Thesis (Ph. D.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Doctor of Philosophy / Department of Grain Science and Industry / Sajid Alavi / Poly(lactic acid) (PLA) is the most common bio-based & compostable polymer available commercially that is cost competitive and combines a range of desirable properties like melt processability, high strength and modulus. The films made from this aliphatic polyester tend to be brittle which can be overcome by blending PLA with another bio-based polymer with high flexibility poly(butylene adipate-co-terephthalate) (PBAT), but the resultant blend is only biodegradable in composting conditions. The primary focus of this study was incorporation of thermoplastic starch (TPS) in PLA/PBAT blends to increase the rate of biodegradability and decrease the cost. In the first part of this study, as a preliminary step only PLA/PBAT blends were investigated along with nanofiller nanocrystalline cellulose (NCC) as a nanofiller for enhancing mechanical and barrier properties. Melt extrusion was used for preparation of nanocomposites and 200 microns thick films were formed by melt pressing. PBAT enhanced elongation but NCC did not have any positive impact on the mechanical and barrier properties of the nanocomposites as NCC was aggregated in the polymer matrix due to the difference in polarity based on the hydrophilic nature of the nanofiller and hydrophobic nature of the polymer matrix. In the second part of study, up to 40%TPS was blended along with the PLA/PBAT/NCC nanocomposites. Joncryl (0.5%) was used as a compatibilizer. TPS addition decreased the mechanical and barrier properties (Tensile strength (TS) = 15- 30 MPa, Elongation at break (EB) = 6-12%, Water vapor permeability (WVP) = 1.6-8.3 g.mm/kPa.h.m2), although addition of NCC helped in increasing the TS and decreasing the WVP. Dispersion of NCC improved with the addition of hydrophilic TPS. Analytical techniques including transmission electron microscopy, fourier-transform infrared spectroscopy, differential scanning calorimetry were used to study the polymer-polymer and polymer-nanofiller interactions. Optimization study of PLA/PBAT/TPS/NCC nanocomposites was done using mixture response surface methods. Quadratic models with good predicted R2 (between 84.3% and 97.59%) were developed for all the responses. Optimization study was done that could yield films with optimum properties comparable to commercial plastics and maximizing the level of TPS. Films with optimum properties (TS = 29.5 MPa, EB = 12%, WVP = 1.99 g.mm/kPa.h.m2) were predicted at levels of 64.3% PLA, 14.5% PBAT, 18% TPS and 2.6% NCC along with 0.5% Joncryl. The improved mechanical and barrier performance suggested that PLA/PBAT/TPS/NCC nanocomposites have potential use in food packaging applications. In the final phase of study, mathematical modeling was used to understand the influence of nanofiller (NCC) on the mechanical and barrier properties of the nanocomposites. The modified Halpin-Tsai equation was used to model the elastic modulus of the nanocomposites, while the modified Nielsen equation was used to model the WVP as a function of nanofiller content, geometry, strength and interactions with polymer matrix. The experimental results in both cases were close to the theoretical predictions by the models. The models predicted an increase in mechanical and barrier properties with increase in aspect ratio and surface interactions of nanofiller with polymer matrix.

