Smoke production in a smoke chamber is characterized by the accumulation of smoke and the continuous consumption of oxygen leading to a vitiated atmosphere. However, a method is proposed to predict the smoke evolution in a smoke chamber at 25 kW/m² by using material properties calculated from a cone calorimeter, as already shown in a previous article. These properties represent the ability of a material to produce smoke at a specific mass loss rate. The influence of a flame retardant on these properties can be used as a quantitative measurement of its action on smoke production. These properties can be calculated at another heat flux than 25 kW/m². The knowledge of the curve “mass loss rate = f(time)” in a smoke chamber is still required, but this curve is close to that measured in a cone calorimeter at the same heat flux. The results prove that the smoke production in a smoke chamber and cone calorimeter is qualitatively similar, i.e., the decrease of oxygen content in a smoke chamber has no influence on smoke (at least as long as optical density does not exceed 800).

The accelerated weathering of flax and miscanthus fibers possessing distinct chemical compositions was investigated. The chosen fibers included raw, extractive-free (EF) and delignified samples (x3), alone and used as fillers in a stabilized polypropylene blue matrix (PP). Modifications in both color and the chemical composition of the fibers throughout the weathering process under ultraviolet (UV) light were meticulously tracked and analyzed by spectrophotometry and attenuated total reflectance with Fourier-transform infrared spectroscopy (ATR-FTIR). The inherent nature and composition of the selected fibers led to varied color-change tendencies. Raw and EF flax fibers exhibited lightening effects, while raw and EF miscanthus fibers demonstrated darkening effects. Extractives exhibited negligible influence on the color alteration of both flax and miscanthus fibers. This disparity between the fibers correlates with their respective lignin content and type, and the significant formation of carbonyl (C=O) groups in miscanthus. Better stability was noted for delignified flax fibers. A comparative study was achieved by weathering the PP matrix containing these various fibers. Contrary to the weathering observations on individual fibers, it was noted that composites containing raw and EF flax fibers exhibited significant color degradation. The other fiber-containing formulations showed enhanced color stability when compared to the pure PP matrix. The study highlights that the UV stability of composites depends on their thermal history. As confirmed by thermogravimetric analysis (TGA), fiber degradation during extrusion may affect UV stability, a factor that is not apparent when fibers alone are subjected to UV aging.

Short flax fibers have been modified by radiation-induced grafting using methacrylate monomers containing phosphorus to give them a flame-retardant character. Two methodologies, namely pre-irradiation and simultaneous irradiation grafting, were examined. Certain parameters, notably the dose and the irradiation source (e-Beam and γ rays), were evaluated. The grafting efficiency, in terms of phosphorus content (mass percentage), was measured by X-ray fluorescence spectrometry (XRF). Using simultaneous irradiation, 2.39 wt% phosphorus could be obtained from 10 kGy, compared to 100 kGy in pre-irradiation. Furthermore, for similar phosphorus levels, the location of the grafted polymer chains was different for the two methodologies. The effect of phosphorus content on thermal properties and fire behavior was evaluated on a microscopic scale using a pyrolytic flow combustion calorimeter (PCFC) and on a laboratory scale using a cone calorimeter. It was then pointed out that flammability was linked to the phosphorus content and likely its location, which is associated with the radiation-induced grafting methodology, showing that the grafting conditions influence the final fire properties. Simultaneous irradiation, thus, proved to be more interesting in terms of efficiency and final properties.

En raison de l'intérêt croissant pour des matériaux durables et respectueux de l'environnement,l'utilisation des ressources lignocellulosiques connaît une augmentation significative. Toutefois,certains inconvénients inhérents à ces matériaux limitent leur application dans divers domaines.Plusieurs stratégies sont envisageables afin d’y remédier et optimiser leurs performances. Parmielles, le radiogreffage, dont les premiers développements datent du milieu des années 1950,présente des caractéristiques intéressantes. Cette technique consiste à exposer un matériau à desrayonnements ionisants afin d'y greffer des monomères fonctionnels, lui conférant ainsi denouvelles propriétés. Plusieurs méthodes de radiogreffage existent, notamment, il est possibled’irradier le matériau avant de la mise en contact avec les monomères (pré-irradiation), ou bien del’irradier en leur présence (irradiation simultanée). Malgré des règles générales qui conditionnent la faisabilité de ces méthodes, pour chaque cas, les conditions opératoires sont à adapter pour mettre en place le procédé le plus efficace possible. Cette thèse a pour objectif d’étudier les possibilités de fonctionnalisation par radiogreffage des fragments de tiges de Miscanthus × giganteus ainsi que du lin sous forme de fibres courtes et longues (tissus). L'étude approfondie des conditions opératoires et des caractéristiques des matériaux traités a permis de déterminer la méthodologie la plus appropriée pour atteindre les résultats désirés. Ainsi, des matériaux lignocellulosiques dotés de propriétés ignifuges ou hydrophobes ont été préparés avec succès. Enfin, ce travail a permis de proposer une nouvelle méthode originale de radiogreffage, qui repose sur une combinaison de plusieurs méthodologies existantes.