Mimosa tannin resins for impregnated paper overlays
Abstract
The surface quality of plywood coated with resin impregnated papers based on tannin/furfuryl alcohol resins was studied. Several hardeners such as hexamine, paraformaldehyde, formurea and a mixture of formurea and paraformaldehyde were added in small quantities to a mimosa tannin/furfuryl alcohol resin. Papers impregnated with resin based on tannin + furfuryl alcohol + paraformaldehyde, or + formurea were found to yield excellent results in standard water vapour resistance and cross-cut tests. Matrix assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry and cross-polarisation-magic angle spinning NMR (CP-MAS C-13 NMR) were used to show coreaction of tannin with furfuryl alcohol and even furfuryl alcohol self condensation under alkaline conditions, as well as coreaction of formaldehyde-yielding compounds such as hexamine with both tannin aromatic rings and the aromatic ring of furfuryl alcohol. Some of the more important oligomers formed were identified by MALDI-TOF.