Neste trabalho estudou-se o efeito de três diferentes tratamentos químicos utilizando- se soluções aquosas de LiCl, NaCl, e HCl sobre o inchamento, a distribuição de tamanho de partículas e a capacidade de troca catiônica (CTC) de uma vermiculita proveniente da jazida de Paulistana, localizada no Estado do Piauí, visando seu uso em compósitos de matriz polimérica. Para os tratamentos com sais inorgânicos foram utilizadas várias concentrações de LiCl e NaCl a 90°C por 144 horas, permitindo a secagem da solução de tratamento. Para o tratamento ácido foram utilizadas soluções 2M de HCl à temperatura ambiente, utilizando tempos de tratamento de 2 a 10 horas. Após os tratamentos, as amostras foram submetidas a agitação mecânica intensa em dispersor de alta energia de cisalhamento (24000 RPM). Todos os tratamentos empregados resultaram em aumentos nos índices de inchamento e reduçães nos tamanhos de partícula em diferentes graus. Os maiores inchamentos antes da agitação mecânica foram observados nas amostras tratadas com soluções 0,8M de LiCl sem lavagem (4 a 5 vezes a da prova em branco). Após agitação mecânica, os maiores inchamentos foram observados nas amostras tratadas com soluções 2M de HCl por 5 horas (11 vezes a da prova em branco). No entanto, após o processo de secagem não foi possível atingir-se os mesmos valores de inchamento. A diminuição mais importante no tamanho de partícula foi observada nas amostras tratadas com soluções 2M de HCl durante 5 horas, enquanto que as quedas mais significativas nos valores de CTC foram obtidas com as amostras tratadas com soluções 2M de HCl (CTC crescentes com o aumento do tempo de tratamento). Foi analisado o efeito da incorporação de vermiculita tratada acidamente em uma matriz polimérica de polipropileno (PP). A presençaa dessa vermiculita provocou um alto nível de degradação na matriz de PP, com a consequentemente perda de propriedades mecânicas. Esta degradação pode ser atribuída à formação de sítios ácidos nas partículas de vermiculita gerados pelo ataque do HCl, bem como à presença de HCl residual da solução de tratamento. / In the present work, the effect of three different chemical treatments using inorganic solutions of LiCl, NaCl, and HCl on the swelling, particle size distribution, and cation exchange capacity (CEC) of a vermiculite clay was studied. The clay is originary from Paulistana mine, located in the State of Piauí, Northeastern Brazil, and the final purpose of the treatment of the clay was its use in polymer-matrix composites. For the inorganic salts treatments, several solutions of NaCl and LiCl at different concentrations were used, at 90°C for 144 hours, allowing the treatment solution to dry out. For the acid treatment, 2M HCl solutions at room temperature were used, using treatment times of 2 to 10 hours. After the treatments, all the samples were subjected to intense mechanical stirring in the high shear energy disperser (24000 RPM). The results showed that all treatments resulted in increases in the rates of swelling and reduction in the mean particle sizes, in different degrees. The largest swelling before mechanical stirring was observed in samples treated with solutions of 0.8M LiCl without washing (4 to 5 times that of the untreated sample). After mechanical desagglomeration, the highest swelling was observed in samples treated with solutions 2M HCl for 5 hours (11 times that of the untreated sample). However, after drying, it was no longer possible to achieve the same values of swelling. The most significant decrease in particle size was observed in samples treated with solutions 2M HCl for 5 hours, whereas the most significant reduction in the CEC values were also obtained with the samples treated with solutions 2M HCl (CEC increasing with the time of treatment). Finally, the effect of the addition of the acid treated vermiculite to a polymeric matrix of polypropylene (PP) was examined. The evaluation of the resultant composite specimens indicated that the presence of vermiculite caused a high level of degradation of the PP matrix, with the consequent loss of mechanical properties. This degradation can be attributed to the formation of acidic sites on the vermiculite particles, generated by the direct attack of HCl, and the presence of residual HCl from the treatment solution.

