Orientador: Antonio Jose de Almeida Meirelles / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T21:50:09Z (GMT). No. of bitstreams: 1 Ninni_Luciana_D.pdf: 1651054 bytes, checksum: a02c4b214cfc69dac3f1eb376a13a6b7 (MD5) Previous issue date: 2003 / Resumo: Métodos de contribuição de grupos têm sido ferramenta útil no cálculo de coeficientes de atividade nos mais variados sistemas. Em sistemas aquosos, e mais especificamente naqueles que possuem compostos biológicos como açúcares, arninoácidos, sais orgânicos, polímeros, etc., o uso de métodos de contribuição de grupos para a correlação e predição do equilíbrio de fases tem crescido nos últimos anos. Em alimentos e em biotecnologia, os sistemas são geralmente multicomponentes e por essa razão, a aplicação de métodos de contribuição de grupos torna-se atraente partindo-se do princípio que, de posse dos parâmetros de interação entre grupos, é possível calcular propriedades de sistemas mais complexos a partir de parâmetros obtidos da correlação a dados experimentais de sistemas mais simples. Neste trabalho, os métodos de contribuição de grupos ASOG, UNIF AC, VERS e UNIMOD foram empregados em diferentes sistemas para a correlação e predição de propriedades fisico-químicas. Os compostos estudados foram: polióis, aminoácidos, maltodextrinas e polietileno glicóis (pEG)s, sendo os três primeiros compostos geralmente encontrados em sistemas alimentícios, e o PEG é bastante utilizado em sistemas aquosos bifásicos para o estudo do equilíbrio e separação de biomoléculas. Propriedades fisico-químicas como atividade de água, solubilidade, depressão do ponto de congelamento, pH, espalhamento de luz, entalpia de diluição e viscosidade, são algumas das propriedades determinadas e/ou retiradas da literatura usadas para a correlação e predição empregando os modelos acima citados. A intenção deste trabalho foi então, testar os métodos de contribuição de grupos para o cálculo de propriedades fisico-químicas tratando também das particularidades de cada sistema estudado, como a dissociação parcial dos aminoácidos, o efeito de proximidade dos grupamentos hidroxilas nos polióis e a polidispersão das maltodextrinas. Também são apresentados resultados da correlação e predição de viscosidades de sistemas aquosos contendo PEGs por um modelo semi-empírico que não trata da contribuição de grupos mas considera a hidratação das moléculas desses polímeros em meio aquoso / Abstract: Group contribution methods have been used as a useful tool for calculating activity coefficients in different types of systems. In aqueous systems, specifically those containing biological compounds such as sugars, amino acids, organic salts, polymers, etc., the use of group contribution models for correlating and predicting phase equilibrium has increased in the last years. In the food and in the biotechnology areas, the systems are generally multicomponent, and for this reason, the use of group-contribution methods becomes an attractive tool considering the possibility of calculation of properties in complex systems with parameters adjusted for simple ones. In this work, the group-contribution models ASOG, UNIF AC, VERS and UNIMOD were utilized in different types of systems for the correlation and prediction of physical chemical properties. The studied compounds were: polyols, amino acids, maltodextrins and polyethylene (glycols) (pEG)s, which the first three compounds are found in food systems, and PEGs are wide used in aqueous-two-phase systems to study equilibrium and separation of biomolecules. Physical-chemical properties such as water activity, solubility, fteezing point depression, pH, light scattering, enthalpy of dilution and viscosity are some of the properties experimentally determined and/or found in literature used in this work for the correlation and prediction using the above cited models. Thus, the objective of this work was to test the group-contribution models for calculating physical-chemical properties considering the particularities of each system such as partial dissociation phenomena in aqueous amino acid systems, proximity effect of hydroxyl groups in polyols, and polydispersity of maltodextrins. It is also presented in this work, the results of viscosity correlation and prediction in aqueous PEG solutions by a semi-empirical equation that does not consider group contributions but take into account the hydration of the polymer molecules in aqueous media / Doutorado / Doutor em Engenharia de Alimentos

