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 À1 and 1500-1800cm À1 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.

Water transport in an epoxy–phenolic coating

“…Conversely, Zhang et al [15] examined two epoxy-phenolic systems and reported greater water sorption for the resin containing less free volume, so concluded that water uptake was dependent only on polarity. Numerous 2D ATR-FTIR investigations have also confirmed the presence of free and bound water for epoxy-phenolic formulations [37,[57][58][59].…”

Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity

“…Less polar resins, such as resin 1, absorbed very little water (Table 4) compared to the more polar species. Water attracted to polar groups forms hydrogen bonds [6] resulting in ''bound water'' and is responsible for plasticizing polymers [22,23]. The increase in discrete, spot-like distribution of silver seen in the TEMs of resins 1-5 (Fig.…”

Evaluation of interfacial relaxation due to water absorption in fiber–polymer composites

“…Hence, these two damage-dependent mechanisms are increasing both the rate and the maximum capacity of moisture absorption in an auto-accelerative manner [15,18]. It may therefore be readily concluded that the mechanisms of moisture penetration in composites [12] are much more complex than in the case of the unreinforced matrix [23][24][25].…”