Mild-depolymerized lignin for reinforced polyvinyl alcohol wood adhesives

Abstract

Developing sustainable bio-based adhesives to replace formaldehyde-based resins has become a critical priority in the wood processing industry. However, current commercially available adhesives face persistent challenges, including insufficient environmental friendliness, limited curing conditions, narrow application scopes, and an unfavorable trade-off between cost and performance. Herein, we report a novel strategy to fabricate high-performance lignin-polyvinyl alcohol (PVA) adhesives. Industrial lignin was slightly depolymerized to reduce its inhomogeneity while increasing its active hydroxyl groups, and was then diffused into a PVA solution, thereby forming a crosslinked supramolecular network. Notably, the adhesives achieve a shear strength of 6.28 MPa on poplar plywood, exceeding the Chinese national standard for Type I plywood (0.7 MPa) by more than eightfold. Remarkably, this exceptional performance is accompanied by an ultra-low free formaldehyde release of just 0.1 g·kg⁻¹ and undetectable volatile organic compounds. Importantly, the enhanced performance stems from selective depolymerization, whereby phenol-rich lignin fragments are generated to form robust cross-links with PVA chains. Furthermore, the adhesive system exhibits exceptional UV aging resistance and environmental stability, maintaining stable bonding across a broad temperature range from -196 °C to 100 °C. We have developed a sustainable, high-performance, and cost-effective adhesive tailored for the wood processing industry.