Crystallization peak

In the PP-PA system, the DSC thermograms showed two peaks corresponding to nylon and PP. For the compatibilized system the crystallization peak of nylon remains unaltered, while that of PP shifted toward a higher temperature in the case of PPacr, and for PPmal, the shift was to lower temperatures (Fig. 1). This may be due to the fact that PPacr was acting as the nucleating agent. The average crystallinity of the blend was also decreased by the incorporation of compatibilizer. The mechanical properties of these blends was improved by the addition of PPmal and PPacr as compatibilizers (Table 1). 

How much of a crystallizable material X can I blend uniformly into a polymer until it starts to form crystals A series of blends with increasing amount of X is prepared. The samples are studied by WAXS (cf. Sect. 8.2) using laboratory equipment. Crystalline reflections of X are observed, as X starts to crystallize. Peak areas can be plotted vs. the known concentration in order to determine the saturation limit. Think of X being Ibuprofen and Y a polystyrene-(7 )-polyisoprene copolymer, and you have an anti-rheumatism plaster. 

Both the fresh gel and the gels after dynamic measurements were examined by X-ray. As shown in Figure 3, there are two intensity maxima peaks at 26 angles about 21.5 and 24 degree also, these two crystal peaks become sharper after the dynamic measurements. Furthermore, the DSC analysis showed that the 4% fresh... 

A glass transition (-75°C) and two broad bands close to 0°C are obtained b y differential scanning calorimetry performed at the cooling rate of 10°C/min from 20°C to -150°C followed by an isothermal at this temperature for 10 min and then heated to 30°C at the same rate. If the heating rate is lowered to 2 or 1 °C/min, a crystallization peak is obtained at 10°C. 

Measure the temperatures for the following Tf, Tm,Tc, and Te, where T is the extrapolated onset temperature, Tm is the melting peak temperature, Tc is the crystallization peak temperature, and Te is the extrapolated end temperature. Report two Tm values if observed. 

Figure 20 shows the thermal traces of (a) nonirradiated and 500 kGy-irradiated PTFE powder and (b) the corresponding PTFE0kGy-EPDM and PTFE500kGy-EPDM composites. The crystallization peak of 500 kGy-irradiated PTFE powder shifts to a lower temperature of about 303.5°C. Also, the crystallization onset occurred at lower temperature and continued down to approximately 290°C. These distinct variations in 500 kGy-irradiated in comparison to nonirradiated PTFE powder is due to the E-beam treatment process, which caused degradation of 500 kGy-irradiated PTFE powder. The molecular weight decreases due to chain scission and leads to PTFE macromolecules of different chain lengths. As a result, the crystallization peak occurs at lower temperatures and the crystallization process continues until much lower temperatures in comparison to nonirradiated PTFE powder. 

The relative degree of crystallinity can also be estimated from the WAXS pattern from the ratio of the integrated intensity of the crystal peak to that of the total amorphous and crystalline scattering (Balta-Calleja and Vonk 1989). For PE, the amorphous scattering below the (110) peak (Fig. 5.7) is relatively insensitive to the degree of crystallinity, so the integrated area of the (110) reflection compared to the broad amorphous halo is directly proportional to XPE. However, the absolute degree of crystallinity cannot be determined in this way (Ryan et al. 1995). 

Fig. 5.38 Normalized intensities obtained from SAXS data for the isothermal crystallization of a PCL-PB diblock (Mw = 12.5 kg mol 45% PCL) following a quench from the homogeneous melt to 26.5 °C (Tom is close to Tm for this polymer) (Nojima et al. 1992a) ( ) melt peak (o) crystal peak. The peak position was found not to change on crystallization.

Fig. 7 DSC melting and crystallization curves of isotactic poly(S)-4-methyl-hexene-l. Note the two melting peaks (at 193.5 and 227.4 °C, respectively, AH 2.5 and 1.5cal/gram) and two crystallization peaks (at 201 and 120 °C, respectively same AH), as well as the significant temperature gap ( 74 °C) between the lower crystallization and melting processes. (From [44])...

Figure 22.1. Typical DSC thermogram for milk fat. Ci and C2 are exothermic crystallization peaks obtained during cooling. h, h2 and h2 are endothermic peaks obtained during heating. (Reproduced with permission from ten Grotenhuis et al., 1999.)...

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). 

Figure 3. (a) DSC scans of PVA and NW composites showing the crystallization peak in the temperature range of 200-240 °C. 

Additional information on the miscibility of sPS/aPS blends was gained by measuring with DSC the crystallization kinetics and the melting and crystallization peaks [20]. 

Fig. 4.11 Photomicrographs of sulphapyridine at two temperatures. Left, 110 °C most of the field contains the metastable form that crystallized (peak B in Fig. 4.10). Right, 180 °C (between peaks E and F in Fig. 4.11), most of the material has been converted to the stable form. (Reprinted from Schwarz and de Buhr 1998, with permission.)...

Simultaneous WAXD and SAXS techniques were applied to reveal the POSS crystal structural and POSS-PU morphological changes under deformation. The WAXD data indicated that POSS molecules formed nanoscale crystals in the hard segment domains. Under stretching, the full-width at half-maximum of the POSS crystal peak was found to decrease, which suggested the destruction of POSS crystals and also the hard segments. 

When partially hydrated samples are cooled down to 77 K, no crystallization peak is detected by differential thermal analysis. The x-ray and neutrons show that an amorphous form is obtained and its structure is different from those of low-and high-density amorphous ices already known [5]. Samples with lower levels of hydration corresponding to one monolayer coverage of water molecules are under investigation. This phenomenon looks similar in both hydrophilic and hydrophobic model systems. However, in order to characterize more precisely the nature of the amorphous phase, the site-site partial correlation functions need to be experimentally obtained and compared with those deduced from molecular dynamic simulations. 

When the amorphous material does not transform into the crystalline material, the measurement of the melting peak allows to determine the degree of crystallinity of mixtures by comparing its value with the melting enthalpy of a pure crystalline material. If the amorphous sample crystallizes upon heating, then the crystallization peak may be used for the determination of the amorphous content. Such an example is given in Fig. 10. In this case itwas possible to attain a limit of detection of 1%. 

Table 3.1. The Tg of AlMq3 varied from about 160°C to 190°C, with no apparent dependence on the quench rate (whether from the melt or vapor) for the few samples available for examination. Because the Tg of Alq3 falls in such a close range with AlMq3, no attempt was made to characterize the miscibility of the blend by observing the change in Tg with composition. Cold crystallization peaks were visible on every sample between Tg and Tm. The melting temperature was constant for each sample at 297°C. Crystal nucleation in AlMq3 films apparently occurs homogeneously at some temperature between Tg and Tc, because even neat evaporated films exhibited a crystallization peak. No crystal nucleation was observed by optical microscopy at temperatures slightly below Tg. It is possible that some variation in the Tg and Tc temperatures observed for the sublimed films is due to small changes in the deposition rate or pressure.

FIGURE 3.17. DSC traces for AlMq3. Crystallization peaks could be seen in neat and scraped sublimed films. Endotherms associated with Tg are observable in the scraped sample, but the signal was too small in the neat sample. Thermal parameters are listed in Table 3.1. 

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