Darmstadt, Techn. Universiẗat, Diss., 2005. / Dateien im PDF-Format.

This project analyses the impact in the mechanical properties of Polyoxymethylene (POM) of three different blends of biodiesels: B0 with 0% of Rapeseed Methyl-ester (RME), B20 with 20% of RME and B100 with 100% of RME. Polyoxymethylene specimens have been subjected to an accelerated aging during 1600 hours at 85ºC. This is the equivalent to 20 years of life time. In addition, a thermal oxidation in air at the same temperature has been performed to check the impact of the temperature in the final degradation.Three different methods have been performed to calculate the diffusion rate, however and one of them has been selected for its reliable results. The second Fick´s law have been chosen to model the diffusion. The diffusion rate has been calculated for the B20 and B100 blend due to the B0 blend has a non-constant diffusion rate. B20 shows also some divergence while B100 fits the Fickian behaviour.A Finite Different approximation method has been used to predict the concentration profiles of the diffusion process of B20 blend. They have been compared with the results of the IR Microscope, with a clear misalignment between the expected and the actual values.Tensile tests have been done in different stages of the test to check the stress-strain behaviour of the specimens for each aging type. The most relevant parameter of degradation is the Elongation At Break (EAB), which decrease considerably a cause of the embrittlement. A study of the real stress-strain has been also done to assure the real behaviour of the material.A fracture surface study through Scanning Electron Microscope (SEM) and Light Microscope has been done to assure the brittle behaviour with the aging and the changes in the structure of the material.The swelling behaviour has been also modelled, and the bases for a future FEM analysis have been exposed.

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Today, there is a great need for polymers made from biorenewable resources due to the increasing price and diminishing supplies of petroleum and the overabundance of plastic waste in landfills. Polyoxymethylene can be produced from biorenewable feedstocks, depolymerized to formaldehyde through chemical recycling, and may be a viable alternative to many polyolefins. However, there has been limited research on varying the thermomechanical properties of polyoxymethylene so that it can be used in a wider variety of applications. Our approach employs the cationic copolymerization of trioxane with various amounts of 1,2-epoxyalkanes and 4-alkyl-1,3-dioxolanes to arrive at polyoxymethylene derivatives with controlled branching and morphology. Branching content has been measured by nuclear magnetic resonance (NMR) spectroscopy and correlates well with the comonomer feed fraction. The melting temperatures of the copolymers, determined from differential scanning calorimetry (DSC), are depressed predictably with increasing amounts of comonomer incorporation. The copolymerizations behaved the same regardless of whether the comonomer was an alkyldioxolane or epoxyalkane. 1,2-Epoxybutane/trioxane copolymers and 4-ethyl-1,3-dioxolane/trioxane copolymers gave the best melting point and % crystallinity results using boron trifluoride diethyl etherate as the cationic initiator.

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An investigation was carried out on a three stage method (extrusion/annealing/uniaxial-stretching) (MEAUS) utilized to produce semicrystalline polymeric microporous membranes. The two semicrystalline polymers studied were selected based on a set-of-prerequisites proposed for the formation of highly porous membranes via the method in question. The prerequisites included "fast" crystallization kinetics, presence of an ac relaxation, ability to form a planar stacked lamellar morphology with a "good" crystalline orientation upon melt-extrusion, and rapid heat transfer of the film during extrusion. The first polymer was isotactic poly(4-methyl-1-pentene) (PMP), and the second was polyoxymethylene (POM). Three PMP resins were studied, which differed in weight average molecular weight. Three POM resins were also investigated where two of resins were characterized by relatively narrow molecular weight distributions (MWD) ca 2 while the third POM resin possessed a MWD ca 5.9. The melt-extruded film morphologies and orientation values were a consequence of the melt-relaxation times as a result of the resin characteristics and/or the melt-extrusion conditions. Following the extrusion stage, the effect of annealing (second stage) on film properties was investigated. The annealing variables investigated included the temperature, time, and level of extension applied during annealing. The annealed films were then subjected to the uniaxially stretching stage (third stage) consisting of a cold and hot step, respectively, where deformation was along the extrusion direction. The variables of interest included the cold and hot stretch temperature and extension level. It was found that starting precursor morphology and orientation, annealing conditions, and stretching variables impact the final film microporous morphology and permeability. Additionally, the proposed prerequisites were verified in both the PMP and POM film series. In addition to the MEAUS study, a comprehensive investigation was conducted of the optical properties of blown and cast films made from conventional Ziegler-Natta catalyzed linear low density polyethylene (LLDPE) as well as metallocene-catalyzed LLDPE resins. From this work, it was determined that in PE blown and cast films made using conventional processing conditions, the optical haze properties are adversely affected due to enhanced surface roughness caused by the formation of spherulitic-like superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics. This optical property study was also published in J. Appl. Polym. Sci., 77(13), 2845, (2000). / Ph. D.

