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Cinética da cristalização não isotérmica de poli(3- hidroxibutirato) em compósitos com fibra de babaçuARRUDA, Salim Abdelnor 26 February 2016 (has links)
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Previous issue date: 2016-02-26 / PRH-L8 Petrobrás / O acúmulo de resíduos plásticos em aterros sanitários, rios e ilhas, além da contaminação da
fauna e da flora com esses dejetos, acarretou uma pesquisa intensa em materiais biodegradáveis
que possam substituir os tradicionais materiais sintéticos advindos do petróleo. Os polímeros
biodegradáveis são uma opção que vem sendo constantemente estudada e que pode, em um
futuro próximo, competir com os polímeros a base de petróleo. O Poli (3-hidroxibutirato)
(PHB) é um polímero produzido por bactérias que utilizam a sacarose da cana de açúcar ou do
milho como fonte de alimento. O PHB possui características interessantes como
biodegradabilidade, sustentabilidade, plasticidade e sua durabilidade. Porém, ele possui um
maior custo, além de ser duro e quebradiço e termicamente instável durante o processamento.
Portanto, torna-se necessário o estudo da cristalização do PHB atrelado a fibras de babaçu, com
o intuito de diminuir o custo do compósito, além de buscar melhorias nas propriedades térmicas,
como cristalinidade relativa, taxa de cristalização, temperatura do pico de cristalização, entre
outras variáveis. Neste trabalho foram estudados os parâmetros de cristalização a partir do
fundido para o sistema PHB/20% fibra de babaçu conduzidos a diferentes taxas de resfriamento
(2, 3, 4, 6, 8, 12, 16 e 24 °C/min) e fluxo de nitrogênio a 50 mL/min e, posteriormente, esses
parâmetros de cristalização, como a granulometria, tempo de processamento e diferentes partes
do babaçu, foram comparados para as diferentes taxas de resfriamento. Uma segunda análise
foi realizada para os parâmetros de cristalização a frio conduzidos a diferentes taxas de
aquecimento. A partir do tratamento de dados obtidos para os parâmetros de cristalização a
partir do fundido, realizou-se a modelagem cinética para os modelos de Pseudo-Avrami, Ozawa
e Mo. Entre as modelagens, o modelo de Pseudo-Avrami apresentou a melhor correlação com
os dados experimentais com erro relativo de aproximadamente 5%. O modelo de Ozawa
apresentou um erro em torno de 8% e Mo aproximadamente 10%. A análise da energia de
ativação foi realizada a partir do Método Isoconversional de Friedman, obtendo energias de
ativação negativas, indicativo que há reações complexas na cristalização a partir do fundido
para o sistema PHB/20% fibra de babaçu. / The accumulation of plastic waste in landfills, rivers and islands, as well as the contamination
of fauna and flora with these wastes, led to intensive research into biodegradable materials that
can replace traditional synthetic materials. Biodegradable polymers are an option that has been
constantly studied and that may, in the near future, compete with petroleum-based polymers.
Poly (3-hydroxybutyrate) (PHB) is a polymer produced by bacteria that use sucrose from sugar
cane or corn as a food source. PHB has interesting features such as biodegradability,
sustainability, plasticity and durability. However, it has a high cost, in addition to being hard
and brittle and thermally unstable during processing. Therefore, it was found convenient to
study the crystallization of PHB/20% babassu compounds, with the intention of reducing the
cost of the composite, in addition to seeking improvements in thermal properties such as relative
crystallinity, crystallization rate, peak crystallization temperature, etc. In this work, the
parameters of melt crystallization were studied for PHB/20% babassu compounds driven at
different cooling rates (2, 3, 4, 6, 8, 12, 16 and 24°C/min) under a nitrogen flow of 50 ml/min.
Subsequently, crystallization parameters determined in compounds prepared with different
filler particle size, processing times, and different parts of babassu, were compared for different
cooling rates. A second analysis was performed for the parameters of cold crystallization
conducted at different heating rates. A kinetic analysis of data obtained for melt crystallization,
using Pseudo-Avrami, Ozawa, and Mo models was performed. Among the models studied,
Pseudo-Avrami showed the best correlation with experimental data, with relative error about
5%. The Ozawa model presented a discrepancy around 8% and Mo approximately 10%. The
activation energy was estimated using the isoconversional Friedman method, obtaining
negative activation energies, which suggests that there are complex reactions involved in the
crystallization from the melt in the system PHB/20% babassu.
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Non-isothermal Crystallization Kinetics, Multiple Melting Behaviors and Crystal Structure Simulation of Poly[(ethylene)-co-(trimethylene terephthalate)]sKo, Chi-Yun 26 July 2003 (has links)
Non-isothermal crystallization of the PET/PTT copolyesters was studied at five different cooling rates over 1-20oC/min by means of differential scanning calorimetry (DSC). Both the Ozawa equation and the modified Avrami equation have been used to analyze the crystallization kinetics. The non-isothermal kinetics of most copolymers cannot be described by the Ozawa analysis, except the copolyester with a composition of 66.3% trimethylene- (TT) and 33.7 %ethylene- terephthalates (ET). It may be due to the inaccuracy of the Ozawa assumptions, such as the secondary crystallization is neglected. From the kinetic analysis using the modified Avrami equation, the Avrami exponents, n, were found to be in the range of 2.43-4.67 that are dependent on the composition of the copolyesters. The results indicated that the primary crystallization of the PET/PTT copolymers followed a heterogeneous nucleation and a spherulitic growth mechanism during the non-isothermal crystallization. In the cases of the copolyesters with either TT or ET less than 10%, we found the molten temperature is a key factor to decide whether the Ozawa equation can be succeeded in analyzing the dynamic crystallization.
