Hevea brasiliensis, un arbre tropical, est la source principale de caoutchouc naturel commercialement viable. La biosynthèse de caoutchouc se passe dans les cellules spécialisées appelées laticifères. Il représente jusqu’à 90% de la matière sèche du latex. Le latex, laiteux, s’écoule de l’encoche faite sur l’écorce de l’arbre jusqu’aux cellules laticifères. La collecte de latex, faite par saignée régulière tous 2-3 jours, est vraiment stressante pour l’arbre. Pour stimuler la production de latex, un générateur d’éthylène peut être appliqué sur le panneau de saignée. Le stress s’intensifie avec l’application hormonale. La production d’espèces activées de l’oxygène (ROS) se fait en réponse aux stress environnementaux ainsi que lors de l’exploitation de l’arbre. Au-delà d’un certain seuil, la production de ROS est massive dans les laticifères. De nombreuses études ont montré que les ROS entraîne une dégradation par peroxydation des lipides insaturés des membranes et ensuite une déstabilisation et lyse des organites. La lyse des lutoïdes permet la libération des facteurs de coagulation dans le latex entraînant la coagulation in situ des particules de caoutchouc dans l’écorce des arbres stressés. Ce syndrome physiologique, appelé syndrome de l’encoche sèche (TPD), est un des facteurs limitant la production de caoutchouc.Ce travail de thèse vise à identifier les gènes associés à la production et la neutralisation des ROS ainsi que leurs caractérisations dans les laticifères. Premièrement, nous avons fait une analyse bibliographique complète sur les gènes associés à la production et la neutralisation des ROS chez l’hévéa et les plantes modèles. La NADPH oxydase a été décrite comme la source principale de ROS chez les arbres stressés. Les enzymes antioxydantes et les antioxydants constituent le système de neutralisation des ROS. Deuxièmement, à partir d’une analyse à l’échelle du génome, 407 gènes impliqués dans la production des ROS et dans leur neutralisation ont été identifiés. Troisièmement, à partir d’une analyse du transcriptome, 164 gènes redox ont été détectés dans le latex du clone SP 217 et 161 dans celui du clone PB 260. Quatrièmement, à partir des petits ARNs et d’une analyse dégradome, 13 gènes ont été identifiés pour être clivés par 11 microARNs et 15 gènes clivés par 16 petits ARNs phasés dans le latex. Enfin, cette étude a mis en évidence des régulations spécifiques de la production des ROS et du système antioxydant dans le latex. HbRBOH2 a été identifié comme la source principale de ROS dans le latex. HbCuZnSOD4 pourrait être le contributeur majeur de la neutralisation des ROS dans le latex des arbres atteints de TPD. / Hevea brasiliensis, a tropical tree, is the main commercial source of nature rubber. The rubber biosynthesis occurs in specialized latex cells of rubber tree. Up 90% dry weight of latex is nature rubber. The milky latex flows out from cut latex cells by tapping rubber tree trunk bark. Rubber exploitation by tapping every several days is very stressful for the bark of rubber tree. To stimulate latex production, ethylene releaser is applied during rubber exploitation in some cases. The stress is increased after hormone stimulation. Reactive oxygen species (ROS) is generated when plant suffers stresses from environment and harvesting activity. Over a certain limit of stress, ROS bursting is motivated in latex cell. A lots of the evidences showed that the ROS lead to the peroxidatic degradation of the unsaturated lipids of the membrane and then to destabilisation and lysis of the organelles. Lysis of the lutoids results in liberation of coagulating factors into latex and coagulation in situ of rubber particles in stressed trees. This serious physiology syndrome is tapping panel dryness (TPD) which is one of main factor limiting rubber production.This PhD aims at identifying ROS production and scavenging genes and their characterizations in latex cell. Firstly, we made a comprehensive bibliography study on ROS production and scavenging genes both in rubber tree and model plant. The NADPH oxidase was considered as the main source of ROS in the stressed trees. ROS scavenging enzymes and antioxidants constituted the ROS scavenging systems in latex. Secondly, based on a genome-wide analysis, 407 genes involved in ROS production and scavenging were identified. Thirdly, based on a transcriptome analysis, 164 redox-related genes were detected expressing in latex of clone SP217 and 161 genes expressing in latex of clone PB260. Fourthly, based on small RNA and degradome analysis, 13 genes were shown to be targeted by 11 microRNAs and 15 genes by 16 phased siRNA in latex. Lastly, this study illustrated specific regulation systems of ROS production and scavenging in latex. HbRBOH2 was identified as the main source gene of ROS in latex. HbCuZnSOD4 might be the most important ROS scavenging gene to detoxify the ROS in latex of TPD tolerant tree.

