Studio e sviluppo di tecniche per la produzione di nanocompositi a matrice di alluminio

Foundry aluminum alloys play a fundamental role in several industrial fields, as they are employed in the production of several components in a wide range of applications. Moreover, these alloys can be employed as matrix for the development of Metal Matrix Composites (MMC), whose reinforcing phases may have different composition, shape and dimension. Ceramic particle reinforced MMCs are particular interesting due to their isotropic properties and their high temperature resistance. For this kind of composites, usually, decreasing the size of the reinforcing phase leads to the increase of mechanical properties. For this reason, in the last 30 years, the research has developed micro-reinforced composites at first, characterized by low ductility, and more recently nano-reinforced ones (the so called metal matrix nanocomposite, MMNCs). The nanocomposites can be obtained through several production routes: they can be divided in in-situ techniques, where the reinforcing phase is generated during the composite production through appropriate chemical reactions, and ex situ techniques, where ceramic dispersoids are added to the matrix once already formed. The enhancement in mechanical properties of MMNCs is proved by several studies; nevertheless, it is necessary to address some issues related to each processing route, as the control of process parameters and the effort to obtain an effective dispersion of the nanoparticles in the matrix, which sometimes actually restrict the use of these materials at industrial level. In this work of thesis, a feasibility study and implementation of production processes for Aluminum and AlSi7Mg based-MMNCs was conducted. The attention was focused on the in-situ process of gas bubbling, with the aim to obtain an aluminum oxide reinforcing phase, generated by the chemical reaction between the molten matrix and industrial dry air injected in the melt. Moreover, for what concerns the ex-situ techniques, stir casting process was studied and applied to introduce alumina nanoparticles in the same matrix alloys. The obtained samples were characterized through optical and electronic microscopy, then by micro-hardness tests, in order to evaluate possible improvements in mechanical properties of the materials.

Ricerca sulle Caratteristiche di Filtrabilità della Birra e Ottimizzazione del Processo di Filtrazione

Il presente lavoro ha avuto lo scopo di identificare le caratteristiche di filtrabilità della birra attraverso lo svolgimento di prove tecnologiche di filtrazione in scala di laboratorio e su scala pilota, utilizzando diverse tipologie di sistemi filtranti e sperimentando diversi materiali di membrana. La fase preliminare della caratterizzazione della filtrabilità della birra è stata condotta presso i laboratori del Campden-BRI – The Brewing Research International, Inghilterra, mentre le prove tecnologiche su scala pilota si sono svolte presso il CERB – Centro di Eccellenza per la Ricerca sulla Birra. Le prove di filtrazione e le analisi sui campioni hanno permesso di verificare le performance delle diverse membrane utilizzate in risposta alla variazione dei principali parametri del processo di filtrazione tangenziale. Sono stati analizzati diversi parametri di qualità della birra filtrata attraverso il monitoraggio del processo e lo svolgimento di prove analitiche sul prodotto volte ad evidenziare gli effetti delle differenti tecnologie adottate. Per quanto riguarda le prove di laboratorio per la caratterizzazione della filtrabilità della birra, l’analisi della PCS (Photon Correlation Spectroscopy) è stata utilizzata per verificare l’influenza di diversi trattamenti enzimatici sulla efficienza del processo di filtrazione e la loro influenza sulla stabilità colloidale della birra filtrata. Dai risultati ottenuti è emerso che il PCS è un valido strumento per determinare la distribuzione in classi di diametro e il diametro medio effettivo delle particelle solide in sospensione nella birra e può essere utilizzato sia per predire la stabilità della birra filtrata, sia per monitorare il processo di filtrazione in tempo reale.

