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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.
311

Análise fotoelástica da tensão de contração da polimerização de compósitos resinosos sob influência de técnicas restauradoras / Photoelastic analysis of polymerization shrinkage stress of composites under the influence of restorative techniques

Oliveira, Karla Mychellyne Costa, 1981- 18 August 2018 (has links)
Orientador: Simonides Consani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-18T19:48:31Z (GMT). No. of bitstreams: 1 Oliveira_KarlaMychellyneCosta_D.pdf: 952044 bytes, checksum: c22646f62ea3f107be3edac38b3a31ef (MD5) Previous issue date: 2011 / Resumo: A tensão de contração da polimerização é uma característica indesejável e inevitável das restaurações adesivas. É importante entender a distribuição da tensão para melhorar a efetividade clínica das restaurações de resina composta. Capítulo 1: o objetivo foi avaliar a tensão de contração da polimerização e o grau de conversão de um compósito resinoso com diferentes modos de ativação e densidades de energia. O compósito Z350 foi inserido no orifício central do disco de resina fotoelástica e fotoativado com LED (Bluephase-2) com densidade de energia de 12, 24 ou 36 J/cm2 usando os seguintes protocolos de fotoativação: contínuo de alta intensidade (HI: 1200 mW/cm2 por 10, 20 ou 30 s), contínuo de baixa intensidade (LI: 650 mW/cm2 por 18, 36 ou 54 s) e soft-start (SS: 150 mW/cm2 por 5 s + 1200 mW/cm2 por 9, 19 ou 29 s) (n=5). A tensão de contração de polimerização foi avaliada por meio de análise fotoelástica e o FTIR foi usado para análise do grau de conversão imediatamente e 24 horas após a ativação. ANOVA 3-fatores foi usado para avaliar os principais efeitos e as interações correspondentes, depois ANOVA 2-fatores foi realizado para cada tempo (p<0,05). As imagens mostraram que a tensão aumentou quando maior densidade de energia foi usada. A tensão não foi estatisticamente significante entre os métodos de ativação de alta e baixa intensidade. O método soft-start gerou tensões menores do que os modos contínuos quando 12 J/cm2 usado. O grau de conversão do modo soft-start foi estatisticamente menor que os modos de alta e baixa intensidade. Não foram encontradas diferenças no grau de conversão entre as doses de energia testadas. Pode-se concluir que a tensão de contração foi influenciada pela dose de energia e pelos protocolos de polimerização. O grau de conversão não foi influenciado pelo aumento das densidades de energia. Capítulo 2: O objetivo foi avaliar a tensão de contração criada em modelos fotoelásticos usando diferentes técnicas de inserção do compósito. Vinte réplicas de dentes em resina fotoelástica com cavidade classe II foram obtidos e distribuídos em quatro grupos (n=5) de acordo com as seguintes técnicas restauradoras: inserção horizontal (H), inserção oblíqua (O), compósito fluido + inserção horizontal (F+H), compósito fluido + inserção oblíquoa (F+O). Os modelos restaurados foram analisados por meio de polariscópio plano. A tensão ao longo de 7 áreas da interface adesiva foi analisada a partir das imagens obtidas após inserção de cada incremento e 24h após a fotoativação. Os valores de tensão máxima foram submetidos a ANOVA 2-fatores, seguido pelo teste de Tukey (p<0.05). As técnicas de inserção horizontal e oblíqua apresentaram diferenças no padrão de tensão. Apesar disso, nenhuma diferença no valor de tensão entre as técnicas horizontal e oblíqua foi encontrada. Os grupos com resina fluida mostraram maior tensão que aqueles restaurados apenas com compósito convencional / Abstract: Polymerization shrinkage stress is an undesirable and inevitable characteristic of adhesive restorations. It is important to understand the stress distribution to improve the clinical effectiveness of resin composite restoration. Chapter 1: The aim was to evaluate the polymerization shrinkage stress and degree of conversion of a resin composite material submitted to different photoactivation protocols. A bulk increment of composite Filtek Z350 was placed in the central perforation of photoelastic disc and photoactivated using LED-based curing unit (BluePhase II) with energy density of 12, 24 or 36 J/cm2 using the following photopolymerization protocols: continuous high intensity (HI: 1200 mW/cm2 during 10, 20 or 30 s), continuous low intensity (LI: 650 mW/cm2 during 18, 36 or 54 s) and soft-start (SS: 150 mW/cm2 during 5 s + 1200 mW/cm2 during 9, 19 or 29 s) (n=5). Photoelastic analysis was used to evaluate polymerization shrinkage stress of composite and FTIR was performed to access the degree of conversion of composite according to the curing modes. Statistical test ANOVA 3-way was used to determine the main effects and the corresponding interactions, then ANOVA 2 way was performed for each time (p<0.05). The images showed that polymerization shrinkage stress increases with higher values of power density. No significant differences should be noticed on polymerization shrinkage stress between high and low intensity modes of activation. Soft-start method generates stresses that were statistically lower than continuous modes except when 12 J/cm2 was applied. Similar degree of conversion was observed for photoactivation modes used, except for soft-start mode with 12, 24 and 36 J/cm2 that showed lowest levels of conversion. It could be concluded that polymerization shrinkage stress was significantly influenced by energy density and the curing protocol. No benefits on degree of conversion were observed by increasing the energy density. Chapter 2: The aim was to evaluate the polymerization shrinkage stress created in tooth photoelastic models using different filling techniques. Twenty class II tooth models were obtained. They were distributed into four experimental groups (n=5) according to the following restorative techniques: resin composite with horizontal insertion (H), resin composite with oblique insertion (O), flowable composite + resin composite with horizontal insertion (F + H) and flowable composite + resin composite with oblique insertion (F + O). Restored photoelastic models were analyzed using a plane polariscope. The stress along seven points of adhesive interface was analyzed from images of each insertion, at the baseline (immediately) and 24 h after polymerization. Maximum shear stress data was obtained and submitted to ANOVA 2-way, followed by Tukey's post hoc test at p = 0.05. Horizontal and oblique techniques have shown differences in stress patterns. No difference between horizontal and oblique techniques was found. Groups restored with flow composite showed significant higher stress levels than those restored only with regular composite. In conclusion, the use of flow composite created higher polymerization stress effects on the class II restoration than does the conventional restoration technique / Doutorado / Materiais Dentarios / Doutor em Materiais Dentários
312

