Hydrothermal ageing of graphene/carbon nanotubes/epoxy hybrid nanocomposites

Abstract

The hydrothermal ageing of hybrid nanocomposites formed by carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) incorporated into an epoxy matrix was studied. In order to avoid the weak interface, amine functionalized GNPs were used which are reactive with the epoxy matrix. The content of CNTs was 0.1 wt% and the GNPs content ranged from 5 to 12 wt%. The isothermal water absorption was measured until very long times (almost two years). Reduction of water absorption with the addition of either carbon nanotubes or graphene nanoplatelets has been found independently of the ageing time. The results can be described by a two-stage diffusion model with the first and second stages being diffusion and matrix relaxation controlled respectively. The obtained diffusion coefficient for the neat epoxy thermoset is higher than those of nanocomposites, which decreases with the increase of GNPs content. The effect of water absorbed on the dynamic-mechanical properties and on the electrical conductivity of the nanocomposites was analyzed. Whatever the temperature the storage modulus shows a continuous increase with the increase of the nanoparticles content, the effect of hydrothermal ageing is to decrease the modulus only in the glassy state (T < Tg). Water aged specimens show broadening of the tanδ peak related to the plasticization of the matrix. Tg of aged specimens coincides with the one of the unaged matrix, indicating that hydrothermal ageing does not produce noticeable matrix damage even after two years. Water aged specimens show similar electrical conductivity than unaged ones, which is another indication of no degradation of samples by water.