Order from thermograms

TG/DTG/DSC investigation of the starch-cellulose composite films was performed in order to study their thermal decomposition behavior. Some thermal characteristics of composite materials which contain different cellulose fillers (beech cellulose, beech wood sawdust) were evidenced from thermograms (data presented in Table 7.4). 

The differential equations Eqs. (10) and (29)3, which represent the heat transfer in a heat-flow calorimeter, indicate explicitly that the data obtained with calorimeters of this type are related to the kinetics of the thermal phenomenon under investigation. A thermogram is the representation, as a function of time, of the heat evolution in the calorimeter cell, but this representation is distorted by the thermal inertia of the calorimeter (48). It could be concluded from this observation that in order to improve heat-flow calorimeters, one should construct instruments, with a small... 

From Tian s equation [Eq. (30)3, it appears that in order to transform the calorimeter response g(t) into a curve proportional to the thermal input f(t), it is sufficient to add, algebraically, to the ordinate of each point on the thermogram g(t), a correction term which is the product of the calorimeter time constant n, by the slope of the tangent to the thermogram at this particular point. This may be achieved manually by the geometrical construction presented on Fig. 10. 

DSC thermograms of the crosslinked enamels revealed onset of glass transitions (Tg) ranging from 15° to 35° for all three types of enamels. Attempts to detect first order transitions in the DSC corresponding to Tm or Ti were unsuccessful due to large exotherms starting at about 90°. An odd-even pattern was not observed. 

Common to these methods, is that only one point, that is, the maximum heat release rate of the thermogram, is used. Even if the method by itself is efficient in terms of simplicity, experimental work, and evaluation time, it represents a waste of information, in the sense that all the available information is not used in the procedure. Nevertheless, from the point of view of safety it is conservative, since it is based on the zero-order approximation. More complex methods are based on a kinetic analysis of the thermograms presented in Section 11.4.3 below. 

Many liquid-crystalline polymers are semi-crystalline and have only one mesophase that is nematic. The DSC thermograms of such polymers are very similar in appearance with Figure 4.22. Many other polymers are noncrystalline but have one and only one mesophase. The DSC will then show a glass transition and a transition from the mesophase to the isotropic liquid phase. Yet many other polymers may have more than one liquid crystalline phase so that their DSC curves should also include the transitions from one mesophase to another. DSC is obviously a very useful and very convenient technique for the characterization of liquid crystalline polymers. Nevertheless, the following points should be emphasized in order to interpret the DSC results with less ambiguity. 

From DSC thermogram, optical anisotropy under polarizing optical microscope (p.o.m.) and wide-angle X-ray diffraction (w.a.x.d.) data it can be deduced that the endothermic peak at 77 °C is due to the mesomorphic-isotropic phase transition. The enthalpy of phase transition is 20.35 J/g. Hence, according to Brandon and Marmur (1996), the structure of PAC8 below 77 °C is ordered in smectic crystalline, which can be classified as smectic B (Sb) type. 

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