29th Annual Technical Conference of the American Society for Composites, ASC 2014; 16th US-Japan Conference on Composite Materials; ASTM-D30 Meeting, California, United States Of America, 8 - 10 September 2014
Moisture absorption in polymers and polymeric composites is well known to lead to significant degradation in mechanical properties. Most epoxy based composites may absorb 2 to 5 wt.% moisture when they are subjected to humid environments. Moisture absorption in polymers has been often characterized with Fickian or various non-Fickian models to describe the time-dependent absorption phenomena. Previous experiments have shown that dispersing moderate amounts of nanoclay in an epoxy resin can: (i) reduce the total maximum moisture absorbed; (ii) slow down the rate of moisture absorption, and (iii) enhance non-Fickian nature of absorption. In this paper, the effect of coating an epoxy laminate with a thin, nanocomposite layer to reduce both the rate of moisture absorption and the saturation moisture level is investigated using a multilayer non-Fickian model. Multilayer hindered diffusion model, which includes the material anisotropy, moisture absorption hindrance and multilayer diffusion kinetics, is introduced. The thin layer is comprised of DGEBA type epoxy mixed with I.30E nanoclay. The effect of nanoclay content ranging from 1 wt.% to 10 wt.% on the moisture absorption of the laminate with a 250μm coating is illustrated. When the nanocomposite coating is considered, the maximum moisture absorption is predicted to be reduced to 1.94 wt.% from the 2.11 wt.% observed for the uncoated laminate. The multi-layer absorption model is also used to determine the effect of coating thickness ranging from 50μm to 250μm. Increasing the coating thickness from 50 μm to 250 μm is shown to reduce the maximum moisture absorption from 2.07 wt.% to 1.94 wt.%. The solution for the one-dimensional non-Fickian multilayer absorption model presented in this work can further be extended to two- or three-dimensional laminates coated on one or both sides, thus facilitating the predictive analysis of geometrically complex, thick composite laminates with various nanocomposite coatings.