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Effects of strain‐induced crystallization on the elastic and thermoelastic properties of some fluoroelastomers
Author(s) -
Hsu Y.H.,
Mark J. E.
Publication year - 1987
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760271514
Subject(s) - hexafluoropropylene , materials science , tetrafluoroethylene , copolymer , crystallization , thermoelastic damping , elongation , swelling , polymer chemistry , yield (engineering) , composite material , chemical engineering , thermodynamics , polymer , ultimate tensile strength , physics , thermal , engineering
A Viton copolymer containing vinylidene fluoride (VF 2 ) and hexafluoropropylene (HFP), and a terpolymer containing VF 2 , HFP, and tetrafluoroethylene (TFE) were cross linked using varying amounts of Bisphenol AF to yield two series of fluoroelastomer networks, Stress‐strain isotherms in elongation were determined for these samples at several temperatures and at two degrees of swelling with phenyl acetate. Strain‐induced crystallization was observed, as evidenced by upturns in the isotherms at high elongations. It appears to be more pronounced in the terpolymer samples, presumably because the TFE units not only can crystallize themselves, but can co‐crystallize with the VF 2 units. The crystallization was found to persist upon moderate increase in temperature, but was suppressed when the networks were swollen, Thermoelastic (force‐temperature) measurements were used to obtain values of the fraction f e / f of the elastic force that is due to energetic effects. Negative values were obtained for both types of samples and, in the case of two samples studied in detail, their magnitudes increased with increase in elongation. The magnitudes were larger and the increases more pronounced in the case of the terpolymer networks, as would be expected from a greater tendency for straininduced crystallization.