Biodiesel and hydrotreated vegetable oil (HVO) are currently viewed by the transportation sector as the most viable alternative fuels to replace petroleum-based fuels. The use of biodiesel has, however, been limited by the deteriorative effect of biodiesel on rubber parts in automobile fuel systems. This work therefore aimed at investigating the degradation of acrylonitrile butadiene rubber (NBR) and fluoroelastomers (FKM) on exposure to biodiesel and HVO at different temperatures and oxygen concentrations in an automated ageing equipment and a high-pressure autoclave. The oxidation of biodiesel at 80 °C was promoted by an increase in the oxygen partial pressure, resulting in the formation of larger amounts of hydroperoxides and acids in the fuel. The fatty acid methyl esters of the biodiesel oxidized less at 150 °C on autoclave aging, because the termination reactions between alkyl and alkylperoxyl radicals dominated over the initiation reactions. HVO consists of saturated hydrocarbons, and remained intact during the exposure. The NBR absorbed a large amount of biodiesel due to fuel-driven internal cavitation in the rubber, and the uptake increased with increasing oxygen partial pressure due to the increase in concentration of oxidation products of the biodiesel. The absence of a tan δ peak (dynamical mechanical measurements) of the bound rubber and the appearance of carbon black particles devoid of rubber suggested that the cavitation was caused by the detachment of bound rubber from particle surfaces. A significant decrease in the strain-at-break and in the Payne-effect amplitude of NBR exposed to biodiesel was explained as being due to the damage caused by biodiesel to the rubber-carbon-black network. During the high-temperature autoclave ageing, the NBR swelled less in biodiesel, and showed a small decrease in the strain-at-break due to the cleavage of rubber chains. The degradation of NBR in the absence of carbon black was due only to biodiesel-promoted oxidative crosslinking. The zinc cations released by the dissolution of zinc oxide particles in biodiesel promoted reduction reactions in the acrylonitrile part of the NBR. Heat-treated star-shaped ZnO particles dissolved more slowly in biodiesel than the commercial ZnO nanoparticles due to the elimination of inter-particle porosity by heat treatment. The fuel sorption was hindered in HVO-exposed NBR by the steric constraints of the bulky HVO molecules. The extensibility of NBR decreased only slightly after exposure to HVO, due to the migration of plasticizer from the rubber. The bisphenol-cured FKM co- and terpolymer swelled more than the peroxide-cured GFLT-type FKM in biodiesel due to the chain cleavage caused by the attack of biodiesel on the double bonds formed during the bisphenol curing. The FKM rubbers absorbed biodiesel faster, and to a greater extent, with increasing oxygen concentration. It is suggested that the extensive biodiesel uptake and the decrease in the strain-at-break and Young’s modulus of the FKM terpolymer was due to dehydrofluorination of the rubber by the coordination complexes of biodiesel and magnesium oxide and calcium hydroxide particles. An increase in the CH2-concentration of the extracted FKM rubbers suggested that biodiesel was grafted onto the FKM at the unsaturated sites resulting from dehydrofluorination. / <p>QC 20170227</p>

L’objectif de ce travail est une approche pluridisciplinaire dans le but de comprendre l’impact des phénomènes microscopiques, l’interaction charge-matrice avec ou sans agent de couplage et la dispersion des charges sur les propriétés macroscopiques. La caractérisation de l’impact de la stratégie de mélange avec ou sans un agent de couplage, la cinétique, l’état final et les différents scénarii de dispersion possibles sont ainsi étudiés. L’incorporation de microperles de silice dans une matrice SBR est réalisée dans un mélangeur interne. Finalement, la silice est dispersée à l’échelle nanométrique (10-100 nm). Les nanocomposites obtenus sont alors caractérisés par des techniques complémentaires (spectroscopie mécanique, MET, mesure du taux d’élastomère lié à la charge) dans le but de caractériser quantitativement les interactions charge-matrice et charge-charge. L’outil rhéologique est un outil très sensible pour caractériser l’évolution de la dispersion de charges dans une matrice élastomère. En particulier, le module de conservation G’ montre un plateau significatif pour les faibles fréquences de déformation. Ce plateau est très sensible à l’état de dispersion ainsi qu’à la nature des interactions entre les charges. En couplant les mesures rhéologiques, l'analyse d'image faite sur des photos MET et la mesure du taux d’élastomère lié, il est possible d’établir un scénario de dispersion de la silice dans l'élastomère en fonction des conditions de mélange et de mettre en évidence les paramètres élémentaires de la dispersion impliqués. En complément, la modélisation de certains modules montre toute sa pertinence dans la caractérisation de la rupture des agglomérats ou de l’évolution des interactions charge-charge au cours du mélangeage. Enfin, la dimension fractale des réseaux de charges obtenus est déterminée à partir de nos descripteurs de la dispersion / Filler dispersion in an elastomeric matrix, states and mechanisms of dispersion had to be investigated throughout the mixing process. This work focuses on a multidisciplinary approach to understand how microscopic phenomena, like rubber-filler interaction or filler dispersions, affect macroscopic properties such as rheological behavior. The incorporation of silica is realized in an internal mixer under temperature control. Finally, silica is dispersed at the nanoscale (10-100 nm). Afterwards, nanocomposites are characterized using complementary techniques in order to discuss quantitatively the nature of rubber-filler and filler-filler interactions and their effect on rheological properties. Thus, the global evolution of dispersion during the mixing is understood through these various tests. Different mechanisms in the dispersion have been observed. First, intense particle size reduction occurs at the earliest mixing times. Then, the aggregate size does not change while the amount of physically bound rubber at the surface of aggregate increases and levels off. For some silica, a second dispersion stage has been observed after the diffusion of the elastomer to the core of the aggregates. Rheology has showed to be a very sensitive tool to characterize the evolution of the dispersion in the system. Particularly, the complex shear modulus exhibits a significant plateau (Ge), at low frequency, which is very sensitive to the dispersion state and the nature of the interaction between the fillers. There is a striking correlation between the value of plateau Ge and the bound rubber content. Finally, a dispersion scenario has been established and fundamental interaction parameters have been identified