Permeability of natural fiber reinforcement for liquid composite molding processes

We investigate the influence of liquid type on the saturated permeability of natural fabrics in liquid composite molding processes. The permeability of flax woven fabric was characterized with two different liquids which have different viscosity, wettability, and sorption characteristics with flax fiber. From the experimental data, it was observed that the saturated permeability values were different for the liquid type. The fiber swell during the mold filling process and the corresponding change of fabric microstructure were assumed to be the main reason for this dependency of saturated permeability on the liquid type. The fiber swell due to the liquid sorption was characterized as a function of time, and the corresponding change of fiber diameter was investigated. The effective fiber volume fraction of wet natural fabric was defined in terms of fiber swelling ratio. The predictions by the classical Kozeny-Carman model and by the modified Kozeny-Carman model with two model constants were compared with the experimental data. It was shown that the modified Kozeny-Carman equation considering fiber swell could predict very well the saturated permeability of natural fabrics regardless of liquid type.