Melamine-Bridged Alkyl Resorcinol Modified Urea- Formaldehyde Resin for Bonding Hardwood Plywood

A powdery product was obtained by the reaction of methylolated melamine with alkyl resorcinols to form melamine-bridged alkyl resorcinols (MARs). The effects of the addition of this powder on the bonding strength and formaldehyde emission of urea-formalde- hyde (UF) resins were investigated. Three types of UF resins with a formaldehyde/urea molar ratio of 1.3 synthesized by condensation at pH 1.0 (UF-1.0), pH 4.5 (UF-4.5), and pH 5.0 (UF-5.0) were fabricated. The addi- tion of MAR to UF-4.5 and UF-5.0 for bonding hardwood plywood enhanced the bonding strength and reduced formaldehyde emission. For UF-1.0, the addition of MAR adversely affected the bonding strength. However, the UF- 1.0 resin yielded the lowest formaldehyde emission of all of the UF resins in the study. The effects of the MAR addi- tion were related to the molecular structures of the UF res- ins. UF-1.0 contained a large amount of free urea, a considerable number of urons, and a highly methylene- linked, ring-structured higher molecular weight fraction and had a smaller number of methylol groups. Therefore, the addition of MAR was considered to cause a shortage of the methylol groups, which in turn, led to incomplete resin curing. In contrast to UF-1.0, UF-5.0 contained a smaller amount of free urea and a linearly structured higher molecular weight fraction and had a larger number of methylol groups. In this case, MAR was considered to effectively react with the methylol groups to develop a three-dimensional crosslinked polymer network to enhance the bonding strength and suppress the generation of free formaldehyde to reduce formaldehyde emission. V C 2010 Wiley Periodicals, Inc. y J Appl Polym Sci 116: 2840-2845, 2010