Дисертації з теми "Natural rubber composite"

The focus of this research was to investigate the effect of thermal degradation upon the mechanical properties of natural rubber compounds and apply those effects to the life prediction of off axis 2-ply cord rubber laminates. The work examined both the quasi-static and dynamic mechanical properties of two natural rubber vulcanizates, which had been subjected to isothermal anaerobic aging. Thermal aging was performed on two different natural rubber vulcanizates. The thermal aging was conducted between the temperatures of 80 and 120°C for times ranging from 3 to 24 days. The effect of thermal degradation was measured from the changes in the chemical composition of the vulcanizates as functions of time at temperature. A master curve relationship between the changes in the chemical composition of the vulcanizates due to thermal degradation and their static and dynamic mechanical properties has been developed. This relationship allowed for the prediction of the vulcanizate mechanical properties after thermal aging. It was found that the mechanical properties correlated with the percentage of poly and monosulfidic crosslinks, where in general higher levels of polysulfidic crosslink gave rise to the highest mechanical properties. Crack propagation in an aged and unaged natural rubber vulcanizate was measured using a double cantilever beam, DCB. This type of testing arrangement exhibits a plane strain condition and resulted in crack growth rates two orders of magnitude faster than traditional plane stress testing geometries. To validate the DCB specimens, an investigation into the potential cavitation inside the rubber of the DCB specimens was performed. It was found that no cavitation occurred due to the high speed of the fracture. DCB samples were thermally aged to determine the effect of thermal aging upon the crack growth rate. It was found that crack growth rates increase with thermal aging. Life prediction of the aged 2-ply laminates was performed using a finite element analysis. In order to verify the finite element models used in the life prediction, the fatigue failure and crack growth characteristics of off axis 2-ply cord-rubber laminates were examined with a delamination analysis. This analysis allowed for the determination of the modulus of off axis 2-ply laminates in the presence of damage as well as the calculation of the crack growth rates of the laminate. The failure of unaged and thermally aged 2-ply laminates was evaluated and compared to the crack growth rates of thermally aged DCB specimens. The trend due to thermal aging between the two types of testing specimens was consistent. The finite element analysis was sectioned into two approaches: crack initiation and crack propagation. The former utilized a residual strength approach, while the latter applied a fracture mechanics approach. The predicted stress versus cycles, S-N, curves were not in complete agreement with the experimental data. The error between the predicted and the experimental is discussed and future work to correct that error is suggested. While there was not complete agreement between the predicted and the experimental data, this dissertation outlines a comprehensive approach to track the effects of thermal degradation and apply those effects to a real world application.
Ph. D.

Cette recherche vise à synthétiser différents types et formes de particules de carbonate de calcium (CaCO3) à l'échelle submicrométrique et nanométrique, et à étudier leurs applications en tant que charges renforçantes pour les composites de caoutchouc naturel (NR). L'étude a donc été divisée en deux parties. Premièrement, la procédure de préparation des particules de CaCO3 était basée sur la méthode de précipitation en solution entre les ions carbonate (CO32-) et les ions calcium (Ca2+). La deuxième partie concerne l'étude des propriétés mécaniques des composites NR/CaCO3. La première partie a commencé par la précipitation de (NH4)2CO3 et de CaCl2 dissous dans 50 % en poids de saccharose comme milieu aqueux. Cette condition a entraîné la formation de CaCO3 sphérique, ce qui a été mis en évidence au microscope électronique à balayage (MEB). L'analyse au microscope électronique à transmission (TEM) a révélé une taille de particule de 0,42 ± 0,14 µm avec un rapport d'aspect d'environ un. Lorsque la réaction de précipitation s'est produite en présence d’huile d'olive saponifiée, la propriété de surface du CaCO3 est passée d'hydrophile (angle de contact avec l'eau de 28 ± 2°) à superhydrophobe (angle de contact avec l'eau de 163 ± 2°). Les phases polymorphes typiques de CaCO3 ont été caractérisées par diffraction des rayons X (DRX), infrarouge à transformée de Fourier par réflexion totale atténuée (ATR-FTIR) et spectroscopie Raman. Ces techniques ont révélé que le CaCO3 sphérique non traité et traité représentait environ 99 % du polymorphe de la vatérite. Dans le processus de précipitation utilisant des solutions aqueuses 1 M de Na2CO3 et 1 M de CaCl2 réalisé à 80 ± 1 °C, du CaCO3 sous forme de fibres agglomérées a été obtenu avec un rapport d'aspect compris entre 8 et 9. Le CaCO3 superhydrophobe sous cette forme a également été synthétisé avec succès. L'angle de contact avec l'eau des fibres traitées et non traitées est respectivement de 29 ± 2° et 167 ± 2°. De plus, le CaCO3 sphérique dispersé dans l'eau à 80°C a donné naissance à des nanoparticules de CaCO3 en forme de fibre qui ont été obtenues via la transformation de la vatérite sphérique en aragonite nanofilaire longue avec le rapport d'aspect le plus élevé de 156,9 par rapport aux autres formes de CaCO3. La fibre CaCO3 non traitée était hydrophile avec un angle de contact avec l'eau de 31 ± 1°, tandis que la fibre CaCO3 traitée avec du savon donnait un angle de contact avec l'eau de 165 ± 5° ; elle était donc superhydrophobe similaire aux autres polymorphes de CaCO3 synthétisés. La DRX a révélé que le CaCO3 en forme de fibres, non traitées et traitées, contenait en majorité de l'aragonite et en moindre mesure de la vatérite et de la calcite. La stabilité thermique de différents types de CaCO3 a également été évaluée par analyse thermogravimétrique (TGA). Les résultats ont montré la calcination des cristaux de CaCO3, du saccharose et du savon. La deuxième partie a consisté à incorporer le CaCO3 préparé (0, 5, 10, 20, 40, à 60 pce) dans du latex naturel (NR). Il a été constaté que la vatérite CaCO3 non traitée et traitée était stable dans le milieu latex NR. De plus, les polymorphes du CaCO3 non traité et traité en forme de fibres étaient également stables dans leurs formes lorsqu'ils étaient ajoutés au latex NR. Les propriétés mécaniques du NR/CaCO3 comprenaient la résistance à la traction, l'allongement à la rupture, la résistance à la déchirure et la dureté Shore A. Il a été constaté que la résistance à la traction des composites NR/CaCO3 augmentait lorsque la charge de CaCO3 augmentait. La résistance à la traction du NR s'est améliorée de 22,68 ± 2,22 MPa de NR pur jusqu'à 23,94 ± 0,97 MPa lorsque des poudres de CaCO3 sphériques non traitées (20 phr) ont été ajoutées, et à 25,28 ± 0,80 MPa de CaCO3 sphérique traité (20 phr) de NR rempli. (...)
This research aims to synthesize different types and shapes of calcium carbonate (CaCO3) particles at a submicrometric and nanoscale, and investigate their applications as reinforcing fillers for natural rubber (NR) composites. The study was therefore divided into two parts. Firstly, the preparation procedure of CaCO3 particles was based on the solution precipitation method between carbonate ions and calcium ions. The second part focused on investigating the mechanical properties of NR/CaCO3 composites. The first part started with the precipitation of (NH4)2CO3 and CaCl2 dissolved in 50% by weight of sucrose as the aqueous medium. This condition resulted in spherical CaCO3 with particle size of 0.42±0.14 µm with an aspect ratio of about one. When the precipitation reaction occurred in the presence of olive soap, the surface property of the CaCO3 was changed from hydrophilic (water contact angle of 28±2o) to superhydrophobic powders (water contact angle of 163±2o). The typical polymorphic phases of CaCO3 were characterized. The results revealed that both untreated and treated spherical CaCO3 were about 99% of the vaterite polymorph. In the precipitation process using Na2CO3 and CaCl2 aqueous solutions performed at 80±1C, bundle-liked CaCO3 was obtained with an aspect ratio in the range of 8–9. The superhydrophobic bundle-liked CaCO3 was also successfully synthesized by soap treatment. The water contact angle of untreated and treated bundle-liked are 29±2o, and 167±2o, respectively. Furthermore, the spherical CaCO3 dispersed in water at 80C resulted in the fiber-shaped CaCO3 nanoparticles which were achieved via the polymorph transformation from spherical vaterite to long nano-wired aragonite with the highest aspect ratio of 156.9. The untreated fiber CaCO3 was hydrophilic with a water contact angle of 31±1o, while the treated fiber CaCO3 with soap resulted in 165±5o of water contact angle, hence it was superhydrophobic similar to other synthesized CaCO3 polymorphs. The XRD revealed that the untreated and treated bundle-liked and fiber-shaped CaCO3 contained the majority of aragonite followed by vaterite and calcite polymorphs. The second part was carried out to incorporate the prepared CaCO3 (0,5,10,20,40,60 phr) in NR latex. It was found that the CaCO3 polymorphs were stable in the NR latex medium. The mechanical properties of NR/CaCO3 included tensile strength, elongation at break, tear strength, and hardness Shore A. It was found that the tensile strength of NR/CaCO3 composites increased when CaCO3 loading was increased. The tensile strength of NR improved from 22.68±2.22 MPa of neat NR up to 23.94±0.97 MPa when untreated spherical CaCO3 powders (20 phr) were added, and to 25.28±0.80 MPa of treated spherical CaCO3 (20 phr) filled NR. The maximum tensile strength of NR/untreated bundle-liked CaCO3 was 30.59±3.50 MPa at 40 phr of loading while 31.51±1.02 MPa of NR/treated bundle-liked CaCO3 at filler loading 20 phr was obtained. The treated CaCO3-filled NR vulcanizates gave higher tensile strength than the untreated ones. This was caused by better compatibility of filler dispersion between the hydrophobicity of treated CaCO3 and hydrophobic property of NR. As a result, it was found that the NR filled with untreated fiber CaCO3 particle provided the highest tensile strength of 31.66±1.80 MPa at 10 phr of filler loading, over other types of CaCO3. The nanoparticle, large surface area, and high aspect ratio of fiber/ long nano wired of CaCO3 enhanced the interfacial adhesion between CaCO3 and NR matrix which could transfer stress from rubber to filler effectively during stretching. This resulted in the reinforcing efficacy of the fiber CaCO3. In summaroze, the prepared CaCO3 powders have the potential to broaden their application not only as diluents or additives but also as reinforcing agents

