Thesis (M.S.)--Ohio University, June, 1990. / Title from PDF t.p.

Thesis (M.S.)--Ohio University, November, 1990. / Title from PDF t.p.

Thesis (M.S.)--Ohio University, August, 1993. / Title from PDF t.p.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 94-104). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 94-104). Also available on the Internet.

Thesis (Ph. D.)--Lehigh University, 2006. / Includes bibliographical references and vita.

No description available.

L’objectif de cette thèse est de mettre au point des formes adéquates d’hydrogels thermosensibles destinées à une application textile transdermique de libération contrôlée de médicament. Les travaux concernent les hydrogels thermosensibles à base de poly(N-isopropylacrylamide) (PNIPAAm). Ce polymère a été combiné sous une forme linéaire et/ou réticulée avec l’alginate, pour former des hydrogels ayant une structure de réseaux de polymères interpénétrés. On améliore ainsi les propriétés du PNIPAAm pur. Des hydrogels de PNIPAAm et d’alginate de calcium (CA) ont d’abord été synthétisés sous forme de films. La présence de CA contribue à l’amélioration des propriétés mécaniques, sans modifier la température de transition de phase du PNIPAAm. Nous avons ensuite appliqué la technique d’extrusion électrostatique pour préparer des microsphères d’hydrogel. Les paramètres du procédé ont été variés afin de comprendre et d’optimiser les conditions de fabrication de microsphères ayant un diamètre inférieur à 20 µm et une forme sphérique régulière. Nous avons utilisé la polymérisation en suspension inverse pour synthétiser des microsphères qui sont de forme plutôt régulière et sphérique, avec un diamètre variant de 20 à 80 µm. Leur structure était poreuse, en forme de nid d’abeille. La libération de l’hydrochlorure de procaïne des microsphères d’hydrogel a été étudiée avec une cellule de diffusion de Franz. L’incorporation de CA dans le réseau de PNIPAAm engendre une libération de type légèrement négatif, tandis que le PNIPAAm pur présente un type positif. La libération de procaïne dépend non seulement du phénomène de diffusion mais aussi du comportement de l’hydrogel au gonflement. / The objective of this thesis is to develop adequate forms of thermosensitive hydrogels intended for a textile-based controlled transdermal drug release application. This work deals with thermosensitive hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm). This polymer was combined in both linear and crosslinked form with alginate to form hydrogels with interpenetrating polymer network structure. Thus, the properties of conventional pure PNIPAAm hydrogel have been improved. Hydrogels of crosslinked PNIPAAm and calcium alginate (CA) were initially synthesized in the form of films. The presence of CA contributes to the improvement of mechanical properties without affecting the volume phase transition temperature (VPTT) of PNIPAAm. The technique of electrostatic extrusion was applied for the preparation of hydrogel microbeads. Operating parameters were varied to understand and optimize the conditions of the production of microbeads below 20 µm in diameter and of regular spherical shape. Inverse suspension polymerization was afterwards used for the preparation of microbeads of regular spherical shape and diameter in the range from 20 to 80 µm. They had porous, honeycomb-like structure. A Franz diffusion cell was employed to investigate the release of procaine hydrochloride from selected hydrogel microbeads. The incorporation of CA in PNIPAAm network resulted in slightly temperature-negative drug release pattern in comparison with temperature-positive drug release from the pure PNIPAAm hydrogel microbeads. The mechanism of the drug release at temperatures above and below the VPTT of microbeads depended on hydrogel swelling behavior and not solely on diffusion.

This thesis is concerned with the derivation, development, and validation of a model for the dynamic behaviour of gas bubbles in molten instant coffee, in response to changes in pressure and temperature. Initially, the material properties of molten instant coffee were investigated. The primary technique used was capillary rheometry, as the viscous behaviour of molten instant coffee is a major contributor to the behaviour of bubbles within the fluid. The experimental technique was supplemented by analytical and computational modelling of the pressure losses in the system, to improve data processing accuracy. Additional thermal and mechanical tests were performed to obtain as much of the necessary material information as possible for the system. The modelling of bubble behaviour was performed using a combination of analytical and computational methods. The relationship between the pressure driving force for bubble growth or shrinkage and the rate of change of bubble size was derived analytically for a number of common generalised Newtonian fluid models. Heat and mass transfer between the bubble and the surrounding fluid was calculated using a finite difference approximation of the governing partial differential equations. The model was written in MATLAB and initial validation was carried out by comparison with existing models for bubble dynamics. Experimental observations of bubble dynamics in flows of molten instant coffee were recorded and used for an extended validation of the model. Bubbles were exposed to step changes in pressure and oscillatory pressure profiles at a range of temperatures, and the observations of 130 individual bubbles were used to validate the model using the same material parameters for each. A final case study in using the bubble model to predict the bubble size and pressure distribution created by an extrusion process is presented as an example of the use of the model, and highlights the additional information about a process that is required to effectively use the model.

Extrusion is a design process where the material is heated and pressed through a metal disc, called a die. The opening through which the material is pressed through forms the material. There are two different types of extrusion: direct and indirect extrusion. Where the difference between them is how the material is pressed through the die. In direct extrusion, the material is pressed against the die with a so-called stem and the material is extruded in the same direction as the pressing force. Indirect extrusion is carried out by pressing the die against the material, the material is extruded in the opposite direction to the compressive force. One wish from the University of Gävle is to extrude chips from chip cutting machining of low-carbon steel. A hydraulic press and dies are available at Högskolan i Gävle, but equipment for holding the die is missing. Therefore, Högskolan i Gävle wants a rig that holds the die and allows extrusion. The objective of the work is to contribute with theoretical design proposals of a rig that allows extrusion. The aim is to develop a theoretical design proposal on a rig that allows extrusion of metal chips.The development of the rig began with a literature study where the goal was to get an understanding of the key components in the extrusion process. Based on the literature study, a list of what functions the rig must have was developed. Afterwards requirements for the rig were developed based on physical limitations for the press to be used, conditions that makes the rig safe to use and functionally requirements. With brainstorming, suggestions were made to achieve the functions of the rig. Each suggestion was compared against the requirements and the suggestions that meet all the requirements were combined with each other to produce different concepts. Two concepts was selected for further development resulting in two different models for direct extrusion and two for indirect extrusion.The work has resulted in four different rigs: one rig for direct and one for indirect extrusion, where each extrusion method has a rig that is two-part and one rig that is solid (not two-part). Where the two-part variant can allow easier access to the extruded bar. In both direct and indirect extrusion, the die will lie on the rigs which are hollow and the extruded rod will be extruded under the die. The chips to be extruded will be pre-pressed in a canister that is of the same material as the chips. The chips will then be extruded together with the canister. Upon direct extrusion, the canister will be centered against the die with a container and the canister will be pressed against the die with a stem. In the case of indirect extrusion, the container will be lowered over the cansiter and the matrix to center them against each other. The container will then be used as a stem and press the canister against the die.