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Stress relaxation of elongated strip of poly(vinylidene fluoride) in ethyl acetate vapor
Author(s) -
Phillips J. C.
Publication year - 1997
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.11671
Subject(s) - materials science , sorption , stress relaxation , polymer , desorption , composite material , stress (linguistics) , relaxation (psychology) , softening , diffusion , fluoride , polymer chemistry , thermodynamics , creep , organic chemistry , chemistry , inorganic chemistry , adsorption , psychology , social psychology , linguistics , philosophy , physics
Poly(vinylidene fluoride) films in ethyl acetate vapor were studied at 30°C for vapor pressures of p = 0, 12, 30, 40, 66, 85 torr and elongations ε = 4.5%, 7%, 9.5%, 19%, 29%, and 44%. A cyclic experiment was also performed at ε = 7% and p = 40 torr for three sorption/desorption cycles. Assuming, as a first approximation, that the stress relaxation of the “dry” and “wet” polymers is proportional to the elastic strain, ε el , empirical calculations were performed and compared to experimental results. In general, the presence of a vapor or gas in a polymer matrix enhances the stress relaxation by softening or plasticizing the polymer and transforming a portion of the elastic strain, ε el , into the plastic strain, ε pl . As the transformation continues, the sorption and stress of the wetted elongated sample change simultaneously with time until an optical “overshoot” and a mechanical or stress “undershoot” is observed. This result seems to be the consequence of the differential change of the stress of the “dry” and “wetted” samples with sorption time, τ = t − t o ( t = time; t o = initial sorption time), which depends on the differential time dependencies of the transformations of the elastic and plastic strains.