Slow-release devices retained in the rumen, are a simple method for continuous administration of bioactives to ruminant animals. To satisfy regulatory requirements and avoid waste of bioactive due to under- or over-dosing, it is advantageous to have a constant and predictable release rate. Existing intraruminal controlled-release technologies cannot easily be adapted for different bioactives or rates of release and can be influenced by the variable physiological environment in the rumen. Some existing commercial products use the pressure generated by a hydrogen gas-producing cell to extrude fluids from a syringe-like device. This technology may provide advantages for ruminal controlled-release as the gas production rate is unaffected by environment in the rumen and can be easily adjusted using electrical resistance applied to the gas cell. This technology was adapted for use in the rumen in these studies. Initial experiments identified the need for greater understanding of the rate that hydrogen is produced by the gas cell and the rate that gas diffuses through the barrel walls. Gas production rate was found to be inversely proportional to the resistance applied to the gas-producing cell. Factors affecting gas diffusion rate from the device were studied and a polymer was identified that reduced hydrogen diffusion to 5% of that for the initial components used. A relationship was developed to predict the release profile of a device. Controlled-release devices were constructed from selected materials. They released blank formulation at in vitro at a constant rate, which was within experimental variation of predicted values. Release rates from the devices used in vivo were slightly higher than predicted. The presence of rumen gases inside in vivo devices suggested that the difference may be due to inward diffusion of these gases; these may be eliminated by further study of barrel materials. Recommendations on the redesign of this technology for use as a generic intraruminal delivery system are given.

Ce travail de thèse est une étude expérimentale et théorique de la contribution de la composante organique réfractaire des comètes à leur phase gazeuse.<br /> Certaines espèces gazeuses observées dans la coma, telles que le formaldéhyde (H2CO) et les radicaux cyanogènes (CN), ne sont pas produites uniquement par la sublimation du noyau ou par la photodissociation d'autres molécules gazeuses. Elles pourraient provenir de la dégradation de la composante organique réfractaire présente dans les grains cométaires.<br /> L'objectif de cette thèse est de tester cette hypothèse. Dans un premier temps, les rendements quantiques et les paramètres cinétiques de production d'espèces gazeuses par irradiation dans l'UV lointain et dégradation thermique de composés organiques solides sont déterminés expérimentalement. Dans un deuxième temps, un modèle physico-chimique de la coma, prenant en compte ces processus de dégradation, a été développé.<br /> Les polymères de HCN et l'hexaméthylènetétramine (ou HMT, C6H12N4) ayant été proposés afin d'expliquer l'origine des radicaux cyanogènes, j'ai irradié et chauffé ces composés solides dans des conditions représentatives de l'environnement cométaire. Je montre ainsi que l'hexaméthylènetétramine est particulièrement stable par irradiation dans l'UV lointain et que ce composé ne se dégrade pas mais se sublime lorsqu'il est chauffé sous vide. Le HMT ne semble donc pas être un bon candidat pour une source de radicaux CN dans l'environnement cométaire. Je me suis ensuite concentré sur l'étude de la dégradation des polymères de HCN. J'ai mis en évidence, par spectroscopie infrarouge à transformée de Fourier (IRTF), la production de HCN, CO, CH4 et C2H2 par irradiation à 122 et 147 nm de ces polymères et celles de NH3, HCN, HNCO et CO par chauffage entre 430 et 580 K. La vitesse de production de l'ensemble de ces espèces gazeuses a été quantifiée grâce à l'analyse de l'évolution temporelle des spectres infrarouge. D'autre part, la mesure par spectroscopie de fluorescence induite par laser (LIF) n'a pas permis d'atteindre la limite de détection nécessaire pour détecter le radical CN à partir de la dégradation des polymères de HCN. J'ai donc modélisé la production des radicaux CN dans la coma en supposant que leur production est égale à celle mesurée pour l'acide cyanhydrique (HCN). Bien que la densité de colonne des radicaux CN ne puisse pas être fidèlement reproduite en prenant en compte la dégradation des polymères de HCN, cette hypothèse ne peut pas être infirmée. Sa confirmation nécessite des études expérimentales supplémentaires. <br /> En parallèle à ce travail sur la production des radicaux CN, j'ai poursuivi une étude précédemment menée au laboratoire afin d'expliquer la production de H2CO dans C/1995 O1 (Hale-Bopp). Dans cette comète, les taux de production de H2CO présentent une évolution héliocentrique plus rapide que celle d'autres composés gazeux similaires, tels que HCN ou H2S. J'ai tout d'abord obtenu de nouvelles données expérimentales concernant la dégradation thermique du polyoxyméthylène (polymère de H2CO, -(CH2-O)n-) dans une large gamme de température et pour deux types de polymères. Ceci me permet alors de reproduire les mesures des taux de production de H2CO dans cette comète et de montrer que l'évolution héliocentrique peut être expliquée par la prédominance de la production de H2CO par dégradation thermique du POM jusqu'à des distances de 3,5 UA. Ce travail confirme donc que la dégradation du POM permet d'expliquer l'origine du H2CO et que, quelle que soit la distance héliocentrique, la contribution de la phase organique réfractaire à la phase gazeuse des comètes doit être prise en compte.

This work examines the chemical and physical effects of a material treatment process on the biopolymers PEEK, POM-h, POM-c, PTFE and UHMWPE. The polymers are analyzed physically and chemically using atomic force microscopy, profilometry, scanning electron microscopy, optical microscopy, contact angle measurement, FT infra-red spectroscopy and energy dispersive X-ray spectrometry. PEEK is found to be the most suitable polymer and FT Infra-red spectroscopy an informative analytic tool.

This work examines the chemical and physical effects of a material treatment process on the biopolymers PEEK, POM-h, POM-c, PTFE and UHMWPE. The polymers are analyzed physically and chemically using atomic force microscopy, profilometry, scanning electron microscopy, optical microscopy, contact angle measurement, FT infra-red spectroscopy and energy dispersive X-ray spectrometry. PEEK is found to be the most suitable polymer and FT Infra-red spectroscopy an informative analytic tool.