Melting and crystallization behavior of poly(tetrafluoroethylene). New method for molecular weight measurement of poly(tetrafluoroethylene) using a differential scanning calorimeter

Suwa, Takeshi; Takehisa, Masaaki; Machi, Sueo

doi:10.1002/app.1973.070171102

Cited by 152 publications

(65 citation statements)

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“…[3,4] Note, that a part of the samples studied in ref. [5,6,25] have a calculated molecular weight,M n , outside the upper limit of Equation (1). That means, those data points are a result of an extrapolation.…”

Section: Resultsmentioning

confidence: 99%

“…Suwa et al [5] investigated in 1973 the heat of crystallisation of PTFE and their correlation to the molecular weight M n using Equation (1). For PTFE with molecular weight M n ranging from 5.2 Á 10 5 to 4.5 Á 10 7 g/mol the following quantitative relationship Summary: The influence of number-average molecular weight M n ranging from 1.4 Á 10 4 to 1.2 Á 10 6 g/mol on the thermal behaviour of polytetrafluoroethylene (PTFE) has been studied.…”

Section: Introductionmentioning

confidence: 99%

“…The thermal properties of radiation-degraded PTFE with molecular weight M n ranging from 1.4 Á 10 4 to 1.2 Á 10 6 g/mol has been studied. The results have been discussed with respect to the quantitative relationships between molecular weight and heat of crystallisation of PTFE proposed by Suwa et al [5] as well as by Weigel and Garske. [6] Experimental Part Material A commercial polytetrafluoroethylene fine powder (Dyneon TM TF 2025) was used as received for the irradiation experiments.…”

Section: Introductionmentioning

confidence: 99%

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The Estimation of the Molecular Weight of Polytetrafluoroethylene Based on the Heat of Crystallisation. A Comment on Suwa's Equation

Lappan

Geißler

Häußler

et al. 2004

Macro Materials & Eng

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Summary: The influence of number‐average molecular weight $\overline M _{\rm n}$ ranging from 1.4 · 104 to 1.2 · 106 g/mol on the thermal behaviour of polytetrafluoroethylene (PTFE) has been studied. Samples have been prepared by radiation‐induced degradation of commercial PTFE. The molecular weight $\overline M _{\rm n}$ has been calculated using end‐group concentration determined by infrared (IR) spectroscopy and 19F solid‐state nuclear magnetic resonance (NMR) spectroscopy. Melting and crystallisation heats were investigated by differential scanning calorimetry (DSC). The results have been discussed with respect to quantitative relationships between number‐average molecular weight and heat of crystallisation of PTFE described in the literature. The molecular weight calculated from Suwa's equation, which is often used in the literature, has been found to be too low.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Estimation of the Molecular Weight of Polytetrafluoroethylene Based on the Heat of Crystallisation. A Comment on Suwa's Equation

Lappan

Geißler

Häußler

et al. 2004

Macro Materials & Eng

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“…23 between the number-average molecular weight and the heat of crystallization about 7 mg of polymer has been heated with a Perkin Elmer DSC-7 at a rate of 20 K min -1 from room temperature to 650 K. The sample has then been held at this temperature for 5 minutes before cooling with 20 K min -l back to room temperature. Heats of crystallization were obtained from the measured DSC exotherms and the molecular weight was estimated to be 44 x 10 5 gmol-1 , 22 x 10 5 gmol-1 , and 2 x 10 5 gmol-1 for G 163, TFl 750, and KU02, respectively.…”

Section: Experiments Almentioning

confidence: 99%

Isothermal Crystallization of Poly(tetrafluoroethylene). Effect of Holding Time in the Melt on Calorimetric Measurements

