Les mélanges de polymères sont fréquemment formulés en vue d'atteindre un compromis de propriétés bien spécifique. C'est notamment le cas dans les bandes de roulement d'un pneumatique, dans lesquelles l'utilisation de plusieurs élastomères permet de régler le comportement dissipatif du matériau, propriété clé au regard des performances d'adhérence et de résistance au roulement. Pour améliorer la rigidité et la tenue mécanique de la gomme, des particules minérales sont également ajoutées aux formulations de la bande de roulement, telles que la silice hautement dispersible qui permet d'améliorer les propriétés de résistance au roulement sans compromettre les propriétés d'adhérence et d'usure. Dans ce contexte, la problématique de ce travail de thèse est d'identifier les leviers permettant de modifier la localisation des charges dans un mélange d'élastomères, puis d'en comprendre l'impact sur les propriétés viscoélastiques et de renfort. La première partie s'attache donc à comprendre quels sont les paramètres influant sur la localisation de la charge dans des mélanges d'élastomères immiscible. Pour cela, l'effet des interactions entre constituants est étudié en modifiant l'état de surface de la charge, la nature de la charge ou encore la nature des élastomères. Puis l'incidence des effets cinétiques est analysée en faisant varier le ratio de viscosité des élastomères, ainsi que la procédure de mise en œuvre des mélanges. Grâce au développement d'une technique innovante en microscopie électronique permettant une caractérisation précise des morphologies de mélanges fortement chargés, le rôle dominant des interactions charge/élastomère sur la localisation finale des particules est mis en évidence dans le cas où charges et élastomères sont introduits simultanément lors du mélange, indépendamment des niveaux de viscosité des phases. Les effets cinétiques ont quant à eux un rôle essentiel sur les morphologies lorsque la silice est spécifiquement prémélangée à l'une des phases. Puis dans la seconde partie de ce travail, nous nous sommes intéressés à l'impact des différentes morphologies obtenues sur les propriétés dissipatives et de renfort des matériaux. Les propriétés viscoélastiques dans le domaine linéaire des mélanges sont tout d'abord analysées. Une relation directe est établie entre la localisation de la charge entre les phases et les propriétés dissipatives et de renfort des matériaux proche de Tg. A plus hautes températures, l'état de dispersion des charges apparaît comme étant un paramètre clé sur les propriétés de renfort. Enfin, l'étude des propriétés mécaniques à plus hautes déformations (effet Payne et tests de traction) montrent une incidence de la localisation de la charge ainsi que de son état de dispersion lorsque des interactions fortes sont considérées. Ce travail a donc permis de mettre en évidence des critères de sélection des interactions et niveaux de viscosités dans des mélanges d'élastomères chargés pour contrôler la localisation des charges, et par extension modifier les propriétés dissipative et de renfort de ces mêmes matériaux / The tradeoff in tread properties is notably controlled by the dependence in frequency of rubber dissipation: a high dissipation of energy improves wet grip at high frequencies, while it may increase rolling resistance at low frequencies. Using silica instead of carbon black has enabled an improvement of this tradeoff, but the physical mechanisms responsible of these properties are still under discussion. Besides, using polymer blends is a well-known technique to obtain materials with tailored properties, allowing for example the tuning of dissipation range and mechanical properties. These unique properties depend not only on the miscibility state of rubbers, but also on rubber phase morphology and particles distribution between phases. In this context, the issue of this work is to understand which parameters enable the modification of filler location between phases, and then to identify the impact of the various morphologies on the viscoelastic and reinforcement properties. We first study the impact of fillers on blends structuration by first varying interactions parameters between the three components (polymer A, polymer B, silica) to obtain various morphologies. It also has been shown that final blends morphologies depend also on rheological parameters. Thus the impact of process and rubber viscosities is studied, in an attempt to decorrelate the influence of rheology and interactions on blend structuration. To study reinforced rubber blends morphologies, a new microscopy technique has been developed to obtain a very clear viewing of silica in the different rubber phases. Then, the blends viscoelastic properties in the linear regime are investigated. Close to Tg, a direct relationship between filler location and dissipative and reinforcement properties is established. At higher temperatures, the filler state of dispersion appears to be a key parameter on reinforcement properties. Finally, the investigation of blends mechanical properties at larger deformations shows and impact of filler location but also filler dispersion when strong interactions are involved. Thanks to the different tools developed, we define criteria to control filler location in immiscible rubber blends, which enables a modification of their dissipative and mechanical properties

