Influence of water on a model carbon fiber/epoxy polymer system

A strong effect of absorbed water on the physical properties of a model epoxy polymer and on carbon fiber/epoxy polymer matrix interaction was observed. Water acts as a plasticizer in the polymer network and effects in a decreased glass transition temperature. After redrying the water-saturated polymer the origin state of the polymer in terms of Tg is restored. The single fiber fragmentation test reveals a strong decrease in the interfacial shear strength when comparing the dry and the water-saturated state of the carbon fiber/epoxy polymer composite. Still, after redrying the single-fiber composites, higher interfacial shear strengths are received. These reversible effects indicate that water essentially is physically absorbed in the polymer bulk and in fiber/polymer interphase.