Preparation of environmentally friendly urea-hexanediamine-glyoxal (Hug) resin wood adhesive

Using non-toxic, low-volatile glyoxal to completely replace formaldehyde for preparing urea-glyoxal (UG) resin adhesive is a hot research topic that could be of great interest for the wood industry. However, urea-glyoxal (UG) resins prepared by just using glyoxal instead of formaldehyde usually yields a lower degree of polymerization. This results in a poorer bonding performance and water resistance of UG resins. A good solution is to pre-react urea to preform polyurea molecules presenting already a certain degree of polymerization, and then to condense these with glyoxal to obtain a novel UG resin. Therefore, in this present work, the urea was reacted with hexamethylene diamine to form a polyurea named HU, and then this was used to react it with different amounts of glyoxal to synthesize hexamethylenediamine-urea-glyoxal (HUG) polycondensation resins, and to use this for bonding plywood. The results show that the glyoxal can well react with HU polyuria via addition and schiff base reaction, and also the HUG resin exhibits excellent bonding strength and water resistance. The shear strength of the plywood bonded with this HUG at 160°C hot press temperature as high as 1.93 MPa, 2.16 MPa and 1.61 MPa, respectively, which meets the requirement of the China national standard GB/T 9846-2015 (≥0.7 MPa), and can be a good choice as a wood adhesive for industrial application. © 2024, Tech Science Press. All rights reserved.