Orientadores: Chang Tien Kiang, Elias Hage Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-07-20T05:26:20Z (GMT). No. of bitstreams: 1 Cardoso_Giselia_M.pdf: 2679256 bytes, checksum: 20c2cfedadeeb83bd8a03e60f9c2c1a4 (MD5) Previous issue date: 1994 / Resumo: Misturas poliméricas binárias de poliamida 6,6 com aditivo macromolecular ¿ poliamida 6 modificada, policarbonato e poli(metacrilato de metila) ¿ em quantidades de 1 a 10% em massa, foram preparados por fusão e moldadas por injeção através do Mini Max Molder de fabricação da Custom Scientific Instruments. Os produtos obtidos foram caracterizados por microscopia ótica (MO), calorimetria diferencial de varredura (DSC) e análise dinâmico-mecânica (DMA). A análise em microscopia ótica foi realizada de forma qualitativa na observação da influência da natureza química e da quantidade de aditivo macromolecular na modificação da microestrutura da poliamida 6,6. as análises de DSC foram realizadas de duas maneiras: varredura de temperatura, na verificação de existência de miscibilidade nas e determinação. Pela equação de Nishi ¿ Wang, do parâmetro de interação de Flory ('X IND. 12¿); e isotérmica, na avaliação do efeito da presença dos aditivos macromoleculares na velocidade de cristalização da poliamida 6,6. A existência de separação de fase no estado sólido das misturas foi verificada através da análise do comportamento dinâmico-mecânico. O estudo conclui que a adição de pequena quantidade de macromoléculas retarda o aparecimento e reduz a taxa de crescimento dos esferulitos na poliamida 6,6 / Abstract: Binary polymeric blends of polyamide 6,6 with macromolecular additive ¿ modified polyamide 6, polycarbonate and poly(methyl methacrylate) ¿ in amounts varying from 1% to 10% in mass, were prepared by melting and injection ¿ molded a Mini Max Molder ¿ Custom Scientific Instruments. The obtained products were characterized by optical microscopy (OM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The optical microscopy analysis was performed as a qualitative observation of the influence of chemical nature and quantity of macromolecular additive in the modification of microstructure of polyamide 6,6. the DSC analysis were done in two ways: temperature scanning, where it was verified the miscibility of mixtures and the Flory¿s interaction parameter 'X IND. 12¿ was determined by Nishi ¿ Wang equation; and isothermally, where the presence of macromolecular additives in the rate of crystallization of polyamide 6,6 was evaluated. DMA of rod samples were performed to evaluate the presence of phase separation in the solid state. It is concluded that blending small amounts of macromolecular additives can delay and reduce the spherulitic crystallization growth in the polyamide 6,6 / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

This work aims to investigate the vapor sensing behavior of conductive polymer composites (CPCs). In connection with the protection of the environment and human beings, sensing of different kinds of chemical vapors is of increasing importance. At the moment, four kinds of vapor sensors are widely investigated and reported, namely semiconducting metal oxide sensors (MO), conjugated polymer sensors, carbonaceous nanomaterial based sensors, and CPC based sensors. Due to their unique component systems, the different sensor types are based on different sensing mechanisms resulting in different potential application ranges. In consideration of cost and processability, CPC based vapor sensors are promising owning to their low cost, excellent processability, and designable compositions. In terms of vapor sensing behavior of CPC sensors, the interaction between the polymer and the organic vapor is a decisive factor in determining the sensing performance of CPCs. Ideally, the chosen polymer matrix should be able to swell without dissolving during vapor exposure so that the conductive network within the matrix can be disconnected, giving rise to the resistance change of CPCs. In some reported cases, polymers such as PLA and polycaprolactone (PCL) are degradable polymers, which are not durable when being exposed to environmental conditions for a long time. Therefore, it is necessary to make sure whether the selected polymers are resistive to vapors or not. There are two options for the polymer selection. One is to select a polymer that is only swellable in a specific or few organic solvents; another one is to select a polymer that is swellable to a variety of solvents. Since CPC sensors are used for detecting as many as possible hazardous chemicals to human beings or environment, the second case is more desired because of its broader window of detection. The solubility parameter is effective to characterize the interaction of polymers and organic solvents/vapors, which was firstly proposed by Charles Hansen. Initially, the Hansen solubility parameter (HSP) was used to predict the compatibility between polymer partners, chemical resistance, permeation rates, and even to characterize the surface of fillers. Liquids with similar solubility parameter (δ) are miscible, and polymers will dissolve in solvents whose δ is similar to their own value. This behavior is recognized as “like dissolves like”. Based on the description above, CPCs that can be used as liquid/vapor sensor materials should meet the following two requirements: 1) the chosen polymer should be swellable to vapors; 2) the CPCs as sensor materials have to be electrically