Cold Crystallization Analysis

Cold Test. The ability of an oil to withstand refrigerator storage is determined by the cold test analysis crystallization resistance is measured as the time in hours before the oil appears cloudy at 32°F or 0°C. Standardized AOCS Method Cc 11-53 requires that dry filtered oil be placed in a sealed 4-ounce bottle and submerged into an ice bath (103). A go/no-go examination after 5.5 hours for clarity is stipulated by the Official AOCS Method however, most laboratories practice the alternative procedure, which continues the clarity examinations until a cloud... 

A typical graph of differential scanning calorimetry analysis of a dimethylsiloxane pol)mier with higher viscosity (350 cSt) is shown in Fig. 2. The glass transition is observed at -127.9 °C, the cold crystallization at -96.5 °C, and melting transitions at -51.7 and -38.3 °C, respectively. 

In 1952, the X-ray crystal analysis of the Jorgensen s product by Kuroya et al. determined it to be a trans-cis isomer. Three years later, the IR spectral examination allowed Majumdar et al. to conclude that Werner s preparation yielded the trans-cis isomer and Jorgensen s preparation the cis-cis isomer. In the same year Shibata et al. reinvestigated Sueda s preparation by aquating the [Co(N03)3(NH3)3] complex in a cold aqueous solution containing a small amount of acetic acid. They suspected that the product was cis-cw-[Co(N02)3(NH3)3] on the tesis of the IR peak at 1052 cm , in view of the fact that the IR spectrum of [Co(ONO) (NH3)s] CI2 showed a Co-ONO characteristic peak at 1065 cm ... 

Elastomeric systems are quite commonly monitored by thermal techniques. Mohler [5] has discussed how DSC is used to characterize the quality of blends of elastomers. Changes in polymer Tg can point to miscible phases that might otherwise require a microscopic techmque to establish. The cold crystallization of a polymer in a blend can also be examined using the relaxation enthalpy of the sample. Vacuum TG can look at plasticizer content separate from polymer degradation. Dynamic mechanical analysis (DMA) is always a powerful technique with elastomers. Dimensional stability, storage modulus, loss modulus and loss factor are all important for this class of materials and are... 

The cold crystallization starts at about 400 K at a supercooling not affected by modulation and registers as nonreversing. For separation of such nonreversing transitions, several modulation periods must occur across the transition, otherwise the pseudo-isothermal analysis would not develop the proper sinusoidal oscillations about , as can be seen from the modeling in Figs. 4.100-102 (loss of stationarity). 

A simple analysis of an irreversible first-order transition is the cold crystallization, defined in Sect 3.5.5. For polymers, crystallization on heating from the glassy state may be so far from equilibrium that the temperature modulation will have little effect on its rate, as seen in Fig. 4.122. The modeling of the measurement of heat capacity in the presence of large, irreversible heat flows in Fig. 4.102, and irreversible melting in Figs. 3.89 and 4.123, document this capability of TMDSC to separate irreversible and reversible effects. Little needs to be added to this important application. 

Quasi-isothermal TMDMA data for PEN are shown in Fig. 6.51 for slow cold crystallization at 418 K [42]. The method consists of dynamic mechanical analysis, DMA (see Sect. 4.5.4), to which temperature modulation was added. The insert is a... 

Further analysis of the two samples of Fig. 6.62 is done by TMDSC, as seen in the left graphs of Fig. 6.64. A comparison of the two reversing heat capacities shows that the cold crystallization and the transition mesophase-to-a-monoclinic crystals do not show, i.e., they are nonreversing. There remains, however, a substantial reversing contribution which is larger for the quenched iPP than for the lamellar, melt-cooled iPP. The upper limit of the devitrification of the RAF seems to occur at 320-330 K,... 

An interesting analysis of a blend of PET/polycarbonate (PC), using MTDSC, was reported by Hale and Bair (Ref 5, p. 804) (Fig. 12). The conventional DSC curve (A) has all the indications of PET, but PC cannot be detected without the de-convoluted reversing curve (B) that indicates PC is present by virtue of its Tg that occurs in the same temperature range as the cold crystallization of PET. Further confirmation of the presence of PC is obtained from the dimamic mechanical storage modulus (curve C). The dynamic modulus technique will be discussed later in this article. 

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