Investigation on tensile properties of epoxy/graphene nano-platelets/carboxylated nitrile butadiene rubber ternary nanocomposites using response surface methodology

In this study, the response surface methodology was used to investigate the tensile properties of epoxy/graphene nano-platelets/carboxylated nitrile butadiene rubber ternary nanocomposites. Box–Benhken method was used to design experiments for four factors consisting of graphene nano-platelets (at 0, 0.75, and 1.5 wt%), carboxylated nitrile butadiene rubber (0, 5, and 10 wt%), hardener contents (80, 90, and 100 phr), and also different post curing temperature (130, 140, and 150°C). After the samples were prepared, a tensile test was performed to obtain the tensile strength, tensile modulus, and elongation at break of nanocomposites. Moreover, field-emission scanning electron microscopy was used to observe the state of graphene nano-platelets dispersion. The results obtained from the tensile tests showed that increasing the graphene nano-platelets, carboxylated nitrile butadiene rubber, and hardener contents and high post curing temperature reduced the tensile strength. The optimum value of tensile modulus was achieved at low concentration of carboxylated nitrile butadiene rubber and high contents of graphene nano-platelets, whereas maximum elongation at break occurred at high content of carboxylated nitrile butadiene rubber and low concentration of graphene nano-platelets and hardener. In addition, a second-order polynomial model was used to correlate the tensile properties of ternary nanocomposites to the desired factors. Finally, contour plots were used to determine optimum values of the desired factors. It was seen that the presence of 10 wt% of carboxylated nitrile butadiene rubber in the epoxy matrix increased the elongation at break by the considerable amount of ∼49%.