Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 41, 81, 130, 183, 270, 315, 336).

Sur la base de précédents travaux de l’unité INSERM 1148, sur des films à base d’alcool polyvinylique, nous avons implanté et évalué des prothèses de moins de 2mm de diamètre. L’ajout de gelatine in vitro a montré des capacités d’adhérence cellulaires, compatibles avec une endothelialisation in situ, des implants garant, d’une perméabilité à long terme. Notre modèle était le remplacement de 1cm d’aorte sous rénale de rat. Ces implants, ont été utilisées comme modèle d’entrainement basse fidélité à la microchirurgie, avec de meilleurs résultats sur l’acquisition de la technique d’anastomose microchirurgicale, que les tubes en silicone antérieurement utilisé, lors de l’enseignement chez 71 étudiants. Un nouveau moyen d’imagerie pour l’exploration vasculaire par angiographie par résonance magnétique, en temps de vol sans injection chez l’animal, et la première application chez l’homme sont rapportés. Apres avoir présenté notre methode de fabrication par reticulation physique (Lyophilisation Congelation) et chimique (STMP) Cdu PVA, directement sous forme de tubes, nous avons confirmé l’hypothèse que les micro implants à base de PVA associé à la gélatine à hauteur de 1%, a permis d’améliorer la perméabilité par rapport au PVA seul, ou à tout autre ratio de gélatine ; et ce grâce à une endothélisation in situ constatées histologiquement. Les performances biomécaniques de l’implant ont aussi étaient évaluées. Au delà de 2 mois la perméabilité chute de 75% à 50%. Le vieillissement du matériel par son enraidissement, et le relargage de la gélatine pourrait expliquer cette diminution des performances au cours du temps. / Non communiqué

No description available.

No description available.

<p> The objective of this work was to investigate the potential of poly(vinyl pyrrolidone) (PVP) as a protein resistant biomaterial. Two types of PVP surface were studied: (1) plasma polymerized N-vinyl pyrrolidone monomer on polyethylene (PE), and (2) grafted PVP surfaces formed by reaction of the activated polymer with plasma polymerized allyl amine on PE. Surfaces were also prepared by grafting polyethylene oxide (PEO), a known protein repellent, to plasma polymerized allyl amine and for comparison to PVP. The surfaces were characterized chemically by water contact angle and X-ray photoelectron spectroscopy (XPS). Protein interactions were studied using radiolabeled fibrinogen in PBS buffer. </p> <p> Plasma polymerized N-vinyl pyrrolidone surfaces were prepared in a microwave plasma reactor. Reactions were carried out both at room temperature and at 50°C (increased vapour pressure) in an attempt to increase the extent of plasma polymer deposition. The resulting surfaces showed structures chemically different from conventional linear PVP. XPS analysis suggested the presence of a variety of functional groups, including amines, amides, hydroxyls, carbonyls and urethanes. Mechanisms for the reactions occurring could not be ascertained but it appeared that the monomer was extensively fragmented in the plasma. Although these surfaces were hydrophilic (contact angles of 20 to 30°), they did not resist fibrinogen adsorption: in fact they showed adsorption levels approximately 10% greater than unmodified polyethylene. </p> <p> Methods for direct grafting of polyvinyl pyrrolidone and polyethylene oxide to plasma polymerized allyl amine (PPAA) surfaces were designed on the assumption that the PPAA surfaces would be rich in amino groups for reaction with appropriate polymer chain ends. Although there was 8-12% of nitrogen on the surfaces, the C1 s high resolution showed that amide and urethane functionalities are also present in addition to amines. The hydroxyl end groups of preformed PEO and PVP chains were activated by reaction with either 1-[3- (dimethylamino) propyl], 3-ethylcarbodiimide and N-hydroxy succinimide (EDC/NHS), and N-N-disuccinimidyl carbonate (DSC). NMR spectra of the products of these reactions showed that for PEO, the yields were moderate, and for PVP, the yields were low. Surfaces grafted using polymers activated with EDC/NHS were more hydrophilic than surfaces grafted with DSC-activated polymers. XPS data did not provide clear evidence that significant polymer grafting had occurred in any of the systems. It was concluded that changes in the allyl amine plasma polymer in different environments following plasma polymerization may affect the efficiency of grafting subsequently. XPS data suggested that the allyl amine plasma surfaces undergo oxidation over time in air. Also the films may be partly removed from the polyethylene surface when placed in buffer as suggested by XPS and contact angle data. Various parameters were examined in an attempt to improve the allyl amine plasma polymerization process for greater stability of the film. Increasing the treatment time from 1 0 to 30 minutes gave surfaces that showed a slower change in contact angle when stored in air. </p> <p> Despite the lack of strong chemical evidence of extensive polymer grafting, all of the grafted surfaces were found to be significantly protein repellent, with reductions of 10 to 36 % compared to unmodified polyethylene. The PEO surfaces were more repellent than the PVP, although the differences were not significant. Surfaces grafted using polymers activated with EDC/NHS were more protein repellent than those grafted with DSC-activated polymers. Protein adsorption was not affected by PVP molecular weight in the range 2,500 to 10,000. Since there is considerable overlap of the molecular weight distributions (MWD) of these two polymers, it is speculated that the MWDs of the grafted polymers may be more similar than those of the polymers themselves, possibly due to "selection" of similar, presumably optimal molecular weights. </p> <p> Discussion of the possible reasons for the better protein resistance of PEO compared to PVP is given in terms of chain structure in relation to the steric exclusion and water barrier theories of protein repulsion. </p> / Thesis / Master of Applied Science (MASc)

