Thermal degradation during composite fabrication is the main impediment for the wide use of agro-based fibers as filler and reinforcement in engineering thermoplastic composites. Different thermal, chemical and physical techniques (e.g., alkali, steam explosion and retting) aiming to increase the fiber-matrix adhesion or reduce the plant fibers water absorption have been presented in the literature. However, there have been very few attempts to solve the difficulties associated with processing engineering thermoplastics with plant fibers. Most of these attempts involved the use of additives (such as plasticizers and salts) to lower the polymers processing temperature and plant fibers with inherent higher thermal stability (such as Curaua and cellulose). Despite all these efforts, no important progress has been achieved. Therefore, to explore the full potential of wheat straw and expand its use in commercial applications, an experimental study was carried out to develop different methodologies to improve the thermal stability of wheat straw fiber. In this thesis, most attention is given to wheat straw because of the relevance and potential of entering the market as commercial filler today. It is reported here that the thermal stability and chemical composition of wheat straw do not seem to significantly vary with wheat straw type and cultivation region. For example, the main thermal degradation of wheat straw samples starts in a narrow window of temperature which goes from 220.8 to 237.8 °C and from 224.8 to 238.1 °C for air and nitrogen atmospheres, respectively. On the other hand, lignin and inorganic materials are the wheat straw components with the highest relative variation. In addition, it is showed here that silane modification is an efficient method to increase the temperature of degradation of wheat straw. The highest improvements were achieved with chlorosilane modifiers and combinations of alkoxysilane and chlorosilane modifiers. In fact, the silane treated samples have lower thermal degradation during the fabrication of composites with polyamide-6. It is observed here that the extruded and injection molded composites containing silane treated wheat straw samples have significant smaller thermal degradation than those utilizing untreated wheat straw samples. Equally important, it seems that the mechanical properties of the composites are not affected by the addition of silane treated samples in comparison with untreated wheat straw. In addition, another efficient treatment method is presented in this thesis. This method employs ultraviolet light to modify and improve the thermal stability of wheat straw. This method offers important economical and environmental benefits. Significant improvements (e.g., 40 ºC increase on the temperature at 2% of weight loss) were achieved after treatment for short periods of time (up to 15 minutes) and without the use of any pre-treatment or production of toxic by-products. This treatment method represents a novel application for ultraviolet light with potential for industrial use.

No description available.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Biomedical Technology In the Faculty of Health and Wellness Sciences At Cape Peninsula University of Technology 2013 / Newly developed and commercial dental resins which are commonly used nowadays have to be tested for their antimicrobial susceptibility. The purpose of this in vitro study was to investigate the antimicrobial activity of a titanium oxide (TiO2) nano-composite which was prepared with different antibacterial substances and used as restoratives in dentistry to combat certain selected bacteria that are considered the principle causes of some tooth diseases, for example, tooth decay and to prevent unsuccessful dental restoration. The TiO2 nano-composite was prepared and divided into four groups: The first group was an untreated TiO2 nano-composite. The second group was silane-treated TiO2 nano-composite. The third group was treated TiO2 nano-composite which was combined with chlorhexidine gluconate (CHxG). The fourth group was treated TiO2 nano-composite which was combined with benzalkonium chloride (BzCl). Five of the selected bacteria were grown overnight in Petri dishes. Four of them, namely, Escherichia coli (E. coli) ATCC 11775, Staphylococcus aureus (S. aureus) ATCC 12600, Enterococcus faecalis (E. faecalis) ATCC 29212, and Pseudomonas aeruginosa (P. aeruginosa) ATCC 10145, were grown on Müller-Hinton Agar (MHA). Streptococcus mutans (S. mutans) ATCC 25175 was grown on Brain Heart Infusion (BHI) agar. All these bacteria were tested against the TiO2 nano-composite, and incubated for 24 hours at 37°C, except S. mutans, which was incubated separately and exposed to CO2. It was placed into a CO2 water-jacketed incubator in an atmosphere of 5% CO2 for 24 hours at 37°C. The obtained results showed that neither of the groups of TiO2 nano-composites, (untreated TiO2 nano-composite and treated TiO2 nano-composite) exhibited antimicrobial activity against the pathogens. Only preparations of TiO2 nano-composites at a concentration of 3 %m/m of both CHxG and BzCl showed antimicrobial activity against S. aureus. Antimicrobial activity against S. mutans, E. coli, P. aeruginosa, E. faecalis and S. aureus, were only realized at a concentration of 10 %m/m for both CHxG and BzCl..

