The influence of low molecular weight additives containing polar groups and modified polyolefin-based compatibilisers on polypropylene (PP)-clay nanocomposites (PPCN) has been studied, in terms of intercalation and degree of exfoliation achievable by melt state mixing processes. PPCN were prepared by melt mixing of two commercial pp homopolymers with organically modified clay (OMMT) in the presence of maleic anhydride grafted pp (PP-MA). X-ray diffraction (XRD) analysis shows that the interlayer spacing of clay increases dramatically, whilst transmission electron microscopy (TEM) results show a significant improvement of clay dispersion in the PP matrix, when nanocomposites are prepared with commercial PP containing short chain organic additives with polar groups (amide-type slip and antistatic additives). Subsequent studies based upon customised PP formulations, with short chain amide molecules (AM), confirm the intercalation of this additive into clay galleries. The maximum interiayer spacing is achieved with low concentrations of this additive (0.5 wt. %). Contact angle measurements and low shear melt flow properties (MF!) further confirm the diffusion of this additive (AM) into the clay galleries rather than migrating away from the bulk of the PPCN. The interaction between the polar group (CONH2) of this additive and polar sites of the clay surface appears to be the driving force for the intercalation. Although this additive intercalates and allows the formation of an intercalated nanocomposite structure with non homogeneous dispersion of clay, an exfoliated PPCN structure is yet to be formed with this additive alone. A new preparation method for PPCN has therefore been developed by co-intercalation of AM and PP-MA. PPCN were prepared by this method with a significant reduction of overall PP-MA concentration in the nanocomposite structure, relative to conventional PPCN prepared with compatibiliser (PP-MA) only. XRD and TEM analysis showed that nanocomposite structures are formed with significantly improved clay dispersion, compared to PPCN prepared using the conventional method. Quantification of clay exfoliation, using image analysis software, showed that higher degrees of exfoliation can be achieved in PPCN from this new cointercalation method. Normalised melt flow index (n-MFI) data showed the relationship between low shear flow properties and clay structure and is an appropriate parameter to examine clay exfoliation and its interaction with pp in PPCN. Enhanced thennal stability of PPCN, in comparison to pure PP, further demonstrates the improved clay dispersion in nanocomposite structures prepared by the co-intercalation method. A possible mechanism for the co-intercalation of AM and PP-MA into clay galleries has been proposed, based upon hydrogen bonding between these additives and the silicate layers. Rheological characterisation of PPCN, using capillary rheometry experiments at high shear rates, shows a shear thinning, pseudoplastic behaviour similar to pure PP. However, a comparatively higher concentration of AM appears to reduce the shear viscosity of PPCN. Die swelling behaviour revealed a reduction in melt elasticity in PPCN melts in comparison to unmodified PP. Reduced die swell occurs as a result, together with a delay in the onset of melt fracture. Sheet extrusion was used to produce PPCN products with increasing clay loading levels that were evaluated for a range of mechanical properties. Significant enhancement of modulus in PPCN is achieved in comparison to pure PP whilst maintaining similar strength characteristics. However, impact resistance of extruded PPCN sheets is not improved in comparison to unmodified PP. Results have been interpreted with reference to the degree of exfoliation, additive content and differences in PP crystallinity.

Research into the processing conditions and parameters of polymeric nanocomposites has always been challenging to scientists and engineers alike. Many have developed tools and procedures to allow materials to be exploited and their properties improved with the addition of nanofillers to achieve the desired end material for various applications. Initial trials are mostly conducted using conventional small scale experiments using specialised equipment within the laboratory that can replicate the larger industrial equipment. This is a logical approach as it could save time and costs as many nanocomposites are relatively expensive to produce. Experiments have previously been done using the likes of the Haake twin screw extruder to manufacture nanocomposites within the laboratory but this research project has used a novel minimixer specifically developed to replicate mixing like large twin screw extrusion machines. The minimixer uses a twin paddle system for high shear mixing in conjunction with a single screw thus theoretically allowing an infinitely long recirculation. It is this ability to mix intensely whilst allowing for as long as desired recirculation which enables the replication in this very small mixer (10-30g capacity) of the mixing conditions in a large twin screw extruder. An added feature of the minimixer is that it can undertake inline data analysis in real time. The main experiments were conducted using a comprehensive DOE approach with several different factors being used including the temperature, screw speed, residence time, clay and compatibiliser loading and two polymer MFI's. The materials used included PP, Cloisite 20A, Polybond 3200, PET, Somasif MTE, Polyurethane 80A and Single / Multi-walled Carbon nanotubes. Detailed experimental results highlighted that rheological analysis of the nanocomposite materials as an initial testing tool were accurate in determining the Elastic and Loss modulus values together with the Creep and Recovery, Viscosity and Phase Angle properties in the molten state. This approach was also used in an additional set of experiments whereby the temperature, speed, residence time and compatibiliser were kept constant but the clay loading was increased in 1% wt. increments. These results showed that the G' & G'' values increased with clay loading. Another important finding was the bi-axial stretching step introduced after the processing stage of the nanocomposite materials which highlighted a further improvement in the modulus values using rheological testing. Other tests included using inline monitoring to look into both the viscosity and ultrasound measurements in real time of the molten polymer nanocomposite through a slit die attachment to the minimixer.

