Kinetic model study of moisture sorption–desorption–resorption in triangular-shaped vinyl ester filler/epoxy composites
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A phenomenological diffusion model was used to study and describe moisture sorption–desorption–resorption kinetics in triangular-shaped vinyl ester filler/epoxy composites at 80 °C. The model was derived to predict the experimental anomalous weight gain behaviors of epoxy composites during moisture sorption and resorption, and estimate the degree of material degradation and loss observed as negative weight change during desorption. To verify the applicability of the model, acid anhydride–cured epoxy composites were prepared at varied alignment (parallel or staggered), spacing (1 or 5 mm), and orientation (pointed or flat) of triangular-shaped vinyl ester fillers. Moisture sorption–desorption–resorption experiment was performed by immersion of specimens in deionized water for 1200 h, followed by vacuum drying for 300 h, and water reimmersion for 300 h. The parameters of the model were calculated from nonlinear regression of percent weight change versus time experimental data. The model was found to be in good agreement with the weight change kinetic curves of all specimens. Results of three-way analysis of variance of model parameters showed the degree of material degradation and moisture diffusion coefficients during sorption, desorption, and resorption to be significantly affected by triangular-shaped filler alignment, spacing, and orientation. Using staggered over parallel alignment and 5-mm over 1-mm spacing decreased material degradation and moisture transport rate during desorption in composites. Increasing the spacing from 1 to 5 mm decreased moisture diffusion during sorption. Orienting the fillers from pointed to flat decreased moisture diffusion during resorption. Effect of interaction of filler spacing and orientation was also found to be statistically significant on the diffusion rate during sorption.
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