Nanostructured coating based on epoxy/metal oxides: Kinetic curing and mechanical properties

In this work nanocomposites were prepared by means of a twin-screw extruder using a solid epoxy resin DGEBA/biguanidine matrix and metal oxides filler. Two different nanoparticles were employed as-received, alumina and zinc oxide at the composition of 3% phr in both cases. Cure kinetics analysis was investigated by means of DSC in a set of non-isothermal experiments. In the neat polymer, the activation energy of the curing reaction was 65 kJ/mol, whereas after adding ZnO, a minimum of 53 kJ/mol was reached. The lower activation energy of this nanocomposite allows longest reaction and consequently enhanced crosslinking network. Thus, the glass transition temperature is increased from 368 K in the neat polymer to 377 K after reinforcement. The nanocomposite filled with alumina has corresponding activation energy of 61 kJ/mol, in this case, short chain segments must possess higher reticulation near to surface particles, influenced by the presence of hydroxyl groups. The mechanical properties were examined by means of instrumented indentation and scratch test. An increase of around 10% of the elastic modulus and hardness was observed. Toughening mechanisms are induced by alumina, as observed by the scratch test, nevertheless, zinc oxide increased the matrix fragility because to its catalytic influence on cure reaction. In addition dispersion state of the particles into the nanocomposites was investigated. Finally, connections between cure kinetic, interphase and mechanical properties in this system are addressed.