Behavior of amine‐modified urea–formaldehyde‐bonded wood joints at low formaldehyde/urea molar ratios

Abstract

AbstractUrea–formaldehyde‐bonded wood products are limited to interior nonstructural applications because of their poor durability under cyclic moisture or humid environments. The stability of solid‐wood joints and particleboards can be enhanced by bonding with urea–formaldehyde adhesives modified with di‐ and trifunctional amines at an effective resin formaldehyde‐to‐urea mol ratio (F/U) of 1.6; however, particleboard formaldehyde emissions were not improved over those from boards made with unmodified adhesives and were unacceptably high. The relative effectiveness of selected modifications was investigated at resin form aldehyde‐to‐urea (F/U) molar ratios of 1.4 and 1.2 Solid‐wood joints and particleboards made with modified adhesives, an unmodified adhesive, and a phenol formaldehyde (PF) resin were subjected to cyclic soak‐dry (cyclic stress) treatments and moist‐heat aging. Formaldehyde emissions from particleboards were also determined. At F/U 1.4, the resistance of solid‐wood joints made with modified adhesives to cyclic stress and moist‐heat aging was equal to that of PF‐bonded joints and superior to that of joints bonded with unmodified adhesive. The resistance of particleboards made with modified adhesives was greater than that of boards made with unmodified adhesive but less than that of PF‐bonded board. Solid‐wood joints and particleboards made with F/U 1.4 resins performed better than did those made with F/U 1.2 resins. Particleboards made with F/U 1.2 resins had formaldehyde emissions well below the standard, and room temperature aging or bonding at high temperature reduced emissions substantially. © 1994 John Wiley & Sons, Inc.1This article is a US Government work and, as such, is in the public domain in the United States of America.