EFFECTS OF WATER ON A GRAPHITE EPOXY COMPOSITE/

The effects of water-induced physical and chemical property modificati on on a graphite/epoxy (GrEp) laminate were investigated. The laminate was consolidated using unidirectional T300/934 graphite/epoxy prepreg . Specimens were conditioned, hydrothermally, by immersion in distille d water at 45, 60, 75 and 90 degrees C for more than 9000 hours. The c omposite properties were characterized by evaluating the specimen's we ight change due ro water absorption and desorption, by hygrothermally induced expansion, and by water-induced change of the glass transition temperature (T-g). Optical microscopy and scanning electron microscop y (SEM) were conducted to assess surface modification associated with resin cracking and resin mass loss. Water sorption in the Gr/Ep materi al exhibited both Fickian and non-Fickian diffusion behavior. Diffusio n data showed that the lime For the onset of non-Fickian behavior was Inversely related to the increase in exposure temperature. Anomalous ( i.e., non-Fickian) behavior in the composite resulted from both chemic al modification and physical damage to the epoxy resin. Moisture-induc ed cracks, voids, and surface resin peeling were revealed by SEM and o ptical microscopy. Surface cracking and resin mass loss phenomena were used to-describe water sorption behavior in composites. Thermomechani cal analysis (TMA), water desorption, and infrared (IR) spectral resul ts suggest that water retention in the composite can be characterized: (1) by water trapped at defects such as crack tips, interfaces, and v oids; (2) by water interaction associated with weak hydrogen bonding w ithin the resin; and (3) by water bonded to hydrophilic functional gro ups of the polymer chains.