Partial replacement of melamine by benzoguanamine in MUF resins towards improved flexibility of agglomerated cork panels

Abstract Melamine-urea-formaldehyde (MUF) resins are highly effective adhesives for lignocellulosic materials. However, their high stiffness hinders applications where flexibility is desired. In this work, MUF resins were modified with benzoguanamine by partially replacing melamine in two different steps of the synthesis. The purpose was to obtain a less densely crosslinked, and hence more flexible, structure after cure. All modified MUF resins were characterized using gel permeation chromatography (GPC). Results suggest that benzoguanamine and its derivatives were integrated into the polymer structure. FTIR and 13C-NMR analysis confirmed the presence of benzoguanamine in the modified resins. The addition of benzoguanamine to the MUF resin synthesis significantly improved the flexibility of agglomerated cork panels bound with modified resins. The minimum mandrel diameter on which the panels could be bent by 180° without failure decreased from 18 mm to 12 mm diameter, while the remaining key properties of the panels were maintained (tensile strength and boiling water resistance). The formaldehyde content of the panels (determined according to EN120) corresponds to E1 class.