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Orientador: Ana Rita Morales / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-24T18:19:30Z (GMT). No. of bitstreams: 1 Pereira_RenatoBrisigueli_M.pdf: 31889860 bytes, checksum: dc126cb07343f751172187cc992844e7 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho foram avaliados os efeitos de aditivo modificador térmico (MT), aditivo modificador de impacto (MI) e tratamento de recozimento nas propriedades térmicas e mecânicas do poli(ácido lático), PLA. As propriedades térmicas foram avaliadas por meio de ensaios de temperatura de deflexão térmica (HDT) e ponto de amolecimento Vicat e a partir de curvas de calorimetria diferencial de varredura (DSC) de cada composição testada. As propriedades mecânicas foram avaliadas a partir de ensaios de resistência à tração. As alterações morfológicas na estrutura cristalina das amostras também foram analisadas por análise de difração de raios¿X. O uso dos aditivos propostos não se mostrou viável para o aumento da temperatura de deflexão térmica (HDT) e do ponto de amolecimento Vicat do PLA estudado. Estas propriedades mostraram-se sensíveis ao aumento do grau de cristalinidade que aumentou de 3% do PLA puro para aproximadamente 12% do PLA modificado, porém não foi suficiente para promover as melhorias esperadas. O tratamento de recozimento foi mais efetivo que os aditivos promovendo aumento no grau de cristalinidade para valores de até 44% e elevou os valores de HDT em torno de 10ºC e de Vicat em mais de 70ºC. A temperatura de transição vítrea, Tg, foi pouco alterada, sendo observados uma tendência de redução pela presença dos aditivos e um discreto aumento pelo recozimento. A cristalização a frio do PLA foi acelerada pelo aditivo nucleante e totalmente eliminada pelo tratamento de recozimento. O módulo de elasticidade apresentou aumento significativo pela adição dos aditivos testados, o que não foi observado para a resistência à tração e para o alongamento. O recozimento também foi significativo, porém, diferentemente do esperado, causou redução em todas as propriedades mecânicas. A maior cristalinidade observada deveria ter aumentado o módulo elástico, bem como a resistência à tração, o que não ocorreu por uma possível degradação causada pelas condições empregadas no tratamento térmico. As modificações no estado cristalino também foram acompanhadas pela alteração na transparência das amostras e por difração de raios-X que identificou a predominância da fase ?, caracterizada por uma célula unitária ortorrômbica. Para potenciais aplicações industriais os teores adequados de aditivos e uma análise detalhada do processo são necessários, incluindo-se o tempo e temperatura de resfriamento durante o processo de moldagem, para que o material final possa apresentar as propriedades desejadas / Abstract: This work evaluated the effects of a thermal modifier additive, an impact modifier additive, and an annealing treatment over the thermal and mechanical properties of the poli(lactic acid) (PLA). The thermal properties were evaluated through heat deflection temperature (HDT) and Vicat softening point measurements and through differential scanning calorimetric (DSC) curves of each tested composition. The mechanical properties were evaluated through tensile strength measurements. Morphological changes in the crystalline structure of the samples were also analyzed through X-ray diffraction. The use of the proposed additives was not feasible to increase the heat deflection temperature (HDT), and the Vicat softening point of the studied PLA. These properties were sensitive to the degree of crystallinity that was increased from 3% of the pure to around 12% of the modified PLA, but was not sufficient to promote the expected improvements. The annealing treatment was more effective than the additives and promoted an increasing of the degree of crystallinity to values up to 44%, it also increased the HDT values in approximately 10°C and the Vicat in more than 70°C. The glass transition temperature, Tg, was slightly altered, being observed a tendency of reduction by the presence of additives and a minor increase by the annealing treatment. The cold crystallization of the PLA was accelerated by the nucleating additive and completely eliminated by annealing treatment. The modulus of elasticity was significantly increased by the addition of the tested additives, but not for the tensile strength and the elongation. Annealing was also significant, however, unlike the expected, caused a reduction in all the mechanical properties. The higher crystallinity observed should have increased the elastic modulus and the tensile strength, which did not occur because of a possible sample degradation caused by annealing treatment conditions employed. Changes in the crystalline state were also accompanied by changes in the transparency of the samples and through X-ray diffraction where it was identified the prevalence of the ? phase, characterized by an orthorhombic unit cell. For potential industrial applications the appropriate levels of the additives and a detailed analysis of the process is required, including time and temperature of cooling during the molding process, so that the final material can offer the desired properties / Mestrado / Engenharia Química / Mestre em Engenharia Química