Analisi sperimentale dell'influenza dei parametri di processo sulla resistenza di contatto tra polimero e stampo durante la formatura

Con gli strumenti informatici disponibili oggi per le industrie, in particolar modo coi software CAE, le possibile simulare in maniera più che soddisfacente i fenomeni fisici presenti in natura. Anche il raffreddamento di un manufatto in polimero può venire simulato, a patto che si conoscano tutti i dati dei materiali e delle condizioni al contorno. Per quanto riguarda i dati dei materiali, i produttori di polimeri sono molto spesso in grado di fornirli, mentre le condizioni al contorno devono essere padroneggiate dal detentore della tecnologia. Nella pratica, tale conoscenza è al più incompleta, quindi si fanno ipotesi per colmare le lacune. Una tra le ipotesi più forti fatte è quella di una perfetta conduzione all'interfaccia tra due corpi. Questo è un vincolo troppo forte, se paragonato alla precisione di tutti gli altri dati necessari alla simulazione, e quindi si è deciso di eseguire una campagna sperimentale per stimare la resistenza al passaggio flusso termico all'interfaccia polimero-stampo ovvero determinare la conduttanza termica di contatto. L'attività svolta in questa tesi di dottorato ha come scopo quello di fornire un contributo significativo allo sviluppo e al miglioramento dell'efficienza termica degli stampi di formatura dei polimeri termoplastici con tecnologia a compressione.

Electronic transport in the heavy fermion superconductors UPd 2 Al 3 and UNi 2 Al 3

This work addresses the electronical properties of the superconductors UPd2Al3 and UNi2Al3 on the basis of thin film experiments. These isotructural compounds are ideal candiates to study the interplay of magnetism and superconductivity due to the differences of their magnetically ordered states, as well as the experimental evidence for a magnetic pairing mechanism in UPd2Al3. Epitaxial thin film samples of UPd2Al3 and UNi2Al3 were prepared using UHV Molecular Beam Epitaxy (MBE). For UPd2Al3, the change of the growth direction from the intrinsic (001) to epitaxial (100) was predicted and sucessfully demonstrated using LaAlO3 substrates cut in (110) direction. With optimized deposition process parameters for UPd2Al3 (100) on LaAlO3 (110) superconducting samples with critical temperatures up to Tc = 1.75K were obtained. UPd2Al3-AlOx-Ag mesa junctions with superconducting base electrode were prepared and shown to be in the tunneling regime. However, no signatures of a superconducting density of states were observed in the tunneling spectra. The resistive superconducting transition was probed for a possible dependence on the current direction. In contrast to UNi2Al3, the existence of such feature was excluded in UPd2Al3 (100) thin films. The second focus of this work is the dependence of the resisitive transition in UNi2Al3 (100) thin films on the current direction. The experimental fact that the resisitive transition occurs at slightly higher temperatures for I║a than for I║c can be explained within a model of two weakly coupled superconducting bands. Evidence is presented for the key assumption of the two-band model, namely that transport in and out of the ab-plane is generated on different, weakly coupled parts of the Fermi surface. Main indications are the angle dependence of the superconducting transition and the dependence of the upper critical field Bc2 on current and field orientation. Additionally, several possible alternative explanations for the directional splitting of the transition are excluded in this work. An origin due to scattering on crystal defects or impurities is ruled out, likewise a relation to ohmic heating or vortex dynamics. The shift of the transition temperature as function of the current density was found to behave as predicted by the Ginzburg-Landau theory for critical current depairing, which plays a significant role in the two-band model. In conclusion, the directional splitting of the resisitive transition has to be regarded an intrinsic and unique property of UNi2Al3 up to now. Therefore, UNi2Al3 is proposed as a role model for weakly coupled multiband superconductivity. Magnetoresistance in the normalconducting state was measured for UPd2Al3 and UNi2Al3. For UNi2Al3, a negative contribution was observed close to the antiferromagnetic ordering temperature TN only for I║a, which can be associated to reduced spin-disorder scattering. In agreement with previous results it is concluded that the magnetic moments have to be attributed to the same part of the Fermi surface which generates transport in the ab-plane.

