NMR Imaging of the Interfaces of Epoxy Adhesive Joints

Nuclear magnetic resonance imaging (NMRI) is used to study epoxy adhesive bonded structures at a proton resonance frequency of 300 MHz. Oligomeric and almost pure monomeric diglycidyl ethers of bisphenol-A, triethylenetetramine and xylene representing typical raw materials of epoxy adhesives are imaged at 25 and 50°C with varying repetition times to optimize measurement conditions for the adhesives. NMR images with good signal-to-noise ratios from the liquid epoxy adhesives are obtained at 50°C using the shortest possible echo times and a repetition time of 1 s. Chemical shift images of the glue-lines are presented and their possible uses in adhesive studies are discussed. The use of NMRI to detect heterogenous resin/resin and resin/curing agent mixtures is demonstrated. A non-invasive glue-line analysis is made of an aluminium/epoxy/aluminium sample with a model debonding by recording cross-sectional NMR images and a proton shadowgram.