A Perspective on Solid State Microstructure in Polytetrafluoroethylene

Davidson, Theodore; Gounder, Raj N.; Weber, David; Wecker, Sheldon M.

doi:10.1007/0-306-46919-7_1

Cited by 6 publications

(8 citation statements)

References 16 publications

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“…The results suggest that PTFE and PTFE copolymers exhibit a deformation mechanism in which lamellar thickness is not the only parameter influencing the yielding behaviour. For PTFE homopolymer it has been suggested that plastic deformation initially proceeds primarily by chain slip which involves a translation of molecules past each other parallel to the chain direction and is not dependent upon dislocation movements 12, 17, 34, 35. Melt crystallized PTFE is non‐spherulitic and primarily consists of thick lamellae of significant extent, often bedded parallel to one another 35.…”

Section: Resultsmentioning

confidence: 99%

“…For PTFE homopolymer it has been suggested that plastic deformation initially proceeds primarily by chain slip which involves a translation of molecules past each other parallel to the chain direction and is not dependent upon dislocation movements 12, 17, 34, 35. Melt crystallized PTFE is non‐spherulitic and primarily consists of thick lamellae of significant extent, often bedded parallel to one another 35. When slowly cooled from the melt, PTFE exhibits a banded structure containing parallel striations perpendicular to the length of the bands.…”

Section: Resultsmentioning

confidence: 99%

“…The proposed model of PTFE deformation is supported by the fact that PTFE chains adopt a helical conformation and that is characterized by a smooth molecular profile. Therefore, if neighbouring molecules interlock along the grooves between helices, slip along these grooves may progress easily 35…”

Section: Resultsmentioning

confidence: 99%

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Relationship between Structure and Mechanical Properties of Melt Processable PTFE: Influence of Molecular Weight and Comonomer Content

Frick

Sich

Heinrich

et al. 2012

Macro Materials & Eng

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The influence of molecular weight and comonomer content on the mechanical properties of several melt‐processable polytetrafluoroethylene (MP PTFE) materials is studied. Additionally, a comparison of mechanical properties including tensile properties and their dependence on environment as well as fatigue life of PTFE, MP PTFE and perfluoroalkoxy copolymer (PFA) is made. PTFE homopolymer and PTFE copolymers exhibit considerably different mechanical properties. The small strain deformation behaviour up to yielding correlates with the degree of crystallinity and comonomer content, whereas the large strain deformation was found to depend on intercrystalline connections, such as tie molecules and chain entanglements. The special role of these elements in determining the fatigue life and sensitivity to environmental stress cracking is also demonstrated.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Relationship between Structure and Mechanical Properties of Melt Processable PTFE: Influence of Molecular Weight and Comonomer Content

Frick

Sich

Heinrich

et al. 2012

Macro Materials & Eng

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“…Os valores médios de largura das lamelas variaram entre 125 e 275 nm, para as condições de sinterização de 360 ○ C por 10 min e 390 ○ C por 1.000 min, respectivamente. Os valores de espessura e largura das lamelas encontrados nas análises de MEV são compatíveis com os valores reportados na literatura [1,7,23] .…”

Section: Strabelli P G Et Al -Influência De Variáveis De Sinterizunclassified

Influência de variáveis de sinterização na microestrutura de peças de PTFE moldadas por prensagem isostática

