This work investigates the humidity absorption process in the polyester/glass fiber composite materials containing fillers and low profile additives. These composite materials were exposed to both distilled and sea water at different temperatures. The moisture diffusivity and the moisture equilibrium reached by these composites were determined using the gravimetric test method and their humidity distribution profile across the thickness direction was characterized using the microtome technique. The obtained results indicate that the distilled water diffuses in all composites much more rapidly than the sea water, particularly at high immersion temperatures. However, the opposite is observed at low immersion temperature (5°C), since at this temperature the distilled water is almost in its icy state. For high immersion temperatures, a mass loss of the aged specimen in the sea water was observed 2 months after the first immersion. Such behavior was not observed during the immersion in the distilled water. Moreover, it is observed that the water absorption is higher in the composite materials containing low profile additives. This behavior is explained in terms of microvoids formation promoted by low profile additives. The microtome technique reveals clearly that the humidity profile across the thickness of the aged specimen follows a parabolic trend with a maximum at the outside surface of that specimen and a minimum at its center. These experimental results were found to confirm the theory. POLYM. COMPOS., 28: 355–364, 2007. © 2007 Society of Plastics Engineers

In this article, the distribution through the thickness of both the matrix's modulus and the interfacial shear strength (IFSS) in dry and aged pultruded polyester/glass fiber composites containing fillers and low profile additives are experimentally evaluated, using the nanoindentation test. The obtained results indicate that for the dry composite, both the matrix's modulus and the IFSS are constant across the thickness of that material. As a consequence of the immersion in distilled water at high temperature (65°C), the IFSS was found to exhibit a parabolic trend through the thickness of the aged specimen, with the lowest value at the external surfaces. Such minimum was reached after a short time of immersion. At the saturation time, the IFSS at all layers of the aged specimen reaches lowest value. This was not the case for the matrix's modulus, since the later was found to be not affected by the amount of the absorbed humidity. Similar results were obtained after immersion in sea water at the same temperature. However, the only difference noted was at the external surface of the aged specimen where additional degradation had taken place in the matrix and at the fiber/matrix interface. This was attributed to the accumulation of a large amount of salt molecules at the external surface of the aged specimen during the exposure process. Additional mechanical tests show that after 120 days immersion in hot water the interlaminar shear strength of the material as measured according to the ASTM standard D2344, is reduced by 35%. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers