Polytetrafluoroethylene (PTFE) has some unique properties such as high hydrophobicity and high resistance to elevated temperatures, chemicals and solvents, which make it of interest for numerous fibre and textile applications. However, PTFE normally has a very high viscosity and poor flowability in the melt due to its ultra-high molecular weight, meaning that it cannot be readily melt-spun into textile fibres. In addition, PTFE is insoluble in all common organic solvents, prohibiting its use in common solution spinning methods such as dry, wet or electrospinning. Here we aim to develop an easy and environmentally friendly alternative for the production of PTFE nanofibres, using a modified island-in-the-sea spinning process. For this, first a dispersion of PTFE homopolymer, PVA and water was compounded to create a blend of PTFE particles in PVA solution using different methods, including casting, single-step extrusion and two-step-compounding and extrusion. After solid-state drawing of this blend and removal of the PVA, we were able to collect PTFE nanofibres with finest diameters of around 50nm and lengths up to 15μm. The effects of blend composition, morphology and drawing on PTFE fibre formation and properties were studied and discussed. Furthermore, some other material modification systems, including plasticized PVA, or the use ethylene glycol as a solvent, was studied with the aim of scaling up the fabrication of PTFE nanofibres by spinning the PTFE/PVA blend fibres directly for a twin-screw extruder.

Thesis (doctoral)--Göteborg Universitet, 1993. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Göteborg Universitet, 1993. / Added t.p. with thesis statement inserted. Includes bibliographical references.

No description available.

Orientador: Steven Frederick Durrant / Banca: José Humberto Dias da Silva / Banca: José Roberto Ribeiro Bortoleto / Banca: Johnny Vilcarromero Lopez / Banca: Adriana de Oliveira Delgado Silva / Resumo: O politetrafluoretileno (PTFE) e a poliamida 6 (PA 6) são polímeros que têm excelentes qualidades mecânicas, elétricas e químicas. Por isto, são utilizados em diversos componentes de equipamentos mecânicos e elétricos entre várias outras aplicações. Entretanto o PTFE possui um ângulo de contato com a água (WCA) de cerca de 120º e a PA 6 um WCA de cerca de 60º. Isto, especialmente no caso do PTFE, diminui a sua adesividade com outros materiais. Para resolver este problema várias técnicas têm sido sugeridas, como, por exemplo, tratamentos químicos e tratamento a plasma. Entre elas o tratamento a plasma, que tem a vantagem de produzir modificações apenas na superfície, não alterando o interior do material. O objetivo deste trabalho é estudar como o WCA varia em função dos parâmetros do tratamento a plasma de nitrogênio, a pressão do gás (p), a potência (P) e o tempo de tratamento (t). O nitrogênio foi escolhido por ser um gás cujo plasma, segundo a literatura, causa reduções significativas no ângulo de contato da superfície de polímeros. Várias séries de tratamento foram conduzidas, tanto para o PTFE quanto para a PA 6. Foram obtidas reduções significativas no WCA, ocorrendo o resultado notável de WCA = 0º para p = 2,6 Pa, P = 300 W e t = 30 min, tanto para o PTFE quanto para a PA 6. Em função dos resultados, dentro do intervalo de parâmetros utilizado, concluiu-se que, de uma forma geral, o WCA diminui com a potência e com o tempo de tratamento, e que o WCA tem um comportamento... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Polytetrafluoroethylene (PTFE) and polyamide 6 (PA 6) are polymers that have excellent mechanical, electrical and chemical properties. Therefore, they are used in diverse mechanical and electrical equipment components among many other applications. However, PTFE has a water contact angle (WCA) about of 120º and PA 6 has a WCA about of 60º. This, especially for PTFE, decreases their adhesiveness with other materials. To solve this problem, many techniques have been proposed, such as chemical and plasma treatments. Among them the plasma treatment has the advantage of producing modifications on the surface only, altering the bulk. The objective of this work is to study how the WCA varies as a function of the nitrogen plasma treatment parameters, the gas pressure (p), the applied power (P) and the treatment time (t). Nitrogen plasmas were used in this study since, according the literature, such plasmas significantly reduce the surface contact angle of polymers. Several series of treatment were conducted, for PTFE as for PA 6. Significant reductions in WCA were obtained, including a WCA of 0º notable for p = 2.6 Pa, P = 300 W and t = 30 min, for PTFE as for PA 6. Thus, from the results, within the range of the parameters studied, it was concluded that, in general, the WCA diminishes as the power and as the treatment time increases, and that the WCA has a notable behavior as a function of the gas pressure, initially decreasing to reach a minimum (optimum) value of 0 º for p = 2.6 P... (Complete abstract click electronic access below) / Doutor

