Novel Highly Branched Polymer Wood Adhesive Resin

We propose a new idea for facile and green synthesis of urea-based highly branched polymers (HBPs) using polyamines and urea via deamination. More importantly, our strategy is to directly use the synthesized HBPs to construct plywood. The HBPs would be further condensed and solidified during the hot pressing process, resulting in the aldehyde-free wood adhesive with a high bonding performance. In this work, water-soluble HBPs were synthesized by one-pot and one-step strategy via polycondensations between urea (U) and tris(2-aminoethyl)amine (TAEA), with no solvents and catalysts used, as well as purification was also avoided. Here, the TAEA was selected as a model compound of polyamine. Urea was used in this synthesis because of it is one of the cheapest chemicals. Structure characterizations show that the polymers contain both terminal amine and urea groups and their relative contents varied with respect to different monomer ratios. For the first time, the performances of the HBPs water solutions directly used as wood adhesive resins were investigated. The resins showed excellent water resistance, as the bonding strengths were still greater than 1.8 MPa after 7 h boiling water soaking, indicating that the cured resins that consist of polyurea and biuret linkages are quite stable toward hydrolysis. In a wide range of monomer ratio of 1.5–2.5, the bonding performance of the resins did not vary significantly. This study extended the potential applications of HBPs to the wood industry and provides a possible and potential solution to the formaldehyde emission problem of the wood-based products. The advantages of HBP resins over traditional wood adhesives in the synthesis and applications make large-scale application of such resins practical and attractive.