Vanillin production from ferulic acid with Pseudomonas fluorescens BF13-1p4

Bioconversion of ferulic acid to vanillin represents an attractive opportunity for replacing synthetic vanillin with a bio-based product, that can be label “natural”, according to current food regulations. Ferulic acid is an abundant phenolic compound in cereals processing by-products, such as wheat bran, where it is linked to the cell wall constituents. In this work, the possibility of producing vanillin from ferulic acid released enzymatically from wheat bran was investigated by using resting cells of Pseudomonas fluorescens strain BF13-1p4 carrying an insertional inactivation of vdh gene and ech and fcs BF13 genes on a low copy number plasmid. Process parameters were optimized both for the biomass production phase and the bioconversion phase using food-grade ferulic acid as substrate and the approach of changing one variable while fixing the others at a certain level followed by the response surface methodology (RSM). Under optimized conditions, vanillin up to 8.46 mM (1.4 g/L) was achieved, whereas highest productivity was 0.53 mmoles vanillin L-1 h-1). Cocktails of a number of commercial enzyme (amylases, xylanases, proteases, feruloyl esterases) combined with bran pre-treatment with steam explosion and instant controlled pressure drop technology were then tested for the release of ferulic acid from wheat bran. The highest ferulic acid release was limited to 15-20 % of the ferulic acid occurring in bran, depending on the treatment conditions. Ferulic acid 1 mM in enzymatic hydrolyzates could be bioconverted into vanillin with molar yield (55.1%) and selectivity (68%) comparable to those obtained with food-grade ferulic acid after purification from reducing sugars with a non polar adsorption resin. Further improvement of ferulic acid recovery from wheat bran is however required to make more attractive the production of natural vanillin from this by-product.

Integrated analysis and design of optimization and up-scaling of inductively coupled plasma synthesis of nanoparticles

This study is focused on radio-frequency inductively coupled thermal plasma (ICP) synthesis of nanoparticles, combining experimental and modelling approaches towards process optimization and industrial scale-up, in the framework of the FP7-NMP SIMBA European project (Scaling-up of ICP technology for continuous production of Metallic nanopowders for Battery Applications). First the state of the art of nanoparticle production through conventional and plasma routes is summarized, then results for the characterization of the plasma source and on the investigation of the nanoparticle synthesis phenomenon, aiming at highlighting fundamental process parameters while adopting a design oriented modelling approach, are presented. In particular, an energy balance of the torch and of the reaction chamber, employing a calorimetric method, is presented, while results for three- and two-dimensional modelling of an ICP system are compared with calorimetric and enthalpy probe measurements to validate the temperature field predicted by the model and used to characterize the ICP system under powder-free conditions. Moreover, results from the modeling of critical phases of ICP synthesis process, such as precursor evaporation, vapour conversion in nanoparticles and nanoparticle growth, are presented, with the aim of providing useful insights both for the design and optimization of the process and on the underlying physical phenomena. Indeed, precursor evaporation, one of the phases holding the highest impact on industrial feasibility of the process, is discussed; by employing models to describe particle trajectories and thermal histories, adapted from the ones originally developed for other plasma technologies or applications, such as DC non-transferred arc torches and powder spherodization, the evaporation of micro-sized Si solid precursor in a laboratory scale ICP system is investigated. Finally, a discussion on the role of thermo-fluid dynamic fields on nano-particle formation is presented, as well as a study on the effect of the reaction chamber geometry on produced nanoparticle characteristics and process yield.

Polymeric membranes for CO2 separation: effect of aging, humidity and facilitated transport

