Non-Fickian Moisture Absorption in Polymers Coated with a Thin Nanocomposite Layer

摘要

Moisture absorption in polymers and polymeric composites is well known tornlead to significant degradation in mechanical properties. Most epoxy basedrncomposites may absorb 2 to 5 wt.% moisture when they are subjected to humidrnenvironments. Moisture absorption in polymers has been often characterized withrnFickian or various non-Fickian models to describe the time-dependent absorptionrnphenomena. Previous experiments have shown that dispersing moderate amounts ofrnnanoclay in an epoxy resin can: (i) reduce the total maximum moisture absorbed;rn(ii) slow down the rate of moisture absorption, and (iii) enhance non-Fickian naturernof absorption.rnIn this paper, the effect of coating an epoxy laminate with a thin, nanocompositernlayer to reduce both the rate of moisture absorption and the saturation moisturernlevel is investigated using a multilayer non-Fickian model. Multilayer hinderedrndiffusion model, which includes the material anisotropy, moisture absorptionrnhindrance and multilayer diffusion kinetics, is introduced. The thin layer isrncomprised of DGEBA type epoxy mixed with I.30E nanoclay. The effect ofrnnanoclay content ranging from 1 wt.% to 10 wt.% on the moisture absorption of thernlaminate with a 250μm coating is illustrated. When the nanocomposite coating isrnconsidered, the maximum moisture absorption is predicted to be reduced to 1.94rnwt.% from the 2.11 wt.% observed for the uncoated laminate. The multi-layerrnabsorption model is also used to determine the effect of coating thickness rangingrnfrom 50μm to 250μm. Increasing the coating thickness from 50 μm to 250 μm isrnshown to reduce the maximum moisture absorption from 2.07 wt.% to 1.94 wt.%.rnThe solution for the one-dimensional non-Fickian multilayer absorption modelrnpresented in this work can further be extended to two- or three-dimensionalrnlaminates coated on one or both sides, thus facilitating the predictive analysis ofrngeometrically complex, thick composite laminates with various nanocompositerncoatings.