Extraction de fibres de lin oléagineux pour des applications textiles techniques : influence des paramètres de pré-traitement sur le rendement en fibres, la répartition granulométrique et les propriétés mécaniques.

Cultivé principalement pour ses graines, le lin oléagineux pourrait également être valorisé pour les différentes fractions végétales qui peuvent être extraites de la paille. Cependant comme les pailles ne sont pas récoltées avec la même technique et le même soin que pour le lin textile, la technique classique de teillage ne peut pas être utilisée. Par conséquent, un dispositif "toutes fibres" a été utilisé pour effectuer la séparation des différents constituants des pailles de lin oléagineux. Les différentes fractions ont été quantifiées pour deux niveaux de rouissage et pour deux degrés de ré-humidification des tiges. Les propriétés physiques et mécaniques des fibres ont ensuite été évaluées. Il apparaît que la quantité relative de fibres extraites des pailles de lin oléagineux est comparable à celle du lin textile (c'est-à-dire 40 % de la masse de la tige sèche) et que leurs propriétés en traction se situent dans la partie inférieure de la gamme du lin textile. Ce travail montre que la longueur individuelle des fibres de lin oléagineux (entre 3 et 6 cm) est comparable à celle des fibres de lin textile teillé. Elles sont donc adaptées à la production de fils de fibres alignées cardés pour les textiles techniques de renforcement (par exemple, composites ou géotextiles). Ces résultats démontrent l'intérêt et la valeur ajoutée potentielle de la récolte des tiges pour des applications techniques des fibres

Investigation of the potential of hemp fibre straws harvested using a combine machine for the production of technical load-bearing textiles

In western Europe, hemp is mainly cultivated for the seeds and the fibre rich straws, randomly aligned following the harvesting with a combine harvester. The straws are mainly valorised for low added value products such as pulp for paper and for insulation. They are also valorised in low property short fibre composites. With the view to use hemp fibres extracted from randomly aligned straws for higher added values, this work proposes to study a different process (fibre opener) for extracting the fibres than the one which is classically used in the industry (hammer mill) and to investigate the extraction performances and the impact of the process on the hemp morphological and mechanical properties. The morphological and mechanical properties measured at different moments of the extraction indicate that, even in the less favourable case, the length of the fibres (∼ 5 cm) is high enough for textile processing via the carded route. The tensile strength (∼ 660 MPa) and modulus of elasticity of (38 GPa) of the individual hemp fibres are situated above most of the ones of fibres extracted mechanically using a hammer mill (630 MPa and 25 GPa for strength and modulus respectively) despite the fact that large quantities of kink band defects are observed on each fibre. This therefore shows that the “all fibre” opener is suitable for the production of fibres that can be considered for the manufacturing of technical textiles such as load-bearing woven geotextiles or midrange load-bearing composite reinforcements

Impact of extraction processes on fiber properties of linseed flax fibers

This work of a preliminary nature has for goal to investigate the potential of the linseed flax straw for industrial valorization in technical textiles. The impact of two extraction systems (“all fiber” extraction device and a scutching/hackling device) was investigated. In a first part of the paper, it was demonstrated that it is possible to extract the fibers from the other components of the straw such as the shives and vegetal dusts. The fiber yield is of about 38% of the stem mass. This very high fiber yield is particularly interesting and is higher than the one of hemp for example. The fiber properties were also investigated. The fiber length was shown to be in the adequate range of length to be considered for the carded spinning route, and the tensile properties of the individual fibers, even if decreased by about 45% in comparison to carefully manually extracted, are still at a sufficient level of performance for semistructural composites applications for example. When using a scutching/hackling line, the length of the fibers is preserved and the impact of the fiber extraction was shown to be lower than the all fiber extraction line, particularly for the strength. These fibers could therefore be used for higher load bearing applications. Finally, the amount of fiber that can be extracted from the linseed flax fibers is large and this could certainly be at the origin of an industrial technical textile value chain