Influencia da modulação da energia luminosa e da densidade energetica sobre a resistencia da união de restaurações de compositos fotoativados por LED ou luz de lampada halogena

Segreto, Dario Raimundo 25 February 2005 (has links)
Orientador: Mario Alexandre Coelho Sinhoreti / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-04T03:44:27Z (GMT). No. of bitstreams: 1 Segreto_DarioRaimundo_M.pdf: 667315 bytes, checksum: f8321716fe38251826ea9b052af1183b (MD5) Previous issue date: 2005 / Resumo: O objetivo deste estudo foi avaliar o efeito da variação da densidade de energia na resistência da união de compósitos odontológicos à estrutura dental, a partir da interação intensidade de luz versus tempo de exposição, com diferentes fontes de luz. Foram confeccionados 260 preparos cavitários classe V em incisivos bovinos, separados em 26 grupos (n = 10) que, na seqüência, foram restaurados com dois compósitos de marcas comerciais diferentes (Z250 - 3M/ESPE e Esthet-X - Dentsplay). As cavidades foram padronizadas (formato de ¿caixa com expulsividade emergente¿ configurando um troncocônico tridimensional com dimensões de 4 x 4 x 2,4 mm) e obtidas com ponta diamantada tronco-cônica 3131 (KG-Sorensen) com ângulo aproximado de 4o, montada em caneta de alta rotação adaptada a uma mesa de coordenadas. As restaurações foram confeccionadas em incremento único sendo a fotoativação realizada com aparelho de lâmpada halógena ou LED emitindo irradiância inicial de 700mW/cm2 e 600mW/cm2 respectivamente. Após o procedimento restaurador, seccionou-se longitudinalmente a coroa, respeitando-se o plano mésio-distal e, em seguida, realizou-se desgaste cuidadoso, via câmara pulpar, da parede axial da cavidade restaurada, com a finalidade de expor totalmente a base menor da restauração. Os corpos-de-prova foram levados à máquina de ensaio universal Instron (modelo 4411) para realização do teste de push-out. A velocidade do teste foi de 0,5mm/min até a ruptura da união e os dados coletados em Kgf foram transformados em MPa e submetidos a análise de variância e comparados pelo teste de Tukey (5%). Os resultados mostraram que o compósito Z250 apresentou médias de resistência da união estatisticamente superiores (p<0,05) tanto para o aparelho de lâmpada halógena quanto para o LED em todas as simulações clínicas estudadas, quando comparado ao Esthet-X. O aparelho LED, para o compósito Z250, proporcionou valores de resistência da união estatisticamente superiores (p<0,05) quando comparados com à lâmpada halógena e para o Esthet-X isso não foi observado. De modo geral, a densidade de energia disponível durante a fotoativação mostrou ter maior influência na resistência da união que intensidade de luz em restaurações com alto Fator-C / Abstract: The aim of this study was to evaluate the effect of the maintenance of the energy density by the light intensity and exposure time modulation, with different light sources, on the bond strength of dental composites to tooth structure. Two hundred and sixty expulsive box shaped Type V cavities (4 x 4 x 2.4mm) had been prepared in selected bovine incisors, which were divided in 26 groups (n=10) restored immediately with two composites of different brands (Z250 - 3M/ESPE and Esthet-X - Dentsply). Cavities were standardized (trapezoidal 3-D box shaped expulsive cavity with 4x4x2.4mm) and prepared with truncated diamond bur # 3131 (KG-Sorensen) with 4 degrees, mounted in air turbine adapted to a specific device. The restorations were bulk filled and light cured