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

Neste trabalho foram preparados nanocompósitos de Poliestireno (PS) e argilas organofílicas. As argilas, inicialmente hidrofílicas, foram modificadas organicamente utilizando três sais quaternários de amônio diferentes: Cloreto de hexadecil trimetil amônio (CTAC), Cloreto de alquil dimetil benzil amônio (Dodigen) e Cloreto de dimetil dioctadecil amônio (Praepagen). A argila organofílica Cloisite 20A foi também utilizada neste estudo. Os nanocompósitos foram preparados por intercalação no polímero fundido por três técnicas diferentes: adição de argila em suspensão de álcool etílico por uma bomba dosadora de líquidos durante a extrusão, adição de argila em pó por um alimentador mecânico durante a extrusão e adição de suspensão de argila em álcool etílico durante obtenção por batelada. Os materiais obtidos foram caracterizados por difração de raios-X (DRX), microscopia óptica (MO) e microscopia eletrônica de transmissão (MET) e ensaios reológicos de Cisalhamento Oscilatório de Pequenas Amplitudes (COPA). As propriedades térmicas foram analisadas por análise termogravimétrica (TG) e as propriedades mecânicas foram analisadas por ensaios de tração e impacto Izod. As três técnicas se mostraram eficazes na preparação dos nanocompósitos, e seus resultados apresentaram uma similaridade muito grande. Os resultados de DRX e microscopia mostraram que a maioria dos nanocompósitos apresentou estruturas compostas de fases intercaladas e esfoliadas. As análises térmicas mostraram que a adição de argila ao PS o tornou mais estável termicamente, suportando maiores temperaturas antes de iniciar o processo de degradação. Os ensaios reológicos de COPA e ensaios mecânicos dos nanocompósitos obtidos não apresentaram grandes variações em relação ao PS puro. / In this work nanocomposites of polystyrene (PS) and organophilic clays were prepared. The clays were organically modified using three different ammonium quaternary salts: cetyltrimethyl ammonium chloride (commercial name: CTAC), alquildimethyl benzyl ammonium chloride (commercial name: Dodigen) and distearyl dimethyl ammonium chloride (commercial name: Praepagen). The organoclay Cloisite 20 A was also used in this work. The nanocomposites were prepared by melt intercalation using three different techniques: adding the organoclay as a diluted organic solvent supension to the extruder using a motor-driven metering pump, adding the organoclay as powder to the extruder using a mechanical feeder and adding the organoclay as a diluted organic solvent suspension to the mixer. The materials obtained were characterized by X-ray diffraction (XRD), optical microscopy (OM), transmission electron microscopy (TEM) and by rheological studies through small amplitude oscillatory shear tests (SAOS). The thermal properties were studied by thermogravimetrical analyses (TG) and the mechanical properties were studied by tensile and impact Izod strength tests. The three techniques were efficient to prepare nanocomposites, and their results were very similar. The DRX and microscopy results showed that the most nanocomposites presented structures composed by intercalated and exfoliated phases. The thermal analyses showed that the addition of organoclay turned PS more thermally stable, increasing their degradation temperatures. The results of rheological studies (SAOS) and the mechanical tests did not present significant variations compared to the neat PS.

L’amidon, de par son faible coût et son abondance, est un candidat de choix dans le développement de nouveaux biopolymères. Cependant, les propriétés mécaniques de l’amidon thermoplastique (TPS) étant inférieures à celles des polymères pétro-sourcés, il est très souvent mélangé à une polyoléfine (PO) résultant en un mélange incompatible dont la morphologie doit être optimisée. L’objectif de cette étude est d’améliorer la compatibilité de mélanges PO/TPS en modulant les propriétés de l’interface via l’utilisation de polyoléfines de polarité différente d’une part, et d’autre part, par l’ajout de nanocharges à l’interface du mélange. Le suivi de l’évolution de la structure des mélanges par SAXS lors d’essais de traction in situ a montré que les premiers signes de décohésion apparaissent pour des taux de déformation plus élevés lorsque le TPS est mélangé avec une PO plus polaire, indiquant l’existence d’une meilleure interface. Des nanocharges de carbonate de calcium (CaCO3) de polarité différente ont ensuite été ajoutées aux mélanges. Selon leur polarité, les CaCO3 peuvent être localisées à l’interface ou dans la phase dispersée amylacée donnant lieu à une réduction ou à une augmentation de sa taille selon la nature de la PO. L’étude du comportement mécanique a montré une augmentation des contraintes avec la PO la plus polaire indépendamment de la localisation des CaCO3 dans le mélange. Ceci met en évidence le fait qu’une compatibilisation par ajout de nanocharges ne nécessite pas uniquement de contrôler la dispersion pour les placer à l’interface du mélange, il faut également prendre en compte les propriétés intrinsèques de chaque composant. / Among the various bio-based polymers considered as potential alternative of oil-based plastics, starch appears as one of the most interesting materials due to its wide availability and low cost. However, thermoplastic starch (TPS) exhibits poor mechanical properties as compared to synthetic polymers. One strategy used to overcome this drawback consists in blending TPS with a polyolefin (PO) resulting in an incompatible blend which morphology has to be optimized. In that frame, the main objective of this work is to enhance the mechanical performances of PO/TPS blends via a modulation of the interface properties by using polyolefins with different polarity and by adding nanoparticles to compatibilize the blends. The structural evolution of the blends induced by strain has been followed in situ by SAXS and revealed that the first signs of decohesion appear at higher strain rates when the TPS is mixed with the more polar polyolefin indicating a better adhesion in this blend. Calcium carbonate nanoparticles (CaCO3) with different polarities were then added to the blends. According to their polarity, the CaCO3 were located at the interface or in the dispersed phase composed of TPS, resulting in a refinement or a coarsening of the morphology depending on the polyolefin used. The study of the mechanical behavior shows an increase in the tensile properties for the more polar PO. These observations were made regardless the localization of the CaCO3 in the blends, meaning that achieving a compatibilization with nanoparticles does not only require to control their dispersion and their localization, the intrinsic properties of the raw materials have also to be taken into account.