et al. 2014

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Resumo: O politetrafluoretileno (PTFE) é utilizado em extensa gama de aplicações críticas devido à sua excelente resistência química e térmica, baixa energia superficial e propriedades tribológicas. Devido à sua elevada viscosidade no estado fundido, o PTFE não pode ser transformado pelos métodos tradicionais de extrusão e injeção, sendo o principal método de transformação deste polímero a prensagem sob temperatura ambiente, seguida de sinterização a temperaturas acima do ponto de fusão. O tempo de sinterização é definido de acordo com as dimensões da peça fabricada, podendo variar de poucas horas até vários dias para peças de grande volume. Avaliações sobre a influência dos extremos de tempo e temperatura de sinterização, atualmente adotados na indústria, sobre a microestrutura cristalina do PTFE, são escassas na literatura científica, sendo o principal objetivo deste estudo. Placas em PTFE foram sinterizadas variando-se a temperatura entre 360 ○ C e 390 ○ C e o tempo entre 10 e 10.000 min. Calorimetria exploratória diferencial (DSC), medidas de perda de massa e de densidade e microscopia eletrônica de varredura (MEV) foram utilizadas. Os resultados das medidas de perda de massa indicaram que a degradação do PTFE aumenta com o tempo e temperatura de sinterização. Análises das entalpias de fusão e medidas de densidade apontam indiretamente a redução na massa molar e aumento no grau de cristalinidade com o aumento do tempo e temperatura de sinterização. As análises em MEV possibilitaram a observação direta da microestrutura cristalina, indicando uma tendência de aumento da largura das lamelas com o tempo e temperatura de sinterização. Os resultados obtidos podem auxiliar no controle da microestrutura do PTFE durante o processamento, o que é bastante útil para a fabricação de peças em PTFE com desempenho otimizado. Palavras-chave: PTFE, sinterização, degradação térmica, cristalinidade. Effects of Sintering Variables on the Microstructure of Isostatically Pressed PTFE PartsAbstract: Polytetrafluorethylene (PTFE) is used in a wide range of critical applications because of its outstanding chemical and thermal resistance, low surface energy and special tribological properties. Because of its high melt viscosity, PTFE cannot be processed by traditional extrusion and injection methods. Cold pressing followed by sintering above its melting temperature is the main processing technique. The sintering time is defined according to the dimensions of the manufactured part and may last from a few hours to several days for large parts. Studies of the influence of sintering time and temperature on the PTFE crystalline microstructure are scarce in the scientific literature, being the main objective of this study. PTFE plates were isostatically pressed and sintered at temperatures from 360 ○ C and 390 ○ C for periods of times between 10 e 10,000 min. Differential Scanning Calorimetry (DSC), measurements of mass loss and density and Scanning Electron Microscopy (SEM) were performed. The results of mass loss indicated that degradatio...

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“…Because of its high molecular weight and internal resistance to rotation within repeating units, PTFE has difficulty crystallizing from the melt. Furthermore, it is typically necessary to sinter PTFE versus extruding or molding via common processing techniques . Combined, these characteristics present a challenge for using non‐contact deposition techniques to create a dense, physically and chemically homogeneous solid …”

Section: Introductionmentioning

confidence: 99%

Microwave dielectric properties of polytetrafluoroethylene‐polyacrylate composite films made via aerosol deposition

O'Keefe

Luscombe

2016

Polymer International

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Few studies have examined the deposition of polytetrafluoroethylene (PTFE) using additive manufacturing and their subsequent properties in microwave devices. The present study examines polytetrafluoroethylene-polyacrylate (PTFE-PA) composite films made via aerosol deposition to assess the potential use of PTFE in additive manufacturing processes. The composites are composed of PTFE-PA core − shell nanoparticles, synthesized using a seeded emulsion polymerization, containing various PTFE weight fractions up to 50%. The synthesized nanoparticles were sprayed onto a heated glass substrate and subsequently annealed at a temperature above the glass transition temperature of PA and below that of PTFE, rendering a solid film approximately 40 m thick. A cavity perturbation resonance technique was employed to determine the complex permittivity of the films. As the volume fraction of PTFE increased, the real part of the permittivity ′ decreased while the imaginary part of the permittivity ′′ showed little variation. The results demonstrate a promising approach for incorporating PTFE into additive manufacturing processes, particularly for microwave devices.

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A Perspective on Solid State Microstructure in Polytetrafluoroethylene

Cited by 6 publications

References 16 publications

Relationship between Structure and Mechanical Properties of Melt Processable PTFE: Influence of Molecular Weight and Comonomer Content

Relationship between Structure and Mechanical Properties of Melt Processable PTFE: Influence of Molecular Weight and Comonomer Content

Influência de variáveis de sinterização na microestrutura de peças de PTFE moldadas por prensagem isostática

Microwave dielectric properties of polytetrafluoroethylene‐polyacrylate composite films made via aerosol deposition

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