with halogen light or LED emitting irradiance of 700mW/cm2 and 600mW/cm2 respectively. After the restorative procedure, the specimens were longitudinally sectioned, respecting the mesiodistal plan. The axial wall of the cavities was ground via pulp chamber to completely expose the smaller base of the restoration. The samples were submitted to push-out test in a universal tester machine Instron (model 4411) with crosshead speed of 0.5mm/min. The data in Kgf were transformed in MPa, which were submitted to ANOVA and means compared by Tukey's test (5%). The results had shown that the composite Z250 presented higher bond strength means compared to Esthet-X in all tested conditions (p< 0.05), as with the halogen light as with LED. Moreover, for the composite Z250, light-curing with LED resulted in higher bond strength compared to halogen light (p< 0.05), what was not verified for Esthet-X. In general, the energy density supplied during light curing showed to be more important than light intensity in the bond strength of restorations with high C-factor / Mestrado / Materiais Dentarios / Mestre em Materiais Dentários
313

An optimisation study into the synthesis of o-cresol novolacs.

Sitetyana, Pindiwe 19 May 2008 (has links)
The phenolic resin chemistry is an old chemistry that started in the late 1800’s. A lot of research work to gain understanding of phenolic resins has been done and reported in literature. However, most of the studies are based on phenol novolac resins. It was necessary to acquire more knowledge on specifically o-cresol novolac (OCN) resins because of the interest in the production of these resins. The chemistry in question was new to Sasol and one of the major objectives of doing this work was to build in-house competency in this field. This was achieved by first investigating whether the available feed materials containing certain impurities can be used to synthesise o-cresol novolacs with set specifications of purity and physical characteristics. The suitability of the Sasol o-cresol in terms of its contamination with sulfur (which is sometimes found in relatively higher amounts due to operating conditions) was investigated. The results showed that the sulfur in o-cresol did not have a significant contribution in the sulfur of the OCN. Another contaminant, formic acid, an auto-oxidation product found in formalin solutions was also investigated. It was also observed that, at formic acid levels of up to 4000 ppm, there was no effect on the softening point of the OCN. Secondly, it was important to study and understand the effect of different reaction variables on the quality of the OCN resins. The effect of formaldehyde: o-cresol molar ratio was investigated, the softening point increased with the increase in the molar ratio. The effects of other reaction variables (catalyst, reaction time, temperature and formaldehyde feed rate) on the softening point of the OCN were also investigated using p-toluenesulfonic acid and oxalic acid as catalysts. With p-toluenesulfonic acid as a catalyst, the temperature had no effect on the softening point, while all the other variables showed an effect on this parameter. A softening point model was formulated, which predicted the softening point with 98% accuracy. With oxalic acid, only the amount of catalyst had an effect. In addition, the chemical structures of these compounds were studied using 13C-NMR spectroscopy. The focus was on the isomer distribution of the methylene linkages. / Prof. D.B.G. Williams
314

