Auto-accelerative water damage in an epoxy composite reinforced with plain-weave flax fabric

Water diffusivity was measured through 12 wet–dry cycles, for epoxy resin reinforced with plain-weave flax fabric. Electron microscopy revealed micro-cracks that provided routes for water uptake. Water damage was characterised by the volume of pores, expressed as percent of the total volume of the composite. Water diffusivity doubled for every increase of 2.3% in the volume of pores, until a plateau was reached after several cycles, when water diffusivity was 10 times as great as on first immersion. The amount of water absorbed by the flax–epoxy composite was an order of magnitude larger than that reported for unsaturated polyester resin reinforced by plain-woven E-glass fabric, yet the extent of water damage and associated changes in diffusivity were similar. Results were consistent with a damage mechanism in which both flax fibres and matrix become swollen when wet, but the fibres shrink faster than the matrix when dried.