Application of polymer matrix composites in engineering structures has been steadily increasing over the past five decades. Multidirectional polymer composites are one class of continuous fiber reinforced polymer matrix composites used in aerospace structures, where the desired mechanical performance outweighs the cost. Their modulus and strength degrade with time (known as creep and creep rupture) during the service, owing to the viscos-elasticity of the polymer matrix. Additional contribution to this degradation comes from various damage modes developed in the plies of the composite with time and identified in this thesis as TDD (Time Dependent Damage). These damage modes may also develop due to process-induced residual stresses, and during loading to the service load, identified as TID (Time Independent Damage). TID influences the TDD, the creep and the creep rupture. The objective of this thesis is to develop a model to predict the evolution of TID and TDD in multiple plies of a laminate and their influence on creep. The predominant damage mode, transverse cracking, is modeled in this study. The model consists of four modules, PIS, QSL, SL, and VA. The PIS, QSL, and SL moduli predict changes in ply stresses for incremental change in temperature, stress, and time respectively, using lamination theory and assuming linear elastic behavior of the plies during an incremental step. In parallel, each module predicts the stored elastic energy in each ply after each incremental step and compares it with a critical stored elastic energy criterion to determine if a ply would crack. If fracture is predicted, the VA module based on variational analysis, is invoked to determine the crack density and the perturbation in ply stresses due to cracking. The perturbation stresses are used by the module that invoked the VA module to determine the ply stresses after cracking during the current incremental step. The model predictions for a [±45/90]s laminate, at two test temperatures (80C and 180C) and four stresses in the range of 20–54 MPa, compare very well with experimental results validating the model.

Application of polymer matrix composites in engineering structures has been steadily increasing over the past five decades. Multidirectional polymer composites are one class of continuous fiber reinforced polymer matrix composites used in aerospace structures, where the desired mechanical performance outweighs the cost. Their modulus and strength degrade with time (known as creep and creep rupture) during the service, owing to the viscos-elasticity of the polymer matrix. Additional contribution to this degradation comes from various damage modes developed in the plies of the composite with time and identified in this thesis as TDD (Time Dependent Damage). These damage modes may also develop due to process-induced residual stresses, and during loading to the service load, identified as TID (Time Independent Damage). TID influences the TDD, the creep and the creep rupture. The objective of this thesis is to develop a model to predict the evolution of TID and TDD in multiple plies of a laminate and their influence on creep. The predominant damage mode, transverse cracking, is modeled in this study. The model consists of four modules, PIS, QSL, SL, and VA. The PIS, QSL, and SL moduli predict changes in ply stresses for incremental change in temperature, stress, and time respectively, using lamination theory and assuming linear elastic behavior of the plies during an incremental step. In parallel, each module predicts the stored elastic energy in each ply after each incremental step and compares it with a critical stored elastic energy criterion to determine if a ply would crack. If fracture is predicted, the VA module based on variational analysis, is invoked to determine the crack density and the perturbation in ply stresses due to cracking. The perturbation stresses are used by the module that invoked the VA module to determine the ply stresses after cracking during the current incremental step. The model predictions for a [±45/90]s laminate, at two test temperatures (80C and 180C) and four stresses in the range of 20–54 MPa, compare very well with experimental results validating the model.

Polymer nanocomposites are an important research interest in the area of engineering and functional materials, including the search for more environmentally materials for renewable energy and materials. The ability to analyze and optimize morphology is crucial to realizing their potential, since the distribution of materials in the composite strongly influences its properties. This dissertation presents research into three different polymer nanocomposite systems with three different applications that underscore the need to understand and control the composite morphology to succeed. The first project details work on development of a copolymer compatibilizer to enhance the dispersion of the plant-derived biopolymer lignin in composite blends with polystyrene. The copolymer was designed with hydroxyl functionality that can form hydrogen bonds with lignin, and the effect of modulating the density of these groups was investigated, both on bulk dispersion and interfacial mixing. The second project presented concerns resolving the interfacial morphology of composite bulk heterojunction organic photovoltaic devices based on a polythiophene-based photoactive polymer and a modified carbon fullerene, which are archetypical of the highest performing cells yet produced. Neutron reflectivity was extensively employed to probe the interfacial width and degree of intermixing between the components to elucidate the morphological impact on device performance. The final project involves modifying nanoscale cellulose crystallites, dubbed nanowhiskers, by replacing a portion of the hydroxyl groups with acetate groups to improve their dispersion in polymethyl methacrylate. Neutron reflectivity was again employed to probe the interface between the two materials to observe and quantify intermixing.

