Phosphorylated Lignin–Cellulose Nanofibrils: Elucidating the Preparation Pathway and Structural Features

Lignocellulosic nanofibrils (LCNFs) represent a promising resource-efficient alternative to lignin-free cellulose nanofibrils. Yet, developing eco-friendly pretreatments and energy-efficient disintegration of lignocellulosic biomass is essential to enable the facile production of high-quality LCNFs at low cost. This study addresses these challenges by producing multifunctional phosphorylated lignin-cellulose nanofibrils (PLCNFs) from giant reed fibers. PLCNFs containing 22.1 wt % lignin were produced through direct phosphorylation of unbleached fibers in an H₃PO₄/urea system, followed by alkali-swelling and microfluidization. This simple approach provided a higher yield than conventional lignin-free CNF production. The resulting PLCNFs exhibited a width of 3-5 nm, high aspect ratio, negative zeta potential (-30 mV), and shear-thinning behavior characteristic of a gel-like network. The incorporated phosphate moieties further enhanced flame retardancy. Overall, this work presents an inexpensive, energy-efficient, and sustainable approach to produce multifunctional PLCNFs from unbleached biomass, demonstrating the potential of renewable lignocellulosic resources for developing robust and eco-friendly nanostructured materials.