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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.
261

Efeito de ácidos carboxílicos em blendas de polipropileno e amido termoplástico

Martins, Andréa Bercini January 2015 (has links)
Neste trabalho, blendas de polipropileno/amido termoplástico (PP/TPS) foram preparadas como um material alternativo para uso em embalagens descartáveis. Este material apresenta características morfológicas típicas de blendas imiscíveis e um agente compatibilizante é necessário. Para obter o amido termoplástico (TPS), amido de milho foi misturado com glicerol, na proporção amido/glicerol de 70/30 m/m. As blendas PP/TPS com e sem agentes compatibilizantes foram produzidas em extrusora dupla rosca. Utilizou-se como agentes compatibilizantes naturais (ACN) três diferentes ácidos carboxílicos: mirístico (C14), palmítico (C16) e esteárico (C18), em concentração constante de 3 % m/m. O efeito dos ACN nas propriedades mecânicas, físicas, térmicas e morfológicas foram investigadas e comparadas com blendas de PP/TPS com polipropileno graftizado com anidrido maléico (PPgMA). Entre as blendas, as com C14 apresentaram propriedades equivalentes ou melhores que as com PPgMA, como resistência à tração e deformação na ruptura (18,1 e 18,9 MPa, e 263 e 216 % respectivamente). A blenda PP/TPS/C14 mostrou a maior resistência ao impacto (370 J/m), boa adesão e interação interfacial entre PP e TPS como demonstrado nas imagens de microscopia eletrônica de varredura (MEV). Após 180 dias de exposição ao intemperismo natural, a tensão na ruptura da blenda PP/TPS não se alterou, enquanto que a blenda PP/TPS/C14 apresentou 80 % de redução. Em relação a deformação na ruptura, a blenda não compatibilizada mostrou 75 % de redução e a blenda com C14, 97 %. As imagens de MEV da superfície dos materiais expostos mostram um início degradação biótica, devido a presença de possíveis microrganismos. Após o intemperismo as amostras foram submetidas ao ensaio de respirometria por 120 dias. Os resultados mostraram que a exposição ao intemperismo afeta diretamente a taxa de biodegradação, onde períodos maiores foram responsáveis por índices maiores de gás carbônico, principalmente para a blenda PP/TPS/C14. Assim, o ácido mirístico atuou como um agente compatibilizante e também como um foto-iniciador, catalisando a degradação abiótica das blendas PP/TPS. / In this work, polypropylene/thermoplastic starch (PP/TPS) blends were prepared as an alternative material to use in disposable packaging. This material displays morphological characteristics typical of immiscible blends and a compatibilizer agent is needed. For obtaining the thermoplastic starch (TPS), starch granules were plasticized with glycerol in a weight ratio of starch/glycerol 70/30. PP/TPS blends with and without compatibilizer agent were manufactured in a twin-screw extruder. It was used as natural compatibilizer agent (NCA) three different carboxylic acids: myristic (C14), palmitic (C16) and stearic (C18), in constant concentration of 3 % w/w. NCA effect on the mechanical, physical, thermal and morphological properties of PP/TPS blends were investigated and compared against PP/TPS with PP-grafted maleic anhydride (PPgMA). When compared to PP/TPS with PPgMA, blends with C14 presented equivalent or even better properties, as tensile strength and elongation at break (18.9 and 18.1 MPa, and 216 and 263 % respectively). PP/TPS/C14 blend showed the highest impact strength (370.4 J/m), good adhesion and interfacial interaction between PP and TPS was observed in scanning electron microscopy (SEM) images. After 180 days of natural weathering exposure, the tensile strength of the PP/TPS has not changed, while the PP/TPS/C14 showed 80 % reduction. For elongation at break, the non-compatibilized blend showed a 75 % reduction and blend with C14, 97 %. SEM images of exposed surface suggest the presence of microorganism. After the natural weathering, the samples were subjected to respirometry test for 120 days at 58 °C. Natural weathering exposition directly affects the rate of biodegradation, where longer period were responsible for higher rates of carbon dioxide, mainly for PP /TPS/C14. Thus, myristic acid served as a compatibilizer agent and also as a photo-initiator, catalyzing the abiotic degradation of the blends PP/TPS.
262

Thin films of polyfluorene:fullerene blends - Morphology and its role in solar cell performance