Polymeric membranes represent a promising technology for gas separation processes, thanks to low costs, reduced energy consumption and limited waste production. The present thesis aims at studying the transport properties of two membrane materials, suitable for CO2 purification applications. In the first part, a polyimide, Matrimid 5218, has been throughout investigated, with particular reference to the effect of thermal treatment, aging and the presence of water vapor in the gas transport process. Permeability measurements showed that thermal history affects relevantly the diffusion of gas molecules across the membrane, influencing also the stability of the separation performances. Subsequently, the effect of water on Matrimid transport properties has been characterized for a wide set of incondensable penetrants. A monotonous reduction of permeability took place at increasing the water concentration within the polymer matrix, affecting the investigated gaseous species to the same extent, despite the different thermodynamic and kinetic features. In this view, a novel empirical model, based on the Free Volume Theory, has been proposed to qualitatively describe the phenomenon. Moreover, according to the accurate representation of the experimental data, the suggested approach has been combined with a more rigorous thermodynamic tool (NELF Model), allowing an exhaustive description of water influence on the single parameters contributing to the gas permeation across the membrane. In the second part, the study has focused on the synthesis and characterization of facilitated transport membranes, able to achieving outstanding separation performances thanks to the chemical enhancement of CO2 permeability. In particular, the transport properties have been investigated for high pressure CO2 separation applications and specific solutions have been proposed to solve stability issues, frequently arising under such severe conditions. Finally, the effect of different process parameters have been investigated, aiming at the identification of the optimal conditions capable to maximize the separation performance.

Prozessanalytische Technologien "PAT" zur Optimierung von Wirbelschichtgranulationsprozessen

