Design of Polyurethane Fibers: Relation between the Spinning Technique and the Resulting Fiber Topology

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Study of the thermal and mechanical properties of biocomposites via numerical homogenization

Ce travail de thèse porte essentiellement sur la détermination des propriétés mécanique et thermique des biocomposites HDPE-particules de bois et PET-fibres de chanvre, en utilisant des approches expérimentales, numériques et analytiques. La recherche des propriétés effectives de ces biocomposites prend en compte différents paramètres tels que la morphologie et l’orientation des fibres, d'une part, la porosité, et l’interphase, d'autre part. En effet, une étude basée sur la technique d'homogénéisation numérique a été réalisée en vue de vérifier l'influence des fibres courtes et logues sur les propriétés apparentes des différents matériaux étudiés. Aussi, des calculs numériques ont permis d'évaluer les propriétés élastiques ainsi que la conductivité thermique des biocomposites en fonction de la fraction volumique des fibres et des particules. L'objectif ultime de ce travail consiste à une modélisation de la mise en forme des biocomposites par thermoformage. En effet, une étude a été axée sur la thermoformabilité d’un coffrage en biocomposite HDPE-particules de bois, en utilisant des données expérimentales pour mieux décrire le comportement mécanique et thermique en vue d'une modélisation numérique des différentes étapes du thermoformage, en fonction de la teneur en particules de bois.This thesis work concerns the determination of mechanical and thermal properties of HDPE-wood particles and PET-hemp fibers biocomposites using experimental, numerical and analytical approaches. The search for the effective properties of these biocomposites involves different parameters such as the fiber morphology and orientation on the one hand, and the porosity and the interphase on the other. A study based on the numerical homogenization technique has been carried out in order to verify the influence of short and long fibers on the apparent properties of the different materials. Numerical calculations have also allowed the estimation of the elastic properties as well as the thermal conductivity of the biocomposites in relation to the fiber and particle volume fraction. The ultimate objective of this work consists in the modelling of the thermoforming procedure on the biocomposites. A study on the thermoformability of the HDPE-wood particles biocomposite into a formwork in relation to the wood particle content has been carried out by using experimental data of the mechanical and thermal behavior for the numerical simulation of the thermoforming procedure

Effective thermal and mechanical properties of randomly oriented short and long fiber composites

International audienceThe microstructure studied in this paper is a Composite made up of Randomly oriented Short Fibers (RSFC) and a computational homogenization is performed to investigate its effective properties. The area fraction is also varied to study its effect on the size of the Deterministic Representative Volume Element (DRVE). It appeared that at certain area fractions, the RSFC does not respect the convergence of the apparent properties calculated under different boundary conditions. This indicates that it does not adhere to the definition of the DRVE in the studied range of scale. The concerned area fraction is found to be around the percolation threshold. The present work consists primarily in investigating the causes of this problem by studying an extreme example of a percolating medium which is a Composite made up of Randomly oriented Long Fibers (RLFC). By identifying the contributing factors, the calculability of the DRVE of a random composite can be predicted by simple verification of the microstructure morphology

Design of Polyurethane Fibers: Relation between the Spinning Technique and the Resulting Fiber Topology

International audienc

Design of polyurethane fibers: Relation between the spinning technique and the resulting fiber topology

Properties or characteristics of fibers are affected by their topology. In fact, these topologies are found to have significant impacts in the functionalities of many applications. Hence, in this study, the relations between the spinning techniques and the topology of the resulting fibers are studied with the aim to provide a guideline for future reference where fibers with certain topology can be fabricated to suit specific applications. For this purpose, polyurethane is chosen to be the raw material to fabricate the fibers due to its versatility to be applied in various fields. The surface morphology, structures, and alignments of the fibers are studied. It is found that the polymer solution properties largely influence the mechanisms in the spinning process and can significantly affect the topology of the fibers. For instance, viscous solutions enable the spinning of coiled and smooth fibers, whereas conductive solutions encourage the splaying of the solution jet which results in the spinning of straight fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47706. © 2019 Wiley Periodicals, Inc