Investigation of capillary impregnation for permeability prediction of fibrous reinforcements

Abstract

In thermoplastic pultrusion process, unidirectional glass fibre bundles are very often used as reinforcement. This study was motivated by the industrial requirement to evolve from low viscosity thermoset resin processes to high viscosity thermoplastic polymers. The key parameters to control the impregnation process are the permeability of the fibrous reinforcement and the capillary pressure. The current study's objectives are threefold: (1) study the fibres arrangement by X-ray tomography, (2) determine the longitudinal and transversal permeabilities as well as capillary pressure to use them as input parameters of impregnation process in pultrusion and (3) carry out sensitivity analyses of the permeability measurements to the perturbation of fibre structure. To reach these purposes, two theoretical models were used to determine both axial and transversal tow permeability. The axial impregnation of aligned fibres was described by Washburn equation applied to 1D infiltration into the bundles. The in-plane impregnation was described by Darcy's law. The elliptical equation for highly anisotropic medium was resolved. Results show that permeability measurements are subjected to large variations, caused by perturbation of the fibre architecture during experiments. Besides, it was shown that the tensile force applied on fibres during pultrusion has a great effect on impregnation. Indeed, the permeability increases with the applied tension.

Numerical modeling of local capillary effects in porous media as a pressure discontinuity acting on the interface of a transient bi-fluid flow

“…This value represents approximatively one third of the 1 bar driving force available in the LRI process, which is too significant to be neglected and even permits to manufacture composite parts that could not be without its contribution. Consequently, the aim of this paper is to introduce these local capillary effects, in order to assess their influence on the filling stage scenarios at the scale of composite parts [46,70]. Indeed, following the multi-scale nature of high performance composites, the study can be conducted at three different scales as shown in many studies [15,22,36,60]: at the fiber or microscopic scale (∼ 10 −6 m), at the tow or mesoscopic scale (∼ 10 −3 m) and at the process or macroscopic scale (∼ 10 −1 m).…”

Effect of Solvent and Drug Impregnation Techniques on Total Drug Content in Rifampicin Impregnated Hydroxyapatite for Localized Bone Tuberculosis Treatment

“…All vacuum assisted techniques could help in increasing rifampicin content in the samples compared to immersion sample which was simply immersed in drug solution at atmospheric condition especially when using methanol. The mechanism of drug solution impregnation in immersion sample was achieved by capillary motion which drew the solution to flow through the pores of hydroxyapatite sample in opposition to gravity due to the pressure of cohesion and adhesion between solid and liquid [10]. However, there was a limitation in the distance of liquid to flow by capillary action especially when the pores were minute [11].…”

Capillary Effects in Fiber Reinforced Polymer Composite Processing: A Review

“…Similarly, some researchers performed wicking experiments on single tows (Hamdaoui et al, 2007;Pucci et al, 2015a;Koubaa et al, 2016;Castro et al, 2020) or a single layer of fabric (Lebel et al, 2013;Pucci et al, 2015b, Pucci et al, 2016Vo et al, 2020) and were able to extract the values of the capillary pressure and the dynamic advancing contact angle using the Lucas-Washburn method (Washburn, 1921) which describes the capillary rise of a liquid inside a capillary tube, and by extension into a porous media. However, the Lucas-Washburn approach assumes a constant geometry of the porous medium during the experiment and does not take into account attraction forces between vertical cylinders resulting from elasto-capillary effects and neither the swelling effect in natural fibers which leads to densification phenomenon, this is why some modifications have been proposed over the years (Rieser et al, 2015;Koubaa et al, 2016;Pucci et al, 2016;Vo et al, 2020). Lebel et al (LeBel et al, 2014) proposed a simple methodology to obtain the optimal flow injection conditions for a given fluid/fabric system based on the Lucas-Washburn imbibition model, which was thereafter used in Refs.…”