In der Herstellung fester Darreichungsformen umfasst die Granulierung einen komplexen Teilprozess mit hoher Relevanz für die Qualität des pharmazeutischen Produktes. Die Wirbelschichtgranulierung ist ein spezielles Granulierverfahren, welches die Teilprozesse Mischen, Agglomerieren und Trocknen in einem Gerät vereint. Durch die Kombination mehrerer Prozessstufen unterliegt gerade dieses Verfahren besonderen Anforderungen an ein umfassendes Prozessverständnis. Durch die konsequente Verfolgung des PAT- Ansatzes, welcher im Jahre 2004 durch die amerikanische Zulassungsbehörde (FDA) als Guideline veröffentlicht wurde, wurde der Grundstein für eine kontinuierliche Prozessverbesserung durch erhöhtes Prozessverständnis, für Qualitätserhöhung und Kostenreduktion gegeben. Die vorliegende Arbeit befasste sich mit der Optimierung der Wirbelschicht-Granulationsprozesse von zwei prozesssensiblen Arzneistoffformulierungen, unter Verwendung von PAT. rnFür die Enalapril- Formulierung, einer niedrig dosierten und hochaktiven Arzneistoffrezeptur, wurde herausgefunden, dass durch eine feinere Zerstäubung der Granulierflüssigkeit deutlich größere Granulatkörnchen erhalten werden. Eine Erhöhung der MassRatio verringert die Tröpfchengröße, dies führt zu größeren Granulaten. Sollen Enalapril- Granulate mit einem gewünschten D50-Kornverteilung zwischen 100 und 140 um hergestellt werden, dann muss die MassRatio auf hohem Niveau eingestellt werden. Sollen Enalapril- Granulate mit einem D50- Wert zwischen 80 und 120µm erhalten werden, so muss die MassRatio auf niedrigem Niveau eingestellt sein. Anhand der durchgeführten Untersuchungen konnte gezeigt werden, dass die MassRatio ein wichtiger Parameter ist und zur Steuerung der Partikelgröße der Enalapril- Granulate eingesetzt werden kann; unter der Voraussetzung dass alle anderen Prozessparameter konstant gehalten werden.rnDie Betrachtung der Schnittmengenplots gibt die Möglichkeit geeignete Einstellungen der Prozessparameter bzw. Einflussgrößen zu bestimmen, welche dann zu den gewünschten Granulat- und Tabletteneigenschaften führen. Anhand der Lage und der Größe der Schnittmenge können die Grenzen der Prozessparameter zur Herstellung der Enalapril- Granulate bestimmt werden. Werden die Grenzen bzw. der „Design Space“ der Prozessparameter eingehalten, kann eine hochwertige Produktqualität garantiert werden. rnUm qualitativ hochwertige Enalapril Tabletten mit der gewählten Formulierung herzustellen, sollte die Enalapril- Granulation mit folgenden Prozessparametern durchgeführt werden: niedrige Sprührate, hoher MassRatio, einer Zulufttemperatur von mindestens > 50 °C und einer effektiven Zuluftmenge < 180 Nm³/h. Wird hingegen eine Sprührate von 45 g/min und eine mittlere MassRatio von 4.54 eingestellt, so muss die effektive Zuluftmenge mindestens 200 Nm³/h und die Zulufttemperatur mindestens 60 °C betragen, um eine vorhersagbar hohe Tablettenqualität zu erhalten. Qualität wird in das Arzneimittel bereits während der Herstellung implementiert, indem die Prozessparameter bei der Enalapril- Granulierung innerhalb des „Design Space“ gehalten werden.rnFür die Metformin- Formulierung, einer hoch dosierten aber wenig aktiven Arzneistoffrezeptur wurde herausgefunden, dass sich der Wachstumsmechanismus des Feinanteils der Metformin- Granulate von dem Wachstumsmechanismus der D50- und D90- Kornverteilung unterscheidet. Der Wachstumsmechanismus der Granulate ist abhängig von der Partikelbenetzung durch die versprühten Flüssigkeitströpfchen und vom Größenverhältnis von Partikel zu Sprühtröpfchen. Der Einfluss der MassRatio ist für die D10- Kornverteilung der Granulate vernachlässigbar klein. rnMit Hilfe der Störgrößen- Untersuchungen konnte eine Regeleffizienz der Prozessparameter für eine niedrig dosierte (Enalapril)- und eine hoch dosierte (Metformin) Arzneistoffformulierung erarbeitet werden, wodurch eine weitgehende Automatisierung zur Verringerung von Fehlerquellen durch Nachregelung der Störgrößen ermöglicht wird. Es ergibt sich für die gesamte Prozesskette ein in sich geschlossener PAT- Ansatz. Die Prozessparameter Sprührate und Zuluftmenge erwiesen sich als am besten geeignet. Die Nachregelung mit dem Parameter Zulufttemperatur erwies sich als träge. rnFerner wurden in der Arbeit Herstellverfahren für Granulate und Tabletten für zwei prozesssensible Wirkstoffe entwickelt. Die Robustheit der Herstellverfahren gegenüber Störgrößen konnte demonstriert werden, wodurch die Voraussetzungen für eine Echtzeitfreigabe gemäß dem PAT- Gedanken geschaffen sind. Die Kontrolle der Qualität des Produkts findet nicht am Ende der Produktions- Prozesskette statt, sondern die Kontrolle wird bereits während des Prozesses durchgeführt und basiert auf einem besseren Verständnis des Produktes und des Prozesses. Außerdem wurde durch die konsequente Verfolgung des PAT- Ansatzes die Möglichkeit zur kontinuierlichen Prozessverbesserung, zur Qualitätserhöhung und Kostenreduktion gegeben und damit das ganzheitliche Ziel des PAT- Gedankens erreicht und verwirklicht.rn

Caratterizzazione e simulazione di processi di colata in sabbia di ghise sferoidali

