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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Ion exchange properties of poly(vinylimidazoline) resins

Abonijim, M. N. January 1987 (has links)
No description available.
2

Modificação química de resinas à base de estireno através do processo de sulfonação: estudo experimental e modelagem matemática / Chemical modification of styrenic resins by sulfontation process: experimental and mathematical modelling

Theodoro, Thiago Romanelli 24 May 2018 (has links)
A proposta deste trabalho consistiu em realizar o estudo experimental e matemático do processo de sulfonação de resinas estirênicas reticuladas com etileno-glicol dimetacrilato (PS-EGDMA) e trietileno-glicol dimetacrilato (PS-TEGDMA). O processo de sulfonação de resinas estirênicas é uma das modificações químicas mais utilizadas na indústria e permite conferir características como seletividade às resinas, favorecendo seu uso em diversos processos. Foi utilizado um planejamento de Taguchi L9 com os fatores: fração monomérica, fração de agentes reticulantes e fração de solventes inertes (tolueno e heptano), referentes ao processo de polimerização. As resinas produzidas foram utilizadas na sulfonação, na qual a temperatura foi variada para determinar o ponto ótimo em termos de capacidade de troca iônica e variação de massa. Por meio de balanços de massa e fazendo o uso do modelo do núcleo não reagido foi feita a modelagem matemática do processo. Os resultados obtidos mostram que as resinas reticuladas com etileno-glicol dimetacrilato (EGDMA) e trietileno-glicol dimetcrilato (TGDMA) apresentam boa capacidade de troca iônica (CTI) quando comparadas às resinas comerciais de estireno-divinilbenzeno (S-DVB), como, por exemplo, a Amberlyst®. As partículas sulfonadas de PS-EGDMA apresentaram CTI de 3,988 meq/g com ganho de massa de 30% enquanto as de PS-TEGDMA apresentaram capacidade de 3,477meq/g com ganho de massa de 47% no ponto ótimo tendo sido produzidas com temperaturas de sulfonação de 57,5ºC e 65ºC respectivamente. O modelo desenvolvido apresentou bom ajuste no intervalo entre o início da reação e o ponto máximo de capacidade de troca iônica, sendo capaz de prever as constantes cinéticas e de difusão da reação. Além disso, as partículas produzidas foram testadas na catálise heterogênea e conversões acima de 78% foram obtidas mostrando-se um eficiente catalisador. / The purpose of this work was to carry out the experimental and mathematical study of the sulfonation process of styrenic resins cross-linked with ethylene glycol dimethacrylate (EGDMA) and triethylene glycol dimethacrylate (TEGDMA). The sulfonation process of styrenic resins is very used in industry and allows particles to achieve characteristics like selectivity, favoring its use in several processes. It was used Taguchi L9 experimental design with the following factors: monomer molar fraction, fraction of crosslinking agents and fraction of inert solvents (toluene and heptane), referring to the polymerization process. The resins produced were used in the sulfonation process, in which the temperature was varied to determine the optimum point in terms of ion exchange capacity and mass variation. Mass balances and the unreacted core model were in order to develop the mathematical model. The results showed that PS-EGDMA and PS-TGDMA crosslinked resins exhibit good ion exchange capacity when compared to styrene-divinylbenzene (S-DVB) commercial resins, such as Amberlyst®. The sulfonated PS-EGDMA particles showed ion exchange capacity of 3,988 meq/g with a mass gain of 30% while those of PS-TEGDMA presented a capacity of 3,477meq/g with mass gain of 47% at the optimum point and were produced with sulfonation temperatures of 55.7ºC and 65ºC respectively. The developed mathematical model showed a good fit in the interval between the beginning of the reaction and the maximum point of ion exchange capacity, being able to predict the kinetic and diffusion constants of the reaction. In addition, the produced particles were tested in the heterogeneous catalysis and conversions above 78% were obtained proving an efficient catalyst.
3

Tenue au feu des goujons collés dans le bois et dans le béton / Fire resistance of chemical anchors in wood and concrete

