The key role of lignin in the production of low-cost lignocellulosic nanofibres for papermaking applications

• Papermaking industry needs to adopt new production strategies.
• TEMPO-oxidized CNF provide a great increase of mechanical properties to paper.
• There is the need of looking for competitive but low-cost alternatives.
• Lignocellulosic nanofibres are a strong alternative to TEMPO-oxidized CNF.
• LCNF impart the same mechanical properties enhancement than TEMPO CNF.

The use of cellulose nanofibres (CNF) for the enhancement of paper’s mechanical properties has been reported by many authors. Concretely, the available literature is mainly focused on TEMPO-oxidized cellulose nanofibres. However, recent industrial research projects, in which LEPAMAP group has been involved, have demonstrated that this type of nanocellulose has unaffordable production costs for the papermaking industry. In this sense, the present work aims to produce low-cost lignocellulosic nanofibres (LCNF), finding some strong alternatives to TEMPO-mediated oxidation. For that, lignocellulosic nanofibres (LCNF) were produced from stone groundwood pulp (SGW) from pine after a chemical pulping process (sodium hydroxide and antraquinone). The effect of lignin content was studied and controlled through bleaching steps and quantified. It was found that high lignin content makes nanofibrillation difficult. The reinforcing effect of CNF was mechanically characterized by the addition of 3 wt% of CNF into different papermaking pulps. The results showed that it is possible to obtain low-cost LCNF that provide the same increase in mechanical properties than TEMPO-oxidized CNF when they are used for paper reinforcement. It was also found that lignin plays an important role in the obtaining of LCNF by fully mechanical treatments, where lower lignin contents expedite the nanofibrillation.