Evaluation of urea-formaldehyde adhesives performance by recently developed mechanical tests

Abstract

In the open literature, two main strategies can be found for synthesizing urea-formaldehyde (UF) resins. One is the alkaline–acid process, which takes place in three steps, usually an alkaline methylolation followed by an acid condensation and then the addition of a final amount of urea. The other process consists of four steps, the main difference being an initial condensation in strongly acid environment. In this work, we evaluate the curing behaviour of four resins produced using the aforementioned processes by the Integrated Pressing and Testing System (IPATES) and the Automated Bonding Evaluation System (ABES). The characterisation of the bond strength development during hot pressing by ABES and IPATES shows that the four resins will have different performances in the bonding process of wood-based composites. For each resin, the effect of pressing parameters such as temperature, adhesive and hardener ratios on shear strength (ABES) and internal bond (IPATES) during hot pressing is put into evidence.