Köln, Universiẗat, Diss., 2001.

Techn. Hochsch., Diss., 2000--Aachen.

Techn. Hochsch., Diss., 2002--Aachen.

The time dependence of the physical properties of ethylene/1-octene (EO)-copolymers after primary crystallization is investigated by calorimetry, density, and creep measurements. The temporal evolution of the multiple melting of EO-copolymers is monitored by differential scanning calorimetry. The low temperature endotherm displays an evolution similar to that observed for the enthalpy recovery in glasses after physical aging. Using this analogy, a calorimetry-aging rate is defined, which quantifies the change in the low endotherm temperature with time. Similarly a density-aging rate is defined from the evolution of density with time. A non-classical creep behavior is observed for short aging times, consistent with crystallization-induced shrinkage. The change in crystallinity during aging leads to a change in the shape of the relaxation spectrum. Hence, analysis of creep data cannot be carried out using Struik's superposition method. For both short and long aging times, the creep rate exhibits a dependence on copolymer composition similar to those associated with the calorimetry- and the density-aging rates, suggesting a common origin for the evolution of the low endotherm, the creep behavior and the bulk density. The calorimetry, density, and creep data are reexamined based on the following assumptions: First, a single population of small crystals is formed during crystallization at low temperature; Second, these small crystals increase in stability under isothermal conditions, easily melt and recrystallize during heating and serve as efficient thermo-reversible cross-links to increase the conformational constraints in the residual amorphous fraction. These assumptions appear to be consistent with all observations made to date. / Master of Science

Des travaux de recherche en fermentation liquide ont montré que P. canescens est une souche hyperproductrice de xylanases non contaminées par des activités cellulolytiques et amylolytiques. Selon les scientifiques, lintérêt de lutilisation industrielle de ces hémicellulases dans différents secteurs (particulièrement dans la formulation daliments pour le bétail, en industries des jus de fruits et brassicoles, en amidonnerie, en industrie du papier, en pharmacie, dans les textiles et dans la production du bioéthanol) va croître significativement. Mais le développement de ces enzymes est fréquemment limité par le coût de production. Ce travail sest intéressé à loptimisation de la production des xylanases de P. canescens à partir de matières premières peu coûteuses telles les résidus agro-industriels par fermentation solide, une technique traditionnellement utilisée dans la fermentation des aliments en Asie. Létude a démontré que le tourteau de soja est un bon inducteur de la production des xylanases. La teneur initiale en eau, le pH initial, la température de la culture et laération active influencent la synthèse de l'enzyme. Compte tenu des résultats obtenus à léchelle du laboratoire, la transposition à léchelle industrielle serait facilitée naturellement par de fines épaisseurs de cultures statiques, ce qui réduit de moitié le coût de production comparativement à la fermentation liquide. Les expérimentations ont confirmé que la production de xylanases par P. canescens répondait à des phénomènes dinduction et de répression dépendant du substrat et des conditions physico-chimiques de croissance, et non pas à des phénomènes de régulation de type quorum sensing. Lenzyme sous forme liquide concentrée présente une bonne stabilité pendant six mois sans protection préalable (stérilisation, stabilisation ou inhibition de protéases).

Universiẗat, Diss., 2003--Stuttgart.

No description available.