L’oggetto principale delle attività di tesi è la caratterizzazione numerico-sperimentale di processi di colata in sabbia di ghisa sferoidale. Inizialmente è stata effettuata un’approfondita indagine bibliografica per comprendere appieno le problematiche relative all’influenza dei parametri del processo fusorio (composizione chimica, trattamento del bagno, velocità di raffreddamento) sulle proprietà microstrutturali e meccaniche di getti ottenuti e per valutare lo stato dell’arte degli strumenti numerici di simulazione delle dinamiche di solidificazione e di previsione delle microstrutture. Sono state definite, realizzate ed impiegate attrezzature sperimentali di colata per la caratterizzazione di leghe rivolte alla misura ed alla differenziazione delle condizioni di processo, in particolare le velocità di raffreddamento, ed atte a validare strumenti di simulazione numerica e modelli previsionali. Inoltre sono stati progettati ed impiegati diversi sistemi per l’acquisizione ed analisi delle temperature all’interno di getti anche di grandi dimensioni. Lo studio, mediante analisi metallografica, di campioni di materiale ottenuto in condizioni differenziate ha confermato l’effetto dei parametri di processo considerati sulle proprietà microstrutturali quali dimensioni dei noduli di grafite e contenuto di ferrite e perlite. In getti di grandi dimensioni si è riscontrata anche una forte influenza dei fenomeni di macrosegregazione e convezione della lega su microstrutture e difettologie dei getti. Le attività si sono concentrate principalmente nella simulazione numerica FEM dei processi fusori studiati e nell’impiego di modelli empirico-analitici per la previsione delle microstrutture. I dati misurati di temperature di processo e di microstrutture sono stati impiegati per la validazione ed ottimizzazione degli strumenti numerici previsionali impiegati su un ampio intervallo di condizioni di processo. L’impiego di strumenti affidabili di simulazione del processo fusorio, attraverso l’implementazione di correlazioni sperimentali microstrutture-proprietà meccaniche, permette la valutazione di proprietà e difettologie dei getti, fornendo un valido aiuto nell’ottimizzazione del prodotto finito e del relativo processo produttivo.

HCl gas gettering of 3d transition metals for crystalline silicon solar cell concepts

In order to reduce the costs of crystalline silicon solar cells, low-cost silicon materials like upgraded metallurgical grade (UMG) silicon are investigated for the application in the photovoltaic (PV) industry. Conventional high-purity silicon is made by cost-intensive methods, based on the so-called Siemens process, which uses the reaction to form chlorosilanes and subsequent several distillation steps before the deposition of high-purity silicon on slim high-purity silicon rods. UMG silicon in contrast is gained from metallurgical silicon by a rather inexpensive physicochemical purification (e.g., acid leaching and/or segregation). However, this type of silicon usually contains much higher concentrations of impurities, especially 3d transition metals like Ti, Fe, and Cu. These metals are extremely detrimental in the electrically active part of silicon solar cells, as they form recombination centers for charge carriers in the silicon band gap. This is why simple purification techniques like gettering, which can be applied between or during solar cell process steps, will play an important role for such low-cost silicon materials. Gettering in general describes a process, whereby impurities are moved to a place or turned into a state, where they are less detrimental to the solar cell. Hydrogen chloride (HCl) gas gettering in particular is a promising simple and cheap gettering technique, which is based on the reaction of HCl gas with transition metals to form volatile metal chloride species at high temperatures.rnThe aim of this thesis was to find the optimum process parameters for HCl gas gettering of 3d transition metals in low-cost silicon to improve the cell efficiency of solar cells for two different cell concepts, the standard wafer cell concept and the epitaxial wafer equivalent (EpiWE) cell concept. Whereas the former is based on a wafer which is the electrically active part of the solar cell, the latter uses an electrically inactive low-cost silicon substrate with an active layer of epitaxially grown silicon on top. Low-cost silicon materials with different impurity grades were used for HCl gas gettering experiments with the variation of process parameters like the temperature, the gettering time, and the HCl gas concentration. Subsequently, the multicrystalline silicon neighboring wafers with and without gettering were compared by element analysis techniques like neutron activation analysis (NAA). It was demonstrated that HCl gas gettering is an effective purification technique for silicon wafers, which is able to reduce some 3d transition metal concentrations by over 90%. Solar cells were processed for both concepts which could demonstrate a significant increase of the solar cell efficiency by HCl gas gettering. The efficiency of EpiWE cells could be increased by HCl gas gettering by approximately 25% relative to cells without gettering. First process simulations were performed based on a simple model for HCl gas gettering processes, which could be used to make qualitative predictions.

