Miscibility, microstructure, and in situ cure analysis of epoxy–SAN–cloisite 20A nanocomposites
Reaction induced phase separation is a characteristic of thermoset/thermoplastic blend systems. Herein, we report the effect of organically modified cloisite 20A nanoclay on the miscibility and curing parameters of an epoxy blend system containing diglycidyl ether of bisphenol A (DGEBA) and poly(styrene-co-acrylonitrile) (SAN) and cured with diamino diphenyl sulphone (DDS). The examined blend compositions were chosen based on the difference in the microstructure. The epoxy/5 phr SAN blend and the epoxy/5 phr SAN/3 wt% cloisite 20A nanocomposite showed a dispered SAN phase in the epoxy matrix. The epoxy/15 phr SAN blend and the epoxy/15 phr SAN/3 wt% cloisite 20A nanocomposite showed a double phase structure. Quantitative analysis of the epoxide conversion during the curing reaction was done by in situ FTIR spectroscopy. The epoxide conversion obeyed first order kinetics in the initial stages of curing. Enhanced viscoelastic effects by the nanoclay decreased the rate of epoxide conversion, which is evident from the in situ cure analysis. Finally, the growth of the complex viscosity during curing was determined by in situ rheometry and theoretically analysed by fitting with the Williams–Landell–Ferry equation. An exponential growth in complex viscosity was observed which was induced by crosslinking. Acceleration of the curing reaction by the nanoclay contributed to the increase in the complex viscosity for the nanocomposites compared to the blends.