Made available in DSpace on 2014-06-11T19:27:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-08Bitstream added on 2014-06-13T18:55:37Z : No. of bitstreams: 1 bandeira_cf_me_guara.pdf: 2529578 bytes, checksum: 3ce5e71049e75732be8d65ca09414dca (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O estudo do comportamento viscoelástico e das suas temperaturas de transições térmicas são imprescindíveis para que produtos sejam desenvolvidos, construídos e aplicados corretamente em cada setor de mercado. Assim, qualquer método analítico que vise à redução de tempo de laboratório, na análise de propriedades viscoelásticas de compósitos poliméricos, está contribuindo diretamente para a otimização de metodologia de avaliação de materiais estratégicos. Com isto, o presente trabalho tem como objetivo validar o método Synthetic-Oscillation (multiplex) na obtenção de curvas de DMA (análise dinâmico-mecânica). Este aplicativo computacional, (multiplex), realiza em um único ensaio, medidas do comportamento viscoelástico de materiais em diferentes frequências. As curvas, geradas através deste aplicativo computacional, foram comparadas com as curvas obtidas em experimento real (multifrequência), para se determinar estatisticamente a confiabilidade do método multiplex em medir as propriedades viscoelásticas de compósitos poliméricos. Uma vez dominada esta metodologia, avaliou-se a influência da exposição à radiação ultravioleta, à umidade e ao combustível aeronáutico, na temperatura de transição vítrea (Tg) dos compósitos poliméricos. Os resultados mostram que o método multiplex é tão eficiente quanto o método de multifrequência, na obtenção de curvas de DMA de compósitos poliméricos, com a vantagem de ser mais rápido. A Tg dos compósitos estudados foi afetada apenas pela exposição a umidade e a radiação UV / The study of viscoelastic behavior and its thermal transitions temperatures are essential to new products development, construction and property application in each market sector. Thus, any analytical method that aims to reduce laboratory time on analysis of viscoelastic properties of polymer composites, is directly contributing to the methodology optimization for evaluation of strategic materials. With this, the present study aims to validate the method Synthetic-Oscillation (Multiplex) to obtain curves of DMA (dynamic mechanical analysis). This computer application, (multiplex), in a single run, measures the viscoelastic behavior of materials at different frequencies. The curves generated by this computer application, were compared with the curves obtained in a real experiment (multifrequency), to statistically determine the reliability of the multiplex method to measure the viscoelastic properties of polymer composites. Once dominated this methodology, was evaluated the influence of exposure to ultraviolet radiation, humidity and jet fuel in the glass transition temperature (Tg) of polymer composites. The results show that the multiplex method is as efficient as the method of multifrequency, in obtaining curves of DMA polymer composites, with the advantage of being faster. The Tg of the composites studied was affected only by exposure to moisture and UV radiation

Resumo: O estudo do comportamento viscoelástico e das suas temperaturas de transições térmicas são imprescindíveis para que produtos sejam desenvolvidos, construídos e aplicados corretamente em cada setor de mercado. Assim, qualquer método analítico que vise à redução de tempo de laboratório, na análise de propriedades viscoelásticas de compósitos poliméricos, está contribuindo diretamente para a otimização de metodologia de avaliação de materiais estratégicos. Com isto, o presente trabalho tem como objetivo validar o método Synthetic-Oscillation (multiplex) na obtenção de curvas de DMA (análise dinâmico-mecânica). Este aplicativo computacional, (multiplex), realiza em um único ensaio, medidas do comportamento viscoelástico de materiais em diferentes frequências. As curvas, geradas através deste aplicativo computacional, foram comparadas com as curvas obtidas em experimento real (multifrequência), para se determinar estatisticamente a confiabilidade do método multiplex em medir as propriedades viscoelásticas de compósitos poliméricos. Uma vez dominada esta metodologia, avaliou-se a influência da exposição à radiação ultravioleta, à umidade e ao combustível aeronáutico, na temperatura de transição vítrea (Tg) dos compósitos poliméricos. Os resultados mostram que o método multiplex é tão eficiente quanto o método de multifrequência, na obtenção de curvas de DMA de compósitos poliméricos, com a vantagem de ser mais rápido. A Tg dos compósitos estudados foi afetada apenas pela exposição a umidade e a radiação UV / Abstract: The study of viscoelastic behavior and its thermal transitions temperatures are essential to new products development, construction and property application in each market sector. Thus, any analytical method that aims to reduce laboratory time on analysis of viscoelastic properties of polymer composites, is directly contributing to the methodology optimization for evaluation of strategic materials. With this, the present study aims to validate the method Synthetic-Oscillation (Multiplex) to obtain curves of DMA (dynamic mechanical analysis). This computer application, (multiplex), in a single run, measures the viscoelastic behavior of materials at different frequencies. The curves generated by this computer application, were compared with the curves obtained in a real experiment (multifrequency), to statistically determine the reliability of the multiplex method to measure the viscoelastic properties of polymer composites. Once dominated this methodology, was evaluated the influence of exposure to ultraviolet radiation, humidity and jet fuel in the glass transition temperature (Tg) of polymer composites. The results show that the multiplex method is as efficient as the method of multifrequency, in obtaining curves of DMA polymer composites, with the advantage of being faster. The Tg of the composites studied was affected only by exposure to moisture and UV radiation / Orientador: Michelle Leali Costa / Coorientador: Edson Cocchieri Botelho / Banca: Luiz Claudio Pardini / Banca: Pedro Carlos de Oliveira / Mestre

