Hot–Wet Environmental Effects on Glass Transition Temperature of IMA/M21E Aircraft Grade CFRP Composites

Carbon fiber-reinforced plastic (CFRP) composites used in aerospace is mainly due to their lower weight with high strength and stiffness. As composite aircraft structures in their service life usually comes in contact with a range of environmental conditions like hot–wet (hygrothermal), chemical environments, UV radiation, biological conditions etc., this causes degradation in material properties of these parts. When these composite parts subjected to hot–wet environments, water or moisture gets infused into matrix or interface region between matrix and fiber of composite. This infused water or moisture act as plasticizer resulting in increasing space between the polymer chains. This leads to a significant deterioration in glass transition temperature (Tg) and mechanical properties. In this present research work, a comprehensive approach has been adopted to study both the diffusion and degradation effects in a new carbon epoxy composite, subjected to different hot–wet conditions (temperature and humidity in terms of % water), immersion in aviation fuels — aviation turbine fuel and piston engine fuel. All these conditions have great relevance to aerospace and allied applications. The CFRP Composite HexPly® M21E/34%/UD/194/IMA material was studied here. This composite was exposed to different hot–wet environments up to moisture saturation limits. The effect of moisture absorption on physicochemical properties like glass transition temperature (Tg) of the CFRP was evaluated using differential scanning calorimeter (DSC) for the specimens after conditioning in all the environments of study. Tg got deteriorated by about 8% due to hygrothermal aging.