Thermograms isothermal crystallization

Figure 10.10. Nor-isothermal DSC scans of different PEEK/SWCNT nanocomposites containing 1 wt% CNT loading, from 30 to 380°C, at rates of 10°C/ min. Top crystallization thermograms Bottom heating thermograms. The inset is a magnification showing the T decrease in the nanocomposites. From ref 10 and 11.

Fig. 3. Isothermal crystallization thermogram obtained by differential scanning calorimetry (DSC) indicating the determination of f, and reduced crystallinity (f) (adapted from Ref. 9).

Figure 7.2 DSC thermograms of a-trd s-polyisoprene crystals crystallised isothermally from hexane and amyl acetate at -20 °C. Scanning rate 10 °C/min.

Hamisch and Muschik (164) derived the Avrami equation from non-isothermal crystallization thermograms where... 

A DSC heating thermogram for the same fat sample can conveniently be measured as soon as isothermal crystallization has gone to completion. 

Also, after determining the temporal distribution of crystallization peaks in a complete isothermal experiment, the melting thermogram of a particular polymorph can be determined. First, the sample is remelted completely, and held to erase its thermal memory. Then, the isothermal crystallization process is repeated, but only up to the time at which the polymorph of interest has completely solidified (exothermic peak fully formed). A heating scan is then performed immediately (Kawamura, 1980, 1981). 

A number of methods are available for deriving reaction kinetics constants from DSC thermograms (Wright, 1984). For example, the thermogram obtained during an isothermal DSC experiment at a temperature at which crystallization of a fat occurs can be analyzed in a way similar to that described earlier for the determination of solid fat content, but in this case the evolution of peak area (representing the formation of solid fat crystals) is related to time rather than temperature (Chong, 2001). 

Figure 20.2 sPS/PPE blends (75 25 wt%) at different isothermal crystallization temperatures. (a) DSC thermograms (b) WAXD patterns. Reprinted from Polymer, vol. 39, Hong B. K., Jo W. H., Lee S. C., Kim J., Correlation between melting behavior and polymorphism of sPS and its blends with PPE , p. 1793, Copyright 1998, with permission from Elsevier Science... 

Fig. 23.10. iPS, quenched to the glassy state and then crystallized at various temperatures (Left) Variation of during a subsequent heating, obtained by SAXS experiments. Crystallization line and melting line. (Right) DSC thermograms of samples, measured after isothermal crystallization processes with a heating rate of 0.5 K min [9.20]... 

Fig. 14.1 Characteristic mDSC thermograms of amorphous solids undergoing non-isothermal crystallization (solid line) and the same of the amorphous solid containing moisture (dashed line)...

Both pure PEN and the PEN/CNT nanocomposites exhibited multiple melting peaks in the DSC heating thermograms. The small and low melting peaks observed at approximately 10-15 °C above the isothermal crystallization temperature was attributed to the melting of... 

We use differential scanning calorimetry (DSC) thermograms to monitor the crystallization process, for example, isothermal crystallization from the melt. We pack the sample in a DSC pan, heat it, and maintain it at the temperature of the melt for a short time in order to erase the sample preparation history. Then we reduce the temperature to the preset crystallization temperature Tc, and trace the thermal energy change. Figure 5.12a is a schematic illustration of this curve. In many cases the curve follows the Avrami equation ... 

Figure 10.13 DSC melting thermograms of ethylene-propylene copolymer (EPS 3.0 mol-% ethylene), propylene-(l-bu-tene) copolymer (BPS 7.6 mol-% 1-butene), and BPS/EPS 50/50 blend after isothermal crystallization in the range of 60-110°C (heating rate 10°C/min). Reprinted from Bartczak et al. [66], Copyright 2006, with permission from Elsevier.

Melting thermograms of Ny6/PP-AA blends with polyamide as dispersed phase, isothermally crystallized from the melt, revealed also the presence of melting peaks of Ny6 at temperatures lower than the usual melting temperature of a form (221 °C), indicating the existence of a considerable amount of y form crystals (215 C). No melting peak of /phase was observed for Ny6/iPP blends at any Ny6 content. 

With this background with regard to the origin of the endothermic peaks in the thermogram the crystallization kinetics can be analyzed. It needs to be recognized that within the data to be analyzed there are two distinctly different, and separate, kinetic processes involved. One is the formation from the melt, or solution, of a distinct crystallite structure, such as the extended form, once-folded, twice-folded, etc. The other involves the isothermal transformation from one form to another. When the two are intermixed a very complex situation results. At this point the kinetics of the formation of the distinct forms from the melt (without any further structural changes) will be treated. The consequences when the two kinetic processes are intermixed will also be considered. 

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