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Revisiting the thermal relaxations of poly(vinyl alcohol)
Author(s) -
Betzabe GonzalezCampos J.,
GarciaCarvajal Zaira Y.,
Prokhorov E.,
LunaBarcenas J. Gabriel,
MendozaDuarte M. E.,
LaraRomero Javier,
del Rio Rosa E.,
Sanchez Isaac C.
Publication year - 2012
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.33615
Subject(s) - vinyl alcohol , crystallinity , glass transition , materials science , relaxation (psychology) , dielectric , arrhenius equation , volume fraction , polymer chemistry , thermal analysis , atmospheric temperature range , evaporation , analytical chemistry (journal) , activation energy , composite material , thermodynamics , chemistry , thermal , polymer , organic chemistry , physics , optoelectronics , psychology , social psychology
The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well‐established plasticizing effect of water on the glass‐transition temperature ( T g ) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T g for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low‐ (from 20 to 80°C) and high‐ (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius‐type relaxations. However, once the moisture was properly eliminated, a single non‐Arrhenius α relaxation was clearly observed. X‐ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary β c relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012