Master of Science / Department of Chemistry / Takashi Ito / Solvent swelling of block copolymer microdomains plays an essential role in the improvement of microdomain alignment by solvent vapor annealing and in chemical separations using block copolymer monoliths. Here, investigation of the effects of solvent swelling on the molecular permeability and dimensions of cylindrical microdomains in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) films is done by using single molecule tracking. These films are prepared by sandwiching benzene (with/without methanol) or THF (with/without methanol) solutions containing 5 nM sulforhodamine B (SRB) between two glass substrates. The PEO microdomains are aligned in the solution flow direction during the film preparation. The diffusional motions of individual SRB molecules are measured at different drying times to assess the microdomain radius and permeability. These parameters, on average, gradually decrease with an increase in drying time; however the trend differs slightly from one solvent system to another. A sharp decrease of microdomain radius is observed for benzene, benzene-methanol, THF and THF-methanol swollen films at initial drying condition (for example 2 days). In contrast, microdomain permeability does not decrease sharply; instead a gradual decreasing trend is seen for all solvent systems. In addition, mixing of a small amount of methanol (14% in PEO microdomains) either with benzene or with THF does not produce noticeable difference in the swelling of PEO microdoamins. Importantly, both benzene and THF offer similar microdomain swelling behavior at the same drying temperature, which is evident from the microdomain radius values, however THF shows comparatively larger microdomain permeability and better correlation between permeability and microdomain radius compared with benzene.

Les polyolefins représentent plus de la moitié de la production mondiale de plastiques et 80% de ces polymères sont produits avec des catalyseurs hétérogènes de type Phillips, Ziegler-Natta et métallocènes. En effet, un bon fonctionnement des unités du fait d'un faible encrassement du réacteur ou des autres équipements de l'unité, une activité stable, une bonne morphologie particulaire des polymères et un une densité apparente élevée sont obtenus en utilisant des catalyseurs hétérogènes. D'un autre côté l'hétérogénéisation d'un catalyseur s'accompagne d'une diminution de l'activité et d'un élargissement de la distribution de masses molaires qui est parfois non désiré car cela peut influencer l'aptitude à la transformation et les propriétés mécaniques des polyoléfines. Plusieurs explications ont été avancées dans la littérature afin d'expliquer l'effet de l'immobilisation d'un catalyseur ce qui inclut la résistance diffusionnelle au transport du (des) (co)- monomère(s) vers le site actif et la modification du comportement du catalyseur conduisant à plusieurs espèces actives. Néanmoins l'ensemble de ces explications est en connexion avec les propriétés physiques du support (tailles des particules, surface spécifique, volume poreux, diamètre des pores…) car ce dernier peut en effet impacter la nature des espèces actives ainsi que leur dispersion et la diffusion des monomères. Les catalyseurs métallocène sont considérés comme mono-site et tout changement dans la nature du site actif au cours de son immobilisation et toute résistance au transfert de matière peuvent être détectés par un élargissement de la distribution des masses molaires. Le présent travail a pour objet d'étudier les effets des propriétés physiques des catalyseurs métallocènes supportés sur silice concernant la cinétique de polymérisation et les caractéristiques des polymères produits. Pour cela le traitement thermique de la silice a été fixé à 600°C afin de contrôler son état de surface tandis que la quantité de catalyseur supporté a été gardée autant que possible constante. De plus les protocoles de polymérisation en phases suspension et gaz ont été fixés après avoir évalué différentes conditions de polymérisation et différents composés alkylaluminium. Cette étude systématique a permis d'attribuer les différences observées en termes de cinétique de réaction des catalyseurs métallocènes à la différence des paramètres physiques des silices utilisées comme support et par conséquent à la résistance diffusionnelle au transport du (des) (co)-monomère(s) au(x) site(s) actif(s) durant la polymérisation / Polyolefins account for more than half of the world’s plastic production and about 80% of these polyolefins are commercially produced with heterogeneous olefin polymerization catalysts such as Phillips, Ziegler-Natta and metallocenes. Trouble-free plant operation due to low fouling of the reactor or other plant equipment, relatively stable catalytic activity, good polymer morphology and high polymer bulk densities can be achieved by employing heterogeneous olefin polymerization catalysts. On the other hand, heterogenization of the olefin polymerization catalysts lead to drastic reduction in their activities and broadening of the polymer molar mass distribution which is undesirable in some cases because it can influence the processability and mechanical properties of the polyolefin grade. Various explanations have been proposed in the open literature to explain these effects of catalyst immobilization which mainly include existence of diffusion resistance to (co)-monomer(s) transport at the active sites during polymerization and the change of the active site(s) behavior due to immobilization leading to multiple site types on the final supported catalyst. Nevertheless, both of these explanations have a connection with the physical properties (e.g., particle size, surface area, pore volume, pore diameter etc.) of the support because the support can impact the nature of the final active species formed on it, dispersion of the active species throughout the support particles and, last but not the least, the intraparticle diffusion of (co)-monomer(s) during polymerization. Metallocenes are considered as single-site catalysts and any changes in the nature of the active site(s) upon their immobilization on a support or during the course of polymerization due to mass transfer resistance can be detected from the broadening of polyolefin molar mass distribution. Therefore, the present work is an attempt to study the effects of physical properties of silica supported metallocenes on their ethylene polymerization kinetics as well as on the morphology of the produced polyethylene. For this purpose, the surface chemistry of the used commercial silica supports was fixed by dehyroxylating all of them at 600 °C, whereas, the final metal loadings of the supported catalysts were nearly kept constant by preparing them under identical conditions. Furthermore, slurry and gas phase polymerization protocols along with the used aluminum alkyl scavenger (which can also induce chemical effects on the catalytic behavior of supported metallocenes) were also fixed by testing different polymerization protocols and scavengers. Such systematic study has allowed us to attribute the observed differences in the reaction kinetics of the supported metallocenes, explicitly, to the differences in the physical parameters of the silica supports and, consequently, to the existence of diffusion resistance to (co) monomer(s) transport at the active site(s) during the course of polymerization

