Hygrothermic Behaviour of Carbon/Ninylester, Glass/Ninylester, Carbon/Epoxy and Glass/Epoxy Composites

Moisture absorption behaviour of polymer matrix composites (PMCs) in humid and tropical environments is a complex phenomenon. Moisture diffusion weakens the fibre/matrix interface which leads to deterioration of mechanical properties. Hygrothermic ageing of carbon/vinylester, glass/vinylester, carbon/epoxy and glass/epoxy composites were studied for their suitability in marine applications. The specimens were exposed to 50 degrees C, 60 degrees C and 70 degrees C temperatures and humidity of 95% RH for a maximum duration of 170 days. The specimens were periodically weighed for moisture absorption and tested for mechanical properties (ultimate tensile strength, flexural strength and interlaminar shear strength) degradations. The maximum moisture absorption was observed for epoxy/glass composite and the minimum for vinylester/carbon composite. Diffusion mechanism was studied on the basis of the Fick's law of diffusion. It was found that diffusion coefficient (D) is at highest for epoxy/glass composite and at the lowest for vinylester/carbon composite. Diffusion coefficient increased with increase in temperature for all the specimens. Comparing vinylester/carbon and epoxy/carbon samples data, although both lowered in properties, the former showed still better results in flexural strength (FS), ultimate tensile strength (UTS) and interlaminar shear strength (ILSS) values than the latter. As a whole, Vinylester/glass has behaved superior to epoxy/glass with respect to changes in their mechanical properties. The experimental observations are confirmed by SEM. Vinylester based specimens showed greater chemical stability than the epoxy based specimens. Even after 170 days of hygrothermic exposure, vinylester/carbon showed lower degree of fibre pulls out compared to other three specimens tested.

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