Cette thèse étudie le phénomène de durcissement qui a lieu pendant le stockage des composites de latex de caoutchouc naturel et de noir de carbone fabriqués par hétérocoagulation. Ce procédé consiste à injecter à très grande vitesse une suspension aqueuse de noir de carbone dans du latex de caoutchouc naturel. Le matériau spongieux et très hydraté qui est obtenu est ensuite séché et mis en forme par malaxage ou pressage. Nous mesurons le durcissement des composites à l’aide de plusieurs méthodes rhéologiques parmi lesquelles la rhéologie de torsion et la viscosimétrie de Mooney. L’effet d’un grand nombre de paramètres est étudié : le mode de mise en forme des composites, l’environnement du stockage, la présence d’eau résiduelle, la température, la fraction massique de noir de carbone. Nous définissons des temps caractéristiques de durcissement dont la dépendance en température indique que le durcissement résulte d’un processus activé thermiquement. Les énergies d’activation sont peu dépendantes des paramètres expérimentaux et comparables à celle trouvée pour le caoutchouc naturel pur. Des expériences de gonflement en bon solvant montrent que le durcissement est associé à la formation d’un réseau de macromolécules interconnectées dont nous discutons l’origine en relation avec la microstructure du polyisoprène naturel et la présence de phospholipides et de protéines
This thesis investigates the storage hardening of natural rubber and carbon black composites made by heterocoagulation. Heterocoagulation is a process that consists in injecting a carbon black slurry at high speed into a colloidal suspension of natural rubber. We obtain a squishy and highly hydrated material that is subsequently dried and processed using an internal mixer or a mechanical press. The hardening is characterized using various rheological techniques among which torsional rheology and Mooney viscosimetry. Many parameters are investigated: the processing technique, the storage environment, the presence of residual water, temperature, the carbon black content. We define characteristic times of hardening whose temperature dependence indicates that the hardening results from a activated process. The energies of activation are nearly independent of the experimental parameters and compare well to that found in natural rubber. Swelling experiments in good solvent show that hardening is associated with the buildup of an interconnected network of macromolecules. We discuss the origin of this network in relation with the microstructure of natural polyisoprene and the presence of phospholipids and proteins

Les effets du caoutchouc nitrile (NBR), du traitement de la surface des fibres et du noir de carbone sur les propriétés des composites à base de caoutchouc naturel renforcé par des fibres d'ananas (NR / PALF) ont été étudiés. L'incorporation de NBR et le traitement de surface de la fibre ont été utilisés pour améliorer les propriétés mécaniques des composites à faible déformation, alors que le noir de carbone a été utilisé pour améliorer ces propriétés à forte déformation. La teneur en fibres a été fixée à 10 phr. Les matériaux composites ont été préparés à l'aide d'un mélangeur à cylindres et ont été réticulés sous presse permettant ainsi le maintien de l'orientation des fibres. Ces composites ont été caractérisés à l’aide du rhéomètre à matrice mobile (MDR), par analyse thermique mécanique dynamique (DMTA) et par tests de traction. La morphologie après fracture cryogénique a été observée à l'aide de la microscopie électronique à balayage (MEB). L'effet du NBR dont la teneur varie de 0 à 20 phr par rapport à la teneur totale en caoutchouc, a été également étudié. Le NBR est utilisé afin d’encapsuler totalement les fibres d’ananas (PALF) ; ceci conduisant à un meilleur transfert de contraintes entre la matrice et les fibres. La méthode de mélange a également été étudiée. Plusieurs types de silanes tels que le propylsilane, l'allylsilane et le silane-69 ont été utilisés pour traiter les fibres pré-nettoyées à l’aide d’un traitement alcalin. Les fibres silanisées ont été caractérisées par spectroscopie infrarouge à transformée de Fourier (FTIR), par spectroscopie de photoélectrons aux rayons X (XPS) et par MEB. Le traitement de la fibre par le silane-69 a permis d’augmenter fortement le module du matériau composite à faible déformation. Ce traitement a été plus efficace que l'incorporation de NBR dans les composites NR / PALF. Ceci peut s’expliquer par une possible réticulation chimique entre le caoutchouc et la fibre traitée au silane-69 plutôt qu’une simple interaction physique du NR, du NBR et de la fibre. Cependant, le renforcement par fibre réduit la déformation à la rupture. Par conséquent, du noir de carbone a également été incorporé dans les composites NR/NBR/PALF et NR/ PALF traitée, afin d’améliorer leurs propriétés ultimes. En incorporant du noir de carbone à un taux de 30 phr dans les deux composites, les propriétés mécaniques des composites ont été améliorées et peuvent être contrôlées à la fois à des déformations faibles et hautes
The effects of nitrile rubber (NBR), fiber surface treatment and carbon black on properties of pineapple leaf fiber-reinforced natural rubber composites (NR/PALF) were studied. The incorporation of NBR and surface treatment of fiber were used to improve the mechanical properties of composites at low deformation, whereas carbon black was used to improve these properties at high deformation. The fiber content was fixed at 10 phr. The composites were prepared using two-roll mill and were cured using compression moulding with keeping the fiber orientation. These composites were characterized using moving die rheometer (MDR), dynamic mechanical thermal analysis (DMTA) and tensile testing. The morphology after cryogenic fracture was observed using scanning electron microscopy (SEM). The effect of NBR from 0 to 20 phr of total rubber content was investigated. NBR is proposed to encase PALF leading to higher stress transfer between matrix and PALF. The method of mixing was also studied. For the fiber surface treatment, propylsilane, allylsilane and silane-69 were treated on the alkali-treated fiber. Treated fibers were characterized using Fourier-Transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and SEM. Silane-69 treatment of fiber increased the modulus at low deformation more than the incorporation of NBR of NR/PALF composites due to the chemical crosslinking between rubber and fiber from silane-69 treatment rather than the physical interaction of NR, NBR and fiber. However, reinforcement by fiber reduced the deformation at break. Hence, carbon black was also incorporated into NR/NBR/PALF and NR/surface-treated PALF composites to improve the ultimate properties. By incorporation of carbon black 30 phr in both composites, the mechanical properties of composites were improved and can be controlled at both low and high deformations

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Neste trabalho é apresentado o método de preparação dos compósitos obtidos a partir da mistura de borracha natural (BN) com raspa de couro, gerada em uma das etapas do tratamento do couro nos cortumes. Os compósitos foram obtidos utilizando o método de prensagem e quente, em diferentes proporções em massa (m%). Também será apresentada a proporção calculada a partir da quantidade de BN utilizada (phr) e a técnica usada para a incorporação dos agentes de vulcanização, realizadas para vulcanizar a BN presente na mistura. Os compósitos, que no presente trabalho serão denominados BN/Couro, foram caracterizados utilizando as técnicas de análises de propriedades mecânicas, análises morfológicas, análises estruturais e análises térmicas. Os resultados obtidos foram comparados em função das propriedades físicas dos compósitos com as do couro utilizado comercialmente, com objetivo de se efetuar um direcionamento para uma possível aplicação industrial e comercial dos compósitos. De acordo com os resultados constatou-se que o material apresenta baixa capacidade de deformação, causada pela vulcanização realizada na BN e também pelas partículas de couro. Notou-se também que os compósitos apresentam bom grau de impermeabilidade e desgaste, quando comparado ao couro sola utilizado comercialmente, sendo averiguado que esta propriedades são relacionadas à proporção de BN presente na mistura, que por sua vez atua como agente encapsulador do couro, tornando-se predominante no material produzido. O que investigou o desenvolvimento deste trabalho foi a pretensão de obter um material de baixo custo, pois será produzido a partir de um resíduo gerado às toneladas
This work presents the method of preparation of composites from a mixture of natural rubber (NR) with leather waste, generated in one step in the treatment of leather in tanneries. The composites were obtained using the method of hot pressing, in different proportions by mass (wt%). Also presented the ratio calculated from the amount of NR used (phr) and the technique used for incorporation of curing agents, taken to vulcanize the NR in the mixture. The composites, which in this work will be called NR/Leather, were characterized using the techniques of analysis of mechanical properties, morphological analysis, structural analysis and thermal analysis. The results were compared on the basis of the physical properties of the composities with the leather used commercially, with the objective to make a direction for a possible industrial application and commercial composites. According to the results found that the material has a low capacity for deformation caused by vulcanization perfomed in NR and also by the particles of leather. It was also noted that the composites exihibit a good degree of impermeability and wear when compared to leather soles used commercially, and ascertained that these properties are related to the proportion of BN in the mixture, which in turn acts as an agent wrapper of leather making is predominant in the material produced. What prompted the development of this work was the intention of obtaining a low cost material, which be produced from a waste generated by the ton

Cette thèse porte sur l’étude du comportement mécanique et vibratoire d’un composite biosourcé incorporant un matériau viscoélastique. Les matériaux étudiés sont des stratifiés en composite lin/greenpoxy et des stratifiés viscoélastiques composés d'un noyau viscoélastique en caoutchouc naturel confiné entre deux composites. La première partie du travail a été consacrée à l’étude de l’influence de l’intégration de la couche viscoélastique sur le comportement mécanique des composites. L’analyse des résultats expérimentaux et l’observation des signaux d’émission acoustique obtenus dans ces composites soumis à différentes sollicitations mécaniques en statique et en fatigue ont permis d’identifier les signatures acoustiques des mécanismes d’endommagement prépondérants dans les deux matériaux. Dans un deuxième temps, les propriétés dynamiques de ces composites ont été déterminées à partir des essais de vibration. Les résultats obtenus ont montré que la couche viscoélastique a joué un rôle majeur dans l'amortissement et la dissipation d'énergie des composites. Suite à cette analyse, nous avons mis en place une procédure, utilisant la méthode des éléments finis, pour calculer l’amortissement de ces matériaux. Dans le but de mettre en évidence l’influence des caractéristiques de la couche viscoélastique, une étude paramétrique a été menée sur le composite viscoélastique, permettant d’optimiser l’amortissement de ce matériau en faisant varier divers paramètres. Enfin, le comportement visqueux des composites a été caractérisé par la méthode de résonance non linéaire en faisant varier l’amplitude d’excitation
This thesis focuses on the study of the mechanical and vibration behaviour of a flax fibre reinforced composites with and without an interleaved natural viscoelastic layer. The composite materials have been characterized experimentally using different mechanical and vibrational tests. First, both types of composites were studied using uni-axial tensile and three-points bending tests. Acoustic emission (AE) has been often used for the identification and characterization of micro failure mechanisms in composites. The results showed that these composites have very high specific characteristics. It can be used for applications currently using composites reinforced with synthetic fibres such glass, carbon…. Next, experimental and finite element vibration analyses were carried out on the composites with and without an interleaved natural viscoelastic layer. A good agreement between the two methods was obtained. It has been shown that the viscoelastic layer plays a major role in damping because it has a high level of energy dissipation. Therefore, it improves with a significant way the modal properties of the composite. Finally, nonlinear resonance tests were performed on the composites. It has been shown that the viscoelastic layer generates a nonlinear behaviour in the material. The linear and nonlinear, elastic and dissipative parameters have been calculated to deduce finally that nonlinear parameters are more sensitive to heterogeneities than those derived from linear vibration tests