Orientador: Jorge Luís Akasaki / Banca: Jefferson Sidney Camacho / Banca: Armando Lopes Moreno Júnior / Resumo: O presente trabalho tem como objetivo estudar algumas propriedades de concretos e argamassas, com substituição parcial do agregado miúdo por resíduos de borracha de pneus provenientes do processo de recauchutagem. Para todas as misturas foi utilizado o cimento CP V - ARI PLUS, areia e, para os concretos, brita basáltica. As substituições foram de 12% em volume do agregado miúdo por borracha para argamassa e 10% em volume para concreto. Em argamassa procurou-se verificar a influência do tratamento do resíduo de borracha com solução saturada de hidróxido de sódio. As propriedades estudadas foram: resistência à compressão, resistência à tração, absorção de água e índice de consistência. As propriedades analisadas em concreto à temperatura ambiente foram: resistência à compressão, absorção de água, resistência à tração, resistência à abrasão, módulo de elasticidade e resistência à flexão. Em concreto aquecido a 600ºC, avaliaram-se as propriedades de resistência à compressão e módulo de elasticidade. Os resultados obtidos em argamassas, após o tratamento do resíduo, mostram que este não influencia nas propriedades estudadas. Também é observado, após a substituição de parte do agregado pelo resíduo, queda na trabalhabilidade e nos resultados referentes à resistência mecânica. Os resultados de resistência à abrasão em concreto mostram-se interessantes para o uso da mistura em pavimentação. Após o aquecimento do concreto, observa-se redução na resistência à compressão e módulo de elasticidade para as misturas com e sem borracha. Também é observado que as relações de perda de resistência entre o concreto com e sem borracha são mantidas após o aquecimento. / Abstract: The aim of this work is to study some properties of mortars and concretes, whose fine aggregate was partially replaced by tire rubber from retreading process. It was used in all mixes CPV - ARI PLUS cement, river sand, and basaltic coarse aggregate. The replacement was made in volume of fine aggregate by tire rubber and it was 12% in mortars and 10% in concrete. The influence of the residue's treatment with a sodium hydroxide saturated solution was analyzed through tests in mortar. The studied properties were: compressive strength, splitting tensile strength, water absorption, and consistence index. The properties analyzed in concrete at room temperature were: compressive strength, splitting tensile strength, modulus of elasticity, and flexural tensile strength. The tests made at 600ºC heated concrete were compressive strength and modulus of elasticity. The results from mortars tests, after the rubber's treatment, show that it doesn't influence considerably the studied properties. It is also observed that after the replacement of part of the aggregate by tire rubber; there is a decrease in workability and mechanical tests results. The abrasion resistance tests results show that an interesting use to tire rubber concrete is in precast-concrete paving brick. It can be noted from the heated concrete results that compressive strength and modulus of elasticity decrease in mixes with and without tire rubber. It could be also seen that the relationship between concrete strength losses are kept after heating. / Mestre

Friction on ice is important for many different fields such as winter sports and vehicle traction. In vehicle handling, maximising the friction coefficient between tyres and the ice surface is key to safety. The friction coefficient between tyre rubber and ice has been observed to be as high as unity at low temperatures and as little as 0.05 close to the ice melting temperature. The observed low friction is due to thin water films generated through frictional heating. Little is known about the formation and behaviour of this fluid film and its thickness has been difficult to measure. Previous attempts included techniques such as capacitance, conductivity and fluorescence spectroscopy, however results have been inconsistent. The primary aim of this study was to develop a measurement technique for this lubricating layer, establishing its thickness and the conditions under which its presence results in low friction. This was done by designing a micro-scale linear tribometer (microtribometer) to measure the friction coefficient (μ) on ice under a microscope. Clear