The Interfacial Chemistry of Isocyanate/Metal Systems.

Isocyanate based materials are widely used in many applications such as automotive, construction, thermal insulation, adhesive and coating. The aim of this PhD project is to understand and improve knowledge of the possible isocyanate-metal interaction in order to improve adhesives performance for the metal substrates and process performance by developing release options. A mechanical performance has been assessed by the single lap shear test and the locus of failure has been determined using X-ray photoelectron spectroscopy (XPS) in order to establish the cause of failure. Subsequently, the nature of the interaction between polymeric methylene diphenyl diisocyanate (PMDI) and different metals (stainless steel, aluminium, iron and copper) by the deposition of a thin layer of adhesive on the substrate has been studied using XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The interfacial chemistry of the multi-component of rigid polyurethane foam (RPUF) to metals then has been studied using the peel testing to examine the interfacial failure surfaces by XPS and ToF-SIMS, and also ultra low-angle microtomy (ULAM) technique for sample preparation in combination with ToF-SIMS. Adsorption behaviour of the RPUF on the metal surfaces also has been studied. Significant differences in the behaviour have been established. A fragment, indicative of covalent bond formation between PMDI and aluminium (AICHNO3-) was observed at the PMDI/aluminium interface. However, such specific interaction was not observed at the PMDI/iron and PMDI/stainless steel interfaces, and these interactions might b acid-base interaction. Copper was migrated into the PMDI and this might hinder formation of the strong bond. The catalyst used in the multi-component of rigid polyurethane foam (RPUF) formulation, pentamethylenetriamine (PMDETA), was concentrated at the PU/metal interface area