Thesis (MTech (Biomedical Technology))--Cape Peninsula University of Technology, 2013. / Newly developed and commercial dental resins which are commonly used nowadays have to be tested for their antimicrobial susceptibility. The purpose of this in vitro study was to investigate the antimicrobial activity of a titanium oxide (Ti02) nano-composite which was prepared with different antibacterial substances and used as restoratives in dentistry to combat certain selected bacteria that are considered the principle causes of some tooth diseases, for example, tooth decay and to prevent unsuccessful dental restoration. The Ti02 nano-composite was prepared and divided into four groups: The first group was an untreated Ti02 nano-composite. The second group was silane-treated Ti02 nano-composite. The third group was treated Ti02 nano-composite which was combined with chlorhexidine gluconate (CHxG). The fourth group was treated Ti02 nano-composite which was combined with benzalkonium chloride (BzCI).

Este trabalho apresenta os estudos das principais etapas que envolvem o uso do silano bis-trietoxisililetano (BTSE) na proteção contra a corrosão de laminados de aço carbono que são: o tratamento alcalino, a hidrólise do silano e a cura dos filmes obtidos. Através da técnica de análise espectroscópica na região do infravermelho foi possível obter os espectros de absorção do silano BTSE em concentrações da ordem de 2% em solução aquo-etanólica. O acompanhamento em função do tempo, da transmitância da banda na região de 1067 cm-1, que se refere às ligações hidrolisáveis do silano BTSE (Si-OEt), possibilitou estabelecer as condições ideais de hidrólise do silano BTSE em soluções aquo-etanólica, que se dá por volta de 40 minutos em pH=4. Os estudo das reações de hidrólise do silano BTSE neste tipo de solução possibilitou verificar também que as reações de hidrólise não ocorrem em uma única etapa. Através do planejamento fatorial de experimentos e da espectroscopia de impedância eletroquímica (EIS) foi possível medir a impedância real (Z') dos filmes protetivos desenvolvidos sobre superfícies limpas de aço pré-tratadas com soluções alcalinas em diferentes condições. A análise estatística dos dados obtidos, através do software MINITAB13, permitiu concluir que concentrações moderadas da solução alcalina de NaOH, da ordem de 2,5% e o tempo de imersão do aço nesta solução, da ordem de 10 minutos, contribuem de maneira positiva para aumentar o grau de proteção dos filmes obtidos. Concentrações mais elevadas da solução alcalina não deram bons resultados, devido a menor proteção conferida pelo filme de passivação formado sobre a superfície do aço. Através de EIS foi possível medir também a impedância real de filmes protetivos obtidos em diferentes condições de cura. Verificou-se que o aumento da temperatura de cura exerce um efeito positivo no grau de proteção passando por um ponto ótimo ao redor de 140ºC. Foi realizado o tratamento dos dados de impedância através do software ZVIEW2 e um circuito elétrico equivalente e o respectivo modelo físico para representar o filme de BTSE sobre o aço foi proposto. / This work presents the studies of the main stages involving the use of the silane bis-1,2-(triethoxysilyl)ethane (BTSE) in the protection against corrosion of rolled carbon steel (SCR), which are the steel alkaline treatment, the silane hydrolysis and the cure of the obtained films. Using the infrared spectroscopy technique it was possible to obtain the absorption spectrum of the BTSE silane in concentrations of 2% in aquo-ethanolic solutions. The monitoring of the transmittance in the region of 1067 cm-1, that refers to the hydrolysable groups of the BTSE silane (Si-OEt), made it possible to establish the ideal hydrolysis conditions of the BTSE silane in aquo-ethanolic solutions that happens for 40 minutes in pH=4. The results of the hydrolysis of the BTSE silane allowed to also to verify that the hydrolysis takes place in multiple steps. The factorial design of experiments and the Electrochemical Impedance Spectroscopy (EIS) allowed to measure the real impedance (Z') of the protective films developed on steel surface pre-treated with alkaline solutions in different conditions. The statistical analysis of the obtained data using MINITAB13 software allowed to conclude that moderate concentrations of the alkaline solution of NaOH (2,5% w/v) and 10 minutes of immersion time of the steel sample contribute in a positive way to increase the degree of protection of the obtained films. Higher concentrations of the alkaline solution did not give good