Cette étude s’inscrit dans le cadre de la recherche de nouvelles électrodes négatives de batteries à ions lithium ayant des capacités supérieures à celles du graphite. La synthèse de nouveaux matériaux d’électrode, constitués de nanoparticules métalliques de plomb ou d’alliage étain/antimoine déposées sur le graphite, consiste à réduire des halogénures métalliques, en présence de graphite, à l’aide d’un hydrure alcalin (NaH ou LiH) activé par un alcoolate généré in situ. Les caractéristiques structurales et morphologiques des différents systèmes graphite – métal sont ici étudiées par DRX, MET et MEB afin de mieux comprendre les mécanismes susceptibles d’intervenir lors de l’insertion de lithium. Le système graphite - plomb est étudié dans le but d’appréhender l’importance des interactions graphite - métal sur les performances électrochimiques. En effet, le caractère métallique du plomb paraît conduire à un faible ancrage des nanoparticules au support carboné et à des performances médiocres de ces matériaux comme électrodes négatives de batteries Li-ion. L’investigation systématique des composites graphite/(1-x)Sn/(x)Sb en fonction de la teneur en antimoine montre que le caractère semi-métallique de l’antimoine conduit à une amélioration des propriétés mécaniques et d’ancrage des nanoparticules de l’alliage SnSb au graphite. L’étude structurale et morphologique en fonction de la nature de l’hydrure montre que LiH comparé à NaH conduit à des composites plus homogènes, dont les particules, mieux accrochées à la surface du graphite, présentent une meilleure tenue en cyclage et des capacités massiques plus élevées. / The main propose of this work is to investigate new anode materials possessing high mass capacity and being able of replacing graphite in Li-ion batteries. Electrode materials constituted of Pb and Sn/Sb alloy nanoparticles dispersed on the graphite surface, were obtained by chemical reduction of a metal halide, in the presence of graphite, using an alkoxide - activated hydride (NaH or LiH) as a reducing agent. To collect information about the structural and the morphological characteristics of graphite-metal powders, XRD, TEM and SEM analyses were performed. These results allowed to establish a relation between the powder sample characteristics and the encountered electrochemical performances (mass capacity and cycling stability) during lithium insertion / de-insertion process. Graphite – Pb system was used as model for studying the influence of metal-graphite interactions on the electrochemical behaviour of graphite-metal compounds. The results point out to a weak interaction between Pb metal particles and the graphite surface, which seems to be the main reason for the poor electrochemical performances observed during cycling. The systematic study of graphite/(1-x)Sn/(x)Sb composites as function of Sb content appears to show that antimony semi-metallic character is responsible for SnSb pinning on the graphite surface and improvement of their electrochemical properties. Structural and morphological studies have also shown that hydride nature influences sample homogeneity, since LiH, compared to NaH, conducts to an uniform dispersion of the anchored nanoparticles on the graphite surface and to an higher mass capacity retention and stability upon cycling.

A new class of organic-inorganic hybrid nanocomposites containing well-defined polyhedral oligomeric silsesquioxane (POSS) monomers, which have been copolymerized with organic monomers, were synthesized. Poly(isobutyl methacrylate-co-butanediol dimethacrylate-co-3-methacrylylpropyl-heptaisobutyl(T8)polyhedral oligomeric silsesquioxane) (P(iBMA-co-BDMA-co-MA-POSS)) nanocomposites with different crosslink densities (BDMA loadings of 1, 3 and 5 wt%) and different MA-POSS percentages (5, 10, 15, 20 and 30 wt%) have been synthesized by radical-initiated terpolymerization. Linear P(iBMA-co-MA-POSS) copolymers were also prepared. Viscoelastic properties and morphologies were studied by DMTA (dynamic mechanical thermal analysis) and TEM (transmission electron microscopy). Two types of inorganic-organic hybrid polyhedral oligomeric silsesquioxane (POSS) / vinyl ester (VE) nanocomposites were synthesized. The first type contained a mixture of T8, T10 and T12 cages, each multifunctionalized with 3-methacrylylpropyl groups. The second type contained octa(3-methacrylylpropyldimethylsiloxyl)(T8)POSS. VE/POSS samples with weight ratios of 99/1, 97/3, 95/5, 90/10, 85/15 and 80/20 were prepared of each type. The nanocomposites were characterized by DMTA, TEM, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (X-EDS), swelling, extraction and FT-IR. Three classes of inorganic-organic hybrid phenolic resin/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were also synthesized via condensation polymerization. The POSS macromers employed included multifunctional dichloromethylsilylethylheptaisobutyl(T8)POSS, trisilanolheptaphenyl-POSS, and poly(phenylsilsesquioxane) uncured POSS. A nonfunctional octaisobutyl(T8)POSS was blended into the uncured phenolic resin followed by curing under the same conditions as those used for the other three nanocomposites classes. Phenolic/POSS samples with weight ratios of 99/1, 97/3, 95/5 and 90/10 were prepared of each type. Octaaminophenyl(T8)POSS and dodecaaminophenyl(T12)POSS were synthesized, characterized and then incorporated into two types of thermoset resins: (1) the bisphenol-F-based cyanate ester resin, PT-15, and (2) epoxy (Epon 828, Shell Chemical Corp.)/ 4,4?-diaminodiphenylmethane (DDM) resin, respectively, to make two series of nanocomposites. The sum of amino groups in both DDM and POSS were held in a 1:1 mole ratio to the epoxy groups. EPON-828/POSS/DDM (78.63/0/21.37, 77.48/5/17.52, 76.34/10/13.66, 74.05/20/5.95 and 72.28/27.72/0 wt/wt/wt compositions for both series) was prepared. PT-15/POSS composites (99/1, 97/3 and 95/5 wt/wt compositions for both types) were also prepared.