Comparative bond strengths of stainless steel orthodontic brackets bonded with different bonding agents

Hudson, Athol Peter Gilfillan. January 2007 (has links)
Magister Scientiae - MSc / The aim of this project was to compare the shear bond strengths of three light cure orthodontic adhesive resins with three different stainless steel molar brackets. / South Africa
315

The use of modified urea-formaldehyde resins in soil binder systems

Germishuizen, Willem Andreas 12 January 2007 (has links)
Please read the abstract in the section 00front of this document / Dissertation (M Eng (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted
316

The efficacy of Hibiscus sabdariffa as a fibre-reinforcement material for denture base acrylic resins

Okeke, Kenneth Nkemdilim January 2017 (has links)
Submitted in fulfillment of the requirements for the award of the degree of Master of Health Sciences: Dental Technology, Durban University of Technology, Durban, South Africa, 2017. / The poor mechanical properties of denture base acrylic resins can cause dentures to fracture either through impact or stress fatigue. Various metal reinforcing materials such as powders, nets, plates and wires together with synthetic fibres are therefore used to improve the strength properties of denture base acrylic resins. Despite their benefits, they are difficult to apply during fabrication, are costly, non-recyclable, and not environmentally friendly. The suitability of Hibiscus sabdariffa (H. sabdariffa) as a fibre reinforcement material for denture base acrylic resins was therefore investigated. A quantitative research paradigm and a two-phased experimental research design was used. The preliminary study used Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and field emission scanning electron microscope (FE-SEM) to assess the characteristics of, and the effect of, mercerisation on H. sabdariffa fibres. In determining the suitability of H. sabdariffa fibres, fibre diameter, fibre density, moisture content and absorption were examined. The main study investigated the mechanical and physical properties of two sample groups namely: the unreinforced (control) group and the H. sabdariffa fibre-reinforced (test) group denture base acrylic resins. The flexural strength, impact strength, specific wear rate, hardness and water absorption behaviour were determined in line with ASTM D 790 and D 256, G 99, D 2583 and D 570 methods of testing, respectively. Parametric and non-parametric tests were used to analyse the mean differences (p = 0.05) between the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins. The preliminary study revealed that H. sabdariffa fibres favourably compared to other lignocellulosic fibres in terms of fibre diameter, fibre density, water content and absorption behaviour. In the main study, a t-test revealed that there were significant differences in flexural strength at 0oC (p < 0.0001) and at 65oC (p < 0.0025) between the two sample groups. Similarly, there were significant differences in the impact strength between the two sample groups at 0oC (p < 0.031) and at 65oC (p < 0.0001). In contrast to the 200g load, there were significant differences (p < 0.044) in the specific wear rate of the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins at the 500g load. The hardness values revealed no significant differences (p > 0.707) between the two sample groups. There were however, significant differences (p < 0.041) in the water absorption rate between the two sample groups. Overall, the prominent features of this study showed that H. sabdariffa fibre is a suitable reinforcement fibre material for denture base acrylic resins and is in compliance with ISO 1567: 1999. Although this study found that H. sabdariffa fibres can be used as reinforcement material for denture base acrylic resins, the results cannot be generalised to clinical conditions, therefore in vitro and in vivo investigations are recommended. / M
317

Color stability of direct esthetic restorations = Estabilidade da cor de restaurações estéticas diretas / Estabilidade da cor de restaurações estéticas diretas