results, due to minor protective characteristics of the formed film. EIS was also used to measure the real impedance of protective films obtained in different curing conditions. It was verified that higher curing temperatures exert a positive effect in the protection degree showing an optimum point around of 140ºC. The treatment of the impedance data by ZVIEW2 software and an equivalent electric circuit and the respective physical model to represent the film of BTSE on the steel were proposed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this study, it has been carried out quantum molecular dynamics simulations for the hydrogen abstraction reaction from methane, silane, germane and stannane by H, F, Cl and I atoms and being or not being induced by femtosecond laser pulses with the aim to favor the dissociation of the M-H (M = C, Si, Ge and Sn). All the simulations have been performed using a simulation scheme based on ab initio calculations of molecular dynamics, where the motion of the atomic nuclei is described classically while the electrons are treated quantically by the Density Functional Theory (DFT). The results of the molecular dynamics simulations for the hydrogen abstraction reaction from methane, that is a very inert molecule, show that only the fluorine atom is able to promote the dissociation of the C-H bond. For the simulations performed in the presence of the electromagnetic radiation, it was possible to observe that the femtosecond laser pulse could induce the hydrogen abstraction from methane when the reaction occurs with the hydrogen or fluorine atom. The results of the molecular dynamics simulations for the hydrogen abstraction reaction from silane show that also the fluorine as the hydrogen atoms are able to dissociate effectively the Si-H bond in silane. In the case of the hydrogen abstraction from silane by the chlorine atom, the effective Si-H dissociation does not happen. In the simulations including the pulsed electromagnetic radiation, it is observed that it was possible to favor even more the hydrogen abstraction reaction from silane by the hydrogen and fluorine atoms, moreover, it was possible to turn effective the dissociation of the Si-H bond by the chlorine atom. The GeH4 and SnH4 molecules could be easily dissociated by the hydrogen, fluorine and chlorine atoms. About the iodine atom, it was not able to promote the hydrogen abstraction reaction in germane and stannane, even in the presence of the femtosecond laser pulse. / Neste trabalho foram realizadas simulações de dinâmica molecular quântica para as reações de abstração de hidrogênio nas moléculas de metano, silano, germano e estanano por átomos de H, F, Cl, e I sendo realizadas simulações sem e com o uso do pulso de laser de femtosegundos com o objetivo de favorecer a quebra das ligações M-H (M = C, Si, Ge ou Sn). Todas as simulações foram realizadas utilizando um esquema baseado em cálculos ab initio de dinâmica molecular, onde o movimento dos núcleos atômicos é descrito classicamente, enquanto os elétrons são tratados quanticamente pela Teoria do Funcional de Densidade (DFT). Os resultados das simulações de dinâmica molecular das reações de abstração de hidrogênio no metano mostram que, por esta molécula ser bastante inerte, somente o átomo de flúor é capaz de promover a dissociação da ligação C-H. Para as simulações realizadas na presença da radiação eletromagnética, foi possível observar que o pulso de laser consegue favorecer a abstração de hidrogênio no metano quando a reação acontece com o átomo de hidrogênio ou flúor. Os resultados das simulações de dinâmica molecular para a reação de abstração de hidrogênio no silano mostram que tanto o átomo de flúor quanto o de hidrogênio são capazes de promover a captura do átomo de hidrogênio promovendo a quebra da ligação Si-H. No caso da reação de abstração de hidrogênio na molécula de silano por átomo de cloro, a quebra efetiva da ligação Si-H não acontece. Nas simulações com a radiação eletromagnética pulsada observa-se que foi possível favorecer ainda mais as reações de abstração de hidrogênio no silano por átomos de flúor e hidrogênio, além de tornar efetiva a ruptura da ligação Si-H na reação com o átomo de cloro. As ligações químicas Ge-H e Sn-H nas moléculas de GeH4 e SnH4 conseguiram ser quebradas facilmente nas reações de abstração de hidrogênio por átomos de hidrogênio, flúor e cloro. Quanto ao átomo de iodo, este não foi capaz de promover a reação de abstração de hidrogênio nas moléculas de germano e estanano, mesmo na presença do pulso de laser de femtosegundos.

