Capillary Effects in Fiber Reinforced Polymer Composite Processing: A Review

Abstract

Capillarity plays a crucial role in many natural and engineered systems, ranging from nutrient delivery in plants to functional textiles for wear comfort or thermal heat pipes for heat dissipation. Unlike nano- or microfluidic systems with well-defined pore network geometries and well-understood capillary flow, fiber textiles or preforms used in composite structures exhibit highly anisotropic pore networks that span from micron scale pores between fibers to millimeter scale pores between fiber yarns that are woven or stitched into a textile preform. Owing to the nature of the composite manufacturing processes, capillary action taking place in the complex network is usually coupled with hydrodynamics as well as the (chemo) rheology of the polymer matrices; these phenomena are known to play a crucial role in producing high quality composites. Despite its importance, the role of capillary effects in composite processing largely remained overlooked. Their magnitude is indeed rather low as compared to hydrodynamic effects, and it is difficult to characterize them due to a lack of adequate monitoring techniques to capture the time and spatial scale on which the capillary effects take place. There is a renewed interest in this topic, due to a combination of increasing demand for high performance composites and recent advances in experimental techniques as well as numerical modeling methods. The present review covers the developments in the identification, measurement and exploitation of capillary effects in composite manufacturing. A special focus is placed on Liquid Composite Molding processes, where a dry stack is impregnated with a low viscosity thermoset resin mainly via in-plane flow, thus exacerbating the capillary effects within the anisotropic pore network of the reinforcements. Experimental techniques to investigate the capillary effects and their evolution from post-mortem analyses to in-situ/rapid techniques compatible with both translucent and non-translucent reinforcements are reviewed. Approaches to control and enhance the capillary effects for improving composite quality are then introduced. This is complemented by a survey of numerical techniques to incorporate capillary effects in process simulation, material characterization and by the remaining challenges in the study of capillary effects in composite manufacturing.

Paper-Fiber-Activated Triplet Excitons of Carbon Nanodots for Time-Resolved Anti-counterfeiting Signature with Artificial Intelligence Authentication

“…The fluorescence lifetime (435 nm) of the CNDs was monitored, and the corresponding lifetime was about 1.69 ns, as shown in Figure 1c. When we wrote using the CND aqueous solution as ink, the ink was absorbed by the paper through the capillarity of paper fibers, 36,37 and multiple hydrogen bonds were thus formed after drying, as illustrated in Figure 1d. The strong confinement of the formed hydrogen bonds can activate triplet excitons of the CNDs; thus, the written word "spider" showed a lasting phosphorescence after ceasing excitation (Figure S2).…”

Study on the Hydrophobicity and Antibacterial Activity of Silica Sol-Chitosan-HDTMS Treated Cotton Fabric Dipped in an Aquas Media

“…It is evident from Figure 6 and Table 4 that cotton fabrics that are not coated exhibit wicking behaviour and have a wicking height of 8 cm ± 1 cm. This might be caused by the capillaries that exist within the structure of the yarn (intra-yarn spaces) and between the yarns (inter-yarn spaces) [48,49]. Conversely, the cotton fabric treated with silica sol, chitosan and HDTMS displayed zero evidence of wicking.…”

LCM of thermoset-based fiber reinforced composites for large-scale applications: are process kinetics and structural properties antagonistic?

“…As X-Ray Computed tomography became more readily available in the recent years, 3D imaging of an RVE is now becoming routinely accessible, leading to precise geometrical descriptions of the porous medium, including the presence of non-connected pores ( [10][11][12][13][14][15]). As mentioned, textiles are most often formed of tows or yarns that are assembled into a preform, the porous medium is thus generally described by a bi-modal pore size distribution, as illustrated in Figure 1, and the dual scale nature of the pore size distribution can lead to exacerbated capillary/hydrodynamic effects, as compared to more uniform porous media such as encountered in soil science [16,17]. The underlying physical phenomena for LCM processes include capillary or surface phenomena, transport of fluid, heat, and mass, the mechanics of preform deformation before and during infiltration, matrix chemical cross-linking, and potential matrix/reinforcement chemical reaction during and after the process.…”

“…The underlying physical phenomena for LCM processes include capillary or surface phenomena, transport of fluid, heat, and mass, the mechanics of preform deformation before and during infiltration, matrix chemical cross-linking, and potential matrix/reinforcement chemical reaction during and after the process. For a complete description, the reader is referred to recent reviews [17,19]. In the following, for the sake of simplicity, we consider the general case of infiltration by a liquid of a rigid porous preform (constant volume fraction) in which all initial porosity is interconnected (no closed pores).…”