Viscoelastic and thermal properties of full and partially cured DGEBA epoxy resin composites modified with montmorillonite nanoclay exposed to UV radiation

Effects of UV radiation and associated elevated temperature on properties of polymeric composites have been well documented, limiting the scope of their usage in outdoor applications. In order to improve on this limitation, current study focused on incorporating nanoparticles into epoxy polymer composites and delay onset of deleterious effects of UV radiation by partially curing these samples. Samples were fabricated and cured to 80% conversion (partially cured) based on isothermal cure kinetic studies. Influence of 1, 2 and 3 wt. % loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the study revealed that for optimization of modified epoxy composite properties a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Fabricated samples infused with 1, 2 and 3 wt. % montmorillonite nanoclay were exposed to 2500 h of continuous UV radiation, where effects of UV radiation on viscoelastic and thermal properties were evaluated and compared with identical set of fabricated samples using manufacturers' recommended cycle (fully cured). Addition of nanoclay increased the viscoelastic properties, and at the end of the study, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fully cured samples degraded over the same period. Samples cured to 80% showed delayed UV radiation degradation effects.