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Harrison De La ,rosa Ramírez - One of the best experts on this subject based on the ideXlab platform.

  • Variación de las propiedades estructurales, térmicas y mecánicas del Poli (ácido láctico) por medio del empleo de aditivos derivados de la resina de pino
    'Universitat Politecnica de Valencia', 2019
    Co-Authors: Harrison De La ,rosa Ramírez
    Abstract:

    [ES] El principal objetivo del presente trabajo ha sido la utilización de resinas de pino y algunos de sus derivados en la modificación del ácido poliláctico (PLA), en específico se ha utilizado como modificadores gum rosin y unik tack en diferentes proporciones, 5, 10 y 15 phr en mezclas con PLA, las mezclas fueron realizadas con procesos convencionales de conformado de polímeros. Posteriormente se caracterizaron los materiales obtenidos mediante las principales técnicas de caracterización de polímeros, cuyos resultados cuantitativos y cualitativos permitieron determinar los cambios ocurrido en la propiedades mecánicas, térmicas y microestructurales del material. Además, se incluyeron ensayos de color, ángulo de contacto e índice de fluidez con el objetivo de tener información adicional acerca del material estudiado, así como el estudio de forma exhaustiva de las principales características, propiedades y aplicaciones del PLA y de las resinas empleadas, para tomarlas como punto de referencia al momento de obtener los resultados de la caracterización de los materiales mezclados en sus distintas proporciones.The use of pine resin and some of its derivatives in the modification of Poly (lactic acid) PLA, arises from the interest of knowing how it affects the incorporation of resins in the structure of the PLA, either in increase or decrease of its properties. For them they consider the realization of mixtures of PLA and resins in different proportions. Later, analyze the materials obtained by means of Polymer Characterization Techniques. As well as the exhaustive study of the main characteristics, properties and applications of the PLA and the residences used. To take them as a point of reference when obtaining the results of the Characterization of the materials obtained in their various proportions.[VA] El principal objectiu del present treball ha sigut la utilització de resines de pi i alguns dels seus derivats en la modificació de l'àcid poliláctic (PLA). En concret, s'ha utilitzat com a modificadors gum rosin i unik tuck en diferents proporcions, 5, 10 i 15 phr en mescles amb PLA, les mescles van ser realitzades amb processos convencionals de conformat de polímers. Posteriorment es van caracteritzar els materials obtinguts per mitjà de les principals tècniques de caracterització de polímers, els resultats quantitatius i qualitatius dels quals van permetre determinar els canvis ocorregut en la propietats mecàniques, tèrmiques i microestructurals del material. A més, es van incloure assajos de color, angle de contacte i índex de fluïdesa amb l'objectiu de tindre informació addicional sobre el material estudiat, així com l'estudi de forma exhaustiva de les principals característiques, propietats i aplicacions del PLA i de les resines empleades, per a prendre-les com a punt de referència al moment d'obtindre els resultats de la caracterització dels materials mesclats en les seues distintes proporcions.Rosa Ramírez, HDL. (2018). Variación de las propiedades estructurales, térmicas y mecánicas del Poli (ácido láctico) por medio del empleo de aditivos derivados de la resina de pino. http://hdl.handle.net/10251/115399TFG

Lan Nguyen - One of the best experts on this subject based on the ideXlab platform.

  • Using Polymer Characterization Techniques to Predict LDPE Resin Suitability for Extruded Foam Applications
    Journal of Cellular Plastics, 2001
    Co-Authors: Jim Auger, Lan Nguyen
    Abstract:

    All LDPE resins are not created equal. It is well known that autoclave LDPEs are considered to be the products of choice for extrusion coating applications. On the other hand, LDPE resins produced using tubular reactors have a different structure that makes them more suitable for extruded foam applications. More specifically, within the choices of tubular LDPE resins for extruded foam applications, some are easier to process and produce better quality foam products than others. What makes one resin better than another? This paper discusses the general chemical and rheological differences between autoclave and tubular LDPE resins then focuses in more detail on those differences for a variety of tubular LDPE products used in the extruded foam market.

Bert M Weckhuysen - One of the best experts on this subject based on the ideXlab platform.

  • influence of metal alkyls on early stage ethylene Polymerization over a cr sio2 phillips catalyst a bulk Characterization and x ray chemical imaging study
    Chemistry: A European Journal, 2020
    Co-Authors: Maarten K Jongkind, Florian Meirer, Koen Bossers, Iris Ten Have, Hendrik Ohldag, Benjamin Watts, Theo Van Kessel, Nic Friederichs, Bert M Weckhuysen
    Abstract:

    The Cr/SiO2 Phillips catalyst has taken a central role in ethylene Polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co-catalysts are required in order to attain activity. Nonetheless, co-catalysts in the form of metal-alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring Polymer characteristics. The activation mechanism and related Polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal-alkyl co-catalyst, we can tailor Polymer properties around a single Cr/SiO2 Phillips catalyst formulation. Furthermore, we show that these different Polymer properties exist in the early stages of Polymerization. We have used conventional Polymer Characterization Techniques, such as Size Exclusion Chromatography (SEC) and 13C Nuclear Magnetic Resonance (NMR), for studying the metal-alkyl co-catalyst effect on Short Chain Branching (SCB), Long Chain Branching (LCB) and Molecular Weight Distribution (MWD) at the bulk scale. In addition, Scanning Transmission X-ray Microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early-stage PE within one particle cross-section with high energy resolution and nanometer scale spatial resolution.

Lopez Ferber David - One of the best experts on this subject based on the ideXlab platform.

