Urea-formaldehyde microspheres as a potential additive to wood adhesive

Abstract

Urea formaldehyde (UF) resins are important for wood industry due to their attractive properties at reasonable price. Particulate fillers added to UF are of interest with regard to improving the functionality of UF and also in terms of reduced UF consumption. To study their potential as filler, solid UF microspheres were synthesized and characterised respecting its morphology, chemical curing and thermal stability. Marigold flower structured spheres with diameters between 5 and 20 µm are presented and application trials demonstrated that high amounts of UF may be replaced by solid microspheres without impairing adhesive bond strength of solid wood bond lines. Fluorescence microscopy showed that microspheres greatly reduce adhesive penetration into the wood substrate, retaining the modified adhesive in the bondline. UF microspheres may thus be considered as viable filler for UF adhesives, particularly with regard to the possibility of endowing them with added functionality like self-healing properties.