Abhesion in the manufacture of engineered wood products : aspects of the interaction of i socyanates with stainless steel and wood.

Polymeric methyl diphenyl diisocyanate (pMDI) is a versatile isocyanate-based adhesive commonly used in the manufacturing process of composite wood panels. Its use has constantly been increasing over the past years driven by the great performance that this resin offers in terms of moisture resistance, durability and strength. However, the use of isocyanate-based adhesives carry some challenges related to the composite wood production which need to be improved. In particular, the adhesion of these resins to the stainless steel press platens during the production process. The strong adhesion between the glue and the press platens results in production issues forcing the production to stop. There are a number of methodologies to overcome the production issues, however, all of them incur additional costs or have associated health and safety issues. Therefore, this study aims to expand the understanding of the interfacial chemistry and processes occurring at the press platen/pMDI-wood interface to help to develop approaches to achieve release of isocyanate-based adhesives. In order to achieve the aim of this project, surface analysis techniques, in particular Xray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS), were used. In the first stage of this project, the surface characterisation of pine wood and its extractives, pMDI and the stainless steel used for the manufacture of composite wood panels was carried out. Then, the study of the pMDI/metal interface was performed obtaining important information related to the bonding of pMDI to steel. The interface between the stainless steel/pMDI-wood system was also investigated. The results of this study showed that the pine wood extractives compounds have a significant impact in the adhesion of wood to stainless steel. These findings allowed us to inform strategies which could lead to the release of isocyanate-based adhesives from the steel during the composite wood panel production process