Development of a rubber toughened epoxy adhesive loaded with carbon nanotubes, for aluminium – polymer bonds

This thesis describes the formulation of a ternary thermosetting adhesive which consists of a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin cured with 3,3’-diamino diphenyl sulphone (3,3’-DDS) hardener and modified through the addition of carboxyl- terminated butadiene-acrylonitrile (CTBN) rubber and multi-walled carbon nanotubes (MWCNTs). Processing implications of the novel adhesive in the film form are considered in order to manufacture bonded specimens for characterisation of the adhesive performance in structural joints. The ternary blend which represents the novel adhesive formulation is also characterised in bulk form. The cure kinetics behaviour of the novel ternary blend is investigated using differential scanning calorimetry which shows 10% reduction in the total reactivity, and therefore reduced final crosslinking density, with the addition of the carbon nanotubes. A cure kinetics model is developed for the novel ternary thermoset. From characterisation of cast samples, a toughening effect of the phase separated rubber particles is observed, from 144 to 317 J/m 2 , with a further increase to 551 J/m 2 in the presence of the carbon nanotubes. In the absence of rubber, the nanotubes alone produce a minimal effect upon the thermo-mechanical and mechanical characteristics of the resin. The morphology of the cured material is affected by the presence of the nanoparticles, resulting in the reduction of the mean rubber particle size from 3µm to below 1µm. The electrical conductivity of the cured resin samples is found to increase by six orders of magnitude, up to 3.6 x10 -3 S/m in the ternary blend for a low carbon nanotube concentration of 0.3 wt%. DCB and ELS tests are used to study the performance of the novel adhesive in a joint configuration. The adhesive joint strength is dependent on the substrate type as well as on the surface preparation. The novel adhesive is also examined under fatigue in a ‘bonded crack retarder’ application.