IMPROVEMENT OF PMUF ADHESIVES PERFORMANCE FOR FIREPROOF PLYWOOD

PMUF resins which gave poor performance on salts-treated fire retardan t veneers were upgraded by several systems of molecular doubling direc tly in the glue-mix to solve the problem. This type of solution was de emed necessary from the basic investigation pinpointing the problem. T he problem was found to be that heavy salts coatings of the veneer ins tead of stopping veneer surface wetting by the adhesive instead increa sed excessively adhesive penetration changing completely the rheology of the system. Increasing the degree of polymerisation of the resin wa s the generalised solution to the problem. This however cannot be done at the resin manufacturing stage as too short shelf-lifes ensue. It w as done by the use of very reactive additives added exclusively in the glue-mix. Among these additives the addition of a few percentages (6% -8%) tannin on resin solids proved to be the most successful, and gave good results for PMUF bonding of fireproof plywood. The upgrading of the resin in this manner also allowed bonding of treated veneers of wo od species which could not be bonded at all with the standard PMUF res in.