Influence of PMUF resins preparation method on their molecular structure and performance as adhesives for plywood

Abstract

The preparation method of a PMUF resin manufactured in a single synthesis procedure has been shown to have fundamental importance both at the molecular level and for the resin application performance. 13C NMR spectra of PMUF resins present excellent correspondence with applied tensile strength results of plywood prepared with the same resins. PMUF resins prepared by initial reaction of phenol with formaldehyde followed by standard MUF preparation procedures present better results than resins prepared with the phenol either added during the preparation or added at the end of the MUF resin preparation. The reason for this is the reaction procedure itself which ensures that the phenol is copolymerized with the main MUF chain to form a block copolymer and that both PF and MUF resin blocks still present consistent amounts of reactive methylol groups. Progressive deviation from these molecular level requirements during the course of PMUFs preparation also ensures a progressive deviation from their optimal performance, even leading to PMUF resins of worse performance than their corresponding MUF resin to which phenol has not been added.