For the non-isothermal crystallization, a single exothermic peak was detected in each DSC curve regardless of the composition and the cooling rate. It indicated that a single-mode distribution of the crystallite sizes was formed during the cooling process. After the non-isothermal crystallization, the melting behavior of the specimens was monitored by temperature modulated DSC (TMDSC) in the conventional mode and the modulated mode. Multiple endothermic peaks were observed in both modes. The wide-angle X-ray diffraction (WAXD) patterns of these copolymers showed that the peak height became sharper and sharper as the crystallization temperature increased, but the position of the diffraction peaks did not change apparently. It indicated that the multiple melting behaviors did not originate from the melting of the crystals with different structures. The melting behavior of these PET/PTT copolyesters can be explained logically by using the melt-recrystallization model. From the reversing and non-reversing signals of TMDSC, the melting-recrystallization-remelting phenomena were further verified. In addition, a small endothermic peak was found at the highest melting temperature in the reversing thermogram for TT-enriched copolyesters. It is reasonably to believe that this endotherm is attributed to the melting of the crystals that are formed in regime I during the heating scan.
The cocrystallization of the PET/PTT copolyesters was studied using DSC and WAXD. A clear endothermic peak in the DSC thermogram was detected over the entire range of copolymer composition. A minimum melting temperature was found for the copolyester with 50% ET. The WAXD patterns of these copolymers can be divided into two groups with sharp diffraction peaks, i.e., PET type and PTT type crystals. The transition of crystal structure between PET type and PTT type occurred around the eutectic composition (50 % ET and TT), determined from the variation of the melting temperature with the composition. In addition, the fiber diagram and the WAXD pattern of the copolyester with the eutectic composition showed a different crystalline structure. These results indicated that the cocrystallization behavior of the PET/PTT copolyesters was isodimorphic.
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The Kinetics of Thermal Decomposition and Hot-Stage Microscopy of Selected Energetic CocrystalsJoshua Trevett Dean (8782151) 29 April 2020 (has links)
<p>The thermal decomposition of four energetic cocrystals
composed of 4-amino-3,5-dinitropyrazole (ADNP)/diaminofurazan (DAF),
2,4,6-trinitrotoluene (TNT)/
2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL20), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane
(HMX)/CL20, and 1-methyl-3,5-dinitro-1,2,4-triazole (MDNT)/CL20 were studied
using simultaneous differential scanning calorimetry (DSC), thermogravimetry
analysis (TGA), and hot-stage microscopy. The kinetic parameters of their
thermal decomposition reaction were determined using the Kissinger and Ozawa
kinetic analysis methods. Each cocrystal’s peak exothermic temperature
(decomposition temperature), activation energy, and pre-exponential constant are
reported. Furthermore, these parameters from each cocrystal were compared to
the same parameters from the corresponding stoichiometric physical mixture in
order to identify changes in behavior attributable to the cocrystallization
process. For ADNP/DAF, the cocrystal shows an 8% increase in the peak exotherm
temperature and a 11-13% decrease in peak activation energy as compared to its
physical mixture. For TNT/CL20, this comparison shows a much smaller change in
the peak exotherm temperature (<1%) but shows a 5% decrease in activation
energy. This cocrystal also experiences phase stabilization—where a phase
transition of one or both coformers is omitted from the decomposition process. The
HMX/CL20 cocrystal shows a 1% change in the peak exotherm temperature and shows
a 2% increase in activation energy. Finally, for MDNT/CL20, this comparison
shows nearly a 4% increase and a drastic decrease in peak activation energy by 42-44%.
Cocrystallization clearly affects the thermal decomposition and reaction
kinetics of these materials, offering the potential to create a hybrid-class of
energetic materials which combines the high performance of an energetic
material with the safety and insensitivity of another. </p>
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Keimzellen der Avantgarde - Yasuo Ozawas 'Tokyo Experimental Performance Archive'Krautheim, Ulrike 21 June 2016 (has links)
Das „Tokyo Experimental Performance Archive“ wurde 2014 von Yasuo Ozawa, einem unabhängigen Produzenten im Bereich Musik- und Tanz-/ Körperperformance initiiert. Im ersten Jahr des zunächst auf eine Dauer von drei Jahren angelegten Projekts wurden sechs Performances von Künstlern, die der japanischen experimentellen Musik- und Tanzszene zuzurechnen sind, filmisch dokumentiert und auf einer projektbezogenen Website im Internet veröffentlicht.
In einem Gespräch mit der Autorin erläutert Ozawa seine Vorstellung von einem Archiv als ‚kreativer Kommunikationsplattform’, seine Kurz- und Langzeitvision des „Tokyo Experimental Performance Archive“, sowie seinen Kampf mit den Windmühlen der japanischen Bürokratie.
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