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, significantly below the strict limits of both JAS F4 star (0.3 mg/L) and E0 grade (0.5 mg/L). 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.