A Different Approach to Low Formaldehyde Emission Aminoplastic Wood Adhesives

Abstract

Melamine-formaldehyde resins prepared with a molar defect of formaldehyde (i.e. molar ratio M:F = 1:0.5) were shown to harden in presence of hexamethylenetetramine, at acid pH, without a great proportion of decomposition of hexamethylenetetramine to formaldehyde. Approximately 2/3 of the cross-linking bridges induced by hexamethylenetetramine hardening appear to be stable aminodi- and aminotrimethylene bridges derived by reaction of Hultzsch methylene bases directly with reactive sites on melamine and on the MF resin. This confirms that hexamethylenetetramine is capable of reacting also with aminoplastic resins mostly before its degradation to formaldehyde. The existence of such a type of cross-linking was shown to lead to hardened aminoplastic resins capable of much lower formaldehyde emission from the finished board.