Annealing peaks

Fig. 5A Differential thermal analysis curve of a PPX sample polymaized from the cjclic dimer at 296 K and annealed below the transition to the isotropic state, at 625 K, fm- 12 h. The shoulder at about 475 K is an annealing peak (fusion of imperfect crystals). Transition ot-P, occurs at 500 K (Tj ). Transition P,-P2, at 570 K (Tdj). The endotherm for Tj (7(X) K) is not shown (see Ref.

Line 1 is present in all samples and represents the final melting of a crystals which may, however, have been formed on heating Line 2 is present only in samples with initial y crystals Line 3 is indicative of only little changed y crystals grown at 430 to 460 K, similarly line 4 is caused by a crystals grown at high temp. Line 5 is the annealing peak... 

The DSC curves at the bottom of Fig. 6.96 represent an analogous set of crystallization experiments, but grown from the melt. TTie melt-crystallized polymer shows higher perfection in both the annealing peak and the melting peak for the primary crystals. Ultimately, both peaks are expected to come together. 

Secondary crystallization, which has a time constant of approximately 5 min for the LLDPE. The conuibutions 4 and 5 contribute to the annealing peak, usually characterized by an endotherm at 5-15 K higher temperature (see Fig. 7.42). 

In addition to the normal melting point at 275°C, there is a small peak at about 220°C referred to as an annealing peak. 

The resulting peak was always at 279 K contrary to what one would expect from an annealing peak. These results agree with the X ray data of a lightly crosslinked sample [5]. The... 

After a week, specific melt enthalpy and the annealing peak remain constant, indicating that the physical aging processes are completed. These processes are more pronounced in oxidative atmosphere because of chemo-crystallization (see Section 1.4.2.2) than in inert atmosphere. Figure 5.168 shows the effects of thermal and thermal-oxidative aging on the mechanical properties of polypropylene. 

Now crystallinity remains constant up to the annealing peak, where crystallinity deaeases slightly while the RAF disappears and the MAF increases as it is assumed for the construction of baseline heat capacity. Above the annealing peak crystallinity and because of the assumption of the validity of a two-phase model, MAF stay nearly constant because of the continuous melting-recrystallization-remelting process. At about 200 °C, crystallinity increases by a few percent before final melting. 

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