Björström Svanström, Cecilia January 2007 (has links)
<p>The sun provides us daily with large quantities of energy in the form of light. With the world’s increasing demand of electrical energy the prospect of converting this solar light into electricity is highly tempting. In the strive towards mass-production and low cost solar cells, new types of solar cells are being developed, e.g. solar cells completely based on organic molecules and polymers. These materials offer a promising potential of low cost and large scale manufacturing and have the additional advantage that they can be produced on flexible and light weight substrate which opens for new and innovating application areas, e.g. integration with paper or textiles, or as building materials. In polymer solar cells a combination of two materials are used, an electron donor and an electron acceptor. The three dimensional distribution of the donor and acceptor in the active layer of the device, i.e. the morphology, is known to have larger influence of the solar cell performance. For the optimal morphology there is a trade-off between sometimes conflicting criteria for the various steps of the energy conversion process. The dissociation of photogenerated excitons takes place at an interface between the donor and acceptor materials. Therefore an efficient generation of charges requires a large interface between the two components. However, for charge transport and collection at the electrodes, continuous pathways for the charges to the electrodes are required.</p><p>In this thesis, results from morphology studies by atomic force microscopy (AFM) and dynamic secondary ion mass spectrometry (SIMS) of spin-coated blend and bilayer thin films of polyfluorene co-polymers, especially poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)] APFO-3, and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are presented. It is shown that by varying the blend ratio, the spin.-coating solvent, and/or the substrate, different morphologies can be obtained, e.g. diffuse bilayer structures, spontaneously formed multilayer structures and homogeneous blends. The connection between these different morphologies and the performance of solar cells is also analysed. The results indicate that nano-scale engineering of the morphology in the active layer may be an important factor in the optimization of the performance of polymer solar cells.</p>
263

Barrier Properties of Liquid Crystalline Polymers and their Blends with PE and PETP

Flodberg, Göran January 2002 (has links)
No description available.
264

Thin films of polyfluorene:fullerene blends - Morphology and its role in solar cell performance

Björström Svanström, Cecilia January 2007 (has links)
The sun provides us daily with large quantities of energy in the form of light. With the world’s increasing demand of electrical energy the prospect of converting this solar light into electricity is highly tempting. In the strive towards mass-production and low cost solar cells, new types of solar cells are being developed, e.g. solar cells completely based on organic molecules and polymers. These materials offer a promising potential of low cost and large scale manufacturing and have the additional advantage that they can be produced on flexible and light weight substrate which opens for new and innovating application areas, e.g. integration with paper or textiles, or as building materials. In polymer solar cells a combination of two materials are used, an electron donor and an electron acceptor. The three dimensional distribution of the donor and acceptor in the active layer of the device, i.e. the morphology, is known to have larger influence of the solar cell performance. For the optimal morphology there is a trade-off between sometimes conflicting criteria for the various steps of the energy conversion process. The dissociation of photogenerated excitons takes place at an interface between the donor and acceptor materials. Therefore an efficient generation of charges requires a large interface between the two components. However, for charge transport and collection at the electrodes, continuous pathways for the charges to the electrodes are required. In this thesis, results from morphology studies by atomic force microscopy (AFM) and dynamic secondary ion mass spectrometry (SIMS) of spin-coated blend and bilayer thin films of polyfluorene co-polymers, especially poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)] APFO-3, and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are presented. It is shown that by varying the blend ratio, the spin.-coating solvent, and/or the substrate, different morphologies can be obtained, e.g. diffuse bilayer structures, spontaneously formed multilayer structures and homogeneous blends. The connection between these different morphologies and the performance of solar cells is also analysed. The results indicate that nano-scale engineering of the morphology in the active layer may be an important factor in the optimization of the performance of polymer solar cells.
265

Synthesis Of Liquid Crystalline Copolyesters With Low Melting Temperature For In Situ Composite Applications