Ce travail porte sur la production et la caractérisation de matériaux composites hybrides basés sur un polymère thermoplastique (polyéthylène de haute densité, PEHD), une fibre naturelle (chanvre) et un caoutchouc recyclé provenant de pneus usés (GTR) comme modificateur d'impact. L'addition d'un agent de couplage (polyéthylène maléaté) est également étudiée. Les échantillons sont mélangés par extrusion à double-vis et fabriqués par un moulage en injection. À partir des échantillons obtenus, une caractérisation morphologique et mécanique complète est effectuée. Les résultats montrent que la bonne dispersion est obtenue en raison des bonnes conditions de mélanges sélectionnées et une bonne adhésion interfaciale entre toutes les phases est atteinte en raison de la présence d'anhydride maléique greffée au polyéthylène (MAPE). Enfin, pour des propriétés mécaniques choisies, des modèles de régression non-linéaire sont proposés pour prédire et contrôler les propriétés finales de ces composés par des comparaisons faites sur la base des propriétés de la matrice seule.
Ce travail porte sur la production et la caractérisation de matériaux composites hybrides basés sur un polymère thermoplastique (polyéthylène de haute densité, PEHD), une fibre naturelle (chanvre) et un caoutchouc recyclé provenant de pneus usés (GTR) comme modificateur d'impact. L'addition d'un agent de couplage (polyéthylène maléaté) est également étudiée. Les échantillons sont mélangés par extrusion à double-vis et fabriqués par un moulage en injection. À partir des échantillons obtenus, une caractérisation morphologique et mécanique complète est effectuée. Les résultats montrent que la bonne dispersion est obtenue en raison des bonnes conditions de mélanges sélectionnées et une bonne adhésion interfaciale entre toutes les phases est atteinte en raison de la présence d'anhydride maléique greffée au polyéthylène (MAPE). Enfin, pour des propriétés mécaniques choisies, des modèles de régression non-linéaire sont proposés pour prédire et contrôler les propriétés finales de ces composés par des comparaisons faites sur la base des propriétés de la matrice seule.
This work aims at the production and characterization of hybrid composites based on a thermoplastic polymer (high density polyethylene, HDPE), a natural fiber (hemp) as reinforcement and ground tire rubber (GTR) as an impact modifier. The addition of a coupling agent (maleated polyethylene) is also investigated. The samples are compounded by twin-screw extrusion and produced by injection molding. From the samples obtained, a complete morphological and mechanical characterization is performed. The results show that good dispersion is obtained due to the selected processing conditions and good interfacial adhesion between all the phases is achieved due to the presence of maleic anhydride grafted polyethylene (MAPE). Finally, for selected mechanical properties, nonlinear regression models are proposed to predict and control the final properties of these compounds and comparisons are made based on the neat matrix properties.
This work aims at the production and characterization of hybrid composites based on a thermoplastic polymer (high density polyethylene, HDPE), a natural fiber (hemp) as reinforcement and ground tire rubber (GTR) as an impact modifier. The addition of a coupling agent (maleated polyethylene) is also investigated. The samples are compounded by twin-screw extrusion and produced by injection molding. From the samples obtained, a complete morphological and mechanical characterization is performed. The results show that good dispersion is obtained due to the selected processing conditions and good interfacial adhesion between all the phases is achieved due to the presence of maleic anhydride grafted polyethylene (MAPE). Finally, for selected mechanical properties, nonlinear regression models are proposed to predict and control the final properties of these compounds and comparisons are made based on the neat matrix properties.

Le caoutchouc naturel (NR) et le caoutchouc époxydé (ENR) ont constitué la base de cette étude consacrée à l’étude des composites et mélanges de polymères. La présence du groupe époxyde a conduit à une amélioration des propriétés mécaniques de ces formulations en termes de module et de la résistance à la traction. De plus, l’utilisation de la spectroscopie diélectrique a révélé que les ENRs présentent une conductivité plus élevée que le NR à basse fréquence et à haute température. En particulier, le caoutchouc naturel époxidé contenant 50 mol% de groupes époxyde ENR-50 présente des conductivités et permittivités les plus élevées. Par conséquent, ce dernier a été choisi pour préparer des composites polymères en incorporant des particules de titanate de barium (BT) et de noir de carbone (CB). Les résultats montrent que la permittivité et conductivité des composites élaborés augmentent avec le taux d'incorporation de ces charges. Par exemple, les composites BT/ENR-50 atteignent une permittivité élevée 48.7 pour 50 vol% de BT. De plus, les composites CB/ENR-50 présentent un seuil de percolation de 6.3 vol% de CB. Enfin les mélanges à base de poly(fluorure de vinylidène) (PVDF) et d’ENR ont été étudiés. Il a été observé que la morphologie de ces mélanges dépend du degré d’époxydation du caoutchouc naturel et bien entendu de la composition du mélange. Une morphologie co-continue peut être observée dans l’intervalle 40 et 60% en masse d’ENR-50. En outre, les résultats issus d’analyses dynamiques mécanique et diélectrique montrent que ces mélanges présentent une miscibilité partielle. Enfin, des composites à base de ces mélanges binaires PVDF/ENR- 50 contenant BT ont été préparés. L’étude des morphologies a révélé que les particules de BT étaient dispersées dans la phase d’ENR-50 pour le mélange classique. Cependant, les particules de BT sont localisées à l'interface et dans la phase PVDF pour le mélange réticulé dynamiquement. En termes de propriétés, la permittivité plus élevée est obtenue pour le mélange PVDF/ENR 50 (80/20) ayant été réticulé dynamiquement
Natural rubber (NR) and epoxidized natural rubber (ENR) were chosen to study the composites and blends of polymers. The presence of epoxide group caused to improve the mechanical properties in terms of modulus and tensile strength. Furthermore, dielectric spectroscopy revealed that ENR showed conductivity process at low frequency and high temperature. Epoxidized natural rubber containing 50 mol% of epoxide group or ENR-50 exhibited the highest dielectric permittivity and electrical conductivity. Therefore, ENR-50 was then selected to prepare polymer composite filled with barium titanate (BT) and carbon black (CB) particles. The permittivity and conductivity of the composites increased with the volume content of the fillers. The BT/ENR-50 composites reached a high permittivity of 4 8 . 7 for addition of 50 vol% BT. Meanwhile, CB/ENR-50 composite reached percolation threshold at 6. 3 vol% of CB. The phase development and miscibility of poly(vinylidene fluoride) (PVDF)/epoxidixed natural rubber (ENR) blends were then investigated. It was also found that phase structure depended on epoxidation level and blend compositions. The blend exhibited a co-continuous phase morphology in the region of 40 to 60 wt% of ENR-50. Furthermore, the results from dynamic mechanical and dielectric analysis revealed that these blends present a partial miscibility. Finally, the composites based on binary blends of PVDF/ENR-50 containing BT were prepared. The study of the morphologies revealed that BT was dispersed in ENR-50 phase in the case of simple blend. However, the addition of BT after dynamic vulcanization induced localization of BT in PVDF phase and at interface. The highest increment of permittivity can be observed for the composite based on dynamically cured PVDF/ENR-50 (80/20) blend
ศึกษาอิทธิพลของโครงสร้างโมกุลยางธรรมชาติ (NR) และยางธรรมชาติอิพอกไซด์ (ENR) ต่อสมบัติ พบว่าการมีหมู่อิพอกไซด์อยู่ในยาง ENR ทำให้มีการปรับปรุงสมบัติเชิงกล เช่น มอดุลัสและความต้านทานต่อแรงดึง นอกจากนี้สมบัติไดอิเล็กทริกได้แสดงให้เห็นถึงการนำ ไฟฟ้าที่ความถี่ต่ำและอุณหภูมิสูง ยางที่มีหมู่อิพอกไซด์ 50 โมล% (ENR-50) มีค่าการนำไฟฟ้า และค่า permittivity สูงที่สุด ดังนั้นจึงนำยาง ENR-50 ไปใช้ในการเตรียมคอมพอสิตที่ใช้แบเรียม ไททาเนตและเขม่าดำเป็นตัวเติม ซึ่งพบว่าค่า permittivity และค่าการนำไฟฟ้าสูงขึ้นตาม ปริมาณตัวเติมที่ใส่ลงไป ที่ปริมาณ 50%โดยปริมาตรของแบเรียมไททาเนตในยางให้ค่า permittivity สูงถึง 48.7 ในขณะเดียวกันก็พบว่าการเตรียม ENR-50 คอมพอสิตที่ใช้เขม่าดำมี percolation threshold ที่ 6.3 vol% ของเขม่าดำ สำหรับการศึกษาการเปลี่ยนแปลงของสัณฐาน วิทยาและความเข้ากันได้ของพอลิเมอร์เบลนด์ระหว่างพอลิไวนิลลิดีนฟลูออไรด์ (PVDF) กับยาง ENR พบว่า สัณฐานวิทยาของพอลิเมอร์ที่เตรียมได้ขึ้นอยู่กับปริมาณหมู่อิพอกไซด์ในยาง ENR และอัตราส่วนการเบลนด์ อัตราส่วนการเบลนด์ในช่วง 40 ถึง 60% โดยน้ำหนักของยาง ENR- 50 ให้ลักษณะสัณฐานวิทยาแบบวัฏภาคร่วม (co-continuous) นอกจากนี้ผลการทดสอบจาก สมบัติพลวัตเชิงกลและสมบัติไดอิเล็กทริกแสดงให้เห็นถึงความเข้ากันได้บางส่วน (partial miscibility) ท้ายที่สุดนี้ได้เตรียมคอมพอสิตจากพอลิเมอร์เบลนด์ที่เติมแบเรียมไททาเนต สัณฐานวิทยาของคอมโพสิทที่เตรียมได้นั้น พบว่าแบเรียมไททาเนตกระจายตัวในเฟสยางเป็น หลัก อย่างไรก็ตามการเติมแบเรียมไททาเนตหลังจากการวัลคาไนซ์แบบไดนามิกส์ทำให้ แบเรียมไททาเนตกระจายตัวในเฟสพอลิไวนิลลิดีนฟลูออไรด์ (PVDF) และที่ผิวประจัญ (interface) นอกจากนี้คอมพอสิตที่เตรียมจากเทอร์โมพลาสติกวัลคาไนซ์ของ PVDF/ENR 50 ที่ อัตราส่วนการเบลนด์ที่ 80/20 ให้ค่า permittivity ที่สูง

