Totally-Chlorine-Free Bleaching Alternatives to Produce Sugar Beet Pulp Cellulose Nanofibers

1.1 Background A simple, one-pot process can be applied to sugar beet pulp (SBP), a low-lignin biomass, to produce cellulose nanofibers (CNF). However, this process uses sodium chlorite for bleaching. This work explores both the replacement of sodium chlorite (SC) with the environmentally friendly peracetic acid (PAA), both exogenous and in-situ generated, and how the choice of peroxyl or free-radical bleaching mechanism affects this reaction. 1.2 Results PAA bleached CNFs (PAA-CNF) were very close to SC bleached CNF (SC-CNF) in terms of colour and whilst the peroxyl mechanism whitened the pulp, free-radical bleaching darkened the pulp. PAA and Fenton-oxidised CNFs showed higher levels of lignin content than SC oxidised CNF but were more viscous. The CNFs all showed stability incipiently, with zeta potentials from − 17 to -23 mV. PAA-CNF formed thicker films with a lower tensile strength and higher Youngs modulus than SC-CNF films due to their higher lignin content. Moreover, the in-situ generation of PAA CNFs were similar quality to CNF bleached by exogenous PAA. 1.3 Conclusions In this study, we demonstrate three successful alternatives for replacing sodium chlorite in our CNF production method. After PAA oxidation the lignin remains, yet the resultant CNF suspensions are more viscous and equal in whiteness to SC-CNF. Overall this work shows how we can innovate an entirely chlorine-free, enzyme-mediated production processing that represent an advance for the safety and reduction of toxicity of the process, and further the development of upcycling of secondary biomass into sustainable alternatives for biomaterials.