Entwicklung eines Thermodruckhydrolyse-Verfahrens zur Vorbehandlung von Weizenstroh ohne vorherige mechanische Zerkleinerung für die Produktion von Polyhydroxybuttersäure

In der vorliegenden Arbeit wurde der nachwachsende Rohstoff Weizenstroh für die Produktion des Biopolymers Polyhydroxybuttersäure genutzt. Als Lignocellulose enthält Weizenstroh einen hohen Anteil an Glucose und Xylose in Form von Cellulose und Hemicellulose. Eine Gewinnung ist aufgrund der komplexen Struktur mit Lignin als dritte Hauptkomponente nur durch eine Vorbehandlung möglich. Hierzu wurde ein thermochemisches Vorbehandlungsverfahren im halbtechnischen (125 l Reaktor) und technisch (425 l Reaktor) Maßstab mit verdünnter Salpetersäure (bis 1 % v/v) etabliert und hinsichtlich verschiedener Versuchsparameter (Behandlungstemperatur, Säure-Konzentration, etc.) optimiert. Auf eine mechanische Vorbehandlung wurde verzichtet. Danach erfolgte eine enzymatische Hydrolyse der vorbehandelten Biomasse. Der PHB-Produzent Cupriavidus necator DSM 545 wurde eingesetzt, um aus den freigesetzten Zuckern PHB zu synthetisieren. rnDurch die Optimierung der Vorbehandlung konnten bis zu 90 % der Glucose und 82 % der Xylose nach der enzymatischen Hydrolyse aus dem Stroh als Monomere und Oligomere freigesetzt werden. Außerdem wurde eine erfolgreiche Überführung des Vorbehandlungsprozesses in den 425 l Reaktor demonstriert. In den gewonnenen Zucker-Hydrolysaten konnten hohe Zelldichten und PHB-Gehalte mit bis zu 38 % erreicht werden. Eine vorherige kostenintensive Reinigung der Hydrolysate war nicht nötig. Zusätzlich konnte gezeigt werden, dass die Reststoffe nach der enzymatischen Hydrolyse, Zellkultur und PHB-Extraktion ausreichendes Potential für eine Biogas-Produktion besitzen. rn

Studio dell'attività idrolitica di glucomannano ad opera di alcuni preparati enzimatici industriali

Over the last few decades, polysaccharides have gained increasing attention in the biomedical and drug delivery fields. Among them, glucomannan (GM) has become a particularly interesting polymer in the nutraceutical, pharmaceutical and cosmeceutical field, however the high molecular weight of this natural polymer is the cause of the limits to its application that reflected in a poor solubility in water.Reduce the molecular weight could improve its use and at the same time does not eliminate its properties. In this study, we investigated the ability of enzymes to hydrolyze the polysaccharide structure of glucomannan by two commercial enzymes: Fungamyl Super AX and Celluclast BG. The purpose of the thesis was to identify the enzymatic activity and the process parameters ( pH and temperature) that influence the catalytic activity of the enzymes, the molecular size and the viscosity of products released after enzymatic hydrolysis of glucomannan.

A qualitative risk assessment approach for Swiss dairy products: opportunities and limitations

Switzerland implemented a risk-based monitoring of Swiss dairy products in 2002 based on a risk assessment (RA) that considered the probability of exceeding a microbiological limit value set by law. A new RA was launched in 2007 to review and further develop the previous assessment, and to make recommendations for future risk-based monitoring according to current risks. The resulting qualitative RA was designed to ascertain the risk to human health from the consumption of Swiss dairy products. The products and microbial hazards to be considered in the RA were determined based on a risk profile. The hazards included Campylobacter spp., Listeria monocytogenes, Salmonella spp., Shiga toxin-producing Escherichia coli, coagulase-positive staphylococci and Staphylococcus aureus enterotoxin. The release assessment considered the prevalence of the hazards in bulk milk samples, the influence of the process parameters on the microorganisms, and the influence of the type of dairy. The exposure assessment was linked to the production volume. An overall probability was estimated combining the probabilities of release and exposure for each combination of hazard, dairy product and type of dairy. This overall probability represents the likelihood of a product from a certain type of dairy exceeding the microbiological limit value and being passed on to the consumer. The consequences could not be fully assessed due to lack of detailed information on the number of disease cases caused by the consumption of dairy products. The results were expressed as a ranking of overall probabilities. Finally, recommendations for the design of the risk-based monitoring programme and for filling the identified data gaps were given. The aims of this work were (i) to present the qualitative RA approach for Swiss dairy products, which could be adapted to other settings and (ii) to discuss the opportunities and limitations of the qualitative method.

