DSC endotherms

Figure 5.18 DSC endotherms obtained for samples treated in the solid state at various temperatures (a) 200°C for 4h (b) 210°C for 4h (b) 220°C for 4h (d) 225-230°C for 8h [8]. From Jabarin, S.A. and Lofgren, E. A., J. Appl. Polym. Sci., 28, 5315 (1983), Copyright John Wiley Sons, Inc., 1983. Reprinted by permission of John Wiley Sons, Inc.

FIGURE 5.11 DSC endotherms of rice starch annealed at 70 °C (times are indicated next to each profile) [adapted from Nakazawa et al. (1984) reproduced with permission from Japan Science and Technology Agency]. 

Commercial DDS also contains a small percentage of a crystalline impurity as indicated by a DSC endotherm at 77 °C whose heat of fusion is 3 % of the total heat of fusion associated with the pure DDS m.pt at 165 °C 16). 

A different DTA/DSC endotherm shape would be expected for calcination reactions such as CaCC, ) = CaO(s) + C02(9) (Figure 3.13). Given that the partial pressure of CO2 in dry air is... 

The NC/PCL data present a different situation. Blends of 25 and 40% NC showed the opaqueness and a DSC endotherm, which indicate the presence of crystallinity. Consequently, melting and quenching produced lower Tgs as expected. Pure NC and 50% NC did not show either of these features. Yet, the Tg dropped from 338 to 328 K for NC and from 283 to 271 K for 50% NC after the heating-quenching cycle. Blends of 65 and 75% NC showed high initial Tgs but failed to show any transition after quenching. 

A mixture consisting of water (190 g), ethyl alcohol (10 g), hexadecyl acrylate (70 g), hexyl acrylate (25 g), methyacrylic acid (5g), 3.2% sodium dodecyl sulfate, and ammonium dodecyl benzene sulfonate (5 g) was charged into a reactor and degassed for 30 minutes. Potassium persulfate (0.4 g) was then added, and the polymerization was conducted for 4 hours at 70°C under nitrogen. After the polymer was isolated, a sharp DSC endotherm was observed at 22.5°C. 

Figure 3 DSC endotherms for a potato starch at 42 % and 12 % water content (= 100...

Figure 2, bottom, shows differential-scanning-calorimetry (DSC) measurements on a 12-mg sample (N2 flow, 20°C/min heating). The DSC endothermal also shows a broad precursor terminating in an abrupt transition whose onset appears a few degrees above Tc due to the more rapid heating rate. The area under the precursor and the sharp endotherm is about 6.7 J/g. Attribut-... 

Table I. Position of DSC endotherm as a function of blend composition.

The present DSC results also argue against the possibility of chemical reaction being the dominant mechanism in the blends. If the two component materials had completely reacted to form a single random copolymer, a DSC endotherm for the 50/50 blend at about 270 C is expected. Instead, for this blend, an endotherm at 256 C is observed. The other possibility is that the two materials have reacted but the reaction has not progressed to the level of a completely random copolymer. This also does not seem to be the case because such a block copolymer would be expected to display two DSC endotherms, something which is not observed. 

Figure 1. Loss in the d33 piezoelectric coefficient as a function of annealing temperature correlated with DSC endotherms for the PVDF homopolymer and two TrFE copolymers.

Figure 1 Comparison of the loss of order in the starch fraction of dough during gelatinisation, detected by FTIR ( ), with the integration of the DSC endotherm (solid line)...

The melting behavior of miscible crystallizable blends (section 3.3.5) is often complex, revealing multiple DSC endotherms, which can be ascribed to several causes such as recrystallization, secondary crystallization, liquid-liquid phase separation (3.3.6), etc. 

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