<p> An experimental study of the steric stabilizing ability of a water soluble polyvinyl alcohol (PVA) polymer is presented.</p> <p> The free film thickness of a lamella formed between a drop of n-butylchloride and bulk n-butylchloride stabilized by PVA was measured by the Hodgson and Woods technique in order to evaluate the stabilizing ability of the polymer. A maximum in the stability was observed as the concentration of the polymer was increased. This maximum trend can be explained by the HVO theory.</p> / Thesis / Master of Engineering (MEngr)

Plasticizers are often interchanged with the idea that they will not affect the processing behavior of Polyvinyl Chloride (PVC). However, when the plasticizer type is changed, various complaints are made by the processors that the material no longer processes the same. This research was concerned with the effect of three different plasticizers on the plasticating extrusion behavior of PVC. Di-isodecyl pthalate (DIDP), di-hexyl pthalate (DHP) and 2-ethyl hexyl pthalate (DOP) are the three plasticizers used in this study. First some differences in the extrusion performance of the three differently plasticized PVC compounds were identified. In particular, it was observed that pressure build-up, flow rate and power requirement were affected by the plasticizer type with the DIDP plasticized materials generating higher pressures and requiring more power than the other two plasticized materials. The differences in extrusion characteristics have been observed for two different dies (1/8 and 1/16 inch diameter) attached to the extruder. The differences were most significant between the DIDP and the DHP plasticized mixes. Factors which could influence the processing behavior of plasticized PVC include viscosity, compaction, thermal conductivity, specific heat, and friction coefficient. It was found that all other properties other than the viscosity were unaffected by the plasticizer type. On the other hand, viscosities were significantly affected by the plasticizer type with the DIDP plasticized materials displaying higher values between 160 and 190 °C. The difference in viscosity was larger between the DIDP and DHP plasticized materials than between DIDP and DOP plasticized materials. The differences in viscosity between DIDP and DOP plasticized materials tend to diminish considerably at 190 °C. Two flow regions characterized by different degrees of fusion above and below 165 °C were identified for the plasticized PVC compounds. Plasticized PVC exhibited yield stresses with the DIDP plasticized materials having higher values. The yield stresses were responsible for the significant difference in viscosity at lower shear rates. The yield stress was a more dominant feature at temperatures below 160 °C and this fact was made use of in modeling the solids conveying zone as a fluid with yield stress. Correlation was established between the viscosities and the extrusion behavior of the plasticized PVC compounds. It was observed that the DIDP plasticized mixes had higher viscosities, fused earlier in the screw channel, gave rise to higher pressures, required more power and in general exhibited higher flow rates at the same screw speed. The finite element method was used for the numerical simulations. Based on the experimental results, the numerical modeling of the melt zone was performed in order to predict the differences in the extrusion characteristics. The melt zones were modeled as a temperature dependent power law fluid having two different viscosity expressions above and below 165 °C. The numerical predictions for pressures and flow rates in the extruder with the 1/8 inch diameter die were in good agreement with the experimental results. For the case of the 1/16 inch diameter die attached to the extruder, the numerical and experimental flow rates were in good agreement but the pressure predictions, although indicating the correct trends, were off by 15 to 20% from the experimental results. In general the differences in the physical properties, viz. viscosities, were used to predict the differences in the pressure build-ups and flow rates. Also the solid conveying zone was modeled using a Herschel Bulkley model. It was possible to match the experimental and numerical results for the solids conveying zone by using an average density value for the entire solids conveying zone, but more work needs to be done in order to establish greater validity and applicability of this model. / Ph. D.

