Water absorption behavior and thermal-mechanical properties of epoxy resins cured with cardanol-based novolac resins and their esterified ramifications

To study the effect of chain flexibility and polarity on the water absorption and thermal-mechanical properties of epoxy materials, different kinds of bio-based novolac resin hardeners were synthesized by cardanol-formaldehyde condensation reaction and two esterified ramifications were synthesized by esterifying their corresponding phenolic resin. The cure behaviors were evaluated by differential scanning calorimeter, and the mechanical and thermal properties of cured samples were characterized by dynamic mechanical analyzer and thermogravimetric analysis. Water absorption process was monitored using gravimetric measurement, and time-resolved ATR-FTIR. The diffusion mechanism was also explained using 2D correlation analysis. The addition of cardanol into novolac resins was found to decrease the glass transition temperature due to the plasticizing effect of flexible aliphatic chain. On the other hand, water resistance ability was enhanced due to lower polarity. The effect of esterification on lowering water absorption is prominent for both esterified ramifications. The water absorption mechanism was then characterized and discussed using 2D correlation analysis of time-resolved ATR-FTIR. (C) 2017 Elsevier Ltd. All rights reserved.