Cette thèse se concentre sur la caractérisation, la dispersion, ainsi que les différentes applications d'un nouveau type de matériaux dérivé de la dégradation de biométhane dans le cadre d'un projet Européen, le projet PlasCarb. Nous appelons ces matériaux les nanopalets de carbone (CNP). Notre étude commence avec la caractérisation des CNP, puis nous poursuivons avec l'obtention de dispersions aqueuses bien définies et hautement concentrées de CNP. Ces dispersions ont été utilisées pour la préparation de films conducteurs et de composites conducteurs avec du caoutchouc naturel. Enfin, la photoluminescence des CNP dispersés et solubilisés dans un milieu liquide a été évaluée. Des tests préliminaires montrent une photoluminescence dans le bleu très prometteuse
This PhD thesis is focused on the characterization, dispersion and applications of graphitic material (in this manuscript referred as carbon nanopuck (CNP)) that derives from the splitting of biogas and obtained within the framework of the European project “PlasCarb”. This study starts with CNP characterization. Afterwards, well-defined, high concentrated CNP dispersions in water, calibrated insize have been obtained. These dispersions have been used to prepare conductive films and as components of conductive composites with natural rubber. Ultimately, the photoluminescence of CNP dispersed and dissolved in liquid media has been tested. Preliminary tests of these systems exhibit promising blue PL

Orientador: Aldo Eloizo Job
Banca: Celia Regina Granhen Tavares
Banca: Silvio Rainho Teixeira
Resumo: Neste trabalho é apresentado o método de preparação dos compósitos obtidos a partir da mistura de borracha natural (BN) com raspa de couro, gerada em uma das etapas do tratamento do couro nos cortumes. Os compósitos foram obtidos utilizando o método de prensagem e quente, em diferentes proporções em massa (m%). Também será apresentada a proporção calculada a partir da quantidade de BN utilizada (phr) e a técnica usada para a incorporação dos agentes de vulcanização, realizadas para vulcanizar a BN presente na mistura. Os compósitos, que no presente trabalho serão denominados BN/Couro, foram caracterizados utilizando as técnicas de análises de propriedades mecânicas, análises morfológicas, análises estruturais e análises térmicas. Os resultados obtidos foram comparados em função das propriedades físicas dos compósitos com as do couro utilizado comercialmente, com objetivo de se efetuar um direcionamento para uma possível aplicação industrial e comercial dos compósitos. De acordo com os resultados constatou-se que o material apresenta baixa capacidade de deformação, causada pela vulcanização realizada na BN e também pelas partículas de couro. Notou-se também que os compósitos apresentam bom grau de impermeabilidade e desgaste, quando comparado ao couro sola utilizado comercialmente, sendo averiguado que esta propriedades são relacionadas à proporção de BN presente na mistura, que por sua vez atua como agente encapsulador do couro, tornando-se predominante no material produzido. O que investigou o desenvolvimento deste trabalho foi a pretensão de obter um material de baixo custo, pois será produzido a partir de um resíduo gerado às toneladas
Abstract: This work presents the method of preparation of composites from a mixture of natural rubber (NR) with leather waste, generated in one step in the treatment of leather in tanneries. The composites were obtained using the method of hot pressing, in different proportions by mass (wt%). Also presented the ratio calculated from the amount of NR used (phr) and the technique used for incorporation of curing agents, taken to vulcanize the NR in the mixture. The composites, which in this work will be called NR/Leather, were characterized using the techniques of analysis of mechanical properties, morphological analysis, structural analysis and thermal analysis. The results were compared on the basis of the physical properties of the composities with the leather used commercially, with the objective to make a direction for a possible industrial application and commercial composites. According to the results found that the material has a low capacity for deformation caused by vulcanization perfomed in NR and also by the particles of leather. It was also noted that the composites exihibit a good degree of impermeability and wear when compared to leather soles used commercially, and ascertained that these properties are related to the proportion of BN in the mixture, which in turn acts as an agent wrapper of leather making is predominant in the material produced. What prompted the development of this work was the intention of obtaining a low cost material, which be produced from a waste generated by the ton
Mestre