The study presented here consists in an original piece of work to better understand complex food packaging interactions. The majority of investigations on food polymer interactions related to orange juice and this provided a good base to our study (Literature reviews: cf. Chapters 1a and b). Additionally a rather remarkable finding in 1994 was that limonin, a trace bitter material found in some varieties of orange juice was rapidly absorbed by highly plasticised polyvinyl chloride (PVC plastisol) (Chapter 2). Several commercial absorbants are available for debittering, relying on limonin absorption on the large surface area of the highly porous absorbant pellets. However, the absorptive properties of the smooth plastisols apparently relied on a different mechanism. Limonin is a very large (470.5 g/mol) compound, but some preliminary experiments with another much smaller orange juice constituent d- of absorbates in plastisols, methods used earlier (Moisan 1980, Holland and Santangelo 1988) to measure solubilities and diffusion constants in packaging films could be advantageously used to survey these properties in a wide range of materials, including model compounds of various types, and a number of compounds which may be found in citrus juices (Chapters 3, 4 and 5). Experimentally, the method found most suitable was to use a ‘test film’ of pure plastisol which was wrapped tightly on both sides by a similar ‘supply film’ blended with 1 Molar test material (also called ‘absorbate’), setting up a concentration gradient. The inner test film was removed at regular intervals (minutes to hours) to measure (mainly by weighing) the uptake of the test reagent with time. Rather unexpectedly, it was found in a number of cases that the test film lost weight, either from the beginning, or after a period of time. Three main types of behaviour were identified: Type A lost weight from the beginning and over a long period of time, Type B gained weight initially and then lost weight, and Type C gained weight until a steady state was reached. Often the maximum, or near maximum, mass increase occurred within around 100 minutes, indicating a very rapid, liquid-like diffusion mechanism, in harmony with the rapid uptake of d-limonene and limonin. The major parameters of interest with these compounds are their diffusion rates and their solubilities, and in the presence of aqueous media (orange juice and other foodstuffs) the partition coefficient between the plastisol and water, which is related to the hydrophobicity function LogP for the compound. The major complicating factor in these measurements is the observation that the plasticiser materials themselves also migrate, in the reverse direction, because of the lower effective concentration in the supply film. This effect tends to be small, but is one explanation for the mass loss observed above, and cannot be ignored over the long term, nor in its practical applications to contamination in foods. There are many possible applications for the techniques described above. The removal or addition of compounds in food packaging itself is one. Upgrading foods, such as orange juice, commercially, is another. In many cases ‘scalping’ off-flavours or other minor components takes place exclusively through solid or liquid contact with the packaging. The removal from the headspace measured by the current gas permeation methods is irrelevant for the vast numbers of involatile, but easily diffusable compounds. For such compounds these novel applications are simple and rapid, require little specialised equipment, and fill a niche in the armoury of food and packaging chemists. / Doctor of Philosophy (PhD)

