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.

Influence of glutaraldehyde on the performance of a lignosulfonate/chitosan‐based medium density fiberboard adhesive

“…As a type of lignin derivatives, lignosulfonate, which is obtained from the production of wood pulp using sulfite pulping, is a water‐soluble anionic surfactant containing a large number of functional groups resulting in a unique surfactivity and hence interesting for applications as adhesives. However, the isolated lignosulfonate generally is poor adhesives for MDFs when compared to conventional resin systems …”

“…However, the isolated lignosulfonate generally is poor adhesives for MDFs when compared to conventional resin systems. 5 Incorporation of lignin into other biopolymers is a promising way to modify lignin and enhance its adhesion. As a renewable and biodegradable polymer material obtained by deacetylation of chitin, one of the most abundant natural polysaccharides, next to only cellulose, 6,7 chitosan has received world-wide attention.…”

Formaldehyde-free melamine microcapsules as core/shell delivery systems for encapsulation of volatile active ingredients

“…1), this polymerization can be controlled by the pH as observed with formaldehyde. 39,40 Under basic conditions, the addition of the amino group on the aldehyde formed amino-alcohol 2a (Fig. 1).…”

“…29 Despres et al reported the preparation of urea or melamine prepolymers with 2,2-dimethoxyethanal (DME) as a non-volatile substitute of formaldehyde. 39 They described the mechanism of the polymerization between melamine and DME. Nevertheless, a low conversion was obtained and only dimers of melamine were observed.…”

Molar-mass distribution of urea-formaldehyde resins of different degrees of polymerization by MALDI-TOF mass spectrometry

“…Aft er ha rdening, UF r esins form in soluble thr ee-dimensional networks of therm osetting duromers. [32][33][34] Generally, th e pol ycondensation structu res of UF resins have n ot been studied thoroughly by the MALDI-TOF tec hnique. 5 This variety leads to a wide range of m olar mass distributions in UF r esins, from low molar mass molecules up to more or less polymeric structures.…”