Compared to conventional materials, polymer matrix composites (PMCs) have a number of attractive properties, including light weight, easiness of installation, potential to lower system-level cost, high overall durability, and less susceptibility to environmental deterioration. However, PMCs are vulnerable to fire such that they degrade, decompose, and sometimes yield toxic gases at high temperature. The degradation and decomposition of composites lead to loss in mass, resulting in loss in mechanical strength. This research aims to improve the structural integrity of the PMCs under fire conditions by designing and optimizing a fire retardant nanopaper coating, and to fundamentally understand the thermal response and post-fire mechanical behavior the PMCs through numerical modeling. Specifically, a novel paper-making process that combined carbon nanofiber, nanoclay, exfoliated graphite nanoplatelet, and ammonium polyphosphate into a self-standing nanopaper was developed. The nanopaper was then coated onto the surface of the PMCs to improve the fire retardant performance of the material. The morphology, thermal stability, flammability, and post-fire flexural modulus of the nanopaper coated-PMCs were characterized. The fire retardant mechanism of the nanopaper coating was studied. Upon successfully improving the structure integrity of the PMCs by the nanopaper coatings, a thermal degradation model that captured the decomposition reaction of the iv polymer matrix with a second kind boundary condition (constant heat flux) was solved using Finite Element (FE) method. The weak form of the model was constructed by the weighted residual method. The model quantified the thermal and post-fire flexural responses of the composites subject to continuously applied heat fluxes. A temperature dependent post-fire residual modulus was assigned to each element in the FE domain. The bulk residual modulus was computed by assembling the modulus of each element. Based on the FE model, a refined Finite Difference (FD) model was developed to predict the fire response of the PMCs coated with the nanopapers. The FD model adopted the same post-fire mechanical evaluation method. However, unlike the FE model, the flow of the decomposed gas, and permeability and porosity of the composites were taken into account in the refined FD model. The numerical analysis indicated that the thickness and porosity of the composites had a profound impact on the thermal response of the composites. The research funding from the Office of Naval Research (ONR) and Federal Aviation Administration Center of Excellence for Commercial Space Transportation (FAA COE AST) is acknowledged.

Molding is a simple manufacturing process whereby fluid fills a master tool and then solidifies in the shape of the tool cavity. The precise nature of material flow during molding has long allowed fabrication of plastic components with sizes 1 mm 1 m. Polymer molding with precise critical dimension control could enable scalable, inexpensive production of micro- and nanostructures for functional or lithographic use. This dissertation reports experiments and simulations on molding of polymer micro- and nanostructures at length scales 1 nm 1 mm. The research investigates two main areas: 1) mass transport during micromolding and 2) polymer mechanical properties during nanomolding at length scales 100 nm. Measurements and simulations of molding features of size 100 nm 1 mm show local mold geometry modulates location and rate of polymer shear and determines fill time. Dimensionless ratios of mold geometry, polymer thickness, and bulk material and process properties can predict flow by viscous or capillary forces, shape of polymer deformation, and mold fill time. Measurements and simulations of molding at length scales 100 nm show the importance of nanoscale physical processes distinct from bulk during mechanical processing. Continuum simulations of atomic force microscope nanoindentation accurately model sub-continuum polymer mechanical response but highlight the need for nanoscale material property measurements to accurately model deformation shape. The development of temperature-controlled nanoindentation enables characterization of nanoscale material properties. Nanoscale uniaxial compression and squeeze flow measurements of glassy and viscoelastic polymer show film thickness determines polymer entanglement with cooperative polymer motions distinct from those observed in bulk. This research allows predictive design of molding processes and highlights the importance of nanoscale mechanical properties that could aid understanding of polymer physics.