Study on diffusion behavior of water in epoxy resins cured by active ester

Abstract

Phenol novolac resin and a series of esterified phenol novolac resins with side groups of acetate, butyrate and phenylacetate are used as curing agents for O-Cresol novolac epoxy resin. The cured resins are named as EP, EPA, EPB and EPP respectively. The water diffusion behavior of epoxy networks is studied by ATR-FTIR spectroscopy and gravimetric method. The obtained results show that the diffusion type of EPA and EPP are quite approximate to Fickian diffusion, while EPB displays a typical Case II characteristic and EP follows anomalous diffusion. The diffusion coefficient of EP is much lower than EPA and EPP. In 2D-IR spectra the splitting of water OH vibration band in the range of 2800–3700cm⁻¹ and 1500–1800cm⁻¹ shows the existence of two different states of water as free and bound water. Water molecules first bind with specific hydrophilic groups as bound water and then diffuse into free volume (microvoids) or molecularly disperse with less hydrogen bonding (bulk dissolve) as free water. Evidence is also found for the strength order of hydrogen bonding interactions between water molecules and epoxy networks as EP > EPA > EPB > EPP.