A dielectric study of water uptake in epoxy resin systems
The influence of epoxy resin formulation on the nature and extent of moisture is studied using dielectric and gravimetric analysis for samples cured at 40, 50, 60, and 70 °C and aged at 50 °C and 70 °C.
The equilibrium moisture uptake depends on the difference between the glass transition and aging temperature. Dielectric relaxation data measured from 1 to 3 × 1010 Hz indicates the presence of water in at least two different environments.
Water interacts with OH groups and polyether
The high frequency relaxation ca. 1 × 1010 Hz is associated with water clustered in nano-voids, whereas the relaxation at 105 Hz arises from a combination of OH pendant group reorientation motion coupled with that of molecularly dispersed water molecules. A correlation exist between the dielectric permittivity and the amount of moisture absorbed. Water initially resident in voids is re-dispersed with aging into the resin matrix aiding plasticisation and allowing densification of the matrix. The extent to which changes occur depends on the chemical functions forming the matrix and densification leads to a drop in the amount of water absorbed. In the complex resin systems, water interacts with both OH groups and polyether of the amine curing agent which is not possible with the aliphatic diamine in the simple system.
The study is published in: Applied Polymer Science, Volume 134, Issue 16, April 20, 2017
