Comparison of Modifiers for Durability Improvement of UREA-formaldehyde Resin

Several common organic modifiers, having varying degrees of reactivity and functionality, were evaluated at different levels of addition for their improvements to the relative durability of urca-formaldehyde (UF) glue-wood bonds. The recently developed thermal-softening technique was used to determine the thermal sensitivity of cured samples of these modified resins. Urea-formaldehyde resin containing modifiers with aromatic character and high potential reactivity, such as melamine, furfuryl alcohol, and resorcinol, showed significant increases in thermal-softening points compared with unmodified resin. Accelerated-aging tests on Douglas-fir laminates bonded with UF resins modified with either melamine, 2-imidazolidinone, or furfuryl alcohol showed that durability ranking correlated closely to the softening points of these adhesives. One inorganic modifier, aluminum powder, gave an improvement in softening point, but exhibited poor durability with wood bonds in aging tests