Polymer nanocomposites with organoclay fillers offer improved properties and performance, providing opportunities for commercial applications. The key to significant property enhancement is to exfoliate the individual organoclay platelets into the polymer matrix to utilize their high aspect ratio and modulus. The affinity between the polymer matrix and the organoclay is one of the most important factors for determining the exfoliation level. Although polar polymers, such as nylon 6, exfoliate the organoclay well, hydrophobic matrices, such as polyolefins, generally do not effectively exfoliate the organoclay. Thus, a significant part of this work investigates various routes to improve polyolefin-organoclay interactions and organoclay exfoliation in these systems. Nanocomposites formed from organoclay and blends of high density polyethylene and maleic anhydride-grafted high density polyethylene over the entire range of compositions were melt processed to obtain further insights into the 'compatiblizing' role of maleated polyolefins. The organoclay particle aspect ratio was found to initially increase drastically, reach a maximum, and slightly decrease with increased maleation. As the maleation level increases, the relative modulus increases initially and then levels off at higher loadings To a certain extent, the affinity between the polymer and the organoclay can be enhanced by optimizing the organoclay structure for a given polymer matrix. A silanized organoclay was investigated to determine if reduced agglomeration, improved exfoliation, and matrix reinforcement could be achieved in a polypropylene matrix without using a more costly compatibilizer. The silanized organoclay was found to be superior to the non-silanized precursor, but did not achieve the benefits obtained with a compatibilized matrix. Ionomer matrices have also been used as a means of improving organoclay exfoliation. This study examined the effects of ion type (K⁺, Na⁺), neutralization level, and melt index on the nanocomposite morphology and properties. The Na⁺ ionomers appear to have more favorable interactions with the organoclay. Exfoliation and matrix reinforcement tend to increase with decreased melt index and with increased neutralization, except at high levels. In these cases, it is possible that the additional exfoliation results in particles with lower aspect ratios. Composite properties are highly dependent on the particle aspect ratio. Several theories were used to predict the modulus and the thermal expansion coefficient of composites based on the filler aspect ratio. Novel two-population approaches were applied to enable the modeling of nanocomposites containing organoclay tactoids and single platelets, organoclay particles and glass fibers, or organoclay and elastomer particles. The quantitative agreement between the values predicted using experimentally determined particle aspect ratios and experimental modulus and thermal expansion was vastly improved using these methods. / text

The development of a "cradle-to-cradle" mindset with both material performance during utilization and end of life disposal is a critical need for both ecological and economic considerations. The main limitation to the use of the biopolymers is their mechanical properties. Reinforcements are therefore a good alternative but disposal concerns then arise. Thus the objective of this dissertation is to investigate a biopolymer nanocomposite where the filler is a synthetically prepared layer double hydroxide (inorganic interface); and a biopolymer paper (organic interface) based coating or laminate. The underlying issues driving performance are the packing density of the biopolymer and the interaction with the reinforcement. Since the polyhydroxyalkanoates or PHAs (the biopolymers used for the manufacture of the nanocomposites and coatings) are semicrystalline materials, the glass transition was investigated using dynamic mechanical analysis (DMA) and dielectric spectroscopy (DES), whereas the melt crystallization, cold crystallization and melting points were investigated using differential scanning calorimetry (DSC). Fourier transform infrared (FTIR) spectroscopy was used to estimate crystallinity in the coated material given the low thermal mass of the PHA in the PHA coating. The significant enhancement of the crystallization rate in the PHA nanocomposite was probed using DSC and polarized optical microscopy (POM) and analyzed using Avrami and Lauritzen-Hoffman models. Both composites showed a significant improvement in the mechanical performance obtained by DMA, tensile and impact testing. The degradation and decomposition of the two composites were investigated in low microbial activity soil for the cellulose paper (to slow down the degradation rate that occurs in compost) and in compost. An in-house system according to the American Society for Testing and Materials ASTM D-98 (2003) was engineered. Soil decomposition showed that PHA coating into and onto the cellulose paper can be considered to be a useful method for the assessment of the degradability of the biopolymer. PHA nanocomposite showed enhanced compostability.

