DSC transitions

Figure 9.5 DSC transitions and crystallizability data for PET and PEN copolyesters and blends m, crystallizable copolyesters , amorphous copolyesters M, crystallizable PET/PEN blends -----------, Tg ., Tm...

FIGURE 5.13 Effect of annealing (degree of annealing increases along X axis) on DSC transition temperatures of rice starch held at 55 °C for specific times (indicated next to each profile) (Nakazawa etal., 1984 reproduced with permission from Japan Science and Technology Agency). 

For example, 1.5M KCl elevates the DSC transition in pea starch, and separates the transition into a lower temperature B-type starch transition, and a higher A type. 

In Table III, which lists the DSC transitions of the polyesters, footnote (d) notes that BDA/BD modified with 50 mol %... 

Additional assays may also be conducted on this material to more comprehensively characterize its thermal properties. The following may be considered variable temperature XRD (VT-XRD) studies may be conducted to observe changes in the powder diffraction patterns of the material as a function of temperature. Selection of appropriate temperatures depends on several factors the DSC transition temperatures, corroborating TGA and hot-stage evidence, and the accuracy of the heating controller for the XRD unit. It should also be noted that although XRD data may be collected at several different temperatures to simulate a variable temperature experiment, the follow-up VT-XRD assay is essentially a series of isothermal experiments, and the DSC is a dynamic assay. It is therefore reasonable to expect some variation in transition temperatures. 

The observance of thermal transitions by DSC is insufficient to fully characterize the behavior of a substance on heating. It is not known if an endothermic transition observed in the DSC is a volatilization or a melt without corroborating information, such as TG or HSM data. It is important to understand the origin of the DSC transitions to fully characterize the system and understand the relationship between various solid forms. 

Figure 9.5 DSC transitions and crystallizability data for PET and PEN copolyesters and blends crystallizable copolyesters , amorphous copolyesters ...

Finally, a third type of sample (C) was obtained by slow crystallization from boiling cyclohexanol. This procedure yields a white powder at room temperature. The sample shows three DSC transitions at 283, 313 (shoulder), and 321 K. In the pVT experiments, starting from a type A sample, we found no evidence of a crystalline form with such a high transition temperature. Interestingly, Miller and Michl also report a phase-transition temperature of 320 K for a PD8S sample with a transoid backbone structure. ... 

Figure 6. DSC transition heats of cho-lesterylvinylfumarate polymer/monomer systems...

Experimentally, the careful measurement of the heat capacity of low molar mass liquid crystals shows this "diverging" behavior at the nematic-isotropic transition, and also at the smectic-nematic transition For polymers, there is a limitation in the measurement of heat capacities, since the transition takes place in a relatively large temperature range, and thus, there is at each temperature a mixture of heat capacity and heat of transition. In order to solve this problem, we have built a tool for being able to make the difference between the first and the second order component of a DSC transition peak. The basic idea is that these two contributions of the total recorded heat power will behave in a different manner when the heating rate or the mass of sample are changed. 

The inclusion of cholesterol disturbs the crystalline structure of the gel phase, and the phospholipid chains are more mobile than in its absence. This prevents the crystallization of the hydrocarbon chains into the rigid crystalline gel phase. In the more fluid liquid crystalline phase, the rigid cholesterol molecules restrict the movement of the hydrocarbon chains. In consequence, the addition of cholesterol to lipid bilayers or lamellar mesophases gradually diminishes the gel-liquid crystal transition temperature and the enthalpy and broadens the DSC transition peak [72,73]. No transition can be detected by DSC at 50% cholesterol [73,74] (curve/of Fig. 7), which is the maximum concentration of cholesterol that can be incorporated before phase separation. However, laser Raman spectroscopic studies show that a noncooperative transition occurs over a very wide temperature range [75]. 

All viscosities were measured in chloroform at 25 C. Bromine contents were based on elemental analyses for C, H and Br and were corroborated by nmr. Tg values are averages for the second and third scans on a Perkin-Elmer DSC-2 differential scanning calorimeter (40°/min). In several cases, particularly when the DSC transitions were very weak, the Tg was measured by thermo-optical analysis (TOA)... 

Hz loss peak can be used to characterise on real samples moreover, the loss peak still defines a precise temperature when DSC transitions have become unresolvable from the baseline. The process of cure itself can also be followed by using simple shear or torsion. Figure 7.28 shows the modulus ( ) of a polyester prepreg composite during isothermal cure at different temperatures. Short-time data are lost due to the time required to heat from ambient temperature to the isotherm. Table 7.5 compares time to cure by this method with DSC and DETA [17]. The initial modulus levels are rather ill-defined because the system is basically liquid. The two stages resolved at... 

Note I—Test Method D 87 also monitors energy transfer between wax and a standard environment. The highest temperature DSC transition may differ from the melting point because the two methods approach the solid/liquid phase transition from different directions. 

Ultrasonic properties in bovine bone marrow were investigated. Both wave velocity and attenuation in marrow tended to decrease as the increase of temperature. The decreasing tendency of both velocity and attenuation changed around 33°C. From differential scanning calorimetry (DSC), transition point was found near this temperature. 

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