Atualmente o aço galvannealed é submetido à fosfatização e/ou cromatização como pré-tratamento superficial; no entanto, por questões econômicas e ambientais, estuda-se a viabilidade de utilizar os silanos como pré-tratamento alternativo. Os silanos são moléculas organofuncionais conhecidas por atuar como agentes de ligação entre superfícies orgânicas e inorgânicas, promotores de adesão em sistemas de pintura e também por fornecerem proteção contra a corrosão. A proteção à corrosão depende principalmente do silano a ser utilizado, das condições de hidrólise e de cura. O objetivo deste trabalho é estudar as condições de hidrólise através de um projeto estatístico de experimentos e o efeito na proteção contra corrosão, de um agente promotor de polimerização redox (íons de cério IV) ou de um inibidor de corrosão (íons de cério III) aplicado aos filmes de silanos (bis-silano funcional: bis-1,2- [(trietoxisilil)propil] tetrasulfeto (BTESPT) e bis-(g-trimetoxysililpropil)amina (BTSPA)) obtidos em 1%, 2% ou 3% de concentração de silano em massa de solução solvente água/etanol (50/50%), nos pHs 4,0, 5,0, 6,5 e 9,0, depositados sobre o aço galvannealed. A natureza porosa natural da superfície desse aço, consequência do tratamento térmico do revestimento de zinco, leva à necessidade de tempos maiores de imersão do metal na solução hidrolizada do silano para que seja completamente molhada levando à formação de um filme compacto e homogêneo. A adição de nanopartículas de sílica também foi estudada variando sua concentração nos filmes. A aplicação dos filmes sobre a superfície metálica foi feita pelo processo de dip-coating. Os filmes foram obtidos em mono e bi-camadas. As condições de cura, em estufa, para a mono camada foram à temperatura de 150ºC por 40 minutos. As condições de cura, em estufa, para a bi-camada foram: primeira camada à temperatura de 150ºC por 20 minutos e segunda camada à temperatura de 150ºC por 40 minutos. Os estudos eletroquímicos foram realizados utilizando medidas de técnica de varredura do eletrodo vibratório (SVET) e de espectroscopia de impedância eletroquímica (EIS), medidas de resistência de polarização linear (Rp) e curva de polarização potenciodinâmicas, obtidas respectivamente, em solução aerada de NaCl 0,05 mo.L-1 e 0,1 mol L-1. A caracterização química dos filmes foi feita através das técnicas de espectroscopia no infravermelho (IR) e micro Raman. A caracterização física das amostras foi analisada por medida da viscosidade cinemática. Foram obtidas medidas de ângulo de contato para caracterizar a hidrofobicidade da superfície do metal recoberto pelo filme de polissilanos modificados. As imagens de microscopias óptica, eletrônica de varredura (MEV) e de força atômica (AFM) foram obtidas para conhecer a morfologia do filme e dispersão (homogeneidade) das nanopartículas de sílica no filme. Os resultados mostraram que tanto para o filme de BTSPA como de BTESPT o pH ideal para a obtenção de um filme mais resistente à corrosão foi o pH 4,0. As análises físico-químicas mostram que a adição de íons Ce (III) ou íons Ce (IV) melhoram as propriedades protetoras e reticulação dos filmes, respectivamente, formando um filme mais homogêneo e compacto. As caracterizações morfológicas mostraram que as nanopartículas de sílica, quando em excesso, formam aglomerados na superfície