Isocyanate/Phenolics Wood Adhesives by Catalytic Acceleration of Copolymerization

The reaction of MDI with the hydroxybenzyl alcohol group of phenol-formaldehyde resol (PF) resins can be accelerated by the use of catalysts of urethane formation such as triethylamine and dibutyltin dilaureate (DBTDL). A kinetic study for MDI (4,4'-diphenylmethane diisocyanate) and p-hydroxybenzyl alcohol as a model compound for phenol-formaldehyde resins confirmed this reaction. These catalysts have been used to upprade the performance of MDI/phenolic thermosetting wood adhesives for particleboard, in amounts varying between 0.5% and 2% of PF resin solids content. The use of these catalysts allows the use of simpler, usually slow-reacting, PF resins at pressing times as fast as 5 seconds per mm of board thickness, hence faster than urea-formaldehyde resins. These pressing times are achieved while still mantaining the exterior grade properties of the board