Influence of cellulose chemical pretreatment on energy consumption and viscosity of produced cellulose nanofibers (CNF) and mechanical properties of nanopaper

Lignocellulosic fibers are the main sources for producing nanocellulose, in which mechanical methods are the most appropriate to achieve a high yield and generate low residue. High energy consumption is the major drawback in these processes, although they are the cheapest way to produce nanocellulose. Chemical pretreatment is one approach to further decrease the overall cost during defibrillation; however, the influence over sample viscosity and mechanical properties is yet to be investigated. Here, we study the influence of chemical pretreatments using NaOH and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) on the mechanical, rheological and structural properties of cellulose nanofibers made from bleached eucalyptus pulp. Modification of samples was evidenced by their respective peaks on FTIR spectra. Sample crystallinity increased after partial hemicellulose and amorphous cellulose removal. In addition, a strong correlation between grinding efficiency and lower energy consumption was observed. However, a mild alkaline treatment may improve fiber strength at the expense of suspension stability and energy consumption. Modified nanofibers presented good potential for enhancing mechanical properties and/or improving suspension stability.