Neste trabalho estudou-se o efeito de três diferentes tratamentos químicos utilizando- se soluções aquosas de LiCl, NaCl, e HCl sobre o inchamento, a distribuição de tamanho de partículas e a capacidade de troca catiônica (CTC) de uma vermiculita proveniente da jazida de Paulistana, localizada no Estado do Piauí, visando seu uso em compósitos de matriz polimérica. Para os tratamentos com sais inorgânicos foram utilizadas várias concentrações de LiCl e NaCl a 90°C por 144 horas, permitindo a secagem da solução de tratamento. Para o tratamento ácido foram utilizadas soluções 2M de HCl à temperatura ambiente, utilizando tempos de tratamento de 2 a 10 horas. Após os tratamentos, as amostras foram submetidas a agitação mecânica intensa em dispersor de alta energia de cisalhamento (24000 RPM). Todos os tratamentos empregados resultaram em aumentos nos índices de inchamento e reduçães nos tamanhos de partícula em diferentes graus. Os maiores inchamentos antes da agitação mecânica foram observados nas amostras tratadas com soluções 0,8M de LiCl sem lavagem (4 a 5 vezes a da prova em branco). Após agitação mecânica, os maiores inchamentos foram observados nas amostras tratadas com soluções 2M de HCl por 5 horas (11 vezes a da prova em branco). No entanto, após o processo de secagem não foi possível atingir-se os mesmos valores de inchamento. A diminuição mais importante no tamanho de partícula foi observada nas amostras tratadas com soluções 2M de HCl durante 5 horas, enquanto que as quedas mais significativas nos valores de CTC foram obtidas com as amostras tratadas com soluções 2M de HCl (CTC crescentes com o aumento do tempo de tratamento). Foi analisado o efeito da incorporação de vermiculita tratada acidamente em uma matriz polimérica de polipropileno (PP). A presençaa dessa vermiculita provocou um alto nível de degradação na matriz de PP, com a consequentemente perda de propriedades mecânicas. Esta degradação pode ser atribuída à formação de sítios ácidos nas partículas de vermiculita gerados pelo ataque do HCl, bem como à presença de HCl residual da solução de tratamento. / In the present work, the effect of three different chemical treatments using inorganic solutions of LiCl, NaCl, and HCl on the swelling, particle size distribution, and cation exchange capacity (CEC) of a vermiculite clay was studied. The clay is originary from Paulistana mine, located in the State of Piauí, Northeastern Brazil, and the final purpose of the treatment of the clay was its use in polymer-matrix composites. For the inorganic salts treatments, several solutions of NaCl and LiCl at different concentrations were used, at 90°C for 144 hours, allowing the treatment solution to dry out. For the acid treatment, 2M HCl solutions at room temperature were used, using treatment times of 2 to 10 hours. After the treatments, all the samples were subjected to intense mechanical stirring in the high shear energy disperser (24000 RPM). The results showed that all treatments resulted in increases in the rates of swelling and reduction in the mean particle sizes, in different degrees. The largest swelling before mechanical stirring was observed in samples treated with solutions of 0.8M LiCl without washing (4 to 5 times that of the untreated sample). After mechanical desagglomeration, the highest swelling was observed in samples treated with solutions 2M HCl for 5 hours (11 times that of the untreated sample). However, after drying, it was no longer possible to achieve the same values of swelling. The most significant decrease in particle size was observed in samples treated with solutions 2M HCl for 5 hours, whereas the most significant reduction in the CEC values were also obtained with the samples treated with solutions 2M HCl (CEC increasing with the time of treatment). Finally, the effect of the addition of the acid treated vermiculite to a polymeric matrix of polypropylene (PP) was examined. The evaluation of the resultant composite specimens indicated that the presence of vermiculite caused a high level of degradation of the PP matrix, with the consequent loss of mechanical properties. This degradation can be attributed to the formation of acidic sites on the vermiculite particles, generated by the direct attack of HCl, and the presence of residual HCl from the treatment solution.

