Assessing the influence of refining, bleaching and TEMPO-mediated oxidation on the production of more sustainable cellulose nanofibers and their application as paper additives

Abstract

Agro-wastes valorization focusses on production of high value-added products, such as cellulose nanofibers (CNF), and contributes to reduce the environmental impact of these residues. CNF have been used successfully as papermaking additives and some previsions maintain that this sector will become the most important, demanding CNF at a reasonable cost. Furthermore, the optimization of the production process of CNF from agricultural residues would contribute to the goals of a circular economy, the development of rural areas and the costs reduction by producing CNF of the minimum quality fit-for-use in recycled paper. In this study, CNF was produced from two agricultural residues; corn (C-CNF) and rape (R-CNF) stalk pulps, pretreated with bleaching, refining and TEMPO-mediated oxidation. Coagulant and cationic polyacrylamide (dual system) and chitosan were the retention systems. Results show the difficulty of predicting the effect of CNF based on their properties, as fibrillation degree or anionic charge, on the improvement of mechanical properties of recycled paper. That is proved by the low differences in tensile index (TI) improvement (∼15% by adding 0.5% C-CNF combined with dual system), obtained with CNF with very different properties. The expensive TEMPO pretreatment could be avoid by applying bleaching pretreatment to the corn pulp, increasing the TI up to 15% without affecting drainage and decoupling the simultaneous deterioration of drainage with TI improvement (drainage time decreased nearly 50% and 20% adding bleached R-CNF and C-CNF, respectively, combined with chitosan). Similar improvements on TI can be achieved by replacing the dual retention system by chitosan without addition of CNF, but the combination of CNF and chitosan allows achieving the highest TI values.