Oliveira, Dayane Carvalho Ramos Salles de, 1987- 22 August 2018 (has links)
Orientador: Luis Alexandre Maffei Sartini Paulillo / Texto em português e inglês / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-22T09:44:56Z (GMT). No. of bitstreams: 1 Oliveira_DayaneCarvalhoRamosSallesde_M.pdf: 87880082 bytes, checksum: e54ab93e23fb57efbc026ad0a7bd0491 (MD5) Previous issue date: 2013 / Resumo: O objetivo deste estudo foi avaliar através de espectrometria FT-IR e espectrofotometria de refletância, a estabilidade da cor de restaurações estéticas em resinas compostas após envelhecimento artificial acelerado (EAA). Para tanto, foram utilizados os sistemas adesivos: convencional de 3 passos - Adper ScotchBond Multi-Purpose (3M/ESPE), convencional de 2 passos - Tetric N Bond (Ivoclar Vivadent), autocondicionante de 2 passos - ClearFill SE Bond (Kuraray) e resinas compostas na cor EA1: nanoparticulada Filtek Z350 XT Supreme (3M/ESPE) e microhíbrida IPS Empress Direct (Ivoclar Vivadent). Espécimes simulando restaurações diretas (n=10) foram confeccionadas, com auxilio de matriz padronizada (4x4x1 mm) sobre substrato dentinário. Restaurações sem sistema adesivo foram utilizadas como controle. As avaliações de cor foram mensuradas com espectrofotômetro (EasyShade Advanced, Vita Zahnfabrik) em duas regiões distintas da restauração: na superfície da resina composta e na interface adesiva, em dois períodos de tempo: 48 h após acabamento e polimento da restauração e após 300 h de EAA com ciclos de 50oC alternados de 4 h de condensação e 4 h de exposição com luz UV. Os espécimes foram aferidos sob fonte de luz padronizada com irradiância espectral relativa D65 (Gti MiniMatcher, Gti Graphic Technology Inc.). Os dados do sistema CIE L*a*b* foram utilizados para o cálculo do ?E, ?L, ?a e ?b pela diferença de cada coordenada final pela inicial. Para análise do grau de conversão (GC) das resinas compostas utilizadas, espécimes com 4 mm de diâmetro (n=10) foram confeccionados e após 48 h analisados em espectrômetro FT-IR Spectrum 100 (Perkin Elmer). Os resultados obtidos foram analisados pela análise de variância a dois fatores e teste de Tukey (?=0,05). Os sistemas adesivos não interferiram na alteração de cor (?E) do corpo da restauração (?=0,90) ou da interface de união (?=0,78). Por outro lado, o fator resina composta foi significativo para a estabilidade de cor (?E) e para os valores das coordenadas isoladas (?<0,001). Em relação ao GC, a resina IPS Empress Direct apresentou resultados superiores (67%) frente a Z350XT (61%) com diferença estatisticamente significante (?<0,001). Desta forma, concluiu-se que o sistema adesivo não foi capaz de alterar a cor final de restaurações estéticas diretas. Entretanto, em relação para o fator resina composta foi encontrada diferença quanto à estabilidade da cor pelo EEA e ao GC, no qual a IPS Empress Direct apresentou resultados superiores / Abstract: The aim of this study was tm po evaluate the color stability and degree of conversion of esthetic composite resin restorations after accelerated artificial aging (AAA) by FT-IR and reflectance spectrometry. Thus, two etch and rinse adhesive systems - Adper ScotchBond Multi-Purpose (3M/ESPE) and Tetric N Bond (Ivoclar Vivadent) and one two-step self-etching bond system - ClearFill SE Bond (Kuraray) were used with two EA1 shade composite resins: Filtek Z350 XT nanofilled (3M/ESPE) and IPS Empress Direct microhybrid (Ivoclar Vivadent). The restored specimens (n=10) were made with standardized dimensions using a silicon mold under dentin substrate (4x4x1mm). The color were measured with a spectrophotometer (EasyShade Advanced, Vita Zahnfabrik) on composite resin surface and bond interface: 48 hours after finishing and polishing procedures; after 300 hours of AAA with 50oC cycles with 4 hours of condensation and 4 hours of UV exposure. Specimens were measured in a color-assessment cabinet (Gti MiniMatcher, Gti Graphic Technology Inc.) with a light source simulating the spectral relative irradiance of CIE standard illuminant D65. The CIE L*a*b* data were used to calculate the ?E, ?L, ?a and ?b by the difference between each final and initial coordinate. The degree of conversion (DC) of the composite resins used was measured using 4x4x1 mm samples (n=10). The DC analysis was performed using a FT-IR spectrometer Spectrum 100 (Perkin Elmer) after 48 hours. Data were submitted to two-way ANOVA and Tukey test (?=0.05). As the results, the adhesive systems had no significant influence on the color stability (?E) of the restoration surface (?=0.90) or the bonding interface (?=0.78). Moreover, the composite resin factor was significant and influenced the color as measured by ?E and isolated coordinates (?<0.001). As for the DC, IPS Empress Direct resin showed better results (67%) compared to Z350XT (61%) with statistically significant differences (?<0.001). Therefore, the adhesive system could not affect the final color of direct esthetic restorations. On the other hand, IPS Empress Direct showed better results of DC and color stability after EEA / Mestrado / Dentística / Mestra em Clínica Odontológica
318

Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy.

