Fluorination of carbon fibre sizing without mechanical or chemical loss of the fibre

International audienc

A review about the fluorination and oxyfluorination of carbon fibres

International audienceDepending both on structure and properties of the starting carbonaceous material, and on the fluorination conditions, fluorine can bond to carbon fibres in various ways. This review aims to investigate the versatility of the C-F bonding and its influence on the fibre properties. Morphology and surface properties, such as diameter, Scanning Electron Microscopy observations, specific surface area, wettability and surface acidity are discussed according to the fluorine content and the fluorination route. Structural and bulk properties of fluorinated carbon fibres, regarding Raman spectroscopy, X-ray diffraction analysis, electrical and mechanical properties, and bonding with polymers are also studied. 114 papers are reviewed in order to both extract general trends on those characteristics and highlight applications as fillers in composites and sensitive materials in gas sensing

From the Understanding of Fluorination Process to Hydrophobic Natural Fibers

International audienc

Surface modification of sized vegetal fibers through direct fluorination for eco-composites

International audienceNatural fibers are frequently used as alternatives of glass fibers as polymer matrix reinforcement to form composite materials. However, their natural hydrophilicity prevents them from being easily compatible with hydrophobic polymers, which represent the majority of matrices. To solve this, direct fluorination of sized natural fibers (flax fibers sized with DGEBA) was performed. EDX, FTIR and 19F NMR analysis evidenced the chemical grafting of fluorine on DGEBA structure and the ablation of the oxiranes rings on this molecule. Chemical modifications of DGEBA have induced a hydrophobic character of this layer, by reducing at 0 the polar component of surface tension. Thereby, treated fibers are supposed to be perfectly chemically compatible with the hydrophobic polymer matrices (e.g. polypropylene). Additionally, the fluorination time also allows the dispersive component of surface tension and the rugosity of fibers to be tailored in order to perfectly adjust these characteristics and fit with the polymer. Moreover, this chemical modification was achieved without altering the mechanical properties of fibers for short fluorination times

Vers des éco-composites à base de fibres de lin plus performants et respectueux de l’environnement grâce à la fluoration directe sous F2

National audienc

Towards more efficient and environmental friendly flax-based eco-composite through direct F2 fluorination as a compatibilization treatment

International audienceIn light of current environmental issues and the emerging context of bio-economy aimed atcontinuing economic growth while preserving the environment and earth resources, vegetal fibers areincreasingly used to substitute glass fibers for polymer strengthening to make eco-composites. Indeed,the use of natural fibers allows bio-based and local resources to be valorized while lightening the overallweight and reducing the cost of composites.Flax fibers are usually considered as adequate bio-reinforcements for composites. However, theirhydrophilic character makes them sensitive to moisture sorption and difficult to wet by hydrophobicresins. This incompatibility can induce a defective interface and micro-porosity between fibers andmatrix that would greatly weaken the eco-composite’s mechanical performance[1][2][3]. Several wayshave been explored to improve wettability of bio-based reinforcements towards resins. However, thesetechniques can damage the initial material and/or are generally harmful to the environment through theuse of toxic products and solvents, which is against the idea of making environmental friendly eco-composites.It is in this context that fluorination treatment takes place. Indeed, a fast and controlled reactiontreatment under molecular fluorine (F2 ) of wood[4] or vegetal fibers allows fluorine atoms to becovalently grafted on the outmost surface of lignocellulosic material in substitution of hydroxyl groupsresponsible for hydrophilicity. This grafting, achieved on flax fibers, allowed the fibers’ polarity to besignificantly decreased without modification of their bulk’s mechanical performance. This reduce thegap between the surface energies of the fibers and different polymer matrix (bio-based epoxy andElium®). In other words, the wetting of the fiber by the polymer is improved during the infusion process.Thereby, porosity into the composite thus formed is significantly reduced, increasing its mechanicalperformance, its health, and its life span during a humid environment aging, without any chemicalcoupling agent harmful to the environment [3][5].[1] F. M. AL-Oqla, M. S. Salit, Materials Selection for Natural Fiber Composites, 2017, 23-48[2] P.-J. Liotier, M.F. Pucci, A. Le Duigou, A. Kervoelen, J. Tirilló, F. Sarasini, S. Drapier, Compos. B.Eng. 163, 2019, 86–95.[3] M.F. Pucci, P.-J. Liotier, D. Seveno, C. Fuentes, A. Van Vuure, S. Drapier, Compos. A: Appl. Sci.Manuf. 97, 2017, 31–40.[4] M. Pouzet, M. Dubois, K. Charlet, A. Béakou, J.-M. Leban, M. Bada, 133, 2019, 133–141.[5] F. Saulnier, M. Dubois, K. Charlet, L. Frezet, A. Beakou, Carbohydr. Polym. 94, 2013, 642–646

Elaboration of hydrophobic flax fibers through fluorine plasma treatment

International audienceIn this study, the goal was to compatibilize flax natural fibers (which are inherently polar) with mostly dispersive polymers, while proposing a way to recover greenhouse gases or refrigerants such as CF4 or C2F5H. Such gases exhibit a high global warming potentials (GWPs) and their recovery at the end of their lifecycle is difficult. Therefore, these two representative problematic gases were used as plasma precursor to graft fluorine atoms onto the flax fiber surface. Chemical investigation (FT-IR, 19F NMR and XPS spectroscopies), demonstrates the covalent grafting of fluorine atoms at the fiber surface, that opens the route of tailoring the surface chemistry of flax fibers. These modifications induced a decrease of the fiber polarity, which allows the treated fibers to become perfectly compatible with mostly dispersive polymer. Moreover, both mechanical properties and fluorine release during fibers combustion were investigated and any negative impact was evidenced. Therefore, thanks to the plasma fluorination, the gap between the surface energies of the fibers and mostly dispersive polymer matrix was reduced improving the wettability of the fibers through an eco-friendly way. This phenomenon promising an improvement in the mechanical performance of eco-composites reinforced with these fluorinated fibers