Lahouar, Mohamed Amine 12 December 2017 (has links)
Le scellement chimique est une technique d’assemblage structural permettant de connecter et d’assurer le transfert d’efforts entre deux éléments adjacents en béton, à travers le collage d’une armature en acier à l’aide d’une résine polymère. Les scellements chimiques ont été initialement utilisés dans les ouvrages en béton armé pour la rénovation, l’extension et la réparation des structures à travers l’ajout de nouvelles sections de béton aux éléments existants. L’évolution, au fil du temps, des propriétés mécaniques et des propriétés d’adhérence des résines polymères a permis d’améliorer le comportement mécanique des scellements chimiques, leur permettant d’atteindre des propriétés équivalentes ou même supérieures à celles des ancrages mécaniques classiques, à des températures normales de service. Ainsi, les scellements chimiques ont pu progressivement substituer les ancrages mécaniques classiques dans certaines applications, en proposant des solutions plus avantageuses et en offrant plus de flexibilité pour répondre aux exigences architecturales. Cependant, le comportement mécanique des scellements chimiques est principalement gouverné par celui des résines polymères, qui demeurent très sensibles à la variation de la température. Par conséquent, l’augmentation de la température au niveau des scellements chimiques présente un risque potentiel affectant leur sécurité d’utilisation. Par ailleurs, une situation d’incendie présente un danger sérieux qui doit être considéré lors du dimensionnement des scellements chimiques. Récemment, la technique des scellements chimiques, exclusivement utilisée dans les ouvrages en béton armé, a été transférée à la construction des ouvrages bois, sous l’appellation de « goujons collés ». Cette technique, originellement utilisée dans la rénovation et le renforcement des monuments historiques, est aujourd’hui employée dans la construction neuve grâce à la bonne tenue mécanique et séismique et aussi à la possibilité qu’elle offre pour réaliser des assemblages invisibles. Cependant, les goujons collés sont aujourd’hui confrontés aux mêmes problématiques que les scellements chimiques, notamment vis-à-vis l’augmentation de la température. L’objectif de cette thèse est d’étudier l’évolution du comportement mécanique de ces deux systèmes d’assemblages dans le but de proposer une méthode de dimensionnement permettant d’assurer leur tenue structurale en situation d’incendie. L’étude est répartie sur quatre niveaux :i. Etude du comportement des ancrages chimiques à l’échelle des matériaux à travers des essais de caractérisation des constituants de l’ancrage, avec une focalisation particulière sur l’étude des phénomènes se produisant à haute température dans la résine polymère.ii. Etude du comportement global de l’ancrage par le biais d’essais d’arrachement à haute température, à effort constant et à température stabilisée, réalisés sur des scellements chimiques dans des cylindres en béton et des goujons collés dans des parallélépipèdes en lamellé-collé d’épicéa.iii. Etude du comportement mécanique à haute température des ancrages chimiques à l’échelle de la structure à travers la réalisation d’un essai au feu à l’échelle 1 sur une dalle en console ancrée chimiquement dans un mur en béton par 8 scellements chimiques. Les résultats de cet essai ont permis de valider la méthode de dimensionnement proposée pour prédire la durée de résistance au feu des scellements chimiques lors d’une situation d’incendie.iv. Etude théorique portant sur l’évolution de la distribution des contraintes le long de l’ancrage lors d’une variation de la température, à travers le développement d’un modèle non linéaire de cisaillement différé « Shear-lag », permettant d’obtenir les profils théoriques des contraintes pour une distribution thermique quelconque, à partir des données d’entrée expérimentales obtenues par des essais d’arrachement / Post-installation of rebars is a structural joining technique allowing the connection and the load transfer between two neighboring structural elements using steel rebars and adhesive polymers. Post-installed rebars were initially used in concrete constructions in retrofitting, extension and in repairing structures by adding new concrete sections to existing elements. Over the time, the improvement in mechanical and adhesion properties of polymer adhesives have allowed to enhance the mechanical behavior of post-installed rebars and led to achieve equivalent or even higher mechanical responses than cast-in place rebars at normal operating temperatures. Thus, post-installed rebars have gradually replaced cast-in place rebars in new constructions for some applications by offering advantageous solutions and flexibility allowing meeting the high architectural requirements. However, the mechanical behavior of post-installed rebars is essentially governed by the mechanical properties of polymer resins, which remain highly sensitive to temperature variation. Consequently, the temperature increase of the post-installed rebars presents a potential risk affecting their safety use. Therefore, fire presents a serious hazard that should be considered when designing post-installed rebars. Recently, the technique of post-installed rebars, exclusively used in reinforced concrete structures, has been transferred to wood structures construction, and called "glued-in rods". This technique, initially used in the retrofitting and the reinforcement of historical monuments, is today used in new construction thanks to its good mechanical and seismic behavior in addition to the possibility it offers to make invisible connections. However, glued-in rods face the same problems as post-installed rebars, especially concerning the temperature increase. The aim of this thesis is to study the evolution of the mechanical behavior of these two connection techniques in order to suggest a design method allowing ensuring their safe use in a fire situation. The study is divided into four levels:i- Study of the behavior of chemical anchors at the scale of materials through characterization tests performed on the anchor components, with a particular emphasis on the study of phenomena occurring at high temperature in the polymer resin.ii- Study of the global behavior of chemical anchors by means of pull-out tests performed at high temperature, at constant load and at stabilized temperature, carried out on post-installed rebars in concrete cylinders and on glued-in rods in parallelepipeds of spruce glulam.iii- Study of the mechanical behavior at high temperature of chemical anchors at the scale of the structure through a full-scale fire test carried out on a cantilever concrete slab connected to a concrete wall using eight post-installed rebars. Test results were also used to validate the suggested design method to predict the fire resistance duration of post-installed rebars in a fire situation.iv- Theoretical study on the evolution of the stress distribution along the anchor during a temperature variation, through the development of a non-linear shear-lag model, allowing to obtain the theoretical stress profiles for any thermal distribution, from the experimental input data obtained by pull-out tests

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