oxyl radical (TEMPO) oxidation system or carboxymethyl cellulose (CMC) adsorption, which contributes to a greater extent to fiber total charge and fiber surface charge, respectively. The ultimate aim was to investigate the effects of different fiber charges across the cell wall on the bonding characteristics of the fiber matrix. It was shown that the fiber total charge enhancement was more significant than fiber surface charge enhancement in strengthening interfiber bonding capability. This can be effectively interpreted as being due to a higher deformability of the wet fiber as a result of an increased number of charged sites in the interior of the fiber cell wall (internal charge) for the TEMPO-oxidized fiber, and thus a larger interfiber bonded area. Additionally, the acidic groups on the fiber surface (surface charge) were responsible for the force of unit bonded area. These studies can provide guidance to produce high-strength lignocellulosic fiber-based products (such as fiber-based paper or paperboard) with relatively low density.