Orientador: Teresa Dib Zambon Atvars / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-07T18:45:42Z (GMT). No. of bitstreams: 1 Martins_TatianaDuque_D.pdf: 2747473 bytes, checksum: 159c91a5fa62b3bf93683e4886562cd2 (MD5) Previous issue date: 2006 / Doutorado / Físico-Química / Doutor em Ciências

The polyolefins production is the largest among all types of plastics given their thermal and chemical stability and low cost, which allows them to be used in a wide variety of products worldwide, including polypropylene (PP) and polyethylene (PE) membranes. However, the small percentage of polyolefins being recycled compared to the enormous amount produced has led to severe environmental pollution issues. In addition, the traditional polyolefin membrane fabrication methods utilize mostly toxic non-renewable solvents such as xylenes at high temperatures, causing further negative environmental impact. The objective of this study is to propose a greener alternative for polyolefins in general and in particular for membrane fabrication. For this, two bio-based solvents (α-pinene and Dlimonene) were proposed to dissolve PP and LDPE, and the resulting films and membrane properties were studied. Hydrophobic PP microporous membranes were obtained by thermally induced phase separation from pristine commercial polymers and plastic waste. They were applied for water-in-toluene emulsion separation. The water rejection was above 95% for membranes fabricated from dope solutions containing 25% pristine PP and 30% waste PP heated at 130°C, suggesting that they could be used in oil spill recovery operations. This work aims to contribute to the implementation of more sustainable practices in the membrane industry.

The fire behaviour of linear low-density polyethylene composites containing 10 wt.% of different carbon-based fillers was studied. Cone calorimeter tests conducted at a heat flux of 35 kW_m_2 showed that the expandable graphite sample reduced the peak heat release rate by about 50 % while the flake graphite increased the ignition time by about 80 %. Pyrolysis combustion flow calorimetry results were practically identical for all composites. This reveals shortcomings of this bench-scale flammability test method when the flame retardancy mechanisms relies on either the development of physical barrier layer at the surface of the burning sample or on reflecting the incident heat flux. Similarly, it was found that laser pyrolysis-thermogravimetric analysis generated outcomes that did not correlate with the cone calorimeter results at all. In particular, the composite based on expandable graphite performed poorly. The likely explanation is that the aspect ratios of the small samples were such that the barrier effects on which this system relies, was negated by edge effects. / Dissertation (MSc)--University of Pretoria, 2018. / Chemical Engineering / MSc / Unrestricted

This work uses high-speed video imaging to study the formation of filaments, during impact and rebounding of drops with polymer additives. We use PEO of different concentrations from 10 to 1000 ppm and study how drops rebound from various different surfaces: superhydrophilic, hydrophilic, hydrophobic, and superhydrophobic. Bouncing occurs for all surfaces at low impact velocities. We specifically focus on the phenomenon of the generation of polymer filaments, which are pulled out of the free surface of the drop during its rebounding from micro-pillared or rough substrates. We map the parameter regime, in terms of polymer concentration and impact Weber number, where the filaments are generated in the most repeatable manner. This occurs for regularly pillared surfaces and drops of 100 ppm PEO concentrations, where numerous separated filaments are observed. In contrast, for superhydrophobic coatings with random roughness the filaments tend to merge forming a branching structure. Impacts on inclined surfaces are used to deposit the filaments on top of the pillars for detailed study.

