Synthesis and crosslinking applications of a lignin-derived phenolic monomer-blocked water-dispersible isocyanate

Water-based adhesives are extensively used in the field of wood processing industry. The addition of crosslinking agents based on reactive isocyanates is key to improving the performance of water-based adhesives, while intense and non-uniform reactions can lead to short operation periods and uncontrollable product quality. Herein, this study proposes a green and low-temperature deblocking blocked isocyanate to address this issue. Through Density Functional Theory (DFT) calculations and experimental validation, vanillin was selected as a low-temperature deblocking agent (130 ℃) from lignin-derived phenolic monomers. A novel water-dispersible blocked isocyanate (WDBI) emulsion was successfully prepared using vanillin and HDI trimer. The performance of WDBI, evaluated through appearance, particle size, and zeta potential analyses, showed that WDBI-1 (R=1:0.7) and WDBI-2 (R=1:0.8) achieved good dispersibility and storage stability for over four months. The WDBI emulsions were used as crosslinking agents to formulate water-based composite adhesives with the white latex (EVA), reaching maximal pot life of 7 days. The plywood specimens manufactured using the composite adhesive showed enhanced bonding strength, particularly for wet strength. The maximum wet strength of the plywood was 1.28 MPa, exceeding the Chinese national standard (GB/T 9846–2015).This study confirmed the low-temperature deblocking performance of water-dispersible blocked isocyanate (WDBI), which can be used to formulate high-performance water-based adhesives for clean and green production of Wood-based panel.