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Experimental assessment of the thermodynamic theory of the compositional variation of T g : PVC systems
Author(s) -
Fried J. R.,
Lai S.Y.,
Kleiner L. W.,
Wheeler M. E.
Publication year - 1982
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1982.070270813
Subject(s) - adipate , plasticizer , differential scanning calorimetry , thermodynamics , materials science , glass transition , phase (matter) , phase transition , derivative (finance) , polymer chemistry , chemistry , organic chemistry , polymer , physics , composite material , financial economics , economics
The glass‐transition temperatures ( T g 's) and specific heats ( C p ) of poly(vinyl chloride) (PVC) and PVC plasticized with 5–120 phr di(2‐ethylhexyl) adipate (DOA) and tri(2‐ethylhexyl) trimellitate (TOTM) have been determined by differential scanning calorimetry (DSC). Measured T g 's were compared to predictions by the Couchman and Karasz (C–K) thermodynamic theory, three related empirical equations, and a new equation obtained from the C–K relation by assuming the product T g Δ C p to be constant. It was found that the T g 's of the PVC/TOTM mixtures are adequately predicted only by the C–K and the derivative relation. The T g 's of the PVC/DOA mixtures follow a sigmoidal or cusp‐like dependence on plasticizer composition as has been observed for some other PVC/plasticizer mixtures. In this case, the approximation afforded by the C–K or derivative equations is still superior to the empirical models over a wide composition range. Dynamic mechanical analysis of the PVC/DOA mixtures suggests that the DSC transitions may consist of two overlapping phase transitions. The reported sigmoidal composition dependence of the DSC T g 's may therefore result from the measured T g 's being weighted towards the temperature corresponding to the predominant dynamic mechanical transition (i.e., the high T g phase at low plasticizer concentrations and the low T g phase at high plasticizer concentrations). In such cases of partial phase separation, the C–K or the derivative equation may be used to estimate the composition of the two phases at each overall plasticizer concentration.