Low formaldehyde emission MDF overlaid with wood veneer: bonding problems assessment

Abstract

The aim of this work is to assess wood bonding problems in medium density fibreboard (MDF) surfacing with decorative wood veneer (beech). Three sets of tests were carried out. The first set was carried out using automatic bonding evaluation system (ABES) in order to assess the bond strength development rate of two UF resins produced according to different processes. The second set permitted the study of the behaviour of bonding between MDF and beech veneer using ABES, and for this purpose a special MDF sample was designed. These MDF samples were pressed to conventional beech test strips and pulled at any given time immediately after pressing. A third set of tests were performed in a pilot hot-press used for MDF surfacing with beech veneer. Different operating conditions were tested (pressing time and resin type). The quality of bonding between wood veneer and MDF was evaluated using the surface soundness test (EN311). The tensile load required to pull off a defined surface area of overlaid panel was recorded and it was observed that in all samples the failure mode occurred within the underlying board. An analysis of variance test was performed to evaluate the significance level of the effects of the different factors on surface soundness. The main conclusion of this work is that the MDF surfacing operation seems to induce degradation in the MDF surface layers, probably due to the presence of urea, which could be responsible for a decrease in the surface soundness, which was mostly observed for longer pressing times.