Dans un souci de réduction du volume de déchets nucléaires et de revalorisation des matières combustibles, une stratégie de gestion du combustible des réacteurs à haute température (HTR) est développée dans cette étude. La réduction de volume passe par la séparation des particules TRISO hautement radioactives et du graphite faiblement radioactif (les deux étant réunis dans un assemblage de combustible appelé "compact") tandis que le recyclage total nécessite la séparation du coeur de la particule, valorisable, et de sa gangue, déchet ultime. Les méthodes de séparation doivent préserver l'intégrité des TRISO afin d'empêcher la fuite des radioéléments. Ainsi, le traitement de choc thermique entre l'azote liquide et l'eau chaude permet une division partielle des compacts mais ne permet de récupérer que peu de particules. L'érosion du graphite par jet d'eau à haute pression présente le risque de fracturer les particules. La combustion totale du carbone libère toutes les billes. Le traitement des compacts par les ultrasons dans l'eau érode le graphite en fonction de l'intensité de travail, des direction et distance d'attaque, de la température et du gaz de saturation, nettoyant les particules. L'attaque acide des compacts par un mélange H2O2 + H2SO4 provoque l'intercalation du graphite par l'acide, faisant gonfler la structure et libérant ainsi les billes intactes. Les TRISO d'une part et leurs gangues d'autre part ont ensuite été vitrifiées par frittage de manière à obtenir une forte densité, jusqu'à un taux de 25% vol. Enfin, la lixiviation des composites dans l'eau ultrapure à 90°C montre de fortes propriétés de confinement.

Made available in DSpace on 2016-12-08T17:19:19Z (GMT). No. of bitstreams: 1 Juliana Paz.pdf: 1684316 bytes, checksum: 5c2617141f2eaa7e6d38f5e9791c52b5 (MD5) Previous issue date: 2012-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Epoxy-clay nanocomposites has been widely studied with interests in their thermal, mechanical and structural. A major breakthrough in research can be no use of solvents when the clay dispersion in epoxy resin, which reduces the environmental impact, although epoxies can not be recycled. This paper presents a study of the thermal properties (by Thermogravimetry, Differential scanning calorimetry and Dilatometry), mechanical (for traction, flexion and K1c) and structural (by Fourier Transform Infrared Microscopy and scanning electron) of epoxy-clay nanocomposites and as a rheological analysis (for viscosity) of the solutions of pre-cured composite at the moment of the load as first dispersion parameter selection of samples for later analyzes mechanical, thermal and structural characteristics. In the analyzes were chosen viscosity samples that had higher values, wherein the cured samples were used in two dispersion conditions, with and without sonication, and variations in concentration of 2, 4, 6 and 8 wt% as a means of comparison to obtain clear results improvements or not the properties of these nanocomposites, which are related to the respective condition dispersion. It is understood that nanocomposites with good dispersion is intercalated / exfoliated since the clay used in this work is called montmorillonite and has lamellar structure with nanometer thickness and large surface area, which results in an interface adhesion between clay and epoxy resin. In this, it is also observed that the condition of non-sonicated dispersion nanocomposites showed improvements in their thermal properties, but structurally the dispersion appears to be more efficient in samples sonificadas. The analysis shows improvements in their mechanical properties in samples with intermediate concentration (mainly 4 wt% clay), depending on the destination of the nanocomposite can indicate these materials for various applications, such as coatings and objects that require low chemical reactivity. / Nanocompósitos epóxi-argila vem sendo largamente estudados com interesses em suas propriedades térmicas, mecânicas e estruturais. Um grande avanço nas pesquisas pode ser a não utilização de solventes no momento da dispersão da argila na resina epóxi, o que diminui o impacto ambiental, apesar de os compostos epoxídicos não poderem ser reciclados. Este trabalho apresenta um estudo das propriedades térmicas (por Termogravimetria, Dilatometria e Calorimetria diferencial exploratória), mecânicas (por Tração, Flexão e K1c) e estruturais (por Infravermelho por Transformada de Fourier e Microscopia eletrônica de varredura) de nanocompósitos epóxi-argila, bem como uma análise reológica (por viscosidade) das soluções pré-curadas dos compósitos no momento da dispersão da carga como primeiro parâmetro de seleção das amostras para posteriores análises mecânicas, térmicas e estruturais. Nas análises de viscosidade foram escolhidas amostras que apresentavam maiores valores, na qual foram utilizadas as amostras curadas em duas condições de dispersão, com e sem sonificação e, em variações de concentração de 2, 4, 6 e 8% em massa como via de comparação para obter-se resultados claros de melhorias ou não das propriedades desses nanocompósitos, sendo estes relacionados com a respectiva condição de dispersão. Entende-se que nanocompósitos com boa dispersão são intercalados/esfoliados, uma vez que a argila utilizada neste trabalho é chamada montmorillonita e apresenta estrutura lamelar com espessura nanométrica e grande área superficial, que resulta numa interface de adesão entre argila e resina epóxi. Neste, observa-se também que a condição de dispersão não-sonificada os nanocompósitos apresentavam melhorias em suas propriedades térmicas, porém, estruturalmente a dispersão parece ser mais eficiente em amostras sonificadas. As análises mecânicas mostras melhorias em suas propriedades em amostras com concentração intermediária (principalmente 4% em massa da argila); dependendo do destino do nanocompósito pode-se indicar esses materiais para diversas aplicações, tais como revestimentos e objetos que necessitem baixa reatividade química.