Hydrothermal ageing on self-sensing bonded joints with novel carbon nanomaterial reinforced adhesive films

Abstract

The effects of hydrothermal ageing on adhesive joints with surface treated aluminium substrates and a novel graphitic nanoparticle reinforced adhesive film have been explored. The adhesive doped with carbon nanotubes (CNTs) shows the highest diffusion coefficient whereas the adhesive film doped with graphene nanoplatelets (GNPs) presents the lowest one. This is explained by the combined effect of both barrier properties of graphitic nanoparticles, which is more prevalent in case of GNPs because of their 2D nature, and the amphiphilic behaviour of the surfactant used during the manufacture of the nanoreinforced adhesive film, which is more significant in case of CNTs because of their higher correlation nanoparticle to surfactant. Glass transition temperature shows a similar trend in every case, with a decrease with ageing time due to plasticization effect of hydrogen bonds. However, the lowest degradation takes place in CNT samples due to a reduction of the free volume induced by a higher porosity, so the plasticization effect is not as prevalent as in GNP or neat adhesive specimens, confirmed by DMTA analysis. Single lap shear (SLS) tests were also conducted using aluminium substrates. The results reveal a higher degradation on mechanical properties in GNP and neat adhesive joints, as expected and a stiffening effect from 15 days to 1 month because of a secondary crosslinking at water saturation. Structural health monitoring (SHM) capabilities were also analysed, indicating a good correspondence between interface properties and electrical measurements, confirming their high potential in SHM applications.