A green one-pot strategy for sustainable fully lignin-based adhesives

Abstract

Lignin-based adhesives have emerged as a promising alternative to conventional petroleum-derived adhesives (e.g., urea–formaldehyde and phenol–formaldehyde resins), showing great potential in the plywood industry. However, the highly condensed structure and low reactivity of industrial lignin have limited its utilization in lignin-based adhesives. Here, we present a novel one-pot strategy based on triple-functional modification for the fabrication of fully lignin-based adhesives. An alkaline deep eutectic solvent (ADES) was employed to simultaneously depolymerize, demethoxylate, and hydroxymethylate industrial lignin, facilitating the straightforward preparation of a fully lignin-based adhesive in one-pot. The resulting plywood exhibits excellent overall performance, with dry and 63 °C–water bonding strengths (wet strength) reaching 1.79 MPa and 0.99 MPa, respectively, surpassing the Chinese National Standard for Class II plywood (GB/T 17657–2022). Moreover, the formaldehyde emission level of the plywood is as low as 0.076 mg L⁻¹, significantly below the strict limits of both JAS F4 star (0.3 mg L⁻¹) and E₀ grade (0.5 mg L⁻¹). In summary, this one-pot strategy aligns with the principles of green chemistry by avoiding hazardous reagents (e.g., phenol), valorizing diverse industrial lignin feedstocks, and incorporating solvent recovery, thereby offering a sustainable and scalable route to high-performance fully bio-based adhesives for the plywood industry.