Degradation in seawater of structural adhesives for hybrid fibre-metal laminated materials

Abstract

The adhesives used for applications in marine environments are subject to particular chemical conditions, which are mainly
characterised by an elevated chlorine ion content and intermittent wetting/drying cycles, among others.These conditions can limit
the use of adhesives due to the degradation processes that they experience. In this work, the chemical degradation of two different
polymers, polyurethane and vinylester, was studied in natural seawater under immersion for different periods of time.The diffusion
coefficients and concentration profiles of water throughout the thickness of the adhesiveswere obtained.Microstructural changes in
the polymer due to the action of water were observed by SEM, and the chemical degradation of the polymer was monitored with the
Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The degradation of the mechanical
properties of the adhesive was determined by creep tests withMixed Cantilever Beam (MCB) specimens at different temperatures.
After 180 days of immersion of the specimens, it was concluded that the J-integral value (depending on the strain) implies a loss of
stiffness of 51% and a decrease in the failure load of 59% for the adhesive tested.