Lehnert

Hirschmann

1997

Polym J

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KEY WORDSPoly(tetrafluoroethylene) / Isothermal Crystallization / Calorimetry / Holding Time in Melt / Residual Order in Melt / Crystalline poly(tetrafluoroethylene) (PTFE) exhibits three solid phases at atmospheric pressure with first order solid-solid transitions occurring at 292 and 303 K. Depending on the experimental method and extrapolation used the equilibrium melting point lies between 600 and 620 K. 1 • 2 As-polymerized (virgin) and meltcrystallized PTFE are known to be highly crystalline; fully amorphous polymer has not been observed. The microstructure of melt-crystallized bulk PTFE is unusual in that it consists predominantly of thick lamellae. Fibrillar and striated band-like morphologies have been observed under certain crystallization conditions for polymer of suitable molecular weight 3 • 4 and incipient spherulitic structures with a large degree of imperfection were reported to occur at very slow cooling rates of the order of degrees Kelvin per hour. 3 In a previous calorimetric study it was concluded from non-isothermal data obtained at constant cooling rate that PTFE crystallizes one-dimensionally from pre-existing nuclei which were presumed to be impurities. 5 Neutron and X-ray diffraction, Raman spectroscopic, computational, and several other studies on molten PTFE all suggest that conformational, orientational, and local positional order persists after the polymer has been heated above the equilibrium melting point. 6 -12 The presumption that PTFE can retain some kind of order in the melt is in line with the outcome of a number of studies on the effect of melt holding time on the isothermal crystallization behaviour of polymers such as polyethylene, 13 poly(ethylene oxide), 13 poly(ethylene terephthalate), 14 -16 poly-( ethere ether ketone), 1 7 · 18 poly(phenylene sulfide), 19 • 20 and polycarbonate. 21 Many of the phenomena observed in these studies have been connected to self-nucleation by, for instance, Wunderlich in reference 22 which also provides quotations of similar studies on polymers not quoted above. The mechanism of self-nucleation, thereby microscopic remnants of polymer crystallites remain unmelted and can serve as nucleation sites on cooling below the melting temperature can be presumed to play a role also in the melt-crystallization of PTFE. EXPERIMENT ALAs-polymerized commercial grade polymers were supplied in powder form by ICI, UK (Fluon G 163) 1 To whom correspondence should be addressed. 23 between the number-average molecular weight and the heat of crystallization about 7 mg of polymer has been heated with a Perkin Elmer DSC-7 at a rate of 20 K min -1 from room temperature to 650 K. The sample has then been held at this temperature for 5 minutes before cooling with 20 K min -l back to room temperature. Heats of crystallization were obtained from the measured DSC exotherms and the molecular weight was estimated to be 44 x 10 5 gmol-1 , 22 x 10 5 gmol-1 , and 2 x 10 5 gmol-1 for G 163, TFl 750, and KU02, respectively. The peak melting temperatures Tm were obtain...

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“…There have been a number of attempts in the past to study the influence of molecular weight on crystallinity and crystallization kinetics. 7- 19 Veda and Nakushima l7 found that the density of poly(ethy1ene terephthalate) is limited by its molecular weight in its extent of increase because of thermal treatments. The higher the molecular weight, the lower is the limiting density after maximum possible crystallization by thermal treatments.…”

Section: Introductionmentioning

confidence: 99%

Influence of molecular weight on the ordered state in poly(ethylene terephthalate)

Rao

Dweltz

1986

J of Applied Polymer Sci

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SynopsisWAXS, DSC, and IR methods have been employed to follow the crystallization of poly(ethy1ene terephthalate) as a function of molecular weight. The degree of order, which is a measure of the extent of crystallization, decreased with increasing molecular weight. The degree of reduction in the molecular order with increasing molecular weight differed depending on the technique employed to measure it. Crystallinity indices obtained by x-ray diffraction methods show an almost linear relationship with molecular weight. The Trans-Gauche ratio inferred from the IR spectrum tends to decrease at a very rapid rate with increasing molecular weight. The heat of fusion, computed from the melting endotherm in DSC thermograms, shows a smaller but a defmite decreasing trend with increasing molecular weight. Besides, the thermograms themselves showed distinct changes related to the molecular weight differences. The results have been discussed in terms of two different possible influencing factors known to affect the crystallization procesa in almost all polymers. Up to certain molecular weights, random coiling of molecules appears to be the more dominant factor, but in a much higher range of molecular weights, entanglement in the molecular network may become predominant.

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Melting and crystallization behavior of poly(tetrafluoroethylene). New method for molecular weight measurement of poly(tetrafluoroethylene) using a differential scanning calorimeter

Cited by 152 publications

References 1 publication

The Estimation of the Molecular Weight of Polytetrafluoroethylene Based on the Heat of Crystallisation. A Comment on Suwa's Equation

The Estimation of the Molecular Weight of Polytetrafluoroethylene Based on the Heat of Crystallisation. A Comment on Suwa's Equation

Isothermal Crystallization of Poly(tetrafluoroethylene). Effect of Holding Time in the Melt on Calorimetric Measurements

Influence of molecular weight on the ordered state in poly(ethylene terephthalate)

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