Technological properties of a branched polyethyleneimine derivative as a cross-linker for low molar ratio urea-formaldehyde resins

Abstract

To address formaldehyde release problem, low-molar-ratio UF resin has become the industry's major adhesive for bonding wood-based panels. Unfortunately, its drawbacks of poor water resistance, low bonding strength and slow curing rate lead to low production efficiency and inferior dimensional stability of wood-based products. In this work, a branched polymer-based functional agent (BPG) as a crosslinker was synthesized from branched polyethyleneimine (BPEI), urea and glyoxal via two steps with deamination and Mannich reaction for promoting the performance of low-molar-ratio UF resin in wood bonding. The FTIR confirmed the successful synthesis of the long-branched BPG-bearing active aldehyde group (-CHO) as expected. The effects of BPG on curing characteristics, bonding strength and water resistance of UF resin were evaluated using DSC and tensile shearing strength measurement, respectively. Results showed that UF resin cured by BPG displayed a lower curing temperature, faster curing rate and exhibited superior wet bonding strength, 1.37 MPa, nearly two times higher than that cured by a traditional curing agent (NH4Cl). In addition, TG, XRD, FT-IR and SEM analysis confirmed that UF/BPG mixture showed excellent thermostability, compact and continuous microstructure, and decreased crystal structure due to the dense network structures in cured UF/BPG resin. These results demonstrated that BPG was an efficient crosslinker for improving the bonding strength and water resistance of low-molar-ratio UF polymer.