Double endothermic peak

Figure 2 shows the DT/TG profiles for the host compound and for the organo-LDH C, measured between room temperature and 800 °C. Endothermic peaks due to loss of physisorbed and interlayer water are observed around 105 °C for the host compound, and at 105 and 210 °C for compound C. The total amount of desorbed water is clearly less for the organo-LDH, in agreement with its hydrophobic nature. The dehydroxylation of the brucite-like layer in the host compound results in a double endothermic peak near 360 °C. For compound C, this structural feature is largely masked by the highly... 

There are two theories to explain the behavior of double endothermic peaks. One is the melt-recrystallization mechanism. The peak at lower temperature was from the melting of the initial crystal lamellae formed during the isothermal crystallization. When the... 

C Bosnyak (Dow Chemical Company, Midland, Michigan) I d like to make a comment that sui xHts the point that you get both inter- and intramolecular junction formation. This was seen very clearly in our work with isotactic polystyrene, with time [C.P. Bosnyak, A. Hiltner, and E. Baer, Case Western Reserve University, Cleveland, Ohio, unpublished work (1980)]. We could actually see the appearance of a double endothermic peak corresponding to the melting of the gel. This could also be see as the characteristics of the network in tension. What would happen with isotactic polystyrene gels, in particular, is that you would initially form those network junction points, and dien over a period of time you would form additional junction points, and this obviously you could see in the rise of the enthalpic heat of melting of the gel as a function of time. These additional junction points were considered intramolecular as they tended to be of little effect to the network in tension itself, and yet they could also act as nucleation sites for crystallites in other places than at the network junction points. 

Initial heating runs on particulate (powdered or fibrous) anionic polystyrene specimens indicate a double endothermic peak during the heating cycle one at Tg, the other at Tji, and both agreeing within a few degrees with values measured by TBA. 

In some works [3, 4] it is supposed, that PETP can have two morphological forms of crystals which define double endothermic effect in the field of fusion. Form I, to which more high-temperature corresponds originally endothermic peak of fusion, has been attributed folded structure, and for the form II responsible for more low-temperature peak of fusion, the crystal structure from more extended circuits has been offered. 

The degree of crystallinity of polyethylenes was calculated by comparing the area of the respective endothermic peak with the double peak of dotria-contane. The curve contains two peaks, the first of which is due to a chain-rotational transition a few degrees below the melting point. The resulting degree-of-crystallinity values agreed well with the literature values, as shown in Table 7-25. 

Mucha [214] found multiple endotherm peaks in samples that were isothermally crystallized. The double peaks were observed in samples crystallized at temperatures above 110°C. At lower temperatures, single peaks were observed. Mucha suggested that the two peaks correspond to the melting of the hexagonal and monoclinic crystalline forms. 

The melting endotherm of PTeOX shows a double peak. When the molecular weight of the polymer decreases, the onset and the peak temperatures of the endrtherm diift to lower temperatures, while the profile of the endrthermic peak only changes sU tly. When the polymer yield increases, the lower temperature peak of a double endotherm becomes intense to give a la-oad profile. 

Exothermic and endothermic peak temperatures shifted to the higher temperature side with increasing content of CAR, and both peaks split into double peaks above a certain CAR content. 

In mortars originally formed with both ADP and STPP, there is a small endotherm around 70°C. At early times, e.g., 5 minutes, the superposition of exothermic and endothermic effects (at about 107°C) results in a double endotherm indicating the presence of schertalite. A small exothermic peak above 8 00°C may be due to the formation of Mg(P04)2 coincident with an endothermal effect due to the melting of Na4P20y formed from STPP. 

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