Great interest was recently devoted to the use of inorganic particles as a reinforcing filler in tires for the automotive industry. In fact,the reinforcing of elastomers by the addition of these fillers affects the stiffness, strength, elongation at break, fracture toughness, energy dissipation (rolling resistance), friction to ice or wet grip, wear (abrasion resistance)and on the material processability. Therefore, the technology improvement of tires currently has to satisfy the requirements of sustainable development in order to reduce fuel consumption, environmental pollution and acoustic noise. Carbon black has been the only additive used for this purpose for a long time but silica is now becoming the alternative reinforcing filler; as it offers a lot of advantages, such as better rolling resistance and reduction of the heat buildup; moreover, it can be suitably employed in all cases where the black color is not required. Natural rubber-silica (NR-SiO2) composites are usually prepared by mechanical mixing. Unfortunately, silica particles have a strong tendency to interact with each other within the elastomeric matrix, favoring the inhomogeneous dispersion due to particle tendency to agglomerate and in principle to reduce the filler-rubber interaction. Significant contributions to overcome the disadvantages derived from filler-filler interaction of the silica particles; they are obtainable by enhancing the filler-rubber interaction, which causes additional cross-linking in the rubber structure. The enhancement of filler-rubber interaction is obtained by the use of coupling agents which interact with both the polymer (hydrophobic) and the silica(hydrophilic) surface groups,due to the presence of different functionalities at the ends of the molecules. An alternative approach and object of the present Ph.D thesis,is to prepare composites by in situ formation of the silica filler particles by sol-gel hydrolysis and condensation of tetraethoxysilane(TEOS. Therefore,the aim of this work is to prepare silica-natural rubber (NR-SiO2) composites, with the intention of improving the properties which normally the compound, prepared by mechanical blending possesses. Several factors like nature of the solvent, nature of the catalyst, medium pH, molar ratio between alkoxysilane and water or solvent, gelling and drying temperatures are fundamental sol-gel parameters which can modify the process of the nanocomposite preparation in order to optimize the better homogeneity of the filler distribution inside the rubber matrix. Therefore, considering the filler particle growth in situ in the polymeric matrix, it is possible to distinguish two possible preparation techniques which differ in some of the factors affecting the sol-gel process: aqueous and non-aqueous in situ sol-gel methods. In addition to these factors that influence the preparation of the composite, the amount of the filler present in the silica-rubber composite affects the final performance. In fact, the enhancement in mechanical properties can be achieved when the composite contains the optimal amount of the filler required to form a continuous filler network within the rubber matrix; filler amounts less of this percolation threshold show mostly constant and poor mechanical properties. The presence of a continuous filler network and its homogeneity depends on the filler characteristics, such as size and shape of the particles and on the in situ composite preparation method used. The formation of a convenient filler network is in turn relatable to the physical and chemical interactions among the particles and among their aggregates (filler-filler interaction) and to the chemical and physical interactions between the particles and the matrix (filler-rubber interaction). The presence of functional groups on the particle surface can significantly influence the interface between the filler particles and the rubber matrix; consequently, modifying the filler-filler and filler-rubber interaction leads to the variation of the reinforcement level of the composites. With the intention to investigate and to rationalize the effects induced by surface functionalization of the filler on the properties of rubber composites, during the aqueous sol-gel synthesis of the silica the surface was functionalized by using trialkoxysilane having different functional groups. These functionalities were selected among those which are suitable for promoting the formation of differently shaped silica particles or for modulating the filler-filler and the filler-rubber interactions. Silica particles were modified by molecules containing alkylthiol, thiocarboxylate, alkyldisulfide, alkyltetrasulfide (silica functionalized with containing S groups); vinyl, propyl, octyl chains, alkylamine, alkylcyanate and alkylisocyanate groups (silica functionalized with containing N groups). For this purpose a mixture of TEOS and TMSPM ((3-mercaptopropy)trimethoxysilane) or TESPD (bis(3-triethoxysilylpropyl)disulfide) or TESPT (bis(3-triethoxysilylpropyl) tetrasulfide) or NXT (3-octanoylthio-1propyltriethoxy) or VTEOS (vinyltriethoxysilane) or PTEOS (triethoxy(propyl)silane) or OCTEOS (triethoxy(octyl)silane) or APTEOS ((3-aminopropyl)triethoxysilane) or CPTEOS (3-cyanopropyltriethoxysilane) or ICPTEOS (3-(triethoxysilyl)propylisocyanate) were introduced in NR latex (containing 60 % dry rubber, 39.3 % of water and 0.7% of NH3) during the aqueous sol-gel process. The functionalized molecules were selected with the aim of promoting the formation of different shapes on silica particles (anisotropic or spherical), moreover of modifying the filler-filler and filler-rubber interaction through the chemical functionalities of substituents. In the aqueous in situ sol-gel method, the presence of large amounts of water helps the silica precursors to react quickly in the early stage of the synthesis in rubber matrix, allowing thus to increase the hydroxyl group numbers on particle surfaces, making them less compatible with the rubber and in this way favoring particle aggregation. Through the non aqueous in situ sol gel method, the oxygen present in silica nanoparticles is provided by a suitable reaction and not, as in the aqueous in situ sol gel method, by the water solvent. During this method, the addition of two simple solvents on the metal oxide precursor can generate water in situ that can start sol-gel hydrolysis and condensation reactions. In order to work in an environment without the presence of the water as initial reactant, the silica-rubber composite by the non-aqueous in situ sol-gel method was prepared starting from a solution of dry NR with toluene (inert solvent) and TEOS, which was added to formic acid and alcohol (ethanol of benzylalcohol). Therefore, well defined amounts of water were formed through the esterification reaction produced by formic acid and alcohol, which control the formation of metal oxide growth within the rubber matrix. Moreover, in order to understand better the morphology of the silica particle growth in NR through the in situ sol-gel method, bare silica and functionalized silica powders were prepared by using the same method without the rubber. These powders were morphologically characterized with the intention of more easily evaluating the shape, the size, the surface area, the effect of the metal oxide precursor and the modification of the silica surface. Regarding the composites, the amount of silica was determined by thermogravimetric analysis(TGA) in air. The stability and the reactivity of the functional groups and the hydrolysis rate of the alkoxy groups of the trialkoxysilanes in the early stage of the sol-gel reaction were evaluated by ATR-FTIR. The homogeneity of the particle dispersion, the dimension and shape of silica aggregates were investigated by SEM and TEM, to draw appropriate relations between the filler morphology and the reinforcement of the elastomeric network. The efficacy of the filler network in reinforcing the rubber matrix was assessed by swelling measurements. The Electron Spin Resonance(ESR) behavior of nitroxide radical, introduced as spin probe in order to check the rigidity of the rubber chains, was also investigated. The static and dynamic-mechanical properties of the nanocomposites, both uncured and vulcanized, were investigated and discussed referring to the network morphology, allowing to suggest a connection between the silica precursors used and the functional properties and the amount of the filler. The vulcanization kinetics was also studied, as well as the homogeneity of the dispersion of the filler and the rubber networks. Hardness, abrasion resistance, tensile analysis and compression set results of vulcanized composites were discussed taking into account the structural, morphological and mechanical characteristics determined before. Silica-natural rubber composites for tire applications with a controlled composition and morphology was obtained by in situ sol-gel method and compared with conventional mechanical blending prepared by using silica Rhodia and dried NR. Regarding the in situ sol-gel method of nanocomposite preparation, two different synthetic approaches were carried out by starting from the same silica precursor: aqueous and non aqueous methods. Deep investigation on the relationship between composition, size and morphology of the silica particles, dispersion network degree and dynamic mechanical behavior of uncured composites allowed to rationalize the final performance of the cured composites. In fact, the efficacy of silica filler to improve the mechanical properties of the tires for the automotive industry is related both to the interaction among the silica particles and aggregates (filler-filler interaction) and to their capability to interact with the rubber matrix (filler-rubber interaction). Therefore, the characteristics of the silica such as shape, size, surface area, nature of the surface (OH group, functional molecules and amount), degree of aggregation lead to modify the nature of the interface with the rubber and also the homogenous distribution of the filler network. The obtained results for aqueous in situ sol-gel silica-natural rubber preparation led to the following conclusions: - The aqueous sol-gel method is a promising procedure to prepare nanocomposites from silica precursor TEOS mixed to trialkoxisilanes having different functional groups when the filler precursor doesn’t react quickly through hydrolysis and condensation reactions in water environment and allow to control the filler-filler and filler-rubber interactions. - The functional groups from different substituted silicon alkoxide precursors promote during the sol-gel process the formation of different silica particle shapes and modify the filler-filler and filler-rubber interaction.In particular,the precursor functionalities induced the formation of anisotropic shaped silica particles, unlike the spherical ones derived from TEOS. - Different precursors give rise to particle networks with different degrees of continuity, depending on physical and chemical properties of particles they originate. Spherical or slightly anisotropic particles with homogeneous size show the best self assembling behavior and form continuous networks. When particles contain surface groups able to interact with each other (e.g. hydroxyl, amino and thiol groups), the formation of chemical bonds makes the filler-filler interaction stronger along the network. - The network continuity within the composite is the main prerequisite to obtain strong rubber reinforcement. Not homogeneous distribution of the filler and irregular segregation of particles induce large voids in the network, lowering the dynamic-mechanical properties. However, it appears that a strong chemical interaction among particles can balance the absence of a fully continuous network, preserving high storage modulus. This is the case of the network in NR-TMSPM, where the thiol functionality assists the bonding interaction. On the contrary, the large voids observed in the network of NR-OCTEOS are not compensated by bonding interactions among particles, which are absent or very weak due to the presence of the surface alkyl groups. - The different filler-rubber interaction due to substituents able to chemically interact with the polymer, promotes the homogeneous distribution of the filler particles even if its contribution to the reinforcement properties is less effective than that to the filler-filler interaction. Thus filler-filler interaction governs the dynamic-mechanical properties of silica rubber composites either through the shape induced physical interactions responsible for the network formation, or by the chemical interaction among particle surface groups. - To sum up when a choice among different functionalized silica is required, the suggestion is to look for well assembled and continuous filler networks, eventually assisted by chemical interaction among particles. The second condition seems very important, in fact in the case of NXT network, the homogeneous particle distribution is not sufficient to guarantee strength; instead the dynamic-mechanic behavior of NR-NXT is enhanced after thermal treatment which allows the sulphur-rubber interaction. - Regarding the properties of the vulcanized composites, it is evident that the preparation of the silica in situ improve the rigidity, the hardness, the tensile strength and reduce the dissipation of the energy, which means an improvement in rolling resistance. The obtained results for non-aqueous in situ sol-gel silica-natural rubber preparation led the following conclusions: -The non-aqueous in situ sol-gel synthesis is a procedure to prepare nanocomposites allowing the in situ growth of small particles in rubber matrix in the absence of large amount of water. In addition, due to the slow hydrolysis and condensation reaction rate of the precursors it possible to control at molecular level the growth of the metal oxide particles and therefore the filler-filler interaction and the dispersion in rubber matrix. - Non-aqueous in situ sol-gel silica-natural rubber nanocomposites were prepared by in situ esterification reaction between formic acid and ethylalcohol or benzylalcohol which produce controlled amount of water for the hydrolysis and condensation reaction. Therefore inside the dried NR it is possible to growth high amount of silica particles well distributed in a network were the particles are less aggregated and show lower filler-filler interaction in comparison with the composite prepared by conventional blending route. - Silica-natural rubber composites were obtained containing large amount of well dispersed silica (75 phr or 43% wt) without using coupling agents. -The nature of the alcohol involved in the esterification reaction influences the shape and the size of the silica prepared in swollen natural rubber. Silica particles produced in ethanol environment are bigger than those produced in presence of benzylalcohol, and create an effective reinforcement of the rubber when their amount is higher than 60 phr (37% wt). In spite of the different particle dimensions, silica produced from the two different routes are equally highly dispersed in the rubber matrix, due to the lower hydrophilicity of the surface, and a large amount of filler is required to form an efficient silica network able to reinforce the composite. -This behavior, peculiar of silica particles prepared by non aqueous in situ method, confirm that even if a homogeneous distribution of the particles in the matrix is required to obtain an efficient and strong reinforcement of the rubber, highly separated particles with low filler-filler interaction hinder an efficient filler network. On the other side the non aqueous synthesis allows to load a large amount of silica in the rubber, which could not be loaded with the traditional blending method without using a compatibilizer or disperdent agent.

Le caoutchouc naturel (CN) isolé de l'hévéa brésiliens et renforcé par différents pourcentages de nano-renforts de cellulose a été caractérisé en utilisant les techniques suivantes: la Calorimétrique Différentielle à Balayage, la Spectroscopie Diélectrique et enfin la Spectroscopie vibrationnelle (Infrarouge et Raman). L'objectif était la compréhension de l'impact des nano-renforts cellulosiques à différentes formes et fractions massiques sur les propriétés diélectriques, thermiques et vibrationnelles des matériaux de l’étude. L'ensemble des résultats obtenus nous a permis d’élucider la qualité des interfaces des différents composites étudiés et surtout de prévoir le matériau ayant les meilleures performances pour les applications mécaniques
Natural rubber isolated from Hevea Brasiliens and reinforced with different percentages of cellulose nano-reinforcements was investigated using three characterization techniques: Differential Scanning Calorimetry analysis, Dielectric Spectroscopy and finally Infrared and Raman Spectroscopy. The aim of the research is to understand the impact of cellulosic nano-reinforcements with different shapes and mass fractions in order to choose the nano-composite with high performance for mechanical applications

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho visa à obtenção e caracterização de tecidos e compósitos condutores de eletricidade obtidos a partir de borracha natural e tecidos de algodão tratados com polianilina (PANI). Os tecidos condutores de eletricidade foram obtidos introduzindo-se amostras do tecido de algodão no meio reacional da síntese química convencional da PANI. Este tecido, tratado com PANI, também foi recoberto com borracha natural e submetido à prensagem a quente, formando o compósito polimérico denominado BN/TC. Esse recobrimento protege o tecido condutor de agentes externos que podem danificá-lo (por exemplo, a exposição em meios básicos) provocando uma diminuição na condutividade elétrica. Para a caracterização dos materiais e amostras foram utilizadas as técnicas de análise termogravimétrica (TG), calorimetria exploratória diferencial (DSC), espectroscopia no infravermelho (FTIR) e microscopia eletrônica de varredura (MEV), análise dinâmico-mecânica (DMA), ensaio mecânico (tensão x deformação) e medidas elétricas. Os tecidos de algodão tratados com PANI apresentaram boa condutividade elétrica...
This work aims to prepare and characterize electrically conductive cotton and composites obtained from natural rubber and cotton fabric treated with polyaniline (PANI). The conductive composite was produced introducing cotton fabric samples in the solution of the conventional PANI chamical synthesis. The fabric treated with PANI (CF), was also covered with natural rubber and submitted to a pressure under heating during a short time, forming a composite denominated as NR/CF. Rubber coating protects the conductive fabric from external agents such as an alkaline media impeding the electric conductivity of the fabric to decrease. The characterization of the samples was made using the following techniques: thermogravimetry (TG), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electronic microscopy (SEM), dynamic-mechanical analysis (DMA), mechanic test (stress x strain) and electric conduction measurements. The treated cotton fabric show a uniform deposition of the PANI and presents a good electric conductivity... (Complete abstract click electronic access below)

