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Ce travail consiste à contribuer à la valorisation de la lignine, un sous-produit important de l’industrie du papier. L’objectif est d’utiliser la lignine comme retardateur de flamme (FR) pour les matériaux polymères. Dans un premier temps, la lignine fut phosphorylée. Des analyses structurales ont permis d’établir que du phosphore est lié de manière covalente à la lignine. La conséquence est que la stabilité thermique ainsi que la quantité de résidu charbonné sont fortement améliorées. Les lignines de départ et phosphorylée ont été incorporées dans des polymères thermoplastiques afin d’évaluer l’influence du phosphore ainsi que les performances au feu. Des propriétés prometteuses ont particulièrement été obtenues dans l’acide polylactique (PLA) et l’acrylonitrile-butadiène-styrène (ABS). Des formulations combinant les lignines avec d’autres additifs furent développées, et leurs performances au feu discutées. Ainsi, un large screening considérant la lignine comme FR fut réalisé. Le système comprenant la lignine, de départ ou phosphorylée, dans l’ABS fut finalement étudié en détail afin d’en élucider leur mécanisme d’action. Un effort particulier fut porté sur la réaction au feu ainsi que la dégradation thermique de ce composite. Durant sa dégradation thermique, la lignine produit une couche carbonée qui limite les échanges de masse entre le polymère et la flamme, permettant d’améliorer la réaction au feu de l’ABS. Cette barrière est d’autant plus efficace en utilisant la lignine phosphorylée. Il a été observé que le phosphore est actif dans la phase condensée, provoquant une formation plus rapide de la barrière, qui est également plus stable thermiquement. / The aim of this PhD is to contribute to the valorization of lignin, an abundant byproduct of pulping industry by using it as flame retardant (FR) additive for polymeric materials. First, phosphorylation of lignin was undertaken. According to structural characterization, phosphorus was found to be covalently bonded to lignin. As a consequence, the thermal stability of lignin was enhanced as well as the char yield. Based on these results, both neat and phosphorylated lignin were incorporated in several polymers in order to assess their FR performance and the influence of phosphorus. Promising results were especially obtained in polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS). Then FR performance of formulations combining lignins and other additives was discussed. A large screening using lignin as FR additive in PLA and ABS was therefore achieved. The system considering phosphorylated lignin in ABS was finally investigated in detail. FR performance as well as thermal degradation were deeply studied. Lignin produces a char when exposed to a flame or a heat source which acts as a physical layer by mainly limiting mass transfers between the burning polymer and the flame. The char produced by phosphorylated lignin demonstrated a higher efficiency, thus leading to enhanced FR properties. Phosphorus was indeed active in the condensed phase, promoting the char formation and leading to structures which stabilize the char. The mode of action of lignin and phosphorylated lignin as flame retardant additive in ABS was elucidated.

<p>This thesis reports on an experimental and theoretical study of the bulk polymerization of acrylonitrile to limiting conversions using 2,2' azobisisobutyronitrile initiator in the temperature range, 0°C to 120°C. Molecular weight averages and distributions were measured by gel permeation chromatography for polymers produced in the temperature range, 0°C -120°C. A two-phase model which holds for the bulk polymerization of vinyl chloride was used in a preliminary attempt to explain the kinetic behaviour of the system. It appears that this model does not adequately describe the bulk polymerization of acrylonitrile.</p> / Thesis / Master of Engineering (ME)

This thesis is concerned with the development of a continuous melt extrusion process utilizing CO₂ for the production of materials that cannot be typically melt processed. The first goal of this study is to determine under what conditions it is possible to use CO₂ to plasticize and, thereby, reduce the viscosity of an acrylonitrile (AN) copolymer in an extrusion process and render it melt processable. In order to assess whether it was possible to absorb adequate amounts of CO₂ in short residence times by injection into a single screw extruder, a slit-die rheometer was attached to the end of the extrusion system for the purpose of directly assessing the viscosity reduction. A chemorheological analysis was performed on 65 and 85% AN copolymers to establish the temperature at which the 85% material would be stable for melt processing. This, coupled with studies correlating the degree of Tg and viscosity reduction with the amount of absorbed CO₂, allowed one to establish conditions for melt extrusion of the 85% AN. It was determined that the 85% AN material should absorb at least 5 weight percent CO₂ for a processing temperature reduction of 26°C in the extrusion process. The second goal of this study is to determine to what extent CO₂ can be used as a processing aid to melt process polyethylenes of higher molecular weight than can be typically melt processed. To assess the ability to melt process high molecular weight polyethylenes with CO₂, the viscosity of a 460,000 g/mol HDPE plasticized with various amounts of absorbed CO₂ as determined with the slit-die rheometer. A relationship was developed to determine the maximum molecular weight polyethylene that could be processed at a given viscosity reduction due to absorbed CO₂. The viscosity of a blend of 40 weight percent UHMWPE with the 460,000 g/mol HDPE with 12 weight percent CO₂ was reduced to that of the pure 460,000 g/mol HDPE as predicted by the relationship. Preliminary studies using a pressurized chamber attached to the exit of the die allowed one to assess the conditions under which suppression of foaming is possible. / Ph. D.

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Thesis (M.S.)--Brigham Young University. Dept. of Chemical Engineering, 2003. / Includes bibliographical references (p. 69-74).