The diffusion of small-molecule penetrants in polyethylene is hindered by impenetrable crystals and by the segmental constraints imposed by the crystals on the penetrable phase. Liquid and vapour n-hexane sorption/desorption measurements were performed on metallocene catalyzed homogenous poly(ethylene-co-octene)s. It was shown that the fractional free volume of the polymer penetrable component increased with increasing amount of penetrable polymer. It also increased with the relative proportion of liquid-like component in the penetrable polymer fraction. The detour effect was found to increase with decreasing crystallinity. The experimental study of the morphology of the polymers showed that the geometrical impedance factor followed the same trend with increasing crystallinity as the data obtained from n-hexane desorption. The changes in phase composition and character upon n-hexane sorption were monitored with Raman spectroscopy, WAXS and NMR spectroscopy. Partial dissolution of the orthorhombic and the interfacial component was observed upon nhexane sorption. Changes in the character of the components were furthermore analyzed: an increase of the density in the crystalline component and a decrease of the density in the amorphous component were observed in the n-hexane-sorbed-samples. Molecular dynamics simulations were used for studying diffusion of n-hexane in fully amorphous poly(ethylene-co-octene)s. The branches in poly(ethylene-co-octene) decreased the density by affecting the packing of the chains in the rubbery state in accordance with experimental data. Diffusion of n-hexane at low penetrant concentration showed unexpectedly that the penetrant diffusivity decreased with increasing degree of branching. Spherulitic growth was mimicked with an algorithm able to generate structures comparable to those observed in polyethylene. The diffusion in the simulated structure was assessed with Monte Carlo simulations of random walks and the geometrical impedance factor of the spherulitic structures was calculated and compared with analytical values according to Fricke’s theory. The linear relationship between geometrical impedance factor and crystallinity in Fricke’s theory was confirmed. Fricke’s theory, however, underestimated the crystal blocking effect. By modelling systems having a distribution of crystal width-to-thickness ratio it was proven that wide crystals had a more pronounced effect on the geometrical impedance factor than is indicated by their number fraction weight. / QC 20100909

En la actualidad el mercado carece de prendas elásticas para uso profesional puesto que los elastanos habitualmente utilizados son inestables frente a altas temperaturas y químicos agresivos, e.g. termofijado, mantenimiento de indumentaria industrial etc. Recientemente se han venido utilizado filamentos olefínicos obtenidos a partir de copolímeros al azar de etileno-octeno (Dow XLA fibers producidos por The Dow Chemical Company). Aunque más resistentes a las temperaturas debido a la reticulación, su bajo punto de fusión, alrededor de 50ºC, limita el comportamiento elástico en tejidos pesados y tupidos para indumentaria profesional. La investigación tiene por objeto la obtención de monofilamentos elásticos a partir copolímeros de bloque de etileno-octeno (cuyo punto de fusión es más elevado) y con éstos, tejidos para indumentaria profesional que ofrezcan mayor fuerza de encogimiento a las temperaturas típicas de los pre-tratamientos, tintura y acabado (50ºC-120ºC). El objetivo es hacer que los tejidos encojan más durante las operaciones en húmedo bajo temperatura para mejorar así su elasticidad y aumentar el peso en comparación con los tejidos actuales manufacturados con los convencionales copolímeros homogéneos de etileno-octeno reticulados Los tejidos deberán garantizar las siguientes propiedades durante todo su ciclo de vida: estabilidad dimensional, relación elasticidad-crecimiento mejorado, resistencia química, resistencia térmica, durabilidad ante los lavados industriales y un mejor confort termofisiológico y sensorial. / Due to the lack of stability of elastane based materials against high temperatures and harsh chemicals, e.g. thermofixation and professional wear maintenance, elastic garments with elastane content are not yet fully commercial products. The Dow Chemical Company has recently commercialized a random ethylene-octene copolymer based fiber named Dow XLA fiber. Despite its higher temperature resistance as one of the crosslinking effects, its very low melting point, around 50ºC, establishes some limitations in elasticity such in heavy weight and high densely woven fabric cases typically found in professional wear applications. The target for the investigation is to produce block ethyleneoctene copolymer based filaments in which the melting point is supposed to be higher than in random copolymer materials. Different workwear fabrics will be manufactured with yarns containing such elastic filaments. It is supposed these fabrics to show high shrinkage forces even at dyeing and finishing temperatures, (50ºC-120ºC). The goal is to produce fabrics with superior shrinkage performance in order to achieve an excellent elastic power and the final desired fabric weight. Properties such as dimensional stability, stretch and growth ratio, temperature and chemical resistance and durability against industrial laundering should not be affected by the passage of the time. To validate this point these properties will be measured in the fabrics off loom and after the garment cycle life. These fabrics are also supposed to show better thermophysiological and sensorial properties than random copolymer fiber based textiles

No description available.