Integration of Aromatic Polyurea and Dialdehyde Cellulose as High-Performance Hybrid Resin Adhesives for Bonding Wood

The wood adhesive with excellent bondingstrength and waterresistance was synthesized from aromatic polyurea and dialdehyde cellulose. The development of wood adhesives that exhibit robustadhesion,exceptional water resistance, sustainability, affordability, nontoxicity,and simplicity is highly recommended for practical applications. Inthis study, the structure of microcrystalline cellulose was successfullymodified with dialdehyde groups based on previous reports. Aromaticpolyamines and urea were polymerized into phenyl-polyurea (Ph-U) through fusion and condensation, without the use of catalysts orsolvents. The DAC-Ph-U adhesives were synthesized throughthe reaction between dialdehyde cellulose (DAC) and Ph-U under ambient conditions. Reinforcing and cross-linkingeffects of Ph-U on its properties were systematicallyinvestigated. The mechanical, adhesive, and water repellent propertieswere enhanced through the introduction of aldehyde (from DAC) and amino group (from Ph-U) interactions into thecross-linking structure with Schiff base cross-linking. The interactionof covalent (C=N) and multiple non-covalent bonds in the cross-linkedsystem functions as a hydrophobic barrier, impeding water infiltrationinto the bonding interface. The bonding strength test revealed thatthe optimal strength of DAC-Ph-U adhesives reached 2.91MPa (dry strength), 1.96 MPa (after 63 & DEG;C water immersion), and1.75 MPa (after burning water immersion), respectively. Its comprehensiveproperties were not only superior to traditional formaldehyde-basedresin adhesives but also far higher than the requirements of industrialwood-based panels. This study provides ideas for replacing fossilaldehydes such as formaldehyde, glyoxal, glutaraldehyde, etc. in woodadhesive fields and can be potentially generalized to reinforce theperformance of biocomposites, coatings, plastics, hydrogels, etc.