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Phase transformations of some poly(vinyl alcohol)–NiCl 2 composites
Author(s) -
ElShahawy Magda A
Publication year - 2003
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.1266
Subject(s) - materials science , glass transition , vinyl alcohol , polymer , composite material , differential scanning calorimetry , amorphous solid , crystallization , natural rubber , phase (matter) , dynamic mechanical analysis , differential thermal analysis , thermal analysis , casting , diffraction , thermal , thermodynamics , crystallography , chemistry , organic chemistry , physics , optics
Samples of poly(vinyl alcohol)–NiCl 2 composites containing up to 30 wt% NiCl 2 were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min −1 . For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl 2 addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl 2 had an opposite effect on the heating rate independent crystallization melting temperature ( T m ), relative to that on T g . The DTA thermograms of heat‐treated samples indicated that square planar NiCl 2 molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry