Multiscale modelling of moisture diffusion in polymer/clay/fibre hybrid composites: Influence of nanoclay structure

The growing use of polymer composites poses a major challenge, related to moisture absorption, which can alter their mechanical properties and durability. This study makes two main contributions. First, a method based on the description of a representative elementary volume (REV) was developed for multiscale modelling of moisture diffusion in hybrid polymer/clay/fibre composites. The method considers the morphology of the nanoclay, whether exfoliated or intercalated. Second, the effect of the reinforcing fibres type was analysed: impermeable fibres such as carbon or glass, and permeable fibres such as plant fibres. Simulations performed on polymer/fibre/clay hybrid composites showed a Fick-type diffusion behaviour. The diffusion coefficient decreased as the nanoclay volume fraction increased. For example, with 20 vol% fibre content and 5% exfoliated nanoclay, the diffusion coefficient dropped from 2.60 × 10⁻⁸ mm²/s to 3.30 × 10⁻⁹ mm²/s (≈87% reduction) for composites with impermeable fibres, and from 6.56 × 10⁻⁸ mm²/s to 7.79 × 10⁻⁹ mm²/s (≈88% reduction) for those with permeable fibres, in comparison with clay-free composites. This reduction results from the barrier effect of clay sheets. The results also show that exfoliated structures limit moisture absorption more effectively than intercalated ones. Fibre permeability was found to strongly influence diffusion kinetics.