Orientador: Aldo Eloizo Job
Banca: José Alberto Giacometti
Banca: José Antonio Malmonge
Banca: Marystela Ferreira
O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: Este trabalho visa à obtenção e caracterização de tecidos e compósitos condutores de eletricidade obtidos a partir de borracha natural e tecidos de algodão tratados com polianilina (PANI). Os tecidos condutores de eletricidade foram obtidos introduzindo-se amostras do tecido de algodão no meio reacional da síntese química convencional da PANI. Este tecido, tratado com PANI, também foi recoberto com borracha natural e submetido à prensagem a quente, formando o compósito polimérico denominado BN/TC. Esse recobrimento protege o tecido condutor de agentes externos que podem danificá-lo (por exemplo, a exposição em meios básicos) provocando uma diminuição na condutividade elétrica. Para a caracterização dos materiais e amostras foram utilizadas as técnicas de análise termogravimétrica (TG), calorimetria exploratória diferencial (DSC), espectroscopia no infravermelho (FTIR) e microscopia eletrônica de varredura (MEV), análise dinâmico-mecânica (DMA), ensaio mecânico (tensão x deformação) e medidas elétricas. Os tecidos de algodão tratados com PANI apresentaram boa condutividade elétrica... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work aims to prepare and characterize electrically conductive cotton and composites obtained from natural rubber and cotton fabric treated with polyaniline (PANI). The conductive composite was produced introducing cotton fabric samples in the solution of the conventional PANI chamical synthesis. The fabric treated with PANI (CF), was also covered with natural rubber and submitted to a pressure under heating during a short time, forming a composite denominated as NR/CF. Rubber coating protects the conductive fabric from external agents such as an alkaline media impeding the electric conductivity of the fabric to decrease. The characterization of the samples was made using the following techniques: thermogravimetry (TG), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electronic microscopy (SEM), dynamic-mechanical analysis (DMA), mechanic test (stress x strain) and electric conduction measurements. The treated cotton fabric show a uniform deposition of the PANI and presents a good electric conductivity... (Complete abstract click electronic access below)
Mestre

Une suspension aqueuse de nanocristaux d'amidon de maïs cireux est obtenue par hydrolyse acide de grains d'amidon (longueur:40-60nm, largeur:15-30nm, épaisseur:5-7nm). Le premier objectif de la thèse est l'optimisation de la préparation de ces nanocristaux par la mise en place d'un plan d'expériences. Leur structure moléculaire est ensuite étudiée par dégradation enzymatique, et leur modification chimique de surface est envisagée. Le deuxième objectif est l'utilisation de ces nanocristaux comme charge de renfort dans une matrice polymère. Deux polymères naturels ont été choisis: le latex de caoutchouc naturel et l'amidon thermopalstique. Les nanocomposites, mis en oeuvre par casting, sont caractérisés en termes de propriétés morphologiques, structurales, barrière et mécaniques.

L’objectif de ce travail est de préparer des polymères composites antimicrobiens, utilisant de l’acide polylactique (PLA) et/ou du caoutchouc naturel époxydé et incluant des particules d’argent insérées dans des matrices zéolites (AgZ), agissant en tant que composé actif. Un des verrous contrôlant l’activité antibactérienne des matériaux synthétisés est relié à l’étude de l’absorption de l’eau. En effet la mise en œuvre de composites PLA antibactériens rencontre le problème du caractère faiblement hydrophile de PLA, induisant une faible efficacité antimicrobienne. Ainsi afin d’amplifier l’activité antibactérienne des composites AgZ/PLA, une solution prometteuse consiste à introduire un second polymère hautement polaire et flexible. Le caoutchouc naturel époxydé a été ainsi sélectionné pour être associé au composite AgZ/PLA et le taux d’absorption d’eau mesuré témoigne d’un accroissement notable. La morphologie et la distribution des particules AgZ a été étudiée. L’accroissement remarquable du caractère antibactérien des composites ENR/AgZ/PLA a été démontré ; ainsi des tests menés sur S. aureus montrent que la croissance bactérienne a été inhibée à hauteur de 98-99%. L’étude a aussi été menée en fonction de la proportion de caoutchouc et des particules AgZ. De plus les composites ENR/AgZ/PLA possèdent une plus haute résistance à l’impact comparés à l’emploi de PLA pur, suggérant ainsi que ces nouveaux composites pourront constituer des matériaux de choix pour des applications à la fois antibactériennes et nécessitant une résistance à l’impact forte
The aim of this work is to prepare antibacterial polymers composites, involving especially poly(lactic acid) (PLA) and epoxidized natural rubber (ENR) in the presence of silver-substituted zeolites (AgZ) as an active ingredient. Herein, the key to control the antibacterial activity of the composites which is the water absorption characteristic was thoroughly studied. In general, the fabrication of antibacterial PLA composites encounters with the problem relating to the poor hydrophilicity of PLA which is the cause of antibacterial ineffectiveness. To enhance the antibacterial activity of the composites, blending with the second polymer having high polarity and flexibility is a promising way to produce the antibacterial AgZ/PLA composite. Herein, epoxidized natural rubber (ENR) was selected to blend with AgZ/PLA composites and the increase in the water absorption percentage could be observed. The morphology as well as the AgZ distribution in the composites were also investigated. The remarkable enhancement of antibacterial activity of ENR/AgZ/PLA composites was observed because more than 98-99% inhibition of S. aureus growth was found. Furthermore, the effects of rubber content and amount of AgZ on the antibacterial activity of the composites were investigated. Moreover, the ENR/AgZ/PLA composites possessed the higher impact resistance compared to neat PLA, suggesting that the improved composites might be a choice in applications at which both antibacterial activity and impact resistance property are of great importance

Ce manuscrit présente la synthèse de nouveaux matériaux élastomères dérivés du caoutchouc naturel et de monomères organiques possédant des propriétés antifouling et/ou antibactériennes, liés de manière covalente au réseau polymère. Des monomères acrylates originaux comportant un groupement bioactif (un groupe guanidinium ou des dérivés de l'acide Zostérique) ont été synthétisés et co-polymérisés avec des oligomères acrylates téléchéliques. Aucun relargage significatif des monomères bioactifs n’'a eu lieu après immersion dans l'eau. Les films auto-portés synthétisés uniquement à partir des oligoisoprènes de type acrylate ont montré une faible activité antibactérienne qui a pu être drastiquement améliorée en intégrant aux films des monomères bioactifs. Les revêtements se sont montrés actifs contre plusieurs souches de bactéries pathogènes, parmi lesquelles P.aeruginosa, S.aureus, Bacillus subtilis et S.epidermidis. Afin de greffer de manière covalente des brosses d'oligoisoprène sur des surfaces, de nouveaux oligoisoprènes bifonctionnels comportant un groupe terminal alkoxy-silane ont été préparés puis couplés avec des matériaux à base de silicium. Une autre approche a également été étudiée, consistant à pré-fonctionnaliser la surface avec des groupements amino puis à partir de ces fonctions à greffer des oligomères ayant des extrémités carbonylés. La post-polymérisation à partir des extrémités de chaîne libres à la surface a donné un revêtement épais d’'oligoisoprène offrant une forte résistance à l'immersion dans des solvants (eau, THF). De cette manière, nous avons pu accéder à des couches moléculaires denses et liées, à des films minces et à des revêtements épais
This manuscript presents the synthesis of new elastomeric materials based on natural rubber derived building blocks and organic monomers having antifouling and/or antibacterial properties, covalently bound to the polymer network. Original acrylate monomers bearing an organic bioactive moiety (a Guanidinium group or Zosteric acid derivates) were synthesized and co-polymerized with telechelic acrylate oligomers from polyisoprene. No significant leaching of the bioactive monomers occurred and the material resisted to long water immersions. Freestanding films prepared from acrylate oligoisoprenes also showed a weak antibiofouling activity which was drastically increased by integrating the guanidinium and the Zosteric acid monomers. The coatings were active against several strains of pathogenic bacteria among which Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Staphylococcus epidermidis. In order to covalently graft oligoisoprenes to surfaces, new bifunctional oligoisoprenes bearing an alkoxy-silane end moiety were designed and coupled with silicon-containing materials. An alternative approach was followed by prefunctionalizing the surface with amino groups and by covalently grafting oligomers with carbonyl chain-ends. Post-polymerization from the surface free chain-ends resulted in a thick oligoisoprene coating with strong resistance to solvent immersion (water, THF). In this way, we were able to build dense and tethered molecular layers, thin films and thick coatings

This work, conceived as a second step in the development of high-performance damping materials suitable for seismic application, describes the preparation and characterization of complex natural rubber-based composites containing hybrid nano- and conventional fillers. The cluster–cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. The same model was used to understand the mechanisms of energy dissipation. The damping coefficient was found to be in the sought range between 10% and 20% (at 0.5 Hz and high shear strain).

