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Abstract  

The increment of heat capacity at the glass transition for semi-crystalline poly(ethylene terephthalate) (PET) observed by temperature-modulated differential scanning calorimetry (TMDSC) shows significant deviations from a simple crystalline/amorphous two-phase model. Introduction of a rigid amorphous fraction, which is non-crystalline but which also does not participate in the normal glass transition, allows a much better description of the transition behaviour in semi-crystalline PET. Certain questions arise such as what is the rigid amorphous fraction and over what temperature range do these rigid amorphous segments devitrify? These TMDSC results show that the rigid amorphous component may be treated as an interphase between amorphous and crystalline phases. This interphase does not exhibit a separate glass transition temperature at temperatures above the normal Tg. The suggestion is made that the glass transition of the rigid amorphous component occurs continually between the glass transition temperature of the amorphous phase and up to about 135C for this particular sample of PET.

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Abstract  

A modulated-temperature differential scanning calorimetry (M-TDSC) method for the analysis of interphases in multi-component polymer materials has been developed further. As examples, interphases in a polybutadiene-natural rubber (50:50 by mass) blend, a poly(methyl methacrylate)-poly(vinyl acetate) (50:50 by mass) structured latex film, a polyepichlorohydrinpoly(vinyl acetate) bilayer film, and polystyrene-polyurethane (40:60 by mass) and poly(ethyl methacrylate)-polyurethane (60:40 by mass) interpenetrating polymer networks were investigated. The mass fraction of interphase and its composition can be calculated quantitatively. These interphases do not exhibit clear separate glass transition temperatures, but occur continually between the glass transition temperatures of the constituent polymers.

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Modulated differential scanning calorimetry

III. Applications to measurements of the glass transition temperature and increment of heat capacity

Journal of Thermal Analysis and Calorimetry
Authors: D. Hourston, M. Song, H. Pollock, and A. Hammiche

Abstract  

Modulated-temperature differential scanning calorimetry was used to measure the glass transition temperature,T g, the heat capacity relaxation in the glassy state and the increment of heat capacity, δCp, in the glass transition region for several polymers. The differential of heat capacity with respect to temperature was used to analyseT g and δCp simply and accurately. These measurements are not affected by complex thermal histories.

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