Dual physical-chemical roles of lignin-containing cellulose nanofibrils in in-situ interfacial anchor-regulated hybrid polymerization of transparent PMMA nanocomposites

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Developing strong, transparent, and sustainable biobased poly (methyl methacrylate) (PMMA) nanocomposites is of great significance in the field of high-performance engineering plastics. Here, we report a green and resource-efficient route to PMMA nanocomposites via an in-situ interfacial anchor-regulated hybrid polymerization that extends the role of nanocellulose beyond passive stabilization. Lignin-containing cellulose nanofibrils (L-CNFs), featuring moderate hydrophobicity (water contact angle = 80.6°), high aspect ratio (diameter ~ 1.8 nm, length ~ 1.8 μm), and reactive maleic anhydride groups, stabilize MMA droplets, confine phase separation, and participate in covalent interfacial grafting during polymerization. This droplet-confined hybrid mechanism produces uniformly dispersed PMMA nanoparticles (<300 nm) with high molecular weight (~8.8 × 10 5 Da) and moderate dispersity (PDI = 1.9), independent of initial droplet size. The resulting L-CNF/PMMA films combine high optical clarity (88% transmittance, 5% haze), enhanced stiffness and toughness (Young's modulus +0.8 GPa at 2 wt% L-CNF), and improved thermal stability, while avoiding additional surfactants, crosslinkers, or harsh chemical treatments, demonstrating a step- and resource-efficient, sustainable process. By coupling physical interfacial confinement with chemical anchoring, this work paves a new path to overcome the traditional compatibility barriers between hydrophilic biomass and hydrophobic polymers, offering an adaptable platform for creating transparent and mechanically robust thermoplastic composites.