Co-production of easily hydrolysable cellulosic substrates and UV-blocking lignin nanoparticles through “lignin-first” polyethylene glycol fractionation

A novel polyethylene glycol (PEG 400)-assisted lignin-first strategy was developed to selectively fractionate sugarcane bagasse while co-producing hydrolyzable cellulosic substrates and structurally modified lignin nanoparticles (LNPs). Under mild conditions catalyzed by Lewis acid (120 °C and 1.5 % AlCl₃), the process achieved 92 % cellulose retention, 81 % delignification, and 76 % hemicellulose removal, significantly enhancing hydrolysis efficiency to 86 %. PEG had extensive esterification or etherification modifications on the lignin aromatic monomers, as well as on its C_a position, side-chain aliphatic –OH, and phenolic –OH. PEG-modified lignin retained high β-O-4 linkages, limited recondensation, and improved hydrophilicity, enabling the LNPs preparation with uniform and small particle sizes. Structural analyses revealed that lignin S/G ratio, β-O-4 linkages, molecular weight, and contact angle (R² > 0.84) strongly influenced the self-assembly of LNPs. The application of LNPs has been broadened in UV-blocking materials, particularly for protecting against ultraviolet A wavelengths (320–400 nm). They demonstrated good biocompatibility, with 94 %–99 % cell viability, alongside enhanced antioxidant activities (1.25–7.6 times higher) and photostability. Adding 1 %–7 % of LNPs elevated the sun protection factor of commercial sunscreen (∼46) to an impressive range of 91.6–143.5. This work offers an efficient and sustainable route for co-producing fermentable sugars and functional lignin-based materials, contributing to a circular bioeconomy.