Three dimensional finite element simulation of polymer melting and flow in a single-screw extruder : optimization of screw channel geometry

Single-screw extrusion is one of the widely used processing methods in plastics industry, which was the third largest manufacturing industry in the United States in 2007 [5]. In order to optimize the single-screw extrusion process, tremendous efforts have been devoted for development of accurate models in the last fifty years, especially for polymer melting in screw extruders. This has led to a good qualitative understanding of the melting process; however, quantitative predictions of melting from various models often have a large error in comparison to the experimental data. Thus, even nowadays, process parameters and the geometry of the extruder channel for the single-screw extrusion are determined by trial and error. Since new polymers are developed frequently, finding the optimum parameters to extrude these polymers by trial and error is costly and time consuming. In order to reduce the time and experimental work required for optimizing the process parameters and the geometry of the extruder channel for a given polymer, the main goal of this research was to perform a coordinated experimental and numerical investigation of melting in screw extrusion. In this work, a full three-dimensional finite element simulation of the two-phase flow in the melting and metering zones of a single-screw extruder was performed by solving the conservation equations for mass, momentum, and energy. The only attempt for such a three-dimensional simulation of melting in screw extruder was more than twenty years back. However, that work had only a limited success because of the capability of computers and mathematical algorithms available at that time. The dramatic improvement of computational power and mathematical knowledge now make it possible to run full 3-D simulations of two-phase flow in single-screw extruders on a desktop PC. In order to verify the numerical predictions from the full 3-D simulations of two-phase flow in single-screw extruders, a detailed experimental study was performed. This experimental study included Maddock screw-freezing experiments, Screw Simulator experiments and material characterization experiments. Maddock screw-freezing experiments were performed in order to visualize the melting profile along the single-screw extruder channel with different screw geometry configurations. These melting profiles were compared with the simulation results. Screw Simulator experiments were performed to collect the shear stress and melting flux data for various polymers. Cone and plate viscometer experiments were performed to obtain the shear viscosity data which is needed in the simulations. An optimization code was developed to optimize two screw geometry parameters, namely, screw lead (pitch) and depth in the metering section of a single-screw extruder, such that the output rate of the extruder was maximized without exceeding the maximum temperature value specified at the exit of the extruder. This optimization code used a mesh partitioning technique in order to obtain the flow domain. The simulations in this flow domain was performed using the code developed to simulate the two-phase flow in single-screw extruders.

Microfluidic fabrication of advanced microcapsules for use in self-healing materials

The proposed work aims to facilitate the development of a microfluidic platform for the production of advanced microcapsules containing active agents which can be the functional constituents of self-healing composites. The creation of such microcapsules is enabled by the unique flow characteristics within microchannels including precise control over shear and interfacial forces for droplet creation and manipulation as well as the ability to form a solid shell either chemically or via the addition of thermal or irradiative energy. Microchannel design and a study of the fluid dynamics and mechanisms for shell creation are undertaken in order to establish a fabrication approach capable of producing healing-agent-containing microcapsules. An in-depth study of the process parameters has been undertaken in order to elucidate the advantages of this production technique including precise control of size (i.e., monodispersity) and surface morphology of the microcapsules. This project also aims to aid the optimization of the mechanical properties as well as healing performance of self-healing composites by studying the effects of the advantageous properties of the as-produced microcapsules. Scale-up of the microfluidic fabrication using parallel devices on a single chip as well as on-chip microcapsule production and shape control will also be investigated. It will be demonstrated that microfluidic fabrication is a versatile approach for the efficient creation of functional microcapsules allowing for superior design of self-healing composites.