Würzburg, Univ., Diss., 2009. / Zsfassung in engl. Sprache.

Zugl.: Berlin, Techn. Universiẗat, Diss.

No description available.

No description available.

Contact antimicrobials for use in the medical device industry are being studied extensively to minimize the risk of hospital acquired infections, which are among the top ten leading causes of death in the US. Surfaces modified with quaternary ammonium containing side chains have been known to demonstrate excellent antimicrobial properties. Prior work has indicated that polyurethane surfaces with copolyoxetane soft blocks consisting of fluorinated and quaternary ammonium side chains can act as good antimicrobials. However, stabilizing the positive charge on the surface has been a challenge. The dissertation is aimed at creating a surface modifier that would confer a stable contact kill antimicrobial surface at very low modifier content, that is, less than 2 wt%. To achieve this objective, the study explored the introduction of a different fluorous group in the soft block to enhance stability. In particular, prior studies by other groups and early work by Kurt have shown that replacement of one of the terminal “chaperone” C-F bonds by C-H decreased surface tension. This led to the hypothesis that a –CF2H terminated “chaperone” group would be “amphiphilic” resulting in surface stability under both dry and wet conditions. Keeping this hypothesis in mind, a –CF2-CF2H (4F) terminal “chaperone” group was created in a modifier having two different 4F to quaternerary C12 ratios. It was found that polyurethanes prepared with a 66:34 ratio of 4F:C12 as the diol, performed as a very good surface modifier with high zeta potentials over a long period of time compared to the –CF3 based modifier. Antimicrobial tests performed within one week and four weeks after coating preparation have provided promising results that demonstrate improved biocidal stability. Guided by improved antimicrobial properties obtained with surface modifier polyurethanes made from P[(4F)(C12)-66:34-Mn], a new concept was explored by end-capping the same diol with isocyanatopropyltriethoxysilane and blending the end-capped diol with base polyurethane along with a 10 wt % cross linker. These modifiers show excellent antimicrobial properties (100% kill of bacteria) over one month with no observable changes in the zeta potential or surface morphologies. XPS analysis confirms the presence of quaternary ammonium on the surface. Preliminary kinetic studies show excellent antimicrobial properties for a 2 wt% modifier and 100% kill within 1 hr.

O objetivo deste trabalho foi estudar a síntese de poliol de óleo de andiroba (POA) e utilizá-lo como matéria prima para a produção de poliuretanos (PUs). A síntese do poliol foi realizada por catálise enzimática com a lipase comercial Novozym 435. A reação foi feita em reator de leito fixo, empregando óleo de andiroba e glicerol (GLI) como substrato, em proporção molar 2:1, e t-butanol (TB) como solvente. Foram avaliadas as relações solvente:substrato de 50, 100 e 150 % e temperaturas de 40, 50 e 60 °C. Os produtos da reação, monoglicerídeos (MAGs), diglicerídeos (DAGs) e triglicerídeos (TAGs), foram quantificados através de cromatografia líquida de alta eficiência (CLAE), índice de acidez (IA) e espectroscopia de infravermelho com transformada de Fourier (FTIR). O poliol obtido na condição 50°C e 150 % solvente foi escolhido para a produção dos PUs, devido à sua maior quantidade de MAG (66 %) e menor de DAG (28 %) e TAG (5 %). Os PUs foram produzidos empregando-se poliol, biureto de hexametileno de diisocianato (BHD), dibutil dilaurato de estanho como catalisador e, apenas para produção de espumas, água destilada como agente expansor. Utilizaram-se razões NCO/OH de 0,8 e 1 para os filmes e NCO/OH=1 para as espumas. Na produção das espumas o POA foi combinado com GLI nas proporções de 25 e 50 %. A formação de PU a partir do poliol de andiroba foi confirmada por FTIR e análise termogravimétrica. Os filmes de PU obtidos apresentaram caráter hidrofílico e defeitos de superfície devido à formação de bolhas durante o processo de formação. A resistência à tração dos filmes mostrou-se dependente da quantidade de poliol, não tendo sido possível a obtenção de espumas sem a adição de glicerol. A resistência mecânica das espumas produzidas foi baixa, devido à baixa funcionalidade do POA e a presença de DAG e TAG, porém similar àquela reportada na literatura para alguns outros tipos de espumas de PU. Assim, este trabalho demonstrou a possibilidade da utilização do óleo de andiroba para a produção de PUs e, com base nas propriedades mecânicas dos materiais produzidos e nas características intrínsecas da andiroba, abre novas possibilidades de desenvolvimento de materiais com potencial para aplicações medicinais. / The goal of this work was to study the synthesis of andiroba oil polyol (AOP) and use it as raw material for the preparation of polyurethanes (PUs). The AOP synthesis was performed by enzymatic catalysis employing the commercial lipase Novozym 435. The reaction was carried out in a fixed bed reactor using andiroba oil and glycerol (GLI) at 1:2 molar ratio as substrate, and t-butanol (TB) as solvent. Solvent:substrate ratios of 50, 100 and 150 % and temperatures of 40, 50 and 60 °C were evaluated. The reaction products, monoglycerides (MAGs), diglycerides (DAGs) and triglycerides (TAGs), were quantified through high performance liquid chromatography (HPLC), acidity index (IA), and Fourier transform infrared spectroscopy (FTIR). The polyol obtained at 50 °C and 150% solvent was chosen for PU production, due to its higher content of MAG (66 %) and lower content of DAG (28 %) and TAG (5 %). PUs were prepared from AOP, hexamethylene diisocyanate biuret (BHD), dibutyl-tin dilaurate as catalyst, and, for the foams, distilled water as blowing agent. NCO/OH ratios of 0.8 and 1 were used for the films. For the foams, NCO/OH = 1 and AOP/GLI blends with 25 and 50 % of glycerol were employed. The formation of PU from the AOP was confirmed by FTIR and thermogravimetric analysis. The obtained PU films presented hydrophilicity and surface defects due to the formation of bubbles during the formation process. The tensile strength of the films was shown to be dependent on the amount of polyol, and it was not possible to obtain foams without the addition of glycerol. The mechanical strength of the foams produced was low, due to the low functionality of the POA and the presence of DAG and TAG, but similar to that reported in the literature for some other types of PU foams. Thus, this work demonstrated the possibility of using andiroba oil for the production of PUs. Besides, based on the mechanical properties of the materials produced and the intrinsic characteristics of andiroba, it opens new possibilities for the development of materials with potential for medicinal applications.

