Epoxy resins are widely used as high-performance protective coatings, structural adhesives and matrix resins for composites. When cured, these resins are generally brittle and have poor resistance to crack growth. Toughening of epoxy resins with low-molecular weight liquid rubbers is well developed and the use of rubber-modified epoxy resins as structural adhesives and as matrix for fiber composites is widely accepted.
Rubber is added to the uncured epoxy resins and after the cross-linking reactions the rubber-modified epoxy resins exhibited a two-phase microstructure consisting of relatively small rubber particles dispersed in a matrix of epoxy.
This microstructure resulted in the material possessing a higher toughness than the unmodified one with only a minimal reduction in other important properties, such as modulus. To reduce the brittle nature of cured epoxy, resin formulators have developed technology that permits some thermosets to be toughened by the addition of a second elastomeric phase, but strategies to improve the toughness of rubber modified epoxy should also incorporate the combined benefits of rubber and nanoclay incorporation into epoxy, in order to attain a promising toughened epoxy without compromising the other desired mechanical and thermal properties of the epoxy resin.
In this study, CTBN liquid rubber was added to an epoxy resin cured with Nadic methyl anhydride (N, N-dimethylbenzylamine as accelerator). Nanoclays modified with Trimetyl stearyl ammonium and octadecylamine respectively were used and the composition range of the blends varied according to the following scheme: 100 (epoxy): 10 to 20 phr (CTBN): 1 to 3 phr (clay).The comparison of cure behavior of the neat epoxy, epoxy modified with rubber, epoxy modified with nanoclay and epoxy modified with both rubber and nanoclay has been done . From optical images taken during cure it is well clear that the presence of nanoclay speed up the phase separation of rubber particle from the epoxy matrix.