Carbohydrate-derived multifunctional liquefied cellulose as reactive polyol and filler for high-performance waterborne polyurethane: Toward sustainable wood coatings.

Liquefied cellulose (LMC), derived from microcrystalline cellulose, was investigated as a carbohydrate-based multifunctional component for waterborne polyurethane (WPU) systems. The liquefaction process generated PEG β-glucoside and PEG levulinate structures, providing both reactive hydroxyl functionalities and intrinsic cellulose residues. LMC was directly incorporated as a reactive polyol and dispersed filler to fabricate LMC-modified WPU (LWPU) via a prepolymer method. Structural analyses, including liquid chromatography-hybrid quadrupole time-of-flight mass spectrometer (LC-QTOF/MS), nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR), confirmed the formation of glucopyranoside- and levulinate-derived moieties, which enhanced hydrogen bonding interactions and promoted crosslinked network formation. Compared with conventional WPU, LWPU films exhibited significantly improved Young's modulus and thermal stability, attributed to the synergistic effects of grafted polymer structures and cellulose reinforcement. The LWPU films also demonstrated excellent ultraviolet shielding performance, with transmittance below 1% at 300 nm, arising from n-π* transitions associated with carbonyl-containing chromophores introduced during liquefaction. Thermogravimetric (TG) analysis revealed comparable thermal stability below 260 °C, while carbohydrate-derived structures contributed to enhanced char formation at elevated temperatures. These results indicate that LMC can function simultaneously as a reactive component and as an intrinsic cellulose-based reinforcing phase. LWPU1.8, prepared with a PTMG/LMC OH/OH ratio of 1/1, an NCO/OH ratio of 1.8, and 8.2 wt% LMC, showed the best performance, including high modulus, hardness, adhesion, lightfastness, and chemical resistance, confirming LMC as both a reactive polyol and reinforcing phase for sustainable waterborne coatings with improved coating durability.