Heat capacity determination using MTDSC

The evolution in calorimetry technology has also led to the development of protocols for quantitative analysis (Buckton and Darcy 1999). Fiebich and Mutz (1999) determined the amorphous content of desferal using both isothermal microcalorimetry and water vapour sorption gravimetry with a level of detection of less than 1 per cent amorphous material. The heat capacity jump associated with the glass transition of amorphous materials MTDSC was used to quantify the amorphous content of a micronised drag substance with a limit of detection of 3 per cent w/w of amorphous... 

For small concentrations of a given component in a polymer blend (less than 10 wt%), the resulting weak transition is typically very difficult to resolve using conventional DSC or DMTA [5,15]. Using MTDSC, Tg determinations were performed [32] on a physical blend containing four components pure PS plus PPO-30 (a PS/polyphenylene oxide (PPO) blend at a composition ratio of 70/30) plus PPO-70 (a PS/PPO blend at a composition ratio of 30/70) plus pure PPO. The amount of each component was 44.0 7.1 13.4 34.5, by weight. Figure 3.9 shows both the heat capacity and... 

There is considerable interest in the values of ACp at the Tg and various generalisations [33,34] have been suggested either for ACp or for the product ACpTg. ACp measurement is complex and time-consuming by conventional DSC [13,35], Heat capacity values at Tg from conventional DSC studies have been obtained [36] by extrapolation of the linear equations used to describe the glass and liquid states. Based on the new MTDSC method, the determination becomes very simple and rapid. Later, we will discuss how this makes it a convenient way to analyse multi-phase polymeric materials. 

MTDSC can measure Cp quasi-isothermally (Jin et al. 1993 Boiler et al. 1994 Thomas 2006 Reading and Hourston 2006) to a high degree of accuracy (Ishi-kiriyama and Wunderlich 1997), but the measurements take more time because the temperature dependence of Q, is determined point by point. In MTDSC the amplitude of the modulated heat flow, not its average value, is used for determination of reversing heat capacity (referred to as complex heat capacity for the 2920 DSC), therefore eliminating the need for a stable baseline as in traditional DSC. 

Thus, in MTDSC the reversing heat capacity is determined using the following formula ... 

Different from the other MTDSC techniques is the TOPEM technique, which is based on a quasistochastic temperature modulation superimposed on a conventional DSC temperature program as seen in Fig. 2.90 (Schubnell et al. 2005). This allows separate determination of the reversing and nonreversing heat flows and the quasistatic (zero-frequency) heat capacity, as well as a complex heat capacity (Schawe and Hutter 2005). Since the response at a desired frequency is determined after the run, multiple run parameters can be used to optimize the analysis of different transition regions during a run as noted in text below (see also Fig. 2.91). 

A detailed experimental procedure for measuring thermal conductivity is given in the ASTM standard E1952 using MTDSC. Essentially, for determination of thermal conductivity, heat capacity measurements are made under two... 

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