ice, and ice with fluorescent particles of various sizes were created. The two ice types were then joined and tested on. During a friction test on the microtribometer, the particles displaced in the direction of sliding due to melt water presence. Images of the ice surface were taken before and after a friction measurement was made, and the amount of particle movement was assessed. The size and displacement of particles were correlated to the range of melt water thickness for a given sliding condition. This study is the first direct measurement method for the melt water layer on ice. Frictional heating is generated through the physical contact of rubber and ice asperities. By conducting friction measurements with rubbers of varying shear modulus (G*) and surface roughness (Ra) on both the microtribometer and on our large–scale tribometer, FRIMA, analysis of the contact can be made over a range of length scales. Further insight into the interfacial effects was provided by surface roughness measurements of both ice and rubber before and ice after microtribometer tests and in FRIMA. Finally, the use of differential interference contrast in reflected light microscopy with ice friction measurements provided visual evidence of the melt water presence. It was found that the melt water thickness based on particle displacement was between 0.1 to 2μm, for a velocity of 4.3 ⇥ 10−4 ms−1 and 0.5MPa nominal load, between –6°C to 0°C. A decreasing film thickness was found with decreasing temperature and the friction coefficient increased with decreasing temperature. At higher temperatures, the differences between the rubbers on both FRIMA and the microtribometer were found to be negligible because of the lubricating layer. Increasing the rubber surface roughness was found to increase at high and decrease friction significantly at low temperatures. These phenomena can be explained by the decreasing amount of solid-solid contact. A simple analytical approach to interpret the results suggests that the rubber compresses significantly and the surface roughness is smoothened upon contact with ice. Furthermore, simple hydrodynamic shear calculations show that pure liquid shear is insufficient to account for the measured low μ values close to melting temperatures. The combined effect of the increasing melt water presence reducing the real contact area and the significant deformation of the rubber asperities failing to compensate for this reduced contact area can account for the results. It is anticipated that these results provide direction for finding ways to improve solid-solid contact between rubber and ice, as there is some viscoelastic dissipation even at conditions close to the melting temperature. Some topics for example are: improving the thermal conductivity of tyre compounds or further investigating the surface roughness of rubber and ice separately and with the thin liquid film in between.

This thesis is concerned with the design, analysis and optimisation of semi-solid or non- pneumatic tyres. More specifically, the thesis is intended to show how the FEA software package Abaqus can be used to determine whether or not an AirBoss tyre meets performance criteria in regards load/deformation criteria and if there is a likelihood of failure through overheating of the tyre during service.The work is intended to clearly explain the nature of natural rubber from a molecular description through to phenomenological descriptions used to solve for stresses, strains, creep and relaxation phenomena and temperature generation through hysteresis losses within the structure of the rubber compound.The thesis examines practical ways to obtain data for use in the analysis and describes test equipment (both "off-the-shelf" and purpose built) to obtain the required information.The objective is to progress, step by step, through the stages of analysis beginning with information to predict static loading conditions for the tyre. Viscoelastic behaviour, such as creep and relaxation are predicted and then tested to determine the correlation and refine test data before proceeding to the next stage of analysis.Ultimately, a prediction is made as to the temperature distribution throughout a section of the non-pneumatic tyre. A testing rig is described which has been built to test the analysis and enable a comparison to be made between FEA prediction and "real life".