porosa do galvannealed, promovendo trincas e diminuindo as propriedades anticorrosivas dos filmes. / Currently, galvannealed carbon steel has been submitted to phosphatizing and/or chromatizing as surface pre-treatment; however, for economic and environmental issues, the viability to use silanes as an alternative pre-treatment has been studied. The silanes are organofunctionals molecules known for acting as coupling agents, adhesion promoters in paintings as well as for supplying protection against corrosion. The protection against corrosion depends mainly on the silane to be used, cure and hydrolysis conditions. The aim of this work is to study the conditions of the hydrolysis by a statistical project of experiments and the effect on corrosion protection, of either redox polymerization agent(ions of cerium IV) or a corrosion inhibitor (ions of cerium III) added to silane films (bis-functional silane: bis-[trimethoxysililpropyl]amine (BTSPA) and bis-1.2- [triethoxysilylpropyl]tetrasulfide (BTESPT)) obtained at silane concentration of 1%, 2% or 3% in mass of the solvent solution (50/50%) at pHs 4,0, 5,0, 6,5 and 9,0, deposited on galvannealed steel. The natural porous nature of the galvannealed steel surface as a results of thethermal annealing treatment o the zinc coating leads to higher needed immersion times inthe hydrolised silane solution in order to promote a complete wetting of the surface to reach a compact and homogeneous film. The addition of silica nanoparticles was also studied at different concentrationsin the films. The samples of galvannealed steel were immersed in the hydrolysis solution by dip-coating process. The films were obtained in mono and double layers. The cure conditions for the monolayer were obtained at temperature of 150ºC for 40 minutes. The cure conditions for the double layer were obtained: at temperature of 150ºC for 20 minutes for the first layer and at temperature of 150ºC for 40 minutes for the second layer. The electrochemical studies were performed using the scanning vibrate technique (SVET), electrochemical impedance spectroscopy (EIS), linear polarization resistance (Rp) and potenciodinamyc polarization curves, all measurements were obtained in aerated NaCl 0.1mol.L-1or 0.05 mol.L-1solution . The chemical properties of the films were analyzed by infrared (IR) and micro Ramanspectroscopies. The physical characterization of samples was performed by measuring the kinematic viscosity. The contact angle measurements were obtained in order to characterize the hydrophobicity of the silane film coated metal surface. The images from optical y, scanning electron (SEM) and atomic force microscopies (AFM) were performed to characterize the morphology of the film and/or the dispersion of silica nanoparticles in the film. The results showed that for BTSPA as well as for BTESPT the ideal pH to obtain a more corrosion resistant silane film is pH 4.0. The physico-chemical analysis showed that the addition of cerium (III) or cerium (IV) ions increases the cross linking of the film, and the film obtained was more homogeneous, compact and corrosion resistant. The morphological characterization showed that in the porous of galvannealed surface silica nanoparticles agglomerated, consequently promoting cracks and the decrease of anti-corrisive properties of the films.

