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The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.

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Abstract  

In this work the usefulness of Modulated Temperature DSC (MTDSC) for characterizing petroleum products is illustrated with some typical examples of recent applications. Specifically, the reliability of the method is outlined on the basis of the freezing behaviour of distillate fuels and the thermal analytical characterization of lubricating greases. The results of experiments performed on the evaporation residue of distillate fuels, aimed at providing insights into the structure of degradation products, will also be presented. The experiments were carried out using a DSC 2910 module from TA Instruments Inc., upgraded with the MTDSC option. The samples were exposed to a cyclic heating profile which was generated by an underlying heating (or cooling) rate of 2C min−1 while superimposing a sinusoidally varying time-temperature wave with an amplitude of 0.5C and a period of 40 s.

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Abstract  

A simple method of application of light heating modulated temperature DSC to a study of miscibility of polymer blends has been developed. In this method only the sample was measured and the standard materials were not used. The total heat flow, the complex heat capacity, the reversing and non-reversing heat flows were obtained as values measured from those quantities in hypothetical glassy state at T>Tg. The values of the hypothetical glassy state were calculated by extrapolation from T<Tg. The present method gives relative values but useful information can be obtained from the results. Some results from miscible and immiscible polymer blends are shown.

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Abstract  

The DSC curve obtained in conventional equipment usually only shows the resultant thermal effect due to simultaneous phenomena, which may occur during isothermal or dynamic analyses. This does not allow one to identify the processes properly and may cause an erroneous interpretation of the resulting curves. Modulated DSC equipment enhances the operating conditions and the analysis capacity of conventional DSC by superimposing a sinusoidal temperature modulation on the linear temperature control. Thus reversing and non-reversing heat flow curves are obtained, which are, respectively, the heat capacity and kinetic components of the DSC curve. Therefore, events that are related to these components can be separately analyzed. A method to obtain curves similar to the MDSC reversing and non-reversing components was developed using conventional DSC equipment in a non-conventional way. It was applied to analyze samples of poly(ethylene terephthalate) (PET) taken from bottles of mineral water. The second PET crystallization step that occurs during its melting was quantified and an apparent initial crystallinity was obtained from the resulting data.

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Modulated temperature differential scanning calorimetry

Characterization of curing systems by TTT and CHT diagrams

Journal of Thermal Analysis and Calorimetry
Authors: A. Van Hemelrijck and B. Van Mele

Abstract  

Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the (heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.

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Modulated temperature differential scanning calorimetry

Considerations for a quantitative study of thermosetting systems

Journal of Thermal Analysis and Calorimetry
Authors: G. Van Assche, A. Van Hemelrijck, and B. Van Mele

Abstract  

The influence of temperature modulation and signal treatment (deconvolution procedure) of modulated temperature differential scanning calorimetry is discussed with respect to the investigation of cure kinetics of thermosetting systems. The use of a ‘dynamic’ heat capacity calibration is not important for this purpose due to normalization of the heat capacity signal in all cure experiments. The heat flow phase during isothermal and non-isothermal cure is always small, giving rise to negligible corrections on the heat capacity and reversing heat flow signals in-phase with the modulated heating rate. The evolution of the heat flow phase contains information on relaxation phenomena in the course of the chemical reactions.

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Journal of Thermal Analysis and Calorimetry
Authors: C. A. Gracia-Fernández, P. Davies, S. Gómez-Barreiro, Beceiro J. López, J. Tarrío-Saavedra, and R. Artiaga

, 2 ]. Differential scanning calorimetry (DSC) and modulated temperature DSC (TMDSC) are extensively used to monitor the curing reaction of these materials [ 3 ]. Most of the curing reactions are thermally induced, but there are important applications

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comparison between experiments using nitrogen or air as purge gas. The thermal properties of photo-polymerized samples were studied by modulated temperature DSC (MTDSC). Complementary FT-IR measurements were carried out to evaluate the conversion of the

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Abstract  

The nature of the β to α phase transition in silver iodide was investigated by conventional and modulated temperature DSC and dielectric property measurements. On cooling, the high temperature phase remained stable 2.5C below its normal transition temperature even at a very slow cooling rate 0.2C h–1. Dielectric property measurements under conventional and microwave heating suggested an anomalous effect of the latter on the β to α phase transition in this material.

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Summary Modulated temperature DSC was investigated, comparing data found experimentally to that derived from theory. Deviation from theory was found with regard to the amplitude of the modulated heat flow signal when large modulation amplitudes were employed in the experiment. These deviations were determined to be dependent on the absolute temperature and it was concluded that further investigation of the heat flow signal obtained during MTDSC experiments is required.

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