Assessing the influence of flax fibers humidity on the properties and processing of composites with infusion at controlled capillary number
Topic(s) : Manufacturing
Co-authors :
Antoine LEVEE (FRANCE), Jean-Baptiste JOUENNE (FRANCE), Valentin ROUGIER , Joel BREARD (FRANCE)Abstract :
The manufacturing of plant fiber-reinforced composites has been a challenge since the beginning of the 21st century. It has been established that the plant fibers specificities, all the more so flax fibers, differ from those of synthetic ones. One of the major differences between these two types of materials lies in the hydrophilic nature of plant fibers. Many studies have shown that controlling the amount of water contained by the fibers during processing leads to a better understanding microstructural material state (Bachchan et al., 2022). Moreover, manufacturing process used for plant fiber-reinforced composites are mostly carried out through the direct transposition of methods and technologies used for the production of synthetic ones. Therefore, it does not ensure preservation of the structural integrity of the flax fibers, nor does it optimize the properties of the composite material produced.
Liquid composite molding processes (LCM) such as liquid resin infusion are commonly used in many industrial fields to fabricate composites (Bickerton et al., 2013). In liquid resin infusion, the pressure difference between the polymer bucket and the mold outlet drives the polymer flow (Hindersmann, 2019). As the polymer infiltrates the fibrous preform, the pressure gradient decreases. Consequently, the velocity ν of the polymer flow front also decreases with time. Using the capillary number in injection process, authors have demonstrated the necessity to monitor polymer flow front velocity in order to minimize the void content in the final composite part (Chung Hae Park & Woo, 2011; Rougier, 2021).
In addition to these physical parameters, the water contained by plant fibers can have a significant impact during processing. Authors have highlighted that “water sorption in fibers and their composites has been found to significantly affect their dimensional and structural properties” (Celino, 2013). Therefore, when compressing preforms, hygro-thermal conditions must also be controlled and monitored, in order to take hygro-mechanical specificities of plant fibers into account. Other authors (Boutin et al., 2021) (Jouenne, 2023) showed that water contained in plant fibers also influences the resin crosslinking.
A dedicated setup has been developed in the laboratory allowing to control the flow front velocity v by controlling the inlet pressure. In this work, it is first proposed to measure the influence of plant fiber water content on the resin viscosity and surface tension. In a second stage, flax preforms with controlled water content will be impregnated in order to assess how void content is influenced by v at different levels of fiber humidity. The resulting composites will be tested to evaluate the influence of humidity on their mechanical properties. A second outlook for this work is to show that our new setup enables the manufacturing of optimized plant fiber-reinforced composites by piloting resin flow at the appropriate capillary number.
Liquid composite molding processes (LCM) such as liquid resin infusion are commonly used in many industrial fields to fabricate composites (Bickerton et al., 2013). In liquid resin infusion, the pressure difference between the polymer bucket and the mold outlet drives the polymer flow (Hindersmann, 2019). As the polymer infiltrates the fibrous preform, the pressure gradient decreases. Consequently, the velocity ν of the polymer flow front also decreases with time. Using the capillary number in injection process, authors have demonstrated the necessity to monitor polymer flow front velocity in order to minimize the void content in the final composite part (Chung Hae Park & Woo, 2011; Rougier, 2021).
In addition to these physical parameters, the water contained by plant fibers can have a significant impact during processing. Authors have highlighted that “water sorption in fibers and their composites has been found to significantly affect their dimensional and structural properties” (Celino, 2013). Therefore, when compressing preforms, hygro-thermal conditions must also be controlled and monitored, in order to take hygro-mechanical specificities of plant fibers into account. Other authors (Boutin et al., 2021) (Jouenne, 2023) showed that water contained in plant fibers also influences the resin crosslinking.
A dedicated setup has been developed in the laboratory allowing to control the flow front velocity v by controlling the inlet pressure. In this work, it is first proposed to measure the influence of plant fiber water content on the resin viscosity and surface tension. In a second stage, flax preforms with controlled water content will be impregnated in order to assess how void content is influenced by v at different levels of fiber humidity. The resulting composites will be tested to evaluate the influence of humidity on their mechanical properties. A second outlook for this work is to show that our new setup enables the manufacturing of optimized plant fiber-reinforced composites by piloting resin flow at the appropriate capillary number.