conductive. Therefore, the relationship between conductive network and vapor sensing behavior of CPCs was investigated from the following aspects: 1) According to the previous studies, CB/polymer composites exhibit poor reversibility in cyclic vapor sensing tests because of the susceptible conductive network formed by CB particles. Thus, there is a need to improve the reversibility and increase the relative resistance change (Rrel) of CPCs. MWCNTs, as 1-dimensional carbon fillers with high aspect ratio, have excellent electrical and mechanical properties. Therefore, a hybrid filler system (MWCNT and CB) was utilized and incorporated in polycarbonate (PC) via melt compounding. PC was selected as the polymer matrix of CPCs because it showed high affinity with many commercial organic solvents/vapors as well as high and fast volume change upon organic solvents/vapors. In order to discuss the effect of conductive network formation on the vapor sensing behavior of PC/MWCNT/CB composites, two MWCNT contents were selected, which were lower and higher than the electrical percolation threshold of the PC/MWCNT composites. In the following, three CB contents were selected for the mixtures with MWCNT. The conductive networks composed of either MWCNT or hybrid CB/MWCNT are compared. The morphology of CPCs with different hybrid filler ratios was observed and investigated using SEM and OM. Moreover, to quantify the vapor sensing behavior of CPCs, some organic solvents were chosen and characterized by Flory-Huggins interaction parameter to demonstrate the polymer-vapor interaction. Afterwards, the cyclic vapor sensing was applied to illustrate the vapor sensing behavior of CPCs with different conductive network formations. 2) At moment, the filler dispersion is still a big challenge for MWCNT filled polymer composites due to the fact that the strong Van der Waals force among nanotubes makes them easily to entangle with each other resulting in the formation of agglomerates. A good filler dispersion state is desirable to achieve CPCs with low φc and. In order to reduce the φc of CPCs, immiscible polymer blend systems are introduced, which can have different blend microstructures by adjusting the polymer component ratios. In the second section, an immiscible polymer blend system based on two amorphous component, namely PC and polystyrene (PS), was chosen aiming to explain the influence of the blend morphology on the sensing performance of CPCs. PC/PS blends with different compositions filled with MWCNT were fabricated by melt mixing. The selective localization of MWCNTs in the blends was predicted using the Young’s equation. Moreover, the composite morphology, filler dispersion, and distribution were characterized by SEM and TEM. In the following, three kinds of CPCs ranging from sea-island structure to co-continuous structure were selected for the cyclic sensing measurement. The relationship between composite microstructure and resulting vapor sensing behavior was evaluated and discussed. 3) The poor reversibility of CPCs towards good solvent vapors is still a problem that hinders the cyclic use of CPC sensor materials. As an important class of polymer, crystalline polymers are rigid and less affected by solvent penetration because of the well-arranged polymer chains. Therefore, the effect of polymer crystallinity on the vapor sensing behavior of CPCs is imperative to be studied. In the third section, poly(lactic acid) (PLA), a semi-crystalline polymer, was selected to melt-mixed with PS and MWCNTs with the aim to improve the sensing reversibility of CPCs towards organic vapors, especially good solvent vapors. Thermal annealing was utilized to tune the PLA crystallinity and the polymer blend microstructure of CPCs. The electrical, morphological, and thermal behavior of CPCs after different thermal annealing times is discussed. In the following, the effect of crystallinity on the vapor sensing behavior of the CPCs was studied in detail. Besides, the different sensing performances of the CPCs towards different vapors resulted from the selective localization of MWCNTs and increased polymer matrix crystallinity were investigated and compared. 4) As discussed for the amorphous polymer blends and crystalline polymer blends and their vapor sensing behavior. The comparison of compact and porous structure of CPCs is going to be studied. In the fourth section, studies to further improve the sensing performance and to find out the exact sensing mechanism of CPCs were performed. Therefore, poly(vinylidene fluoride) (PVDF), a solvent resistive polymer, was chosen to be melt-mixed with PC and MWCNTs. In order to compare the MWCNT dispersion and localization in the blends, three kinds of PCs with different molecular weights were selected; hence, the viscosity ratio of immiscible blends was varied. Rheological, morphological, and electrical properties of CPCs were characterized. After that, the cyclic sensing and long-term immersion tests of CPCs towards different vapors were carried out to evaluate the vapor sensing behavior of compact CPCs with different blend viscosity ratios. Moreover, porous CPC sensors were prepared by extracting the PC component. The same sensing protocols were also applied to these porous sensor materials. The sensing mechanisms between compact CPC sensor and porous CPC sensor were compared and investigated.

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