Rubber and plastics companies are using mixing equipment (‘internal mixers') which was invented by Banbury in 1916 and which has hardly evolved since then. There is an urgent need for the modernization of such equipment and the market is demanding higher and higher performances for rubber goods. The physics of the dispersion of porous or fibrous agglomerates in a flow field has not been widely addressed in the past, despite of its importance. This is mainly due to the technical difficulties associated with the observations of the kinetics of this disagglomeration and the wide range of size that must be probed. Two mechanisms are recognized : erosion and rupture. Actually, different software solutions to simulate the 3D transient behavior of a flow in internal batch mixer are available. In all existing codes, it is assumed that mixing and flow calculations are decoupled : the analysis of the mixing (distributive or dispersive mixing) is performed after the calculation of the flow. To sum-up, hierarchical modeling including micro-macro models is considered in this work. In this thesis, we developed new distributive tools and new dispersive mathematical model. We compared the numerical prediction with several experiments. Finally, we use this model to design a new rotor shape in the framework of a European project.

Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their rheological properties can be controlled continously, rapidly, and reversibly by an applied magnetic field. They consist of magnetically polarisable particles in an elastomer matrix and they can be made to respond to changes in their environment; hence, they are considered as "smart" materials. Examples of potential applications for these materials are adaptive tuned vibration absorbers, stiffness-tuneable mounts and suspensions, and automotive bushings. The purpose of this work was to increase the knowledge relating to magnetorheological materials for damping applications. The materials should exhibit a large response to an applied magnetic field, and have good mechanical and long-term properties. MR rubber materials were made from nitrile, natural and silicone rubber, with irregularly shaped iron particles several micrometres in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, i.e. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated so that they behave like large irregular particles. The iron particle concentration must be very close to the CPVC in order to obtain a large MR effect without alignment of the particles. The absolute MR effect (MPa) in an isotropic MR rubber material with large irregular iron particles is independent of the matrix material, and the relative MR effect (%) can thus be increased by the addition of plasticisers. However, the obtainable effect is limited by the reinforcement of the particles and by friction between the particles. Therefore, it is very difficult, if not impossible, to achieve an MR effect larger than 60%. Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for MR rubber materials. The incorporation of large amounts of iron into the rubber matrix decreases the oxidative stability dramatically. This is probably due to iron oxides on the surface of the particles, and to the fact that the oxidation rate is enhanced by iron ions, which are able to diffuse into the matrix. Standard antioxidants do not provide sufficient stabilisation for MR rubbers. Thus, proper stabilisation systems have to be found in order for these materials to be successful in applications.

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Imperial Europes relationship with the tropical world was characterized by intrigue and fascination combined with a fear of difference. This combined intrigue and fear developed over time into a set of stereotypes and myths about the tropics, which by the 19th century had solidified into a powerful discourse historian David Arnold calls tropicality. As Europes interaction with the tropical world increased and its need for tropical resources grew, tropicality became a powerful tool for legitimizing European interference in and exploitation of the tropics. Embedded in the language of science and the promise of progress, it reaffirmed European superiority and its necessary role as the bearer of civilization for the tropical world. <p>Perhaps the most powerful characteristic of tropicality was its inherent ambivalence. The Amazon basin has been a particularly important source for the creation and maintenance of these stereotypes about the tropical world. Reinvented by Alexander von Humboldt as an exotic paradise at the beginning of the nineteenth century, the Amazon basin continued throughout the century to inspire commentary, exploration, and exploitation from abroad. As contact with the Amazon increased, ideas about the tropics began to change. What once was thought of as a pristine paradise became perceived as sinister, diseased, and savage. By the end of the nineteenth century, the tropical world, its people and nature, was considered to be an obstacle to civilization, and its very ability to become civilized began to be questioned.<p>Rubber, an increasingly important and lucrative imperial resource at the end of the nineteenth century, brought people from around the world to the Amazon basin. This resulted in the creation of a contact zone of different peoples, cultures, and idea, which was important for the moulding and maintenance of tropical stereotypes and myths. This was especially the case in the Putumayo, a border zone between modern day Colombia and Peru, where the brutal treatment of workers and the promise of civilization clashed. Through an exploration of travel diaries, newspapers, parliamentary papers, and other works about the tropics and rubber, this thesis argues that the manner in which rubber and its environment were depicted legitimized its control and exploitation from the outside. Couched in the rhetoric of civilization, tropicality helped justify the exploitation of rubber, the environment in which it grew, and the peoples that lived there.