Durability of Urea-Formaldehyde Adhesives: Effects of Molar Ratio, Second Urea, and Filler

Relative durabilities were determined for Douglas-fir laminated samples prepared from 16 different urea-formalde hyde resins. Molar ratio ranges of F/U = 2.0 to 1.8 exhibited slower bond deterioration under accelerated aging conditions than resin with ratio ranges of F/U = l.6 to l.4. Addition of walnut-shell flour improved the relative durability ranking of F/U = l.6, but caused a significant decrease in initial shear strength for most resins. Glues containing filler and made from resins of molar ratio 1.6 and l.4 showed improved durability with increasing amounts of second urea.

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