Au cours des dernières années, le développement de matériaux composites avancés fabriqués à partir de fibres naturelles a été principalement axé sur l'obtention de matériaux à haut module et à haute résistance. Cependant, la résistance élevée n'est pas suffisante, car certains des matériaux possèdent une nature fragile (l'allongement à la rupture est faible), et l'un des critères de performance les plus importants devrait être la capacité à absorber l'énergie et à résister aux chocs. La manière dont un matériau composite se déforme et subit des endommagements dépend à la fois des propriétés chimiques et mécaniques de trois constituants de base : les fibres, la matrice et une fine région d'interphase (parfois appelée interface) chargée d'assurer le lien entre matrice et fibre. En raison de leurs propriétés uniques et de leur nature abondante, les fibres à base de cellulose émergent comme un choix privilégié pour les communautés scientifiques, techniques et commerciales qui recherchaient des matériaux durables dans diverses applications. Bien que ces fibres possèdent plusieurs avantages par rapport aux charges synthétiques, l'adhérence entre la fibre et la matrice, la sensibilité à l'humidité et les propriétés au feu restent des domaines difficiles à traiter. Dans ce contexte, une nouvelle technique basée sur la méthode par pulvérisation-séchage-durcissement a permis de fabriquer un revêtement sol-gel hydrophobe sur la surface de la fibre de coco lignocellulosique. La modification de surface des fibres de coco a été effectuée à l'aide d'un plasma oxygène à basse pression suivi d'un enduit sol-gel polymérisable à sec avec un siloxane à fonction fluoroalkyle (FAS). Le prétraitement par plasma a augmenté la concentration effective du réseau FAS sur les fibres de fibre de coco dans le but de créer la surface extrêmement hydrophobe. L'efficacité du traitement plasma et du sol gel FAS sur fibre de coco a été étudiée en utilisant différentes techniques de caractérisation telles que l'analyse de l'angle de contact, l'absorption d'eau, la microscopie électronique à balayage, la microscopie à force atomique et la spectroscopie photoélectronique. Les propriétés mécaniques, morphologiques, rhéologiques et thermiques de différentes formulations de mélanges PP/EPDM ont été étudiées pour trouver la composition optimale du mélange pour la préparation de composites. Les composites résultants à base de polypropylène, d'EPDM et de fibre de coco possèdent des propriétés de résistance aux chocs élevées et des propriétés de traction et de flexion comparables. Les propriétés mécaniques, morphologiques, rhéologiques et thermiques des composites PP/EPDM/Coir ont été étudiées en détail pour examiner la stabilité des composites
In recent years, the development of advanced high performance composite materials made from natural fibers was mainly focussed on achieving high modulus and strength materials. However, the high strength is not sufficient, as some of the materials possess brittle nature (the overall elongation to fracture is small), and one of the more important performance criterion should be the ability to absorb energy and resist impact loadings. The manner in which a composite material deforms and subjected to fractures depends upon both the chemical and mechanical properties of three basic constituents: the fibers, the matrix and a fine interphase region (sometimes referred to as the interface) responsible for assuring the bond between the matrix and fiber. Due to its unique properties and abundant in nature, lignocellulose based fibers are emerging as a preferred choice for scientific, engineering and commercial communities who were looking for sustainable materials in various applications. Though these fibers possess several advantages over synthetic fillers, adhesion between the fiber and matrix, moisture repellence, flame retardant properties etc are still challenging areas to be addressed. In this context a novel technique based on spray-dry- cure method to establish a hydrophobic sol-gel coating on the lignocellulosic coir fiber surface. The surface modification of lignocellulosic coir fibers was done with the use of low-pressure oxygen plasma, followed by the application of a spray-dry-cure sol–gel coating with the water and oil repellent organic–inorganic hybrid precursor fluoroalkyl-functional siloxane (FAS), with the aim of creating the extremely hydrophobic coir fiber surface. The plasma pre-treatment increased the effective concentration of the FAS network on the lignocellulosic coir fibers. The effectiveness of plasma treatment and FAS sol gel coating on the coir fiber was studied using different characterisation techniques such as contact angle analysis, water absorption studies, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The mechanical, morphological, rheological and thermal properties of different PP/EPDM blend formulations were carried out to find out optimum blend composition for composite preparation. The resulting composites based on polypropylene, EPDM and coir possess high impact strength properties and comparable tensile and flexural properties. The mechanical, morphological, rheological and thermal properties of PP/EPDM/Coir composites were studied in detail to examine the stability of the composites

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Diariamente toneladas de resíduos industriais são gerados, os quais necessitam de estratégias de gerenciamento a fim de serem descartados ou reciclados corretamente. Por esse motivo, o reuso de resíduos orgânicos e industriais como cargas em compósitos poliméricos tem surgido como um novo campo de estudo. Nessa dissertação, demonstrou-se pela primeira vez o uso do resíduo Grits como carga natural em compósitos de borracha natural a fim de reutilizar os resíduos provenientes da indústria de celulose Kraft de eucalipto, assim como diminuir os custos de produção dos compósitos através da substituição, ainda que parcial, do carbonato de cálcio e do óxido de cálcio, cargas comerciais comumente utilizadas. Os tratamentos com Silano, Lauril sulfato de sódio, Dodigen 1611, além da correção de pH, variação da granulometria e quantidade de enxofre na formulação foram testados com a finalidade de melhorar a adesão interfacial do resíduo com a matriz polimérica, otimizar a formulação e consequentemente melhorar as propriedades mecânicas. Compósitos com 20 phr de Grits mostraram um aumento na tensão de ruptura de aproximadamente 20% comparado à borracha natural. Compósitos com 10 phr do resíduo apresentaram a maior resistência a abrasão, com 72,26 mm3 de perda por abrasão. Os compósitos foram aplicados na produção de chinelos atingindo as especificações recomendadas pelo Instituto de Ensaios e Pesquisa para a Fabricação de Calçados (PFI - Prüf- und Forschungsinstitut), Pirmasens, Alemanha. Ao compósito BN/20 phr Grits foi adicionado celulose de fibra curta de eucalipto para verificação da influência no tempo de degradação em solo. Amostras de celulose padrão, borracha natural, compósitos BN/20 phr Grits e BN/Grits/celulose foram expostos ao solo durante 180 dias para avaliação da biodegradação em solo, onde observou-se alteração na superfície das amostras após tempo de exposição. Os ensaios biológicos de toxicidade aguda e crônica não mostraram mortalidade significativa para a borracha natural e o resíduo Grits, assim como para os compósitos com boracha natural, Grits e celulose.
Daily tons of industrial residues are generated which require management strategies in order to correctly disposes or recycling. Therefore, the reuse of organic and industrial waste as fillers in polymeric composites has emerged as a distinct new field. Here, it was demonstrated for the first time the use of Grits as filler in natural rubber composites in order to reuse residues from eucalyptus cellulose Kraft industrie as well as decreasing the final cost from rubber products through calcium carbonate or calcium oxide replacement even partially. Treatments with Silane, Sodium Lauril sulfate, Dodigen 1611, besides pH correction, granulometry variation and sulfur content in the formulation were tested in order to improve the adhesion of the waste in the polymeric matrix, optimizing the formulation and consequently improving mechanical properties. The better treatment was prepared with pH correction and treatment with Dodigen 1611. Composites with 20 phr of Grits showed an increase on stress values around 20% compared to the natural rubber and, with 10 phr, presented the highest abrasion resistance of 72.26 mm3. The composites were applied on sandals production reaching the specifications recommended from Testing and Research Institute for the Manufacture of Footwear (PFI - Prüf- und Forschungsinstitut), Pirmasens, Germany. It was added eucalyptus cellulose fiber in order to verify the influence on soil degradation time. Standard cellulose, natural rubber, composites NR/20 phr Grits and NR/Grits/cellulose samples were exposed to the soil for 180 days to evaluate the soil biodegradation where it was observed a change in the surface of the samples after exposure time. Biological tests of acute and chronic toxicity showed no significant mortality for natural rubber and Grits waste, as well as composites with natural rubber, Grits and cellulose fiber.

碩士
國立屏東科技大學
機械工程系所
95
Because of the unique mechanical and electrical properties, carbon nanotube is considered a desirable reinforcement in composite materials. Recently, there are many researches on the polymer/carbon nanotube composite materials, such as PU/carbon nanotube composites, Rubber/carbon nanotube composites, etc. The main objective is to promote mechanical and electrical properties of polymer composite. The purpose of this thesis is to study isolation characteristic on MWCNT/Natural rubber composite. First, Taguchi Method is used to aim at MWCNT/Natural rubber composite to obtain the robust optimal parameters of dispersion processing. Second, Narrow bandwidth and octave bandwidth spectrum Analysis are used to syudy isolation characteristic on MWCNT/Natural rubber composite isolator in various frequencies. Finally, the finite element analysis (FEA) and experimental modal analysis (EMA) are to perform model verification for MWCNT/Natural rubber composite isolator, and to obtain modal parameters, such as natural frequency and mode shape.

Ballistic fabrics made from high performance polymeric fibers such as Kevlar®, Twaron® and Spectra® fibers and composites utilizing these fabrics are among the leading materials for modern body armor systems. Polymeric fibers used to produce ballistic fabrics often behave viscoelastically and exhibit time- and rate-dependent stress-strain relations. This necessitates the study of the constitutive behavior of composites filled by ballistic fabrics. Rheological models based on discrete rheological components (including spring and dashpot) have been widely used to study the viscoelastic behavior of polymeric fabrics. Such rheological (or viscoelasticity) models are qualitatively useful in understanding the effects of various micro-mechanisms and molecular features on the macroscopic responses of ballistic fabrics. In the present work, the constitutive behavior of Twaron CT709® fabric/natural rubber (Twaron®/NR) composite is studied using three viscoelasticity models (i.e., a four-parameter Burgers model, a three-parameter generalized Maxwell (GMn=1) model, a five-parameter generalized Maxwell (GMn=2) model) and a newly developed para-rheological model. The new model utilizes a three-parameter element to represent the Twaron® fabric and the affine network based molecular theory of rubber elasticity to account for the deformation mechanisms of the NR constituent. The uniaxial stress-strain relation of the Twaron®/NR composite at two constant strain rates is experimentally determined. The values of the parameters involved in all the models are extracted from the experimental data obtained in this study. The stress-relaxation response (under a uniaxial constant strain) and the creep deformation (under a uniaxial constant stress) of the composite are also experimentally measured. The three viscoelasticity models considered here are capable of predicting the viscoelastic constitutive behavior of the composite with different levels of accuracy. The stress-strain relation at each strain rate predicted by the newly developed para-rheological model is seen to be in good agreement with the measured stress-strain curve over the entire strain range studied. It is shown that the new model also predicts the elastic moduli and ultimate stress of the Twaron®/NR composite well. All the four models are found to predict the initial relaxation response of the composite fairly well, while the long-term stress relaxation is more accurately represented by the para-rheological model. An implicit solution provided by the para-rheological model is shown to predict the creep response of the composite more accurately than all the other models at both the primary and secondary stages. The mathematical complexity that arises from including an additional Maxwell element to the GMn=1 model to obtain the GMn=2 model with enhanced predictability is traded with the use of simple characteristic time functions in the para-rheological model. These functions are found to greatly improve the predictability of the newly developed model for the stress relaxation modulus and creep compliance. This study also explores the utility of the para-rheological model as a tool to probe the micromechanisms and molecular features that are causally related to the macroscopically observed viscoelastic behavior of the composite. The relaxation and creep trends predicted by the para-rheological model indicate that the long time viscoelastic response of the composite lies between that of a crosslinked polymer and a semi-crystalline thermoplastic.

