Succinaldehyde induced water resistance improvements of UF wood adhesives

Addition of succinaldehyde to UF resins for plywood directly in the glue-mix improves markedly the water resistance of the hardened UF glue line in plywood as well as diminishing its formaldehyde emission. Best water resistance results are obtained by adding small amounts of succinaldehyde: in the present study optimum water resistance was obtained for a urea-formaldehyde-succinaldehyde (UFSA) resin of U:F:SA molar ratio of 1:1.3:0.2. Increasing the proportion of formaldehyde substitution by succinaldehyde does not improve water resistance, but rather the water resistance deteriorates indicating that: or the excess of succinaldehyde is not able to copolymerise in the hardening UF network, or that the excess of dimethylene chains of the aldehyde decreases excessively the cross-linking density per unit volume of the hardened resin network. C-13 NMR analysis of a hardened UFSA resin indicated that the improved water resistance can be ascribed to the presence of the dimethylene chains coming from the aldehyde portion which is capable of copolymerising with the UF resin. Deterioration of water resistance by strong increase of the amount of wheat flour filler affects considerably less the UFSA resins than the UF resins.