The amorphous fraction of semicrystalline polymers has long been thought to be a significant contributor to creep deformation. In polyethylene (PE) nanocomposites, the semicrystalline nature of the maleated PE compatibilizer leads to a limited ability to separate the role of the PE in the nanocomposite properties. This dissertation investigates blown films of linear low-density polyethylene (LLDPE) and its nanocomposites with montmorillonite-layered silicate (MLS). Addition of an amorphous ethylene propylene copolymer grafted maleic anhydride (amEP) was utilized to enhance the interaction between the PE and the MLS. The amorphous nature of the compatibilizer was used to differentiate the effect of the different components of the nanocomposites; namely the matrix, the filler, and the compatibilizer on the overall properties. Tensile test results of the nanocomposites indicate that the addition of amEP and MLS separately and together produces a synergistic effect on the mechanical properties of the neat PE Thermal transitions were analyzed using differential scanning calorimetry (DSC) to determine if the observed improvement in mechanical properties is related to changes in crystallinity. The effect of dispersion of the MLS in the matrix was investigated by using a combination of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Mechanical measurements were correlated to the dispersion of the layered silicate particles in the matrix. The nonlinear time dependent creep of the material was analyzed by examining creep and recovery of the films with a Burger model and the Kohlrausch-Williams-Watts (KWW) relation. The effect of stress on the nonlinear behavior of the nanocomposites was investigated by analyzing creep-recovery at different stress levels. Stress-related creep constants and shift factors were determined for the material by using the Schapery nonlinear viscoelastic equation at room temperature. The effect of temperature on the tensile and creep properties of the nanocomposites was analyzed by examining tensile and creep-recovery behavior of the films at temperatures in the range of 25 to -100 oC. Within the measured temperature range, the materials showed a nonlinear temperature dependent response. The time-temperature superposition principle was successfully used to predict the long term behavior of LLDPE nanocomposites.

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No description available.

Cette étude porte sur l’élaboration de nanocomposites à matrice polypropylène (PP) chargée de montmorillonite native (NaMMT). La stratégie retenue est basée sur l’utilisation d’une phase polaire intermédiaire sous forme de mélanges maîtres, dont l’élaboration est réalisée par extrusion avec injection d’eau.Dans une première partie la dispersion de NaMMT et à titre de comparaison de montmorillonite modifiée par extrusion assistée eau dans le polyamide 6 (PA6) a été étudiée grâce à une analyse de la morphologie et de son influence sur les propriétés thermomécaniques. Par la suite, des mélanges maîtres à base de PA6 ont été élaborés par ce procédé et dispersés dans le PP via une compatibilisation réactive. L’analyse de la morphologie, en relation avec les conditions d’élaboration et les performances des mélanges nanocomposites est ensuite présentée.Dans une deuxième partie, un copolymère bloc polyether-bloc-amide (PEBA) a été utilisé comme matrice hôte de NaMMT. Sa dispersion dans le PEBA par extrusion assistée eau a été étudiée par une étude morphologique liée aux propriétés thermomécaniques et aux mécanismes de déformation. Le PEBA a ensuite été utilisé comme phase intermédiaire pour disperser NaMMT dans le PP. L’analyse de la morphologie des mélanges nanocomposites est présentée, en lien avec leurs conditions d’extrusion et leurs propriétés macroscopique.Finalement, la comparaison des résultats obtenus dans le cas des mélanges nanocomposites à base PA6 et PEBA est proposée afin de mettre en évidence le rôle de la polarité de la phase intermédiaire, de la rhéologie des constituants et des conditions de procédé sur les propriétés macroscopiques des matériaux. / This work focuses on polypropylene (PP)/clay nanocomposites based on pristine montmorillonite (NaMMT). The elaboration strategy involves the use of a polar polymer based masterbatch to disperse NaMMT in the PP matrix. Water assisted extrusion is used to finely disperse the native montmorillonite in the polar host polymer.In the first part, the dispersion of modified and pristine montmorillonite in polyamide 6 (PA6) using water assisted extrusion is presented. The morphological analysis of the PA6 nanocomposites and its outcome on the thermomechanical properties were studied. PA6 masterbatches were then elaborated using water assisted extrusion and dispersed in PP to obtain nanocomposites blends. Their morphologies are detailed, in relation with the processing conditions, and the related mechanical properties.In the second part, polyether-block-amide (PEBA) was used as host polymer to disperse modified and native montmorillonite. Their dispersion is obtained thanks to the water assisted extrusion process. The morphological analysis and its influence onto the thermomechanical properties and on the deformation mechanisms were studied. PEBA masterbatch were then prepared using water assisted extrusion and dispersed into PP to obtain nanocomposites blends. The study of their morphologies is presented, related to the extrusion conditions, and the corresponding macroscopic performances.Finally, the comparison of the results obtained in the case of PA6 and PEBA nanocomposites blends is discussed to evidence the influence of components rheology and polarity as well as the processing conditions onto the macroscopic behaviors of the materials.

