Preparation and performance of a novel wood adhesive based on hyper-branched polyethyleneimine, urea and glyoxal

To increase water resistance and bonding strength of urea-glyoxal (UG) resin as wood adhesive, using hyper-branched polyethyleneimine (HBPEI), urea (U) and glyoxal (G), a novel resin (HBPEIU-G) was designed and synthesized successfully. The HBPEI polymer was initially reacted with urea under heating condition without using extra catalyst, then glyoxal (40% aqueous solution) was directly added to it at molar ratio of 1.4:1. The structures of HBPEIU and performances of HBPEIU-G resin were distinguished when was applied as wood adhesive. The results of the prepared two-ply panels produced in laboratory showed that both dry and wet bonding strength of HBPEIU-G resin were far higher than that of the controlled UG resin. Especially, the wet bonding strength enhanced significantly from 0 MPa to 0.63 MPa. The results of electron spray ionization mass spectrometry (ESI–MS) and FTIR confirmed that the target products of HBPEIU polymer had been obtained and the chemical reaction between synthesized HBPEIU polymer and glyoxal have been occurred. In HBPEIU-G resin, the dominant oligomers were HBPEI branched polymer which offered enough network structures for excellent bonding strength. Meanwhile, the viscosity of HBPEIU-G resin was higher than that of the UG resin, and differential scanning calorimeter (DSC) analysis also indicated that the curing peak temperature of HBPEIU-G resin was much lower than that of the UG resin. © 2021, Iran Polymer and Petrochemical Institute.