Developing a water-resistant cellulose-based wood adhesive based on dual dynamic Schiff base and disulfide bonds

Cellulose-based adhesives have been a research focus in the wood composites industry in view of their eco-friendly characteristics with little negative impacts on human health and ecology. Water-resistant property of the adhesives, however, is still a remaining challenge in the wood-based industries to compete with conventional petroleum-based ones. Herein, microcrystalline cellulose (MCC), a natural and renewable biomacromolecule with extensive resource, was selected as matrix material. Firstly, the hydroxyl groups on C2 and C3 in MCC were oxidized to aldehyde groups in the presence of periodate, resulting in the formation of dialdehyde cellulose (DAC). In consideration of the weak water-resistance of DAC, an integrated strategy that combined DAC with cystamine (CA), was proposed, and a water-resistant cellulose-based DAC-CA adhesive was developed through the cross-linking reaction between DAC and CA. Furthermore, in order to make the adhesive adequately exert the function for bonding of poplar veneer, we performed the interfacial treatment on the poplar veneer using sodium periodate. The performance and structural characteristics of the prepared DAC-CA adhesive were systematically and thoroughly investigated using a multi-spectroscopy technique. The results revealed that the wet bond strength of the DAC-CA adhesive for poplar veneer was higher than that of individual DAC, ranging from 0 MPa in DAC to 0.72 MPa in DAC-CA adhesive. This improvement can be attributed to the enhanced cohesion and toughness resulting from the dynamic Schiff base and disulfide bonds present in the DAC-CA adhesive. In addition, after interfacial treatment, the wet bond strength of DAC-CA adhesive for poplar veneer was dramatically improved, increasing from 0.72 MPa without treatment to 1.06 MPa with treatment. Overall, a water-resistant cellulose-based DAC-CA adhesive was prepared by a rapid and efficient method. This study may provide insights into the development and utilization of innovative wood adhesives.