Made available in DSpace on 2014-08-20T14:30:12Z (GMT). No. of bitstreams: 1 Tese _Luciano_de_Vargas_ Habekost.pdf: 2287600 bytes, checksum: 421084441401a2957e40573944b6a691 (MD5) Previous issue date: 2011-01-14 / The objective of this study was to investigate the influence of nanoparticle loading and the use of silane (TSPM), phosphate (PAM) or carboxylic (CAM) methacrylates as coupling agents on key properties of experimental resin luting agents. An experimental photocurable resin blend composed with 50 wt% of Bis-GMA and 50 wt% of TEGDMA was obtained. To study the influence nanoparticle loading, five different experimental resin luting agents were prepared with a total mass fraction of 60% of inorganic fillers. Silanated 2-μm barium borosilicate glass microparticles and 7-nm silica nanoparticles were used; the mass fraction of nanoparticles was set at 0 (control), 1 (G1), 2.5 (G2.5), 5 (G5) and 10% (G10). To study the influence of coupling agents, the resin blend was loaded with a 60% mass fraction of inorganic fillers (59/1 mass ratio of micro/nanoparticles) of Ba-B-Al-Si glass and colloidal silica coated with 5 wt% of TSPM, PAM or CAM; no filler treatment was performed in the control group. The properties evaluated were flexural strength () and modulus (Ef), Knoop hardness number (KHN), and film thickness (FT). Dispersion/interaction of particles with the resin phase was assessed by scanning electron microscopy (SEM).The degree of conversion (DC) was evaluated only to study the influence of coupling agents. Data were submitted to statistical analysis (5%). Results for nanoparticle loading: for , G1 > G2.5 = G5 = G10, and control > G10. For Ef, G2.5 > control = G1 > G5 > G10. For KHN, G5 = G10 > control = G1 = G2.5. For FT, control = G1 < G5 = G10, and G2.5 < G10. Incorporation of nanoparticles was associated with observation of clusters in the SEM analysis. Results for different coupling agents: for  and Ef, TSPM > CAM > control > PAM. For KHN, TSPM > CAM > PAM = control. For FT, TSPM < control < CAM < PAM. The SEM analysis revealed clustering of nanoparticles for all groups and better interaction between the organic-inorganic phases for TSPM and CAM. No significant differences in DC were observed. The results demonstrated that moderate incorporation of silanated silica nanoparticles may improve the properties of hybrid resin cements. However, mass fraction above 2.5% had a detrimental effect on the luting agent properties and the increase of clusters is associated with the increase of nanoparticles. The use of TSPM generated agents with improved properties as compared with the acidic methacrylates, with CAM showing better performance than PAM. The use of PAM generated agents with properties usually poorer compared with the material with no coupling agent. / O objetivo deste estudo foi investigar a influência da incorporação de nanopartículas e o uso de silano (TSPM), monômero ácido fosfatado (PAM) ou monômero ácido carboxilado (CAM) como agentes de união nas propriedades de cimentos resinosos experimentais. Uma matriz resinosa fotopolimerizável modelo foi desenvolvida com 50% de Bis-GMA e 50% de TEGDMA. Para observar o comportamento da incorporação de nanopartículas, cinco cimentos resinosos experimentais foram preparados pela adição de 60% (em massa) de micropartículas de bário borosilicato de vidro (2μm) e nanopartículas de sílica coloidal (7nm). As nanopartículas foram utilizadas nas seguintes proporções (em massa): 0 (controle), 1 (G1), 2.5 (G2.5), 5 (G5) e 10% (G10). Para estudar a influência dos agentes de união, 60% (em massa) de partículas inorgânicas (59/1 de micro/nanopartículas) de vidro de Ba-B-Al-Si e sílica coloidal, cobertas com 5% de TSPM, PAM ou CAM, foram acrescidas à matriz resinosa; o grupo controle foi composto por partículas não tratadas. As propriedades avaliadas foram resistência flexural (), módulo de elasticidade (Ef), número de dureza Knoop (KHN) e espessura de película (FT).A dispersão/interação das partículas com a fase resinosa foi avaliada com microscópio eletrônico de varredura (MEV). O grau de conversão (DC) foi avaliado somente para estudar a influência dos diferentes agentes de união. Os dados foram submetidos à análise estatística (5%). Resultados para incorporação de nanopartículas: para , G1 > G2.5 = G5 = G10 e controle > G10. Para Ef, G2.5 > controle = G1 > G5 > G10. Para KHN, G5 = G10 > controle = G1 = G2.5. Para FT, controle = G1 < G5 = G10 e G2.5 < G10. Nas análises em MEV, a presença de aglomerados foi associada à incorporação de nanopartículas. Resultados para a utilização de diferentes agentes de união: para e Ef, TSPM > CAM > controle > PAM. Para KHN, TSPM > CAM > PAM = controle. Para FT, TSPM < controle < CAM < PAM. As análises em MEV revelaram aglomerados de nanopartículas em todos os grupos e melhor interação entre as fases orgânica/inorgânica para TSPM e CAM. Não foram observadas diferenças para o DC. Os resultados demonstraram que a incorporação moderada de nanopartículas de sílica silanizada pode beneficiar as propriedades dos cimentos resinosos híbridos. Entretanto, proporções de nanopartículas acima de 2,5% possuem um efeito prejudicial nas propriedades destes cimentos, e seu aumento está associado com o aumento da presença de aglomerados. O uso de TSPM gerou cimentos com melhores propriedades quando comparado ao uso de monômeros ácidos, o CAM demonstrou melhor desempenho que o PAM. O uso do PAM gerou cimentos com propriedades inferiores a cimentos sem a utilização de agentes de união.

