Oligolignol-Driven Adhesivity: Integrating Molecular Simulations and Experimental Contact Angle Analysis for Sustainable Lignin-Based Adhesives

The rational design of sustainable, high-performance adhesives from renewable resources requires a fundamental understanding of how molecular architecture dictates the macroscopic properties. Sustainable adhesive formulations, previously developed by our group through the partial substitution of phenol with lignin, were evaluated to elucidate the fundamental interfacial interactions governing their wettability on cellulose substrates. The central aim was to establish a predictive multiscale correlation between the oligolignol molecular composition and macroscopic adhesive performance. The wetting behavior of five formulations (30-70 wt % lignin) was experimentally characterized using optical tensiometry, revealing composition-dependent spreading dynamics, from rapid wetting (F1, <i>K</i> = 15.66 s^-1) to slower equilibration (F5, θ = 61.6°). Critically, molecular dynamics simulations of nonreactive formulations demonstrated exceptional agreement with experimental contact angles for high-phenol (F1: simulated 34.1° vs experimental 35.9°) and high-lignin (F5: 58.7 vs 61.6°) systems. This validation confirms that the atomistic model accurately captures the key noncovalent interactions driving wettability. The divergence for intermediate formulations (F2-F4) suggests the onset of rapid resinification phenomena beyond the scope of the simulated nonreactive model. Hydrogen bond analysis revealed that adhesive forces dominate with solvent components disrupting cellulose intermolecular bonding (up to -7.02 HBs/ns) to facilitate oligolignol adhesion. Combined distribution functions and noncovalent interaction analysis identified that specific oligolignols (CA-ββ-CA and CA-βO4-SA-ββ-SA) govern interfacial behavior through ring-stacking and T-shape conformations with the cellulose Iβ surface, forming strong and directional interactions. This work establishes a robust correlation between simulated and experimental contact angles as a novel predictive tool for lignin-based adhesive design. It directly links molecular architecture to application-critical wetting properties, reducing reliance on exhaustive spectroscopic characterization and providing a rational framework for optimizing sustainable adhesives for fiberboard manufacturing.