A formaldehyde-free amino resin alternative to urea-formaldehyde adhesives: A bio-based oxidized glucose – urea resin

Abstract

Urea-formaldehyde resins (UF) are the most commonly used wood-based panels adhesive in industry. These adhesives are more than 80 % by volume of the wood adhesives market. However, due to formaldehyde toxicicity and extreme volatility UF resins yield panels with formaldehyde emission problem both during wood panels preparation and their in-service use. In order to address this problem, to find an environment friendly replacement for formaldehyde to manufacture novel and safe aminoresins is essential research for wood adhesives. In this article, a bio-based amino resin wood adhesive (OGU) is developed by using oxidized glucose reacted with urea. The research work presented here tests the impact on the adhesive properties of a number of oxidation treatment parameters and of the glucose to urea molar ratio. The molecular structure and thermal properties of the OGU adhesive were studied by different analytical techniques. The results indicate that the bioaldehydes are obtained by glucose under mild oxidation conditions. The bioaldehydes obtained can then be reacted with urea to form a novel oxidized glucose-urea amino resin, suitable to manufacture plywood. Under the specified process conditions at pH 4 and at a urea-to-glucose molar ratio of 1, the OGU adhesive yielded plywood with a dry strength of 0.99 MPa, 24 h cold water soaking wet strength of 0.77 MPa, and 3 h hot water (63°C) soaking wet strength of 0.76 MPa. These results satisfy the requirements of the GB/T 9846–2015 standard. The OGU resin adhesive prepared has then a good market potential to replace the current UF resins used in the industrial production of wood-based panels and as a novel biomass amino resin adhesive.