Integration\nof Aromatic Polyurea and Dialdehyde Cellulose\nas High-Performance Hybrid Resin Adhesives for Bonding Wood

The development of wood adhesives that exhibit robust\nadhesion,\nexceptional water resistance, sustainability, affordability, nontoxicity,\nand simplicity is highly recommended for practical applications. In\nthis study, the structure of microcrystalline cellulose was successfully\nmodified with dialdehyde groups based on previous reports. Aromatic\npolyamines and urea were polymerized into phenyl-polyurea (Ph-U) through fusion and condensation, without the use of catalysts or\nsolvents. The DAC-Ph-U adhesives were synthesized through\nthe reaction between dialdehyde cellulose (DAC) and Ph-U under ambient conditions. Reinforcing and cross-linking\neffects of Ph-U on its properties were systematically\ninvestigated. The mechanical, adhesive, and water repellent properties\nwere enhanced through the introduction of aldehyde (from DAC) and amino group (from Ph-U) interactions into the\ncross-linking structure with Schiff base cross-linking. The interaction\nof covalent (C=N) and multiple non-covalent bonds in the cross-linked\nsystem functions as a hydrophobic barrier, impeding water infiltration\ninto the bonding interface. The bonding strength test revealed that\nthe optimal strength of DAC-Ph-U adhesives reached 2.91\nMPa (dry strength), 1.96 MPa (after 63 °C water immersion), and\n1.75 MPa (after burning water immersion), respectively. Its comprehensive\nproperties were not only superior to traditional formaldehyde-based\nresin adhesives but also far higher than the requirements of industrial\nwood-based panels. This study provides ideas for replacing fossil\naldehydes such as formaldehyde, glyoxal, glutaraldehyde, etc. in wood\nadhesive fields and can be potentially generalized to reinforce the\nperformance of biocomposites, coatings, plastics, hydrogels, etc.