Differential scanning calorimetry melting temperature

Fig. 6. Differential scanning calorimetry melting points of extrudates (at a heating rate of 10 K/min). Extrusion temperature 100 °C, die diameter 2.5 mm. (O) H020-54, (A) R006-60, (V) R40 (for sample description see Table 2)35)...

The melting process of polymeric systems can be studied utilizing dUatometry, calorimetry with thermal analysis, optical microscopy with hot stage, atomic force microscopy (AFM) with microcalorimetry. X-ray diffraction, and other techniques [1-9]. Special modern calorimetries such as standard differential scanning calorimetry (DSC), temperature-modulated differential scanning calorimetry (TMDSC) [3,10,11], and quantita-... 

Fig. 10. Differential scanning calorimetry of cellulose triacetate. Second heating at 20°C/min. glass-transition (T temperature = 177 " C crystallization on heating (T)/j) = 217 C melting temperature (Ta) = 289 C. To convert to cal, divide by 4.184.

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

We analyzed the embedded particles with differential scanning calorimetry to identify the property of polystyrene. As shown in Fig, 1, fhe embedded particles show a small peak around 100 °C, which is typical in atactic polystyrene [7]. It is desirable that embedding polymer has a similar melting tempeiature as the final polymer (polyethylene) because a big difference in the melting temperatures between the two polymers may cause a gel problem and poor mechanical properties. 

Brittle colorless films of PBPP may be cast from tetrahydrofuran solution. The insoluble portion of PBPP is swelled by the tetrahydrofuran and gives rise to free-standing films on solvent evaporation. Differential scanning calorimetry experiments on PBPP show a glass transition temperature at 40 °C, and some indication of a melting transition at 170° C. 

X-ray diffraction studies are usually carried out at room temperature under ambient conditions. It is possible, however, to perform variable-temperature XPD, wherein powder patterns are obtained while the sample is heated or cooled. Such studies are invaluable for identifying thermally induced or subambient phase transitions. Variable-temperature XPD was used to study the solid state properties of lactose [20], Fawcett et al. have developed an instrument that permits simultaneous XPD and differential scanning calorimetry on the same sample [21], The instrument was used to characterize a compound that was capable of existing in two polymorphic forms, whose melting points were 146°C (form II) and 150°C (form I). Form II was heated, and x-ray powder patterns were obtained at room temperature, at 145°C (form II had just started to melt), and at 148°C (Fig. 2 one characteristic peak each of form I and form II are identified). The x-ray pattern obtained at 148°C revealed melting of form II but partial recrystallization of form I. When the sample was cooled to 110°C and reheated to 146°C, only crystalline form I was observed. Through these experiments, the authors established that melting of form II was accompanied by recrystallization of form I. 

Table 2 Melting Temperatures and Enthalpies of Fusion for Compounds Suitable as Reference Materials in Differential Scanning Calorimetry...

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