Crystallization behavior of polytetrafluoroethylene (PTFE)

Abstract

ABSTRACT:For some polymers such as PTFE, the crystallization is so rapid that it is difficult to observe isothermal crystallization by differential scanning calorimetry (DSC). In this investigation, first, isothermal crystallization kinetics of PTFE was followed by DSC and the results were analyzed by the Avrami method, which showed that PTFE crystallizes one-dimensionally from preexisting nuclei, presumably impurities. Furthermore, the crystallization activation energy, the equilibrium melting point, and the nucleation rate parameter K g were calculated in the isothermal crystallization. Second, nonisothermal crystallization was also studied and the result was in accordance with the results of isothermal crystallization. Then, the Kissinger method was used to investigate the activation energy of PTFE in the nonisothermal crystallization. Third, the effect of glass fiber (used as filling) was investigated on crystallization of PTFE matrix.

Preparation and Properties of PTFE-PMMA Core-Shell Nanoparticles and Nanocomposites

“…• C (Figure 9(a)), in agreement with literature data [21]. The crystallization of the PTFE in the nanocomposites at −20 • C/min is observed with minimum at 270…”

Synthesis of perfluoro-t-butyl trifluorovinyl ether and its copolymerization with TFE

“…There were two exotherm processes with small one at 215 8C and large one at 293 8C, which could be attributed to the decomposition process of the side chain of perfluoro-t-butyl trifluorovinyl ether units in the copolymer. The melting (308 8C) and recrystallization (274 8C) processes of the TFE blocks in the copolymer occurred at lower temperatures than that of PTFE (327 and 313 8C, respectively [41]). In summary, perfluoro-t-butyl trifluorovinyl ether has been synthesized by the addition of perfluoro-t-butyl hypofluorite to 1,2-dichloro-1,2-difluoroethylene followed by dechlorination with zinc in DMSO.…”

Isoconversional Kinetics by Fast Scanning Calorimetry

“…7.6. PTFE crystallizes very rapidly, thus limiting regular DSC measurements to very narrow temperature range [35]. Figure 7.6 shows that the regular DSC measurements cover only four temperatures and the temperature range is only 3 K. The use of FSC makes it possible to detect the calorimetric signal at much lower temperatures as seen on Fig.…”

“…7.8). For comparison, Wang et al [35] have obtained K g ¼ 1.5 10 4 K 2 using different temperature range with isothermal DSC data and a standard value U* ¼ 6270 J mol À1 . The value K g(BC) /K g(AC) ¼ 2,6 is close to the theoretical value K g(III) /K g(II) $2 and the break at 312 C was attributed to a transition from regime II to III.…”