Metal-organic framework (MOF) materials are a novel set of porous crystalline materials that have generated great scientific interest within the past two decades due to their attractive properties such as high porosity, surface areas and tunable pore structure. These properties have made them emerge as potential candidates suitable for a broad range of applications such as gas separations and storage, catalysis and drug delivery. Despite their fascinating properties, MOFs are often unsuitable for most industrial applications due to their instability when exposed to mechanical stress. The challenge therefore is to convert the MOFs to high strength materials capable of withstanding such stress while still maintaining their exciting properties. This thesis thus focuses on investigating the effects of different binders on a zirconium based metal-organic-framework, UiO-66, in an attempt to enhance the mechanical strength of the adsorbent samples. Three different binders, kaolinite, polyvinyl alcohol and tartaric acid, are mixed with the parent MOF material in different weight percents, pressed into solid disc pellets at different pressures and calcined at different temperatures. Properties such as changes in structure, density, porosity, surface area, radial crush strength, and the adsorption capacity with CO2 are measured and evaluated. Results gathered from this work reveal that polyvinyl alcohol is the most promising of the three binders due to the increase in the strength of pellets and the slight decrease in CO2 adsorption it offers. Recommendations for future research work aimed at driving these materials towards reaching their maximum application potentials are proposed.

The applications of membrane technologies have dramatically increased during the last few decades due to technology improvement and cost reduction. Membrane applications can be found in water and wastewater treatment, pharmaceutical industry, chemical processing industry, food industry, etc. However, the membrane technology faces two major challenges: membrane fouling and membrane lifetime. During the membrane filtration process, membrane fouling caused by natural organic matter (NOM) is an inevitable phenomenon, and physical cleaning or chemical cleaning are required for recovering the performance of membrane. As a result of these cleaning processes, membrane lifetime is shortened. For this reason, it is necessary to improve membrane's fouling resistance and lifetime in order to apply membrane technology in large-scale facilities. This dissertation focuses on improving the fouling resistance and flux performance of polyvinyl chloride (PVC) membrane and polyvinylidene fluoride (PVDF) membrane. Specifically, it is comprised of four parts. First, I prepared PVC membranes by adding different amounts of amphiphilic copolymer (Pluronic F 127) into PVC casting solutions. I optimized the performance of PVC membranes by changing the amount of Pluronic F127 used in the casting solution. The results show that with the increase of Pluronic F 127 content, the pore size and pore density both decrease. Moreover, the membrane surface becomes more hydrophilic as indicated by lower contact angles. In addition, the PVC membrane exhibits remarkable antifouling characteristics after adding Pluronic F 127. Second, I synthesized PVDF membranes by adding PVDF graft poly(ethylene glycol) methyl ether methacrylate (PEGMA) (PVDF-g-PEGMA) as additive in casting solutions via the phase inversion method. The synthesized PVDF membranes have unique pillar-like structures on surfaces, which gives the PVDF membrane a defect-free feature and allows it to generate high flux under low pressure. Third, I investigated the forming mechanism of the pillar-like structure from aspects of solvent and additive. Finally, I investigated the influence of PEGMA dose on the performance of PVDF membranes. I changed the amount of PEGMA used in the casting solution and compared the performance of the synthesized PVDF membranes. To summarize, this dissertation has deepened our understanding of how to improve the fouling resistance and flux performance of PVC membranes and PVDF membranes by using amphiphilic copolymer. In addition, the PVDF membrane I synthesized has unique pillar-like structures that give it defect-free and high flux properties. Overall, the results of this study provide valuable information for PVC and PVDF membrane synthesis for large-scale production.