Understanding the effect of lignin on the production process and characteristics of lignocellulose nanofibrils from Eucalyptus nitens

Cellulose, hemicellulose, and lignin are the main constituents of lignocellulose nanofibrils (LCNFs). The content and modification of lignin in the pulps affect the production process and characteristics of LCNFs, showing changes in their morphology, surface, rheological, and dielectric behaviors. Due to controversy and relevance in applications, these changes still need to be explained. This work seeks to understand the effect of lignin content and its oxidation on the production process and the characteristics of LCNFs. It was possible to produce pulps with fibers of similar physical characteristics and carbohydrate content after delignification, allowing the identification of the isolated effects of in situ lignin. A lower amount of lignin facilitated the LCNF production process, generating fibrils with smaller widths (up to ~ 48%) but more considerable apparent lengths (up to ~ 73%). In addition, the viscosity of the suspensions increased for LCNFs with lower lignin content (up to ~ 3.5 times to 0.5% (w/v)), due to increased flexibility, specific surface area, and surface charge of the fibrils. Finally, the LCNFs showed four dipolar relaxations, where the glass transition temperature of lignin decreased with oxidation and increased with increasing condensed structures and decreasing S/G ratio.