Preparation, Modeling, and Optimization of Mechanical Properties of Epoxy/HIPS/Silica Hybrid Nanocomposite Using Combination of Central Composite Design and Genetic Algorithm. Part 2. Studies on Flexural, Compression, and Impact Strength

In spite of good tensile strength of epoxy resins, they have brittle nature and show poor resistance to crack propagation. In view of enhancing mechanical strength and fracture toughness of epoxy-based nanocomposite simultaneously, a new combination of thermoplastic and particulate nanofiller is used as a modifier. Here, the obtained ternary epoxy-based nanocomposite includes high impact polystyrene (HIPS) as thermoplastic and silica nanoparticles as its particulate phases. Flexural, compression and impact were the three different mechanical tests investigated, in order to achieve higher strength without attenuating other desired mechanical properties. Central composite design (CCD) is employed to present mathematical models to predict mechanical behaviors of epoxy/HIPS/silica nanocomposite as a function of physical factors. The effective parameters investigated were HIPS, SiO2 and hardener contents. Based on mathematical functions obtained from CCD model, the genetic algorithm - as one of the most powerful optimization tools - is applied to find the optimum values of mentioned mechanical properties. We have found that a combination of HIPS and silica nanoparticles significantly increase compressive and impact strengths of epoxy resin up to 57 and 421%, respectively. Although flexural strength did not change positively, the elongation at break for flexural one increased up to 144%. Finally, the morphology of fracture surface was studied by energy-dispersive X-ray spectroscopy and scanning electron microscopy.