Study of the thermal properties and relaxation transitions in tetrafluoroethene‐ethene copolymers

Abstract

Copolymerization of tetrafluoroethene (TFE) with ethene (E) in wateralcohol medium initiated by 2,2Ј-azo-bis-izobutyronitrile (AIBN) at 338 K and 4.2 MPa was conducted in an autoclave by employing a semiflow procedure to feed the comonomers. The thermal properties of the copolymers under both the static and dynamic conditions of thermal treatment in air (ageing) were studied. The most pronounced changes in the initial temperature of destruction were observed for the compositions containing more than 42 mol % TFE, which corresponded to the formation of alternating copolymers. The reaction of thermal degradation was found to follow the first order kinetic equation, with the activation energy 174 kJ ⅐ mol Ϫ1 . The higher thermal stability of the alternating TFE-E copolymers was proved by IR spectroscopy and DTA analysis. Both the melting and crystallization DSC scans of copolymers of various compositions were analyzed. Monomodal peak of melting (and respectively, crystallization) was observed in both scans for the alternating copolymer, whereas the second peak appeared for the copolymer fractions with the higher content of ethylene block fragments and 30 -40 mol % TFE units. The dynamic-mechanical analysis showed three relaxation transitions (␥, ␤ 1 and ␤ 2 , ␣) in the temperature interval from 173-433 K, related to the mobility of structural units of different type in the copolymers prepared.

Thermal-mechanical stability of ethylene tetrafluoroethylene alternating copolymer, and modification thereof

“…However, such a peak does not appear in the spectrum for pristine ETFE (Fig. 1b) [15], thus verifying that thermal oxidation has occurred. Such thermal destruction behavior could originate from end groups, chain Fig.…”

“…Kostov and coauthors revealed similar results, but obtained a reaction order and E d value of 1.04 and 174 kJ/ mol, respectively. Meanwhile, they also found that ETFEs undergo low-level thermal oxidation (a mass loss of >0.5% was detected below 548±5 K, after thermal oxidation in air for 5 h), whereas IR spectra did not support any significant changes in the functional groups of ETFEs after thermal aging [15]. Loginova and coworkers investigated the thermal decomposition behavior of ETFE [32].…”

“…However, Kostov et al pointed out that T 0 was greatest when the TFE content was 50% [15]. Morisaki et al found that ETFE breaks down randomly with a reaction order and E d value of 0.92 and 194.3 kJ/mol, respectively.…”

“…ETFEs are extensively applied in a wide range of areas, especially those relating to harsh conditions, including high temperature resistance and advanced flame-retardant cables (and wires) used in aerospace and aeronautics (e.g., shuttles), pipes and tubes applied in caustic and strong acid transportation, and membranes used in modern architecture [1,2]. Because of their prominent properties for diverse applications, ETFEs have attracted considerable attention from researchers, who have studied their molecular parameters and microstructures [3][4][5][6][7][8][9][10][11], thermal and crystallization behavior [12][13][14][15][16][17][18][19], steady-state rheological properties [20][21][22], and so on [23][24][25]. However, despite the importance of thermal stability during the processing and application of ETFEs, studies relating to this issue are scarce in the literature; this is particularly true of work done on how to avoid the thermal destruction arising from the thermal-stress-oxidation synergistic effect.…”

Melt rheological properties of ETFE: an attempt to illuminate the fluorine-substitution effect

“…Consequently, ETFEs are intensively explored on the molecular parameters and microstructures [3][4][5][6][7][8][9], thermal and crystallization behaviors [10][11][12][13], and steady-state viscous properties [14][15][16]. However, its capillary flow and high-shear rheological behaviors are scarcely reported, despite their fundamental and technical importance.…”