TMDSC Experimental Conditions

Select a modulation period of 40-100 s. For most samples in standard crimped aluminium sample vessels 60 s is the recommended period of oscillation. Longer periods may be necessary for larger mass hermetic sample vessels. In the presence of a high thermal conductivity purge gas periods as short as 40 s can be used. Periods of 30 s or less are generally not recommended. 

The constant heating rate should be in the range 1-5 K/min. The maximum practical heating rate for TMDSC experiments is 5 K/min. The heating rate should ensure at least four complete temperature oscillations (periods) over the temperature range of each transition studied. 

Large modulation temperature amplitudes ( 1.5-3 K) should be used when measuring weak glass transitions. Smaller amplitudes are recommended for sharp transitions which are only a few degrees wide. Finally, avoid amplitudes smaller than 0.03 K as they are difficult to control. Note that large modulation temperature amplitudes and short periods require a considerable sample 

In order to generate TMDSC data files of reasonable size without compromising the data quality, it is recommended that data be stored at the rate of 1 s/data point. The following raw data are useful for revealing sample behaviour during temperature modulation as well as fine tuning the experimental conditions, and should be stored as part of the TMDSC data file time, temperature. 

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TMDSC data are calculated from three measured signals time, modulated heat flow and modulated heating rate (the derivative of modulated temperature). The raw data are visually complex and require deconvolution to obtain standard DSC curves. However, raw data are useful for revealing the sample behaviour during temperature modulation, as well as fine-tuning experimental conditions and detecting artefacts. 

However, the sum of these signals is quantitative. Linearity is maintained in the baseline, permitting accurate measurement of the onset as well as the end of the endothermic and exothermic events [3]. Melting and crystallization neither start nor end at the same temperatures and therefore different integration limits are required. Finally, the total heat flow signal is quantitatively correct regardless of the modulation conditions. Thus the initial crystallinity of the sample can be estimated by TMDSC (see Table 5.1). The data presented in Table 5.1 reveal that the observed initial crystallinity is approximately constant under various experimental conditions. 

Thermal conductivity measurements by TMDSC [9] involve two experiments on the same sample material, where only the sample thickness varies. Preparing a sample of uniform and known geometry is essential for accurate thermal conductivity measurements by this method. The sample is again in direct contact with the sample holder, so this method is also reserved for experienced users. Selecting a thin sample, the experimental conditions are chosen so that the heat capacity of the sample can be measured by the methods outlined earlier (Section 5.6). The second experiment is performed on a thick sample in such a way that controlled temperature modulation occurs only in that part of the sample in contact with the sample holder. The remainder of the thick sample functions as a heat sink. 

Typical TMDSC heating profile with the following experimental parameters / = 1 K/min, p = 30 s and x = Under these conditions... 

In order to compare the model calculations with experimental calorimetric data, PS samples were modified in a transitiometer used, in this case, as a small reactor to modify PS under equilibrium conditions in the presence of a chosen fluid. Modifications of PS have been done in the presence of N2 and CO2, along isotherms at a given pressure. For these two fluids, a final temperature of 398.15 K and a final pressure of 80 MPa have been attained. The Tg of modified and nonmodified PS samples were determined by temperature-modulated DSC (TMDSC). The solubilities of the different gases were measured using the YW-pVT sorption technique [48, 49] along different isotherms, and the mass fraction of the gas in the polymer was then determined with the following equation ... 

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