On the formation of defects induced by air trapping during cold pressing of PTFE powder

Otavio C. Gamboni (1, 2) , Cassius Riul (3) , René Billardon (2) , Waldek Bose Filho (1) , Nicolas Schmitt (2) , Rodrigo B. Canto (1)

1 EESC-USP - Escola de Engenharia de São Carlos
2 LMT - Laboratoire de Mécanique et Technologie
3 TCNSP - Technological Center of the Navy in São Paulo

The manufacturing of polytetrafluoroethylene products is usually carried out by cold isostatic and/or uniaxial pressing of the powdered polymer, followed by sintering of the “green” parts. During pressing, the air initially present in the loose powder leads to the formation of defects in the material, but the mechanisms involved are not entirely understood. The aim of this study was to better understand the role played by the entrapped air during the cold pressing of polytetrafluoroethylene powder. Observation of the microstructure and determination of some mechanical properties of green and sintered samples, manufactured with different quantities of entrapped air by the cold isostatic pressing process, were carried out. The analysis indicated that defects are formed when the entrapped air pressure in the pressed part leads to internal stresses exceeding the intergranular cohesion resistance of the green part. These defects remain in the microstructure even after sintering, considerably reducing the mechanical strength.

Mots clés: Polytetrafluoroethylene (PTFE); Polymer powder pressing; Air trapping defects

Domaines: Mécanique des matériaux [physics.class-ph]

Otavio C. Gamboni, Cassius Riul, René Billardon, Waldek Bose Filho, Nicolas Schmitt, et al.. On the formation of defects induced by air trapping during cold pressing of PTFE powder. Polymer, 2016, 82, pp.75 - 86. ⟨10.1016/j.polymer.2015.11.014⟩. ⟨hal-01716012⟩