碩士
國立屏東科技大學
機械工程系所
95
Since the carbon nanotubes (CNTs) were discovered by Iijima, researchers used CNTs as reinforcement to enhance the mechanical properties of plastic or ceramic matrices. But the dispersion and the interfacial bonding force of carbon nanotubes are considered as the main influences of carbon nanotubes-reinforced composites material factor. Therefore, the study of dispersion processing for MWCNT/NR composite is very importance research issue. The purpose of this thesis is aim at MWCNT/NR composite to obtain the robust optimal parameters of dispersion processing by Taguchi Method. In the meantime, the damping ratio, resistance, impedance with conductivity of different wt.% percentage of MWCNT content composite, are studied in detail. The finite element analysis (FEA) and experimental modal analysis (EMA) are to perform model verification for MWCNT/NR composite fixed-fixed beam, and to obtain modal parameters, such as natural frequency and mode shape. Finally, the scanning electron microscope (SEM) is used to observe the dispersion condition of MWCNT/NR composite.

Ένας συναρπαστικός τομέας της σύγχρονης έρευνας είναι αυτός των νάνο-συνθέτων υλικών. Το πεδίο αυτό περιλαμβάνει τη μελέτη πολυφασικών υλικών, στα οποία μία ή περισσότερες από τις χωρικές διαστάσεις κάποιας φάσης βρίσκεται στην περιοχή των νανομέτρων (1 nm = 10-9 m = 10 ). Αυτό που ξεχωρίζει τα νανοσύνθετα από τα άλλα συμβατά σύνθετα υλικά είναι η ικανότητα τους να συνδυάζουν ιδιότητες, οι οποίες είναι απαγορευτικές για τα παραδοσιακά υλικά, αλλά και η μεγάλη λειτουργικότητα που παρουσιάζουν. Η εισαγωγή των νάνο-σύνθετων υλικών και οι πολλές επιστημονικές μελέτες που έγιναν τα τελευταία χρόνια στόχευαν και προσδοκούσαν σε μία δραματική βελτίωση των μηχανικών ιδιοτήτων, πράγμα που πολλές φορές δεν επαληθεύθηκε. Τα νάνο-σύνθετα πολυμερικής μήτρας των οποίων η θερμομηχανική συμπεριφορά μελετήθηκε περισσότερο είναι τα συστήματα που περιέχουν ως εγκλείσματα νάνο-σωλήνες άνθρακα (carbon nanotubes), νάνο-σωματίδια αλούμινας και στρωματικά άλατα πυριτίου (layered silicates). Στις μέρες μας υπάρχει ένα αυξανόμενο ενδιαφέρον για τη μελέτη της διηλεκτρικής συμπεριφοράς και αγωγιμότητας των νάνο-σύνθετων πολυμερικής μήτρας - ανόργανων νάνο-εγκλεισμάτων. Στην παρούσα εργασία εξετάσθηκε η διηλεκτρική απόκριση των συστημάτων: (α) πολυμερικής μήτρας (polyurethane rubber, PU) και νάνο-σωματιδίων αλούμινας (alumina- boehmite), (β) πολυμερικής μήτρας (PU ή Natural Rubber, NR ή PU/NR) με στρωματικά άλατα πυριτίου (layered silicates), με παραμέτρους την περιεκτικότητα σε νανοεγκλείσματα, τη θερμοκρασία και τη συχνότητα του εφαρμοζόμενου πεδίου. Η διηλεκτρική φασματοσκοπία (Broadband Dielectric Spectroscopy) έχει αποδειχθεί ως ένα ισχυρό εργαλείο για την έρευνα της μοριακής κινητικότητας, των αλλαγών φάσεων, τους μηχανισμούς αγωγιμότητας και τα διεπιφανειακά φαινόμενα στα πολυμερή και τα σύνθετα πολυμερικά συστήματα. Η διηλεκτρική απόκριση των νάνο-συνθέτων εξετάστηκε με τη βοήθεια της διηλεκτρικής φασματοσκοπίας (BDS) στο εύρος συχνοτήτων 10-1-10 6 Hz και στο εύρος θερμοκρασιών από -100οC έως +70οC. Από τα πειραματικά αποτελέσματα προκύπτει πως παρατηρούνται διηλεκτρικές χαλαρώσεις που οφείλονται τόσο στην πολυμερική μήτρα, όσο και στην ενισχυτική φάση. Τέσσερις διακριτοί τρόποι χαλάρωσης καταγράφηκαν στα φάσματα των συστημάτων που μελετήθηκαν και αποδίδονται στη διεπιφανειακή πόλωση (IP) μήτρας/εγκλεισμάτων, στην υαλώδη μετάβαση (α-mode) των πολυμερών NR και PU, στην κίνηση πλευρικών πολικών ομάδων (β-mode) των αλυσίδων του PU και σε τοπικές κινήσεις εύκαμπτων τμημάτων των αλυσίδων του PU (γ–mode). Στο σύστημα πολυουρεθάνης (PU)–νάνο-σωματιδίων αλούμινας ερευνήθηκε η επίδραση του μέσου μεγέθους των σωματιδίων στην ηλεκτρική απόκριση των υλικών. Από τα αποτελέσματα φαίνεται πως η μείωση του μέσου μεγέθους των νάνο-εγκλεισμάτων οδηγεί σε αύξηση της διεπιφάνειας και των αντίστοιχων φαινομένων που τη συνοδεύει. Τέλος, από τη θερμοκρασιακή εξάρτηση της θέσεως των κορυφών διηλεκτρικών απωλειών, κάθε διεργασίας, προσδιορίστηκαν οι αντίστοιχες ενέργειες ενεργοποίησης.
The impact of nano-materials and nano-structured materials is well known in our days. Nano-composites consists an exciting modern field of scientific research. Nano-composites are multiphase materials where at least one of the dimensions of the reinforcing phase is in nano-scale. The main difference of nano-composites with compatible composites is their ability to achieve superior performance at a very low concentration of the filler. The majority of the active or potential applications of nano-systems is based on their thermo-mechanical behaviour, flame resistance and electrical properties. Under this point of view nano-composites exhibit properties or functions, which seem to be prohibited for traditional materials. Recently, there is an increased interest in studying the dielectric behaviour of polymer matrix – inorganic nano-filler composites. Polymer matrix nano-composites are expected to be useful in replacing conventional insulating materials providing tailored performance, by simply controlling the type and the concentration of nano-inclusions. In the present study is investigated the dielectric behaviour of composites consisted of a polymer matrix and inorganic nano-filler. Natural rubber (NR) and polyurethane rubber (PU) as well as their blend are used as matrices. Nano-composites were prepared by adding synthetic layered silicates (LS) via the latex compounding route. Further, the dielectric response of polyurethane rubber – alumina particles nano-composites, varying the mean particle diameter, is also examined. The dielectric properties of all systems are studied with parameters the temperature and the frequency of the applied field. Broadband Dielectric Spectroscopy (BDS) has been proved to be a powerful tool for the investigation of molecular mobility, phase changes, conductivity mechanisms and interfacial effects in polymers and complex systems. The dielectric response of nano-composites was examined by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range10-1-106 Hz and temperature interval from -100 o C to +70 o C. Experimental results include relaxation phenomena arising from both the polymeric matrix and the filler. Four distinct relaxation modes were recorded in the spectra of all systems containing PU. They were attributed to interfacial polarization, glass transition (α-relaxation), motion of polar side groups and probably motions of the (CH2)n sequence of the PU chain (β and γ-relaxation). NR is a non polar polymer and thus only its glass/rubber transition is recorded in the low temperature range. Interfacial polarization is present in all composites systems. The dielectric response of polyurethane/boehmite alumina nano-composites was examined with an additional parameter, the size of the mean boehmite particle diameter. In order of ascending relaxation rate the following modes were recorded: interfacial polarization, glass/rubber transition (α-mode), motion of polar side groups (β-mode) and re-arrangements of small parts of the PU chain (γ-mode). The intensity and the position of these relaxations appear to vary with the size of the nano-filler. Finally, the activation energies of all the recorded processes were determined via the loss peak dependence on temperature.

As the earliest applied elastomer material, natural rubber has undergone development for nearly I 00 years, and its performance has become a bottleneck. With the development of technology, industry increasingly needs higher performance natural rubber as a new generation of shock absorbing materials to improve the ride comfort of various vehicles, such as automobiles, trains, and aircraft. The performance of natural rubber is mainly related to the fillers and filling amounts used. Even though traditional fillers such as carbon black and silica have been well studied, improving the performance of natural rubber composites is difficult. This study used carbon nanomaterials as a new generation of fillers to prepare highperformance natural rubber composites. Since nanoparticles have strong van der Waals forces, carbon nanomaterials such as graphene and carbon nanotubes need to be modified before preparing the composite material so that they can be uniformly dispersed into the natural rubber matrix. This study used various modification methods, such as acidification, acyl chlorination, and ammoniation to modify the surface property of these carbon nanomaterials. After a variety of different polymers were grafted onto the nanomaterial surface, the modified carbon nanomaterials achieved good compatibility with the natural rubber matrix. Subsequently, different fillers ( carbon nanotubes, graphene, and carbon nanotubes & graphene) were mixed with natural rubber, and composites with different filling amounts were prepared by mechanical blending. The process, mechanical, fatigue and crack propagation properties of the natural rubber composites were investigated under dynamic and static conditions. The results show that only a small filling amount is required and that carbon nanomaterials have better reinforcing effects than conventional fillers, revealing that as a new rubber filler, carbon nanomaterials have superior enhancement efficiency. As the filling amount increases, the mechanical strength of the natural rubber composite material is significantly improved. However, due to factors such as hysteresis loss and tearing energy, overfilling may cause a decrease in the fatigue resistance of natural rubber composites. The experimental results show that when the loading mass ratio of carbon nanotubes to rubber is I :3, the overall performance of the natural rubber composites is optimized. For graphene, when the loading mass ratio is I: 1, the overall performance of the natural rubber composite material is optimal. This study also shows that carbon nanotubes and graphene have synergistic effects when they are simultaneously used as fillers to prepare natural rubber composites.
Thesis (MPhil) -- University of Adelaide, School of Chemical Engineering, 2018