Cellulose nanofibrils (CNF), as a kind of renewable, sustainable and biodegradable natural-based nonmaterial, have shown great potential application in numerous fields owing to their outstanding properties. Some properties of CNF-reinforced materials are strongly associated with their cellulose polymorph and crystalline structure. Herein, the carboxymethylation modification of CNF was carried out by a new twice alkalization method to obtain CMCNF with different degrees of substitution. The influence of alkalization and etherification parameters on the degree of substitution (DS) of the CMCNF samples was systematically investigated. Based on the optimum process, the CMCNF sample with DS of 0.47 was achieved. Subsequently, the application feasibility of CMCNF in paper coatings and surface coating onto cellulosic paper was demonstrated. The effects of CMCNF addition on the rheological properties and water retention of paper coatings, as well as the barrier properties and mechanical properties of the surface-coated paper were studied. Results showed that the as-obtained paper coating samples exhibited a notable shear-thinning behavior and displayed strong dependence of rheological behavior on the DS and addition amount of CMCNF. Meanwhile, the water retention performance of paper coatings was greatly improved with the increased DS of CMCNF. Furthermore, the DS and addition amount of CMCNF was found to have an important influence on the overall properties of surface-coated paper. As the DS of CMCNF increased, the tensile strength, folding resistance, and barrier properties of surface-coated paper were generally improved. SEM images provided further evidence that CMCNF addition generally exerted a positive effect on the dispersion state of pigments, thus facilitating the interface performance of coating layer. The above results might support the conclusion that carboxymethylation modification may provide more opportunities for the high-value added application of CMCNF in paper coating fields.

 

Cellulose nanofibrils; carboxymethylation modification; rheological properties; paper coatings; barrier properties