Lack of potable water is one of the major challenges that the world faces currently and the effects of this are mainly experienced by people in developing countries. This has therefore propelled research in advanced oxidation technologies AOTs to improve the current water treatment methods using cost effective, non toxic and efficient treatment methods. Hence, in this study the sol-gel synthesis method was used to prepare TiO2 nanoparticles that were photocatalytically active under UV and visible solar light as well as possessing antibacterial properties. Silver and nitrogen doping was carried out to extend the optical absorption of TiO2. For easy removal and reuse of the photocatalyst the nanoparticles were immobilized on chitosan and poly (vinyl-alcohol-co-ethylene) using the electrospining technique. The synthesized nanomaterials were characterized by FTIR, XRD, SEM/EDS, TEM, DRS, and TGA. FTIR and EDS analysis confirmed the formation and composition of TiO2 nanopowders for the doped and undoped nanoparticles. XRD analysis showed that the anatase phase was the dominant crystalline phase of the synthesized nanopowders. SEM and TEM respectively illustrated the distribution and size of the electrospun nanofibers and the nanoparticles of TiO2. DRS results showed that there was a significant shift in the absorption band edge and wavelength of Ag-TiO2 to 397 nm, followed by N-TiO2 at 396 nm compared to the commercial titania which was at 359 nm. The photocatalytic activities and antibacterial properties of these materials were tested on methylene blue dye and E.coli microorganism respectively. Ag-TiO2 immobilized on nanofibers of chitosan and PVAE had the highest photocatalytic activity compared to N-TiO2. Similar results were observed when the biocide properties of these materials were tested on E. coli.

This thesis reports on the structural and optical properties of laser surface structured Co nanocylinders-Al2O3 cermets on flexible Aluminium substrate for enhanced solar selective absorbers applications. More accurately, the laser surface nano-structured cermet solar absorbers developed consists of oriented metallic nano-cylinders embedded in porous refractory oxide host matrix. Relatively to the 6 existing primary configurations of selective solar absorbers, the investigated nano-composite can be considered as an additional one. This later, which could be classified between textured surfaces and cermet composites consists of non-percolated aligned tubular metallic regions (nanowires) embedded in an oxide host matrix. The methods that are commonly used to produce such nanowires in porous host matrices include electrodeposition into nanometer wide porous material/template. Molecular sieves, track-etched polymer membranes and porous anodic alumina are examples of some of this family of porous materials. The electrodeposition method has attracted much attention because the pore density of the nanowires is high, with controllable diameters in addition to the pores uniformity. In this particular study, the solar selective absorber coating designed consists of Co nanocylinders embedded into nanoporous alumina template produced by standard electrodeposition and thereafter submitted to femtosecond laser surface structuring. While their structural and chemical properties were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and atomic force microscopy, their optical characteristics were investigated by specular & diffuse reflectance. The optimized samples exhibit an elevated optical absorptance α(λ) above 98% and an emittance ε(λ) ~0.03 in the spectral range of 200-1100nm. This set of values was suggested to be related to several surface and volume phenomena such as light trapping, plasmon surface effect as well as angular dependence of light reflection induced by the ultrafast laser multi-scale structuring. The thermal stability of laser surface structured Co nanocylinders-Al2O3 cermets on flexible Aluminium substrate was investigated at temperatures of 200–600 °C. / Physics / Ph. D. (Physics)

Cellulose nanocrystals (CNCs) are an ideal reinforcing agent for polymer nanocomposites because they are lightweight, nano-sized, and have a high elastic modulus. To date, using cellulose nanocrystals in common matrices has been generally unsuccessful due to their hydrophilicity and incompatibility with hydrophobic polymers. To overcome the poor compatibility, we have grafted poly(methyl methacrylate) (PMMA) onto the surface of the nanocrystals for the first time using a one-pot, aqueous in-situ “grafting from” polymerization reaction with ceric ammonium nitrate initiator to produce poly(methyl methacrylate)-grafted-cellulose nanocrystals (PMMA-g-CNCs). We compared the compounding of CNCs and modified CNCs with PMMA using two processing methods; melt mixing and wet ball milling. We examined the morphological, mechanical and rheological behaviour of the nanocomposites and found that ball milled composites had lower mechanical and rheological performance compared to melt mixed composites for both CNCs and modified CNCs. Additionally, we found that high (>1 wt. %) loadings of CNCs had a positive effect on the performance of nanocomposites, while low loadings of CNCs and all loadings of PMMA-g-CNCs had no net effect on the performance of the nanocomposites compared to the control. The morphology of nanocomposites showed some agglomeration in the samples with CNCs, but more pronounced agglomeration in samples with PMMA-g-CNCs. This is consistent with the decreased rheological and mechanical behaviour of composites with PMMA-g-CNCs compared with CNCs. / Thesis / Master of Applied Science (MASc)

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