Erdogan, Selahattin 01 June 2011 (has links) (PDF)
The objective of this study is to synthesize nematic-thermotropic liquid crystalline polymers (LCP) and determine their possible application areas. In this context, thirty different LCP&rsquo / s were synthesized and categorized with respect to their fiber formation capacity, melting temperature and mechanical properties. The basic chemical structure of synthesized LCP&rsquo / s were composed of p-acetoxybenzoic acid (p-ABA), m-acetoxybenzoic acid (m-ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA) and isophthalic acid (IPA) and alkyl-diacids monomers. In addition to mentioned monomers, polymers and oligomers were included in the backbone such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) polymers, and polybutylene naphthalate (PBN), polyhexylene naphthalate (PHN) and poly butylene terephthalate (PBT) oligomers that contain different kinds of alkyl-diols. We adjusted the LCP content to have low melting point (180oC-280oC) that is processable with thermoplastics. This was achieved by balancing the amount of linear (para) and angular (meta) groups on the aromatic backbones together with the use of linear hydrocarbon linkages in the random copolymerization (esterification) reaction. LCP species were characterized by the following techniques / Polarized Light Microscopy, Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Analysis (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), X-ray Scattering (WAXS, Fiber diffraction), surface free energy, end group analysis (CEG), intrinsic viscosity (IV) and tensile test. According to these analysis LCPs were classified into five main categories / (I) fully aromatics, (II) aromatics+ PET/PEN, (III) aromatics + oligomers (IV) aromatics + short aliphatic diacids, (V) aromatics + long aliphatic diacids. The foremost results of the analysis can be given as below. DSC analysis shows that some LCPs are materials that have stable LC mesogens under polarized light microscopy. In TGA analysis LCPs that have film formation capacity passed the thermal stability test up to 390oC. NMR results proved that predicted structures of LCPs from feed charged to the reactor are correct. In FTIR due to the inclusion of new moieties, several peaks were labeled in the finger-print range that belongs to reactants. In X-ray analysis, LCP24 (containing PET) was found to be more crystalline than LCP25 (containing PEN) which is due to the symmetrical configuration. Block segments were more pronounced in wholly aromatic LCP2 than LCP24 that has flexible spacers. Another important finding is that, as the amount of the charge to the reactor increases CEG value increases and molecular weight of the product decreases. Selected group V species were employed as reinforcing agent and mixed with the thermoplastics / acrylonitrile butadiene styrene (ABS), nylon6 (PA6), polyethylene terephthalate (PET), polypropylene (PP) and appropriate compatibilizers in micro compounder and twin screw extruder. The blends of them were tested in dog-bone and/or fiber form. In general LCPs do not improve the mechanical properties except in composite application with polypropylene. A significant increase in tensile properties is observed by LCP24 and LCP25 usage. Capillary rheometer studies show that the viscosity of ABS decreases with the inclusion PA6 and LCP2 together. In addition to the composite applications, some LCPs are promising with new usage areas. Such as nano fibers with 200nm diameter were obtained from LCP27 by electrospinning method. The high dielectric constant of LCP29 has shown that it may have application areas in capacitors.
266

Creation of crosslinkable interphases in polymer blends by means of novel coupling agents / Erzeugung von vernetzbaren Grenzschichten in Polymerblends durch Einsatz neuartiger Kopplungsagenzien

Sadhu, Veera Bhadraiah 14 August 2004 (has links) (PDF)
The goal of the work is to study possibilities for the modification of interface in immiscible polymer blends, which determine to a large degree of the blend properties. For this purpose novel coupling agents (named SCA) containing 2-oxazoline, 2-oxazinone, and hydrosilane reactive sites have been prepared. In blends of amino- functional and carboxylic acid terminated polymers the oxazoline and oxazinone units of the SCA react selectively with one of the polymers and, therefore, the SCA should locate at the interface. The remaining hydrosilane sites can now be used for further modification, e.g. for crosslinking. In the thesis we discussed the effect of the SCA on the morphology and thermal and rheological properties of blends based on carboxylic acid terminated polystyrene (PS) and amino-terminated polyamide 12 (PA) or poly(methyl methacrylate) (PMMA). The morphology of the blends and the location of the SCA strongly depends on the processing conditions. The crosslinkability of the interface could be proven by changes in the solubility behavior of the blends.
267

Modifizierung und Verarbeitung von Poly(3-hydroxybuttersäure-co-3-hydroxyvaleriansäure) (PHBV) mit kugelförmigen Mikropartikeln

