Micro- and macro-impregnation of fabrics using thermoplastic matrices

In this work, a method developed for the measurement of the transversal permeability of fibrous reinforcement is presented. The permeability of a reinforcement is defined by the Darcy equation and can be obtained once the pressure drop through the reinforcement and the viscosity and average velocity of the fluid are known. The method used in this work is based on a proper modification of a capillary rheometer, obtained by substituting the capillary with a tool, capable of sustaining the reinforcement during reinforcement impregnation and through thickness flow. The developed device was used to measure the pressure built during the flow at different velocities of the rheometer piston. The impregnation tests were performed at different temperatures using a high-viscosity matrix characterized by a Newtonian behaviour. At each temperature, pressure versus velocity plots showed two distinct zones, each characterized by a different slope. The slope observed at low pressures was higher than the slope observed at pressures, suggesting an increase in the permeability with increasing pressure or velocity. The double slope was attributed to the existence of two different impregnation mechanisms, the first one being characteristic of the flow of the matrix around the reinforcement bundles and the second is the characteristic of the flow of the matrix inside each bundle. Dimensionless analysis models and scanning electron micrographs were used to support that the slope of the first portion of the plot is due to inter-bundle flow, whereas the slope of the second portion is due to global flow including both inter- and intra-bundle flow.