Fabrication de panneaux agglomérés de fibres à partir des anas collectés lors de l'extraction mécanique des fibres libériennes de la paille de lin oléagineux

Dans cette étude, des panneaux agglomérés de fibres ont été produits à partir d’anas collectés après extraction mécanique des fibres libériennes de paille de lin oléagineux. Les panneaux ont été mis en oeuvre par thermopressage. Leurs propriétés mécaniques et thermo-mécaniques ont été étudiées ainsi que leur comportement vis-à-vis de l’eau. L’influence d’un prétraitement thermo-mécanique des anas bruts à l’aide d’une extrudeuse bi-vis a été étudiée ainsi que l’ajout de lignine exogène. Tous les panneaux mis en oeuvre possèdent une tenue suffisante pour être manipulés à la main. Le panneau ayant obtenu les propriétés optimales a été obtenu à partir des anas extrudés et sans ajout supplémentaire de lignine. Au regard de ses caractéristiques et du standard NF EN 312, ce dernier remplit complètement les critères d’un panneau aggloméré de type P1 (panneau d’usage général utilisé en milieu sec)

Production of fiberboards from shives collected after continuous fiber mechanical extraction from oleaginous flax

In this study, fiberboards were produced from shives collected after continuous fiber mechanical extraction from oleaginous flax straw. Fiberboards were produced through thermo-pressing, and their mechanical and thermomechanical properties were studied, as well as their water resistance. The influence of two pretreatments for shives and lignin addition was investigated on the different properties. Boards obtained were all cohesive hardboards. The optimal board was obtained from fibers extruded from the shives and without addition of any supplementary lignin amount. Looking at its characteristics and standard NF EN 312, the latter perfectly complied with the requirements for type P1 boards, i.e., boards for general uses in dry conditions

Understanding and remediation of odor phenomena from natural fiber composites for the automotive sector

Dans le secteur automobile, l’utilisation de matériaux composites biosourcés à base de non-tissé fibres lignocellulosiques / polypropylène est bien connue pour la fabrication de pièces d’intérieur. Bien que ces matériaux aient des avantages avérés (légèreté, faible empreinte carbone, bonnes propriétés mécaniques, …), ces derniers libèrent des COVs/Odeurs pouvant impacter la qualité de l’air de l’habitacle des véhicules et freiner leur large déploiement. Dans le cadre de cette thèse, une approche mêlant analyses chimique et sensorielle a permis d’avoir une meilleure compréhension sur l’origine des COVs/Odeurs émis tout au long du processus de transformation industrielle : c’est-à-dire de la fibre au composite. Tout d’abord, pour un composite Lin/PP, l’évolution des COVs/Odeurs a été étudiée aux différentes étapes du processus de fabrication. A l’issus de cette étude, les sources principales d’odeur ont été clairement identifiées avec la mise en évidence d’un fort impact des aldéhydes provenant des fibres de lin. Ensuite, a été étudié l’effet de la température et du temps de thermocompression sur les émissions de COVs/Odeurs et les propriétés mécaniques avec un suivi in situ et en temps réel de la température au sein du non-tissé. Cela a permis de mettre en évidence une température seuil de 210 °C à ne pas dépasser. Enfin l’influence de la nature des fibres lignocellulosiques sur les COVs/Odeurs émis par les composites biosourcés a été étudié avec le lin, le chanvre et le kenaf. Une fois que l’origine des odeurs des matériaux composites a bien été établie, un moyen de remédiation compatible avec l’outil industriel a été mis en œuvre et son efficacité a été mesurée. L’influence des adsorbants sur des non-tissés Lin et des composite Lin/PP a été étudiée. Pour conclure, cette approche a pour originalité de suivre l’évolution des COVs/Odeurs tout au long de l’histoire de composites biosourcés et de proposer différentes stratégies pour réduire les odeurs des matériaux (maîtrise de la température de thermocompression, choix du type de fibres, utilisation d’adsorbants).In the automotive sector, the use of biosourced composite materials based on lignocellulosic fibers/polypropylene nonwoven is well known for the manufacture of interior parts. Although these materials have proven advantages (lightness, low carbon footprint, good mechanical properties, ...), they release VOCs/Odors that can impact the vehicle interior air quality and slow down their wide deployment. In this thesis, an approach mixing sensory and analytical analyses made possible to have a better understanding of the origin of the VOCs/Odors emitted throughout the industrial transformation process: i.e. from the fiber to the composite. First of all, for a Flax/PP composite, the evolution of VOCs/Odors at the different stages of the manufacturing process was studied. As a result of this study, the main sources of odor have been clearly identified with a major impact of aldehydes from Flax fibers. Then, the effect of temperature and thermocompression time on VOCs/Odor emissions and mechanical properties was studied with a real time and in situ monitoring of the temperature within the nonwoven. This allowed to highlight a threshold temperature not to be exceeded of 210 °C. Finally, the influence of the nature of the lignocellulosic fibers on the VOCs/Odors emitted by the biosourced composites was studied with flax, hemp and kenaf fibers. Once the origin of the odors of the composite materials was well established, a remediation method compatible with the industrial tool was implemented and its effectiveness was measured. The influence of adsorbents on Linen nonwovens and Flax/PP composites was studied. To conclude, the originality of this approach is to follow the evolution of VOCs/Odors throughout the story of the biosourced composites and to propose various strategies to reduce the odor of materials (control of the thermocompression temperature, choice of the type of fibers, use of adsorbents)