  • Development and Characterization of Si-M-C-N materials (M= B, Al) and application to the design of ceramic fibers
    2019
    Co-Authors: Lopez Ferber David
    Abstract:

    La limitation de notre impact environnemental passe en partie par la recherche et le développement de nouveaux procédés et matériaux, et les céramiques Techniques ont une place essentielle parmi ceux-ci. Les composites à matrices céramiques (CMCs) permettent le renfort de nombreux types de structures, principalement pour des applications à hautes températures, et notamment dans les turbomachines. Ces CMCs utilisent majoritairement des fibres de carbure de silicium (SiC) en tant qu’agent de renfort. Toutefois, le marché des fibres de SiC est dominé par le Japon. Cet oligopole conduit à des problématiques économiques et stratégiques. De plus, les performances thermomécaniques des fibres SiC se dégradent dès 1400 °C en conditions d’utilisation. Dès lors, il apparaît que l’amélioration des performances des CMCs pourra résider dans la substitution du SiC par d’autres systèmes compositionnels plus stables en température. Dans le cadre de cette thèse, les systèmes quaternaires Si-B-C-N et Si-Al-C-N ont été envisagés en substitution du SiC pour leurs performances thermiques et chimiques de premier plan. La voie PDCs (Polymer-Derived Ceramics) a permis d’ajuster la composition des précurseurs à l’échelle moléculaire. La modularité de cette méthode d’élaboration de céramiques réside dans la possibilité de mettre en forme à façon les précurseurs, permettant la synthèse d’objets, dont des fibres, qui ne sont pas accessibles par les méthodes conventionnelles de synthèses. L’élaboration de fibres creuses de large diamètre pour des applications catalytiques ou membranaires est envisagée en complément des fibres micrométriques pour du renforcement de structures. Dans le cadre de ces travaux de thèse, la synthèse de nouveaux précurseurs à façon a été étudiée en couplant différentes Techniques de caractérisation des polymères. La conversion polymère-céramique (1000 °C) a également été suivie à l’aide de méthodes de caractérisation dites ex-situ et in-situ afin d’identifier les mécanismes de pyrolyse liés à cette transformation. L’évolution microstructurale des céramiques obtenues à 1000 °C a quant à elle été caractérisée par spectroscopies RMN, Raman et IRTF ainsi que par DRX, MEB-EDX et MET afin d’identifier l’effet de la teneur en bore, voire en aluminium, des céramiques sur la structuration du système Si-C-N. La capacité au filage de précurseurs sélectionnés dans les chapitres 3, 4 et 5 a été étudiée et discutée.Limiting our environmental impact involves research and development of new materials and processes. Technical ceramics can have an essential place to meet the current technical challenges. Ceramic matrix composites allow the reinforcement of many types of structures, mainly for applications at high temperatures and especially in the aeronautical and aerospace fields. These composites mainly use silicon carbide fibers as reinforcing agent. However, the production of SiC fibers is dominated by companies from Japan leading to strategic and economic issue. Moreover, the thermomechanical properties of SiC fibers are reduced by use beyond 1400 °C in conditions of use. Therefore, it appears that the improvement of the performances of CMCs will be induced by the substitution of the SiC by other compositional systems more stable at high temperature. In this work, the Si-B-C-N and Si-Al-C-N quaternary systems have been considered as substitutes for SiC because of their extraordinary thermal and chemical performances. The Polymer derived ceramics way allowed to adjust the composition of the precursors at the molecular scale. The modularity of this synthesis way relies on the possibility of customizing the precursors, allowing the synthesis of many shapes, including fibers, which are not accessible by conventional synthesis ways. The development of large diameter hollow fibers for catalytic or membrane applications is considered with the addition of micrometric fibers for the reinforcement of structures. In this PhD thesis, the synthesis of new precursors was studied by coupling different Polymer Characterization Techniques. The Polymer to ceramic conversion (1000 °C) was also followed by Characterization methods in order to identify the pyrolysis mechanisms related to this transformation. The microstructural evolution of the ceramics obtained at 1000 °C were characterized by NMR, Raman and FTIR spectroscopy as well as by XRD, SEM-EDX and MET to identify the effect of the boron or aluminum content on the structure of the Si-C-N system. The spinning capacity of precursors selected in chapters 3, 4 and 5 has been studied and discussed

George Fytas - One of the best experts on this subject based on the ideXlab platform.

  • vibrational eigenfrequencies and mechanical properties of mesoscopic coPolymer latex particles
    Macromolecules, 2010
    Co-Authors: Tim Still, Markus Retsch, Ulrich Jonas, Rebecca Sainidou, P Rembert, Konstantinos Mpoukouvalas, George Fytas
    Abstract:

    We report on the thermally excited resonance vibrations of mesoscopic poly(methylmethacrylate)-poly(n-butylacrylate) (PMMA-PnBA) random coPolymer colloidal spheres with varying nBA volume fractions. All systems but the bulk PnBA are in the glassy state at room temperature. Brillouin light scattering (BLS), dielectric spectroscopy (DS), and standard Polymer Characterization Techniques reveal the homogeneity of this coPolymer system down to the segmental length scale. Theoretical density-of-states calculations allow the determination of the shear modulus of the coPolymer latex spheres from their eigenvibration BLS spectra. The representation of the coPolymer longitudinal modulus by Wood’s law, combining the PMMA and PnBA homoPolymers values, succeeds if a higher fictive “glassy PnBA” modulus instead of the actual modulus of the neat PnBA rubber at room temperature is assumed. This is justified by the dynamic homogeneity of these coPolymers exhibiting a single α-relaxation. A facile tuning of the thermomecha...