Dependence on the adhesive formulation of the upgrading of MUF particleboard adhesives and decrease of melamine content by buffer and additives

The type of MUF adhesive formulation has been shown to have a determinant effect in the performance of MUF adhesives for wood panels upgraded with iminoamino methylene basis of the "hexamine sulphate" type. The high performance sequential MUF formulations are upgraded little or not at all by these additives. Much weaker non-sequential MUF formulations instead are so strongly upgraded for IB boiled strength by the use of these additives to markedly outperform the normally stronger sequential type formulations and even phenolic resins. To the buffering action leading to optimization of the hardening ⇄ degradation equilibrium described previously as the main cause of the functioning of these additives must then be added the effect of the type of formulation. This is quantified and described. It is partly related to the presence of higher or lower levels of unreacted primary amine groups of the melamine and their consequent level of contribution to buffering. It is also partly related to the level of plasticization of the hardened glue line by unreacted urea and the consequent visco-elastic dissipation of energy that would derive from this.