Water transport in an epoxy–phenolic coating

Abstract

a b s t r a c tThermoset coatings commonly rely on high cross-linking density to provide enhanced barrier properties. Hence it is surprising that for the industrial epoxy-phenolic network investigated, equilibrium moisture uptake is found to increase with respect to cure time, i.e., with greater cross-linking. Molecular interactions between absorbed water and the resin are characterised using infrared spectroscopy, and water uptake is correlated to network polymer features such as polarity and free volume.

A bulk and localised electrochemical assessment of epoxy-phenolic coating degradation

“…Water estimation, in this case, agrees with earlier humidity studies [27], where the longer coating curing yields greater coating water capacity ( Figure 10). Comparing these water volumes with the ones calculated initially in Figure 5, we can conclude that a much greater water amount is absorbed by a completely dry coating than by a coating that has just been immersed.…”

“…Opposite to what is usually described in literature, higher water content was detected under humid conditions on coatings with increased curing degree. This statement, even though contradictory to Nguyen's degradation model, can be attributed to the increasing free-volume introduced in the polymer with further curing, leading to coating swelling, lower coating density and subsequently increased water capacity [27]. Free volume presence in epoxies is responsible for many vital coating properties.…”

The degradation mechanism of an epoxy-phenolic can coating

“…Corrosion is then thought to initiate when stress relaxation of the polymer joins these hydrophilic regions to create a percolating pathway through the coating. However, for the epoxy-phenolic coatings studied here, the presence of partially reacted low molecular weight material may be discounted, since the can coatings are shown to be fully cured (confirmed by the absence of any epoxy absorbance at 916 cm -1 in FTIR spectra, Figure 1, and no endothermic peak associated with excess cure observed in DSC thermograms, reported previously [31]). Furthermore, the absence of hydrolysis reactions was here confirmed using in-situ FTIR analysis during immersion, Figure 1, and leaching effects were ruled out using gravimetric analysis.…”

Insights into Epoxy Network Nanostructural Heterogeneity Using AFM-IR

“…This is despite their widespread use as food-contact barrier coatings and encapsulation of semi-conductor devices, where heterogeneous network structure may determine performance, since small molecule transport is closely related to network crosslinking densities. 51,52,53 Dušek has previously proposed that catalysis of epoxy network formation may promote cyclization during the cure, forming the basis of any heterogeneous structure detected. 28,42 In the present case, such a mechanism can be discounted since catalytic content has no effect on heterogeneous domain size, and specimens cured in the absence of catalytic species develop comparable morphologies, Figures 1-4.…”