This thesis aims to utilize graphene nanoplatelets (GNPs) in biobased and biodegradable thermoplastic polylactide (PLA) matrix for improved properties and multifunctionalities. A comprehensive comparative study was carried out on the effect of the addition of GNPs with different sizes. The mechanical, electrical, thermal and barrier properties of resulting PLA/GNP nanocomposites and their inter-relationship with the microstructure of the composites is revealed. The effect of annealing on dynamic percolation and conductive network formation of PLA/GNP composites including the effect of hybrid GNP fillers of different size is reported, indicating the underlying mechanisms for different behaviours of GNP fillers of different size. Multifunctional engineering biopolymers with improved performances (mechanical and electrical) and added functionalities (barrier properties) were successfully developed through controlled filler distribution and orientation using multilayer co-extrusion technology. Changes in mechanical properties of the PLA/GNP multilayer nanocomposites were successfully correlated with GNP orientation in the filled layers. Multilayer PLA/GNP nanocomposites demonstrated excellent mechanical and barrier properties with low filler loadings compared to traditional mono-extruded films.

Nesta dissertação apresentaremos os resultados do estudo da dinâmica molecular em ormolitas ligadas e dopadas com Li+, obtidos com a utilização de métodos de RMN de 13C. A análise das mudanças da anisotropia de deslocamento químico provocada por movimentos moleculares ativados termicamente foi realizada. Neste caso, foram utilizados modelos de simulação de espectros sob os efeitos de dinâmica molecular, permitindo a determinação do comportamento dos tempos de correlação em função da temperatura, e conseqüente estimativa das energias de ativação aparentes relativas às transições vítreas em amostras com diferentes dopagens de Li. Técnicas de RMN de Exchange 2D, também foram utilizadas nos estudos, permitindo determinar as amplitudes de movimentos moleculares em diferentes regiões do polímero, e conseqüentemente, estabelecer um quadro geral das reorientações moleculares neste materiais. Mais especificamente, foi mostrado diretamente que os movimentos moleculares em segmentos mais próximos das estruturas de sílica são altamente restritos, enquanto para segmentos afastados destas estruturas, a dinâmica molecular durante a transição vítrea é bastante similar a polímeros totalmente amorfos. De fato, foi observado que este comportamento ocorre somente em amostras com polímeros de maior peso molecular. Para amostras com cadeias poliméricas menores, o efeito da restrição do movimento pelas estruturas de sílica se estendem para a maioria dos segmentos moleculares do polímero. Finalmente, utilizando a técnica PUREX 1D, a distribuição de tempos de correlação do movimentos moleculares envolvidos na transição vítrea foi estimada para amostras com diferentes concentrações de Li. Neste caso, foi verificado que a distribuição de tempos de correlação é menor para amostras com maior concentração de Li / In this thesis we will present the results of study of molecular dynamics in several bonded ormolytes doped with Li+ obtained with the use of 13C NMR methods. The analysis of the chemical shift anisotropy changes caused by thermicaly-activated molecular motions was accomplished. In this case, the spectra were simulated in order to analyze the effects of molecular dynamics, allowing the determination of the time scale of the correlation times versus temperature and, consequently, estimating the apparent activation energies relative to the sample glass transitions. 2D Exchange NMR, also used in the studies, allowed determining the amplitude of molecular motions of the polymer chain and, consequently, establishing a general picture of the molecular reorientations in these heterogeneous materials. More specifically, it was directly shown that the molecular motions in segments close to the silica c1usters is highly restricted, while for segments far from the inorganic structure the molecular dynamics is quite similar the amorphous polymer in bulk. In fact, it was observed that this behavior is pronounced in samples with polymers presenting larger molecular weights. For samples with smaller polymer chains, the effect of the motion restriction due to the silica structures extends along the polymer. Finally, using the PUREX 1D technique, the distribution of correlation times of molecular motions involved in the glass transition was estimated for samples with different concentrations of Li. In this case, it was verified that the distribution of correlation times is smaller for samples with larger Li concentrations