Fabrication of lignin-containing cellulose nanofibrils with unique properties via a simple PEG-assisted strategy

Lignin-containing cellulose nanofibrils (LCNFs) present a promising avenue for the development of sustainable nanomaterials, leveraging the inherent thermal stability and hydrophobicity of lignin while circumventing energy-intensive delignification processes. Despite this potential, the structural rigidity and poor compatibility of lignin with cellulose have hindered its application in high-performance materials. Here, we report a one-pot pretreatment strategy incorporating polyethylene glycol (PEG) to achieve in-situ lignin modification via α-etherification (PEGylation). This approach effectively suppresses lignin condensation and preserves native β-O-4 linkages, thereby imparting enhanced functionality to lignin, including improved hydrophilicity, surface charge, and optical transparency. The PEG-modified pulp was readily fibrillated into LCNFs with diameters of 3-6 nm. The resulting PEGylated LCNFs suspension exhibited a lighter color, increased viscosity, and stronger gel-like behavior, indicative of enhanced dispersion and interfacial stability. Films fabricated from these LCNFs demonstrated improved mechanical properties, with tensile strength and elongation at break increasing by 148 % and 114 %, respectively. Density functional theory simulations suggested that the long PEG chains were introduced to hydrogen-bonding sites within lignin, thereby reinforcing molecular mobility, interfacial compatibility, and the tunable amphiphilicity of the PEGylated lignin. The introduction of PEG chains intensified lignin-cellulose interactions, which contributed to improved films cohesion and flexibility. Overall, this work provides a scalable approach to engineering lignin within lignocellulosic biomass, enabling the production of high-performance cellulose nanofibril-based composites and advancing the valorization of renewable carbohydrate polymers.