Preparation and characterisation of montmorillonite-ammonium silane surface layers promoting adhesion between steel and a polyurethane adhesive

Novel pro-adhesive surface layers on a steel substrate were created via electrostatic adsorption of montmorillonite platelets on ammonium silane layers based on (3-aminopropyl)trimethoxysilane. Morphology of the mentioned montmorillonite-ammonium silane surface layers (MSL) (prepared using clays with calcium, strontium and diisopropylammonium exchangeable cations) was analysed by means of SEM, EDX and XRD techniques. The MSL significantly reduced dipropylene glycol contact angle (−14°) and roughness (−38%) of the steel substrate as well as increased its corrosion rate (+160%) and shear strength of joints prepared using a commercial 2 K polyurethane adhesive (+77%). Additionally, the steel samples with MSL created by means of Ca- or Sr-montmorillonite exhibited markedly higher shear strength after their exposition in a salts spray chamber (+316% and +311%, respectively) in relation to untreated samples.