A dual-network structure enables synergistic improvement in strength and toughness for nanocellulose-modified UV-cured waterborne polyurethane wood coating.

The UV crosslinking technology for waterborne polyurethane (WPU) coatings integrates the environmental benefits of WPU with the superior performance characteristics of solvent-based polyurethanes, including rapid film-forming ability, exceptional mechanical properties, and superior chemical resistance. However, attaining an optimal balance between mechanical strength and toughness remains a critical challenge. To address this limitation, the present study proposes a multi-scale interface engineering strategy featuring synergistic design at molecular and structural scales. Through the molecular-scale interface design, trimethylolpropane (TMP) and 2-hydroxyethyl methacrylate (HEMA) were employed to introduce crosslinking structures and CC groups into prepolymer chains respectively, significantly enhancing the crosslinking density of polyurethane macromolecular chains, thereby improving the coating's mechanical strength and solvent resistance. Further structural-scale interface design incorporated UV-crosslinkable nanocellulose entanglement networks into the resin crosslinking system, forming a dual-network structure with multi-scale interfacial bonding. This effectively leveraged multi-scale interface effects, resulting in the optimized coating (WPUA-T-K) demonstrated 32.21 % strength and 11.43 % modulus improvements over commercial UV coatings, with 22.06 times higher elongation (41.48 % vs 1.88 %), successfully achieving strength-toughness synergy. Additionally, the coating demonstrated comparable mechanical properties, chemical resistance, and curing time to commercial waterborne UV coatings. This strategy provides new insights for the design, synthesis, and modification of WPU wood coatings.