An experimental study has been carried out to investigate the effects of buoyancy on smoldering of polyurethane foam. The experiments are conducted with a high void fraction flexible polyurethane foam as fuel and air as oxidizer, in a geometry that approximately produces a one dimensional smolder propagation. The potential effect of buoyancy in the process is analyzed by comparing upward and downward smolder propagation through a series of normal gravity and variable gravity experiments. Both opposed and forward mixed (free and forced) flow smolder configurations are studied. In opposed smolder the oxidizer flow opposes the direction of smolder propagation, and in forward smolder both move in the same direction. Variable gravity free flow tests are also conducted in an aircraft flying a parabolic trajectories that provides low gravity periods of up to 25 sec. Measurements are performed of the smolder reaction propagation velocity and temperature as a function of the location in the sample interior, the foam and air initial temperature, the direction of propagation and the air flow velocity. This information is used in conjunction with previously developed smolder theoretical models to determine the smolder controlling mechanisms and the effect of gravity. Three zones in the fuel sample with clearly defined smolder characteristics are identified. A zone close to the igniter where smolder is affected by the external heat, a zone at the end of the sample where smolder is affected by the environment, and a zone at the end of the sample where smolder is affected by the environment, and a zone, in the middle of the foam, that is free from external effects. This last zone is the most characteristic of one dimensional, self-supported smolder, and the one that is studied in greater detail. In mixed flow convection buoyancy induced flows together with the forced flow are the primary mechanism of oxidizer transport to the reaction zone, while diffusion has a secondary importance. In natural convection, downward smoldering is of the opposed type while upward smoldering resembles more the forward type. For opposed flow smoldering, both natural and forced, the smolder propagation velocity is found to increase with the oxidizer mass flux reaching the reaction zone. This result confirms predictions from previously developed theoretical models that the smolder velocity is proportional to the oxygen mass flow. The experimental data is correlated in terms of a non-dimensional smolder velocity derived from these models, the results show very good agreement between theory and experiments for strong smolder. To implement the models, an analysis of the gas flow field is developed where the effect of significantly different permeabilities between char and foam is been Extinction is observed for very low and for very high flow rates, which shows that smolder is controlled by a sensitive competition between oxygen supply and heat losses to and from the reaction zone. Under these conditions the models do not describe the experiments well. The forward flow smolder experiments show that forward smoldering is controlled not only by the competition between oxygen supply and heat losses to and from the reaction zone but also by the competition between pyrolysis and oxidation. For low flow velocities a regime resembling the opposed flow is observed. As the air flow velocity is increased, foam pyrolysis followed by char oxidation is the controlling smolder mechanism. For both these conditions the theoretical models describe the experiments well. Increasing the flow velocity further results in a smolder propagation velocity controlled by total fuel consumption, in downward burining. For upward burning transition to flaming is observed for very high air flow velocities. This last regime is not well predicted by the theoretical models. The results from the experiments in variable gravity environment conducted in the KC-135A and Leajet airplanes confirm the normal gravity observations that the competition between heat losses and oxidizer transport is the major mechanism controlling smolder. The absence of convective flow in low gravity results in higher temperature in the unburnt fuel and char due to smaller heat losses to the surroundings. However, the oxidizer transport to the reaction zone also decreases and as a result the temperature at the reaction zone decreases indicating a weakening of the eaction, The presence of pyrolytic reactions in foward smolder and their capability to inhibit smoldering complicates the above described smolder mechanisms.