The properties and behaviors of charge transport mechanisms in highly insulating polymers are investigated by measuring conduction currents through thin film samples of low density polyethylene (LDPE). Measurements were obtained using a constant voltage method with copper electrodes inside a chamber adapted for measurements under vacuum and over a wide range of temperatures and applied fields. Field-dependent behaviors, including Poole-Frenkel conduction, space charge limited current (SCLC), and Schottky charge injection, were investigated at constant temperature. These field-dependent mechanisms were found to predict incorrect values of the dielectric constant and the field dependence of conductivity in LDPE was not found to be in agreement with SCLC predicted behavior. A model of thermally assisted hopping was a good fit at low applied fields and produced activation energies within the accepted range for LDPE. Low applied field measurements over the range of 213 K to 338 K were used to investigate two prominent hopping conduction mechanisms: thermally assisted hopping and variable range hopping. The observed temperature dependence of LDPE was found to be consistent with both thermally assisted hopping and variable range hopping. Activation energies determined for the range of temperatures were consistent with values reported in the literature for LDPE under similar conditions. A third aspect of charge transport behavior is a bulk response with time dependence. Conductivity behavior is examined in relation to transient current behavior, long time decay currents, and electrostatic discharge. Comparing charging and discharging cycles allowed qualitative separation of polarization and multiple trapping behaviors.

Analysis of seaweed as a vector for microplastics is an integral part of understanding the formation and deposition of micro-sized plastic waste in seawater. The project itself originated due to the influx of seaweed (and mismanaged plastic waste) residing on the shores of St. Kitts and Nevis and the constant deposition of plastic pollution intertwined within the seaweed. The natural occurrence of the two together lead to the consideration of fragmented plastics remaining on the seaweed. The objective of this research is to stain, identify, and quantify the concentration of microplastics sourced from both store-bought and environmental seaweed samples. A Nile red solution dissolved in either acetone or methanol was used to stain the microplastics, as per a proven method. The fluorescence of the stained microplastics was measured (excitation: 523-543 nm and emission: 580-640 nm) to identify potential dissolution. The seaweed was washed of microplastics and the solid particles collected were evaluated using infrared (IR) spectroscopy. The fluorescence and infrared spectrum results were compared to spectra within the Spectral data base system (SDBS) for the most common plastics: polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC). The use of a fluorescence microscope allowed for direct quantification of microplastics over a specific area of the sample and therefore allowed for further identification of microplastic presence.

The occurrence of deformation in plastic bottles is a common problem in the bottling industry where bottles are blow molded, hot filled at high temperatures and sealed. Plastics have unique properties that make it difficult to predict when and why such changes may occur. The root cause of such deformation is unknown by many bottle producers and recent attempts have been made to minimize the occurrence of such defects. The purpose of this research is to determine which variables involved in the bottle production process influence bottle shape. Earlier variables that were tested included both blow molding resin and total bottle sidewall thickness. The result of changing these variables did not create a decrease in defects. The use of an Ishikawa fishbone diagram identified hot filling temperature a major variable that influences final bottle shape. This research summarizes the results of a series of tests that were developed to observe the effect of hot filling temperature on final bottle shape. A positive correlation between sidewall deflection and liquid hot filling temperature was observed. A series of tensile tests were also developed to analyze the strength of various regions of a blow molded bottle. An early Pareto Analysis determined that the parting line is more susceptible to defects than any other region of the bottle. This weakness was confirmed after the tensile tests proved that there is a statistically significant difference between measurements on the sidewall and parting line (pvalue < .001). The results of this thesis highlight the consequences of arbitrarily choosing a filling temperature with little understanding of the bottle's strength at high temperatures. Plastic bottle producers and hot filling companies should unite to determine the appropriate hot filling temperature before bottles are molded and filled.