Formaldehyde‐free aminoresin wood adhesives based on dimethoxyethanal

Abstract Aminoresin precursors prepared by the addition of a new, colorless, nonvolatile and nontoxic aldehyde, dimethoxyethanal (DME), to melamine or urea gave resins for boards that were able to harden, however they were underperforming because of the lower reactivity of DME in relation to formaldehyde. Melamine and urea reacts with one and two (melamine up to three) molecules of DME to form M‐DME and U‐DME (called DU), but the subsequent cross‐linking reaction to form bridges does not occur unless the reaction is catalyzed during resin preparation by the addition of glyoxylic acid. Such bridges between two melamine molecules form only up to the formation of dimers and no more. The use of glyoxylic acid during the reaction has allowed the formation of different oligomers formed by both aldol condensation and condensation of melamine and glyoxylic acid with two molecules of melamine to form dimers. These were observed by 13 C NMR and MALDI‐TOF (matrix‐assisted laser desorption/ionization mass spectroscopy). However, the addition of 20% isocyanate (pMDI) was necessary to satisfy the relevant mechanical strength standards of panels prepared with these resins. pMDI contributed to cross‐linking of M‐DME and DU by its reaction to form urethane bridges according to reactions already described. The adhesive resins so formed had excellent performance and were colorless, and they produced boards that well satisfied the requirements of the relevant standards for interior panels. Formaldehyde emission was down to what would be expected obtained by just heating the wood chips in absence of adhesives. The panels emission was sufficiently low to even satisfy the most severe relevant F**** JIS A 5908 Japanese standard. These adhesives are colorless as MUF and UF resins. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008