Upgrading of MUF adhesives for particleboard production using oligomers of hyperbranched poly(amine-ester)

Abstract

Oligomeric precursors of poly(amine-ester) were synthesized by a two-step condensation reaction of succinic anhydride with diethanolamine under mild conditions. The oligomers formed were characterized at each synthesis step using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. This showed that after step (1), the condensation adduct of both reactants (206 Da) was the main product mixed to high proportion of unreacted diethanolamine (106 Da). After step (2), the adduct at 206 Da decreased substantially, while other compounds at 275, 292, and 375 Da started to increase along with the appearance of a new compound at 392 Da. This indicates that the reaction proceeds slowly under these conditions to give higher branched oligomers (HP). In addition, some cyclic compounds were also identified by the 188, 275, and 375 Da peaks. MALDI-TOF of the melamine–urea–formaldehyde (MUF) resin before and after reaction with the hyperbranched oligomers mix showed clear indication of the coreaction of simple melamine–formaldehyde oligomers with several of the hyperbranched oligomers previously identified. Addition of small proportions of a mixture of the formed HP oligomers to a MUF adhesive improved the internal bond (IB) strength, both dry and wet, of wood particleboards bonded with it. The results obtained indicate that the addition of these HP oligomers can improve the dry IB strength by 17–24% according to conditions of preparation and the wet IB strength by as much as 47% when compared to the control sample.