Fibre extraction from oleaginous flax for technical textile applications: Influence of pre-processing parameters on fibre extraction yield, size distribution and mechanical properties

Cultivated primarily for its seeds, oleaginous flax could also be valued for the different fractions that can be extracted from the straw. However, as the straws are not harvested with the same technique and care than for the textile flax, the classical scutching technique cannot be used. As a consequence, an “all fibre” device was used to perform the separation of the different constituents of the oleaginous flax straws. The different fractions were quantified for two retting levels and for two degrees of rewetting of the stems. The physical and mechanical properties of fibres were then evaluated. It appears that the relative amount of fibres extracted from oleaginous flax straw is comparable to the one from textile flax (i.e. 40% of the stem dry mass), and their tensile properties are situated in the lower part of the textile flax range. This work shows that the individual fibre length of oleaginous flax (between 3 and 6 cm) is comparable to that of the scutched textile flax fibres. This makes them suitable for the production of carded aligned fibre yarns for technical reinforcement textiles (e.g. composites or geotextiles). These results demonstrate the interest and the potential added value of harvesting the stems for technical fibre applications

Influence of the Compression Molding Temperature on VOCs and Odors Produced from Natural Fiber Composite Materials

In the automotive sector, the use of nonwoven preforms consisting of natural and thermoplastic fibers processed by compression molding is well known to manufacture vehicle interior parts. Although these natural fiber composites (NFCs) have undeniable advantages (lightweight, good life cycle assessment, recyclability, etc.), the latter release volatile organic compounds (VOCs) and odors inside the vehicle interior, which remain obstacles to their wide deployment. In this study, the effect of the compressing molding temperature on the VOCs and odors released by the flax/PP nonwoven composites was examined by heating nonwoven preforms in a temperature range up to 240 °C. During the hot-pressing process, real-time and in situ monitoring of the composite materials’ core temperature has been carried out using a thermocouples sensor. A chemical approach based on headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography—mass spectrometry (GC-MS) was used for the VOCs analysis. The olfactory approach is based on the odor intensity scale rated by expert panelists trained in olfaction. The results demonstrate marked changes in the VOCs composition with temperature, thus making it possible to understand the changes in the NFCs odor intensity. The results allow for optimizing the molding temperature to obtain less odorous NFC materials