Evaluation of interfacial relaxation due to water absorption in fiber–polymer composites

Water penetration in composite materials of different interfacial strengths has been studied and explained as the result of two parallel processes, i.e., diffusion through the polymer matrix and through a network of micro-channels formed along the imperfectly bonded polymer-fiber interface. Such channels along the exterior of the loose fiber are presumed to contribute a mesoscopic “free volume” to the composite which is conductive to diffusion. An analytical method based on an adaptation of the free volume theory approach is proposed for estimating the incipient looseness and any further interfacial relaxation caused by water absorption in composite materials.