Oberhoff, Ralph Wilhelm 23 December 2005 (has links) (PDF)
Poly(3-hydroxybuttersäure-co-3-hydroxyvaleriansäure), PHBV, ist ein Copolyester, der auf biologischem Weg durch Bakterien herstellbar und ein steifes sowie relativ festes Polymer ist. Seine Biokompatibilität und biologische Abbaubarkeit weckt das Interesse für diverse Anwendungen in Pharmazie und Medizin. PHBV reagiert mit Abbau empfindlich auf zugleich thermische und mechanische Belastungen, was ein Problem für die Verarbeitung darstellt. Produkte aus PHBV aus einmal geschmolzenem und verarbeitetem Pulver sind hochkristallin. Daher ist das Material spröde. Ferner wirkt sich die hohe Kristallinität sowie eine große Änderung der Dichte beim Abkühlen der Schmelze nachteilig auf die Spinnbarkeit des Materials aus. Nach dem Passieren der Spinndüse ziehen sich die Spinnfäden zusammen, was die Gefahr eines Fadenrisses beim Spinnen erhöht. Aufgrund der relativ hohen Kristallinität des Materials und einer verzögerten Kristallisationskinetik bei gesponnenen Polymerfäden kommt es zur Nachkristallisation in einem erheblichen Ausmaß, die Fäden verkleben nach dem Aufwickeln auf den Galetten und reißen beim Abwickeln. Zur Behebung der Nachteile wurden Verarbeitungsbedingungen vor allem bei Schmelzspinnprozessen mit der Kolbenspinnanlage und bei Mischungsprozessen optimiert. Die Polymermischungen und ?verbundstoffe enthalten kugelförmige Mikropartikel verschiedener Morphologie, die zuvor synthetisiert und charakterisiert wurden. Vor allem mit Vinylgruppen modifizierte Silikat-Submikropartikel mindern die Sprödigkeit von PHBV.
268

Hyperbranched Aromatic Polyesters and Their Application in Blends of Linear Polyamides

Fan, Zhirong 22 September 2009 (has links) (PDF)
In the last two decades, hyperbranched (hb) polymers have drawn much attention and obtained intensive research activities both from industry and academia. They are known to have unique and interesting properties which derive from their three dimensional structure and the large number of functional groups. These structural characteristics provide high possibilities for controlling functional group interactions and modifications of other polymers in blends and therefore, they are expected to result in novel materials with desired properties. Furthermore, the easy synthetic accessibility of hb polymers by one-pot synthesis is advantageous as well and allows easy scale-up of laboratory reactions. Having the characteristics as mentioned above, hb polymers are considered good candidates for blend components or melt processing modifiers. In fact, hb polymers have already been used as blend components or additives aiming for different effects. In many cases, reduced viscosity and formation of miscible blends were observed by modification of a linear matrix polymer with hb polymers. More information will be introduced in the following theoretical section. In this work two hb polyester systems based on AB2 and A2+B3 approaches were synthesized and studied. Their possible applications as additives in the blends of linear polyamides were investigated.
269

Barrier Properties of Liquid Crystalline Polymers and their Blends with PE and PETP

Flodberg, Göran January 2002 (has links)
No description available.
270

Characterization, optimization and modelling of PE blends for pipe applications

Al-Shamrani, Abdoul Ali January 2010 (has links)
Bimodal polyethylene resins are frequently used for pipe applications. In this work, blending was used to produce polyethylenes with comparable properties, particularly with respect to processing, stress crack resistance and tensile properties. Suitable blend components were identified, and their performance screened used ECHIP experimental design software. Blends were characterized using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), tensile testing, stress crack resistance measurements, impact toughness testing, capillary rheometry and melt index measurements. GPC, DSC and melt index results reveal that the method of meltcompounding produced morphologically uniform blends, with different degrees of compatibility depending on the type and level of branching of blend components. Most of the blends produced showed higher crystallinity values compared to a reference bimodal resin. Binary high density polyethylene (HDPE) blends showed better stiffness and strength properties, whereas metallocene catalyzed linear low density polyethylene (mLLDPE) containing blends illustrated superior elongation and toughness properties compared to the reference polymer and other binary blends. The highest resistance to slow crack growth (SCG) was shown by low density polyethylene (LDPE) and mLLDPE containing blends due to their high branching content. The overall blend resistance to SCG or toughness can be enhanced with levels less than 20% by weight of LDPE or mLLDPE in the blend although the tensile properties are relatively unaffected at these low concentrations. The performance of blends was optimized by changing component polymers and their weight fractions, and a model to predict optimum blends was developed using the Maple code. Optimized blends showed higher branching content, comparable molecular weight, molecular weight distribution, tensile properties, viscosity and processing behaviour to the reference polymer. Optimized blend 3, in particular, encountered the same degree of shear thinning as the reference material. Better toughness and resistance to SCG were shown by the optimized blends when compared to the reference polymer.

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