Bilyeu, Bryan 12 1900 (has links)
Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) and by high speed DSC when the reaction rate is high. The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC, temperature-modulated DSC (TMDSC), step scan DSC and high speed DSC, thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram and a continuous heating transformation (CHT) diagram for rapid determination of processing parameters in the processing of prepregs. Shrinkage due to both resin consolidation and fiber rearrangement is measured as the linear expansion of the piston on a quartz dilatometry cell using TMA. The shrinkage of prepregs was determined to depend on the curing temperature, pressure applied and the fiber orientation. Chemical modification of an epoxy was done by mixing a fluorinated aromatic amine (aniline) with a standard aliphatic amine as a curing agent for a commercial Diglycidylether of Bisphenol-A (DGEBA) epoxy. The resulting cured network was tested for wear resistance using tribological techniques. Of the six anilines, 3-fluoroaniline and 4-fluoroaniline were determined to have lower wear than the unmodified epoxy, while the others showed much higher wear rates.
319

Cure Kinetics and Processing Parameters of Neat and Reinforced High Performance Epoxy Resins: Evaluation of Techniques

Bilyeu, Bryan 12 1900 (has links)
Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4’-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions
320

Synthesis, development and characterisation of dehydrated castor oil poly (glyceryl phthalate) alkyd resins

Nzeru, Arnold. January 1994 (has links)
A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the Degree of Master of Science in Polymer Chemistry. / The dissertation studies the synthesis, formulation development, crosslinking and spectral characterisation of dehydrated castor oil poly(glyceryl phthalate) alkyd resins for use as air-dry surface coating vehicles. Synthesis of alkyd resins involves simultaneous dehydration, alcoholysis and polyesterification reactions. Dehydration of castor oil is achieved in situ under phthalic anhydride catalysis. Alcoholysis of dehydrated castor oil by glycerol is also achieved in situ to form predominantly the monoglyceride. Polyesterification of the resultant mono- and diglycerides is realised through interaction with phthalic anhydride. The reaction is carried out at 280°C for 3 hours and at 225°C for 2 hours under azeotropic distillation with xylene. The parent poly(glyceryl phthalate) alkyd resin is synthesized by reaction of castor oil, glycerol and phthalic anhydride to a predetermined acid value. Formulation development experiments were carried out to study the effect of variations in the dibasic acid to polyol/oil and polyol to oil ratios on alkyd resin properties. Model formulations exhibiting the best alkyd performance were developed. Predictive model formulation equations were derived from model formulation data and their limits of reliability and applicability established. The formulation of water soluble alkyd resins is modified to introduce pendant carboxylic acid groups along the polymer skeleton. Water solubility is achieved by neutralisation of the residual pendant carboxylic acid groups by 'fugitive' amines to yield water soluble alkyd soaps. The effect of variations in the nature and level of incorporation of amine is investigated. Alkyd resin solubilisation and resin acidity guide formulae were studied and developed. Cross-linking chemistry of alkyd resins, both in the reactor (gelation) and on application (film formation) is investigated. Gelation manifested itself in two different forms, thermoplastic and thermosetting. An important alkyd constant, K, was established as an indispensable tool in control of premature gelation and in the prediction of resin drying characteristics. Autooxidation and solvent evaporation are the two competing curing mechanisms encountered in film formation. The nature and influence of each curing mechanism on the rate of cure and film characteristics is highlighted. Catalysis experiments were conducted with metallic driers (Co2 Mn2 and Pb2} to bring the rate of drying of resin films to economically feasible limits and catalyst addition levels were established. New spectral characterisation techniques based on Fourier Transform Infrared spectroscopy were investigated. An extensive study was carried out on FT IR spectral data to establish qualitative and quantitative relationships between transmission peak ratios and alkyd resin composition. Series dependent and series independent correlation equations, useful in quantifying alkyd resin components were derived. A new FT IR spectroanalytic characterisation method for dibasic acids is proposed. The method, if adopted, affords both qualitative and quantitative characterisation of the dibasic acid component in the alkyd resin matrix and it is envisaged the technique will supersede conventional methods in terms of speed and simplicity.' / Andrew Chakane 2021

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