Among many useful properties of elastomers, one is their ability to absorb energy by deforming to large strains without fracturing. This property combined with their good adhesion to substrates makes them suited as adhesive films and coatings for protection against impact damage. An example of practical significance is the erosion of helicopter rotor blades where the protection of leading edge is often achieved by mounting a film or applying a coat of polyurethane. Although this is a workable solution, there is currently little knowledge as to the durability of this elastomeric film/coat under impact of hard and angular particles such as sand. A deformation and failure analysis that deals with the angularity of the erodents and captures the local mechanisms responsible for erosion damage in elastomers is the sine qua non. The present endeavor tries to address these issues by considering a polyurethane layer on a quasi-rigid substrate, impacted by hard particles at velocities and angles of attack given by pre-specified distributions. A novel method is devised to address the angularity issue. A series of finite-element calculations are performed on the coating layer-substrate systems subjected to different velocities, incidence and angularity of the impacting erodents. An elasto-plastic material constitution with isotropic hardening is employed in the simulations and material parameters representative of polyurethane are used for the coat. Initial parametric deformation analyses provided an adequate qualitative estimate of erosion parameters. Incorporation of a stress based fracture criterion enabled a quantitative measure of material removal due to erosion to be achieved. The simulation results show good match with experimental trends of target mass loss as obtained under normal and inclined loadings with angular erodents. The current simulation framework has sufficient capability and versatility to incorporate more enriched polymer-models and advanced fracture criteria in the future, thereby allowing parametric studies toward selection of materials and coat-layer thicknesses thus predicting the erosion mass loss as accurately as measured by experiments.

The first objective of this thesis was to assess the feasibility of designing a “smart” degradable polymer that can release anti-inflammatory drugs in response to inflammatory-related enzymes. The drug polymer was synthesized using diisocyanates, poly(caprolactone)diols, and oxaceprol (OC) biomonomers. Biodegradation studies demonstrated that the trimethylhexamethylene diisocyanate-based drug polymer responded to an inflammatory enzyme to release more OC, while a 1, 12-diisocyanatododecane analog demonstrated minimal drug release. The drug delivery response was believed to be a direct function of the molecular structure and distribution of the hard segment. The second objective of this thesis was to elucidate the anti-inflammatory mechanisms of OC by investigating its effects on cytokine-induced monocytic-cells adhesion in human umbilical vein endothelial cells (HUVECs) in vitro. Results showed that OC had no direct effect on the monocyte-endothelium adhesion, suggesting that OC may mediate inflammation by mechanisms other than those suggested by the literature.

The first objective of this thesis was to assess the feasibility of designing a “smart” degradable polymer that can release anti-inflammatory drugs in response to inflammatory-related enzymes. The drug polymer was synthesized using diisocyanates, poly(caprolactone)diols, and oxaceprol (OC) biomonomers. Biodegradation studies demonstrated that the trimethylhexamethylene diisocyanate-based drug polymer responded to an inflammatory enzyme to release more OC, while a 1, 12-diisocyanatododecane analog demonstrated minimal drug release. The drug delivery response was believed to be a direct function of the molecular structure and distribution of the hard segment. The second objective of this thesis was to elucidate the anti-inflammatory mechanisms of OC by investigating its effects on cytokine-induced monocytic-cells adhesion in human umbilical vein endothelial cells (HUVECs) in vitro. Results showed that OC had no direct effect on the monocyte-endothelium adhesion, suggesting that OC may mediate inflammation by mechanisms other than those suggested by the literature.