Abstract : The applications of natural fibers as reinforcing materials have received lots of attentions and interests due to their unique advantages such as direct derivation from earth, sustainability, degradability and so on. In addition, the employment of plant fibers as raw materials in engineering and industries can promote sustainable agriculture. Cultivation of oilseed flax has grown recently from 600,000 to 800,000 hectares in past few years in Canada. This can also provide a great potential to use flax waste (straw), 2,000 kg/ha annually, as reinforcing materials in industry and promote sustainable agriculture. These huge amounts of flax residuals usually burned or thrown away which as result, leads to emission of CO2 into the atmosphere. In two past decades, the employment of natural fibers in bio-composites as an alternative for flax residuals disposal has received lots of interest and attention. The dramatic increase of publications during this period supports this fact. This attention and interest has been attributed to public awareness, Legal restrictions and environmental concerns associated to the synthetic fibers. Moreover, the significant advantages of natural fibers such as low resin consumption, low tools wear, cost effectivity; availability, environmentally friendly, degradability, low density and high specific properties have converted the application of them very favorable. However, the hydrophilic nature of cellulosic fibers as a main disadvantage makes them incompatible with hydrophobic polymeric matrices. This poor compatibility between cellulosic fibers and polymeric matrices mostly attributes to the presence of hydroxyl functional groups on the backbone of the flax fibers that causes to hydrophilic properties of cellulosic fibers and poor interfacial adhesion between cellulosic fibers and polymeric matrices. The main goal of this research thesis is to convert of primary alcoholic groups (OH) available on the surface of flax fiber to carboxyl groups by employment of TEMPO oxidation system in order to facilitate the silane treatment process. Subsequently, carboxyl groups can more easily interact with silane coupling agents. The surface functionality of as-received and treated fibers was characterized using Fourier transform infrared and X-ray photoelectron spectroscopy. Dynamic contact angle tensiometer was used to compare wettability of the oxidized and nonoxidized fibers after the silane treatment. The interaction between flax fiber and polymer was characterized using scanning electron microscopy (SEM). The results indicated that the TEMPO iii oxidation significantly improved the bonding efficiency of the silane coupling agents on the fiber surface. Thus, the compatibility between the flax fibers and the epoxy resin was improved. In addition, the water absorption of the modified fibers was remarkably reduced, while the contact angle of the flax fibers was increased. / Les demandes des fibres naturelles comme matériaux de renforcement ont reçu beaucoup d'attentions et d'intérêts en raison de leurs avantages uniques tels que la dérivation directe de la terre, la durabilité, la dérivabilité, etc. En outre, l'emploi des fibres végétales comme matières premières dans l'ingénierie et les industries peut favoriser l'agriculture durable. La culture du lin oléagineux est passée de 600 000 à 800 000 hectares au cours des dernières années au Canada. Cela peut également constituer un excellent potentiel d'utilisation des déchets de lin (paille), 2 000 kg par an par année, en tant que matériaux de renfort dans l'industrie et promouvoir l'agriculture durable. Ces énormes quantités de résidus de lin sont généralement brûlées ou jetées, ce qui entraîne l'émission de CO2 dans l'atmosphère. Au cours des deux dernières décennies, l'emploi de fibres naturelles dans les biocomposites comme possibilité à l'élimination des résidus de lin a suscité beaucoup d'intérêt et d'attention. L'augmentation spectaculaire des publications au cours de cette période prend en charge ce fait. Cette attention et cet intérêt ont été attribués à la sensibilisation du public, aux restrictions légales et aux préoccupations environnementales associées aux fibres synthétiques. En outre, les