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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cellulose fiber charge is a significant parameter for porous cellulose fibers, and strongly affects the swelling ability of cellulose fibers and the properties of cellulose-based materials as well. Actually, it includes surface charge and inner charge. The surface charge is mentioned often in papermaking wet-end chemistry, however, the inner charge or the total charge is paid less attention to. In this study, the cationic polydiallyldimethyl ammonium chloride (poly-DADMAC) with different molecular weight (Mw) was applied for the accessibility evaluation to the cellulose fiber charges by using polyelectrolyte adsorption technique. Results showed that higher fiber charge was detected by lower Mw poly-DADMAC (7.5-15 kDa) due to its highly efficient penetration into the fiber cell walls and neutralization with inner charges, while lower fiber charge was obtained by using higher Mw poly-DADMAC (higher than 100 kDa) because of its adsorption onto fiber surface. As a consequence, high-Mw poly-DADMAC was used to determine the surface charge of cellulose fibers, and low-Mw poly-DADMAC could be used to measure the total charge under the saturated adsorption and low ionic strength (or salts concentration). This was confirmed by SEM-EDS analysis. The low-Mw poly-DADMAC adsorption had a good agreement with conventional conductometric titration, and a linear regression equation with slope of 1.03 and regression coefficient of 0.99 was obtained. [ABSTRACT FROM AUTHOR]