Sustainable preparation of lignocellulosic nanofibrils and cellulose nanopaper from poplar sawdust

Lignocellulosic nanofibrils (LCNFs) are isolated from poplar sawdust via a sustainable preparation approach based on recyclable p-toluenesulfonic acid (p-TsOH) treatment and high-pressure homogenization. The obtained LCNFs show a network structure with a width of 15–30 nm and a length up to several micrometers. When hydrolysis duration is less than 60 min, the LCNFs exhibit high crystallinity (62.32%), good thermal stability (Tmax = 367 °C), and fine dispersibility in water. Lignocellulose nanopapers (LCNP) are prepared using the LCNFs via simple vacuum filtration, which show superior mechanical performance and excellent UV-blocking function. The optimized LCNP presents high mechanical strength (up to 164.0 MPa) and toughness (up to 12.3 MJ/m3), as well as good flexibility. We conclude that LCNF-derived LCNP can be finely adjusted by varying the residual lignin content, providing a rationale for LCNFs selection. This work offers a sustainable, optimized strategy for valorization and full utilization of low-value poplar sawdust into value-added LCNFs and LCNP.