O desenvolvimento da sociedade humana somente atingiu o estágio atual devido à utilização de materiais compósitos de diferentes misturas, que vem desempenhando um papel fundamental no desenvolvimento da sociedade moderna. Com a finalidade de explorar o crescente interesse nas pesquisas de novos materiais, este trabalho apresenta um estudo sobre as propriedades do compósito elastomérico a base de poli(éter-siloxano) e sólido particulado cerâmico de titanato de bário (3 BaTiO). Amostras com quantidades adequadas dos componentes, matriz polimérica não curada e particulada de titanato de bário, foram curadas em diferentes concentrações (puro, 10, 20, 30, 40 e 50 %) por meio de mistura em massa em uma câmara glove box em ambiente de nitrogênio, até obtenção de mistura homogênea. O copolímero puro e uma série de compósitos com diferentes concentrações foram submetidos a ensaios de inchamento, análises térmicas gravimétricas, calorimetria diferencial exploratória, caracterização morfológica por microscopia eletrônica de varredura, ensaios mecânicos de tração e medidas elétricas. Por meio dessa série de técnicas de caracterização foram observadas propriedades bem distintas entre o polímero puro e os compósitos, caracterizado pelo aumento das ligações cruzadas. Neste trabalho foi também construído um capacitor de placas paralelas para teste de capacitância elétrica dos materiais preparados, visando o estudo do comportamento elétrico dos materiais em estudo. / The present development of the human society should be credited to the use of the composite and blend materials. In this dissertation composites of an elastomer, poly(ether-siloxane), along with barium titanate are prepared and their properties are studied. Nanoparticles of barium titanate were incorporated in the elastomer in the range 0-50 wt% through bulk mixing under nitrogen atmosphere in a glovebox, using a porcelain mortar and pestle. The mixtures thus prepared were placed in molds and allowed to cure in order to prepare specimens for properties analyses. The composites were submitted to swelling tests, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical strength tension test, electrical measurements and electron scanning microscopy (SEM). It was possible to make a correlation between the observed properties and the morphology and composition of the composites. Additionally, a parallel plates capacitor for injection and test of small samples was built and used to evaluate the electrical capacitance of the composites prepared in this work.

Polymers as construction material are common in the industry. Although more recently the use of polymer composites in more demanding applications has increased, requiring more of them mechanically, tribologically and thermally. To enhance the properties various fillers are used, from common glass fibers to more advanced nanoparticles. For this study three types of base polymers have been studied: poly-amide (PA), poly-phenylene-sulphide (PPS) and poly-ether-ether-ketone (PEEK). They have been filled with glass fibers, carbon fibers, poly-tetra-fluoro-ethylene (PTFE), graphite and thermally conductive modifier in various combinations. Fibers are used to increase the mechanical properties, PTFE and graphite are added as lubricating additives to reduce the friction, and the thermally conductive modifier to increase the thermal conductivity. Five general groups of polymer composites were studied. Pure PEEK PPS, PA and PEEK filled with fibers PPS, PA and PEEK filled with fibers and lubricating additives PA filled with lubricating additives PEEK filled with fibers and additives for lubrication and thermal conductivity The polymer composites have been tribologically tested in a reciprocating sliding test set-up. Friction, wear and surface damage have been studied. Three types of counter surfaces have been used: ball bearing steel balls, stainless steel cylinders and anodized aluminum cylinders. Load, surface temperature of the polymer composites and number of cycles were varied to study any changes in friction and wear. The wear marks on the polymer composites were studied using an SEM. Cross sections of some tested samples were prepared to study any subsurface damage. From the tests the polymer composites showed similarities in friction. Lubricating additives gave lower friction, often around 0.05-0.15, while pure and only reinforced gave higher, often around 0.4-0.5. The wear was also less for polymer composites with lubricating additives. There was no clear influence of temperature but for most tests an increase in temperature gave lower friction. The only influence of load was that higher load gave wider wear tracks. Since no cross sections were prepared to compare subsurface damage due to different loads there might be a possibility that there were some differences below the surface as well. Otherwise cross sections showed that polymer composites with only fibers had cracks and cracked fibers below the surface due to the high stresses the polymer composite had been subjected to. With lubricating additives there was no large subsurface damage and it seems as if the lubricating additives formed a protective tribofilm in the wear track, giving both lower friction and wear. The presence of such a tribofilm was confirmed by XPS analysis that showed a surface layer containing F from PTFE. The conclusions are that the tribological properties of a polymer composite are strongly dependent on its fillers. Lubricating additives form a tribofilm that lowers friction and wear. Elevated temperatures might drastically change the tribological behavior of a polymer composite why it is important to do tests at higher temperatures. Cross sections can give information about subsurface damage and might help to understand the wear mechanisms and deformation of polymer composites better. More microscopy and mechanism studies are required in order to further understand the tribological behavior of polymer composites.

No description available.