Fluoropolymers are employed in countless end-user applications across several industries. One such fluoropolymer is polytetrafluoroethylene. This research is concerned with studying and understanding the thermal behavior of polytetrafluoroethylene. Such understanding is critical to predict its behavior in diverse service environments as the polymer ages and for allowing bottom up design of improved polymers for specific applications. While a plethora of experiments have investigated the thermal properties of polytetrafluoroethylene, examining these properties using molecular dynamics simulations remains in its infancy. In particular, the current body of molecular dynamics research on polytetrafluoroethylene has primarily focused on studying polytetrafluoroethylene phases, its physical nature, and its helical conformational structure. The present study is the first molecular dynamics simulations research to study polytetrafluoroethylene behavior near the glassy transition temperature. Specifically, the current research utilizes molecular dynamics simulations to achieve the following objectives: (a) model and predict polytetrafluoroethylene glassy transition temperature at different molecular weights, (b) examine the impact of glassy transition temperature on the volume-temperature and thermal properties, (c) study the influence of molecular weight on polytetrafluoroethylene melt and glassy state, and (d) determine the governing forces at the molecular level that control polytetrafluoroethylene glassy transition temperature. Achieving the aforementioned objectives requires performing four major tasks. Motivated by the scarcity of polytetrafluoroethylene force fields research, the first task aims to generate and test polytetrafluoroethylene force fields. The parameters were produced based on the Optimized Potentials for Liquid Simulations All Atom model. The intramolecular parameters were generated using the automated frequency matching method while the torsional terms were fitted using the nonlinear least squares algorithm. The intermolecular partial atomic charges were obtained using Northwest Computational Chemistry software and fitted using the restrained electrostatic potential at (MP2/6-31G*) level of theory. The final set of parameter was tested by calculating polytetrafluoroethylene density using molecular dynamics simulations. The second task involves building polytetrafluoroethylene amorphous structure using molecular dynamics at periodic boundary conditions for polytetrafluoroethylene cell at different molecular weights. We use the amorphous structure in the molecular dynamics simulations in consistence with research evidence which reveals that polymer properties such as the specific volume will differ as the polymer passes the glassy transition when it is in the amorphous phase structure whereas no variation occurs when the polymer passes the glassy transition while it is in the crystalline structure. The third task includes testing polytetrafluoroethylene melt phase properties: density, specific heat, boiling point, and enthalpy of vaporization. In the fourth and final task, we performed molecular dynamics simulations using NAnoscale Molecular Dynamics program. This task involves the polymer relaxation process to predict polytetrafluoroethylene mechanical behavior around the glassy transition temperature. Properties that are affected by this transition such as density, heat capacity, volumetric thermal expansion, the specific volume, and the bulk modulus were examined and the simulated results were in good agreement with experimental findings.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 109-113).

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 132-139). Also available in electronic format on the Internet.

Orientador: Cesar Renato Foschini / Coorientador: Carlos Alberto Fonzar Pintão / Banca: Eduardo Carlos Bianchi / Banca: Nilton Francelosi Azevedo Neto / Resumo: Materiais poliméricos são comumente usados em aplicações de engenharia, o que tem motivado pesquisadores a estudarem seu comportamento mecânico e o desenvolvimento de sistemas de medida. O Politetrafluoretileno (PTFE), comercialmente conhecido como Teflon, é um destes polímeros. Devido ao fato de que o PTFE é capaz de realizar funções estruturais específicas e ser submetido a esforços mecânicos cisalhantes, é importante que se conheça o valor do módulo de torção, G, não só para predizer seu comportamento mecânico, mas também para usá-lo como parâmetro de rigidez em projetos. Desta forma, o principal objetivo deste trabalho foi apresentar e validar o uso de uma técnica alternativa para determinar o módulo de torção, G, de materiais com ênfase em materiais poliméricos, em particular, o PTFE. Para realizar a medida de G, foi utilizado um sistema mecânico contendo um pêndulo de torção e um sensor de movimento rotativo (SMR) acoplado a ele, que permitisse determinar: a posição angular em função do tempo. Então, uma equação derivada dos estudos de espectroscopia mecânica e da teoria de relaxação foi utilizada para o cálculo de G. A técnica aplicada neste trabalho é considerada como não destrutiva e independe de se conhecer o valor do coeficiente de Poisson do material em estudo. Amostras de diferentes diâmetros de PTFE extrudado foram submetidas a esforços de torção simples variando seu comprimento efetivo, a fim de estudar o seu comportamento à torção. As amostras passaram por aná... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Polymeric materials are commonly used in engineering applications, which has motivated researchers to study their mechanical behavior and development of measurement systems. The Polytetrafluoroethylene (PTFE), commercially known as Teflon, is one of these polymers. Due the fact that PTFE is able to perform a specific structural function and be subjected to mechanical shear stresses, it is important to know the value of the torsion modulus, G, not only to predict its mechanical behavior, but also to use it as a parameter of rigidity in projects. In this way, the main objective of this work was to present and validate the use of an alternative technique to determine the torsion modulus, G, of materials with emphasis on polymeric materials, in particular the PTFE. For this purpose, a mechanical system containing a torsion pendulum and a rotational motion sensor (RMS) coupled to it was used to determine the angular position as a function of time. Then, an equation derived from mechanical spectroscopy and relaxation theory was used for the calculation of G. The technique applied in this work is considered as non-destructive and is independent of knowing the value of Poisson's ratio of a study material. Samples with different diameters of extruded PTFE were subjected to simple torsional stresses varying their effective length in order to study their torsional behavior. The samples were subjected to thermal analysis to determine their degree of purity, thermal stability and to estim... (Complete abstract click electronic access below) / Mestre

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