Characterization of Water-Epoxy Interactions with Spectroscopic Methods in Epoxy

Abstract

Composite materials are widely used in the aerospace and wind energy industries. In most applications these materials undergo mechanical loading coupled with the effects of environmental degradation from moisture and temperature variation. It has been widely reported that absorbed moisture in high humidity environments can significantly reduce the strength of epoxy, while increasing its strain to failure. However this behavior varies significantly depending on the type of the epoxy. Zhou and Lucas [1, 2] show that at a molecular level, water molecules interact with polymer chains in two ways: i) H2O forming one hydrogen bond (H-bond) with a single polymer chains and ii) H2O forming H-bonds with two or more polymer chains. Both interactions change the polymer chain configuration. Based on the type and number of interactions of H2O with polymer chains, either plasticity or stiffness is locally enhanced, which leads to changes in material properties at the macroscopic level. In the current study, Fourier Transform Infrared (FT-IR) spectroscopy along with 2D correlation analysis is utilized to identify various water-epoxy interactions for two different types of epoxies. Furthermore, microtensile tests and dynamic mechanical analysis is performed on hydrated epoxy samples. These results are compared with their dry counterpart. We identify the possible deformation mechanisms based on water-epoxy interactions and changes in mechanical properties.