Phenol–urea–formaldehyde (PUF) co-condensed wood adhesives

• Published in: International journal of adhesion and adhesives 1998-01, Vol.18 (2), p.69-79
• Main Authors: Tomita, Bunichiro, Hse, Chung-Yun
• Format: Article
• Language: English
• Subjects: adhesive strength; Application fields; Applied sciences; co-condensation; curing; Exact sciences and technology; formaldehyde; methylolphenols; phenol; plywood; Polymer industry, paints, wood; resol; structure; Technology of polymers; thermal property; urea; Wood-based materials; Wood. Paper. Non wovens
• ISSN: 0143-7496; 1879-0127
• DOI: 10.1016/S0143-7496(97)00047-X

The reaction of urea with methylolphenol under acidic conditions was investigated. The alternating copolymer of urea and phenol could be synthesized by the reaction of urea and 2,4,6-trimethylolphenol. The reactions of urea with polymethylolphenol mixtures also were investigated by changing the reaction conditions, such as the molar ratio and acidity. The co-condensates were analysed by carbon-13 nuclear magnetic resonance spectroscopy to determine the ratios of co-condensation. Another synthetic method to obtain co-condensed resins was developed by reacting phenol with UF concentrate, which is a type of urea–formaldehyde resin prepared with a high molar ratio of formaldehyde to urea (F/U) such as greater than 2.5. Further, it was found that resol-type co-condensed resins can be synthesized by alkaline treatment of the co-condensed resins that were once prepared under acidic conditions. The curing process and thermal properties of resol-type co-condensed resins were investigated by torsional braid analysis. The co-condensed resins displayed almost the same curing behavior and heat resistance as a commercial resol. Their adhesive performance against plywood was evaluated by conducting a cyclic 4 h boil test and a 72 h boil test. The plywood test results passed the requirements for JAS special-grade structural plywood.