avantages importants des fibres naturelles, comme la faible consommation de résine, l'usure des outils, l'efficacité des coûts; la disponibilité, l'environnement, la dégradabilité, la faible densité et les propriétés spécifiques élevés ont transformé la demande des fibres naturelles très favorable. Cependant, la nature hydrophile des fibres cellulosiques comme inconvénient principal les rend incompatibles avec des matrices polymères hydrophobes. Cette mauvaise compatibilité entre les fibres cellulosiques et les matrices polymères attribue principalement à la présence de groupes fonctionnels hydroxyles sur l'ossature des fibres de lin qui provoque des propriétés hydrophiles des fibres cellulosiques et une faible adhérence interfaciale entre les fibres cellulosiques et les matrices polymères. L'objectif principal de cette thèse de recherche est de convertir des groupes alcooliques primaires (OH) disponibles à la surface de la fibre de lin en groupes carboxylés par l'emploi d'un système d'oxydation TEMPO afin de faciliter le traitement du silane. Par la suite, les groupes carboxylés peuvent interagir plus facilement avec des agents de couplage au silane. La fonctionnalité de surface des fibres reçues et traitées a été caractérisée en utilisant la spectroscopie à infrarouge à transformer de Fourier et à la Spectrométrie photo électronique X. Un tensiomètre à angle de contact dynamique a été utilisé pour comparer la mouillabilité des fibres oxydées et non oxydées après le traitement au silane. L'interaction entre les fibres de lin et le polymère a été caractérisée en utilisant une microscopie électronique à balayage (MÉB). Les résultats indiquent que l'oxydation TEMPO a considérablement amélioré l'efficacité de liaison des agents de couplage silane sur la surface de la fibre. Ainsi, la compatibilité entre les fibres de lin et la résine époxy a été améliorée. En outre, l'absorption d'eau des fibres modifiées a été considérablement réduite, tandis que l'angle de contact des fibres de lin a été augmenté.

The aim of this D.Phil was to develop a range of cyclisation cascades, which initially form a reactive iminium intermediates that can then be attacked by a pendant nucleophile resulting in novel polycyclic structures. This concept has been applied to the development of three methodologies and has resulted in the discovery of new reactivity as well as the synthesis of a wide range of interesting novel structures <b>Chapter 1: Enantioselective chiral-BINOL-phosphoric acid catalysed reaction cascade</b> A highly enantioselective hydroamination / N-sulfonyliminium cyclisation cascade using a combination of Au(I) and chiral phosphoric acid catalysts has been developed. Proceeding by an initial 5-exo-dig hydroamination and a subsequent phosphoric acid catalysed Pictet- Spengler cyclisation, the reaction provides access to complex sulfonamide scaffolds in excellent yields and with high levels of enantiocontrol. The scope can be extended to lactam derivatives, with excellent yields and enantiomeric excesses of up to 93&percnt; ee. <b>Chapter 2: Iridium catalysed nitro-Mannich cyclisation</b> A new chemoselective reductive nitro-Mannich cyclisation reaction sequence of nitroalkyltethered lactams has been developed. An initial rapid and chemoselective iridium(I) catalysed reduction of lactams to the corresponding enamine is subsequently followed by intra molecular nitro-Mannich cyclisation. This methodology provides direct access to important alkaloid, natural product-like structures in yields up to 81&percnt; and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterisation of reaction intermediates. The new methodology has been applied to the total synthesis of (&plusmn;)-epi-epiquinamide in 4 steps. <b>Chapter 3: Iridium catalysed reductive interrupted Pictet-Spengler cyclisation</b> A novel reductive interrupted Pictet-Spengler cyclisation reaction cascade has been created. An iridium(I) catalyzed partial reduction of lactams/amides to the corresponding iminium is subsequently trapped by a pendant indole nucleophile. Interruption of the Pictet-Spengler reaction by indolium reduction provides a wide range of novel spirocyclic indoline moieties in excellent yield and diastereoselectivity.