Effect of laminate thickness on moisture diffusion of polymer matrix composites in artificial seawater ageing

The influence of laminate thickness of polymer matrix composites on moisture diffusion in seawater immersion, as well as the resulting mechanical property degradation for composites of glass/ isopolyester ( G/ IPE), carbon/ isopolyester ( C/ IPE), glass/ vinylester ( G/ VE) and carbon/ vinylester ( C/ VE), was investigated in this paper. Laminates 3 and 10mm in thickness, fabricated using the wet hand lay- up technique, were characterized for moisture absorption in artificial seawater medium, and their flexural strength and interlaminar shear strength ( ILSS) degradations were studied. Moisture diffusion was observed to be anamolous to the Fick's law for both 3 and 10mm thick samples in the later stage of diffusion. Moisture permeability of 10mm thick samples was two to three order greater than that of 3mm thick ones, while the time to moisture saturation remained unchanged. With the increase of laminate thickness, moisture saturation increased by 1.4% for C/ VE and 7% for G/ IPE. The residual flexural strength and ILSS were greater in case of 10mm thick specimens after 200 days of exposure. SEM examination of the fractured specimens showed greater levels of fibre/ matrix debonding in 10mm thick specimens.