| Abstrakt: |
Conventional wood adhesives are formaldehyde-based adhesives, isocyanates, and epoxy, accounting for nearly 90%–95% of the world demand in 2021. Among them, urea-formaldehyde (UF) resins dominate the global wood adhesives market because of low prices, fast curing, and short pressing time. However, the main drawback associated with the use of UF resins is the formaldehyde emission from UF-bonded products. Therefore, this study aimed to synthesize ultra-low formaldehyde emission UF resin adhesive by tuning the final formaldehyde to urea (F/U) mole ratio at 0.8/1.0. Three types of organic acids (20% w/v) were added at a 3% level based on the solids content of UF resins as the hardener, namely acetic acid (AA), maleic acid (MA), and citric acid (CA). Basic properties such as non-volatile solids content, viscosity, gelation time, and free-formaldehyde (HCHOfree) of ultra-low molar ratio UF resins were affected by adding different organic acids. Generally, incorporating organic acids hardener reduced the solids content, viscosity, gelation time, and HCHOfree of UF resins. Markedly, the HCHOfree decreased by 14.2% by adding CA. Only a small reduction of HCHOfree by 7.0% was obtained with an addition of MA and AA. This could be due to the reaction between carboxylic groups of the organic acids with the free aldehyde groups of UF resins. This work showed that the addition of CA hardener increased the adhesion strength of UF resins in plywood as indicated by the result of tensile shear strength. This study suggested incorporating CA as the hardener for ultra-low molar ratio UF resins for plywood adhesive in the future. [ABSTRACT FROM AUTHOR] |
