Abstract
Polytetrafluoroethylene (PTFE) powder of a high molecular weight (~ 107) was drawn by solid-state extrusion in the temperature range 100–340°C, which covers the glass transition temperature (125°C) and the ambient melting point (334°C). Draw was attainable only above 100°C. The maximum achievable extrusion draw ratio (EDRmax) was almost constant, ~ 10, from 100–280°C, yet increased rapidly with further increasing temperature, reaching a maximum of 60 at 330–340°C. At yet higher temperatures, the drawability was lost due to melting. The structure and properties of drawn products were found to be complexely affected by extrusion temperature and EDR. For extrusion at 330–340°C, near the melting point, an effective and high draw was achieved. The crystalline chain orientation function, crystallite sizes, both along and perpendicular to the chain axis, differential scanning calorimetry heat of fusion, and flexural modulus increased with EDR and approached a maximum at EDR of 30–40, depending on the extrusion temperatures. Above a specific EDR, the efficiency of draw decreased due to the formation of flaws. The highly oriented PTFE consisted of microfibrils of a significantly large lateral dimension (~ 45 nm) compared to those (6–20 nm) generally found in oriented polymers. The modulus of a drawn PTFE was sensitive to the test temperatures, reflecting the reversible crystal/crystal transitions at ~ 19 and 30°C. The optimization of the extrusion conditions resulted in the maximum achieved flexural modulus at 24°C of 20 GPa at an EDR 40 for extrusion at 340°C.
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Okuyama, H., Kanamoto, T. & Porter, R.S. Solid-state deformation of polytetrafluoroethylene powder. JOURNAL OF MATERIALS SCIENCE 29, 6485–6494 (1994). https://doi.org/10.1007/BF00354009
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DOI: https://doi.org/10.1007/BF00354009