Exothermal crystallisation peak

Cooling and melting thermograms of palm olein are illustrated in Figures 3.4 and 3.5. In contrast to the thermograms of palm oil, those for palm olein reveal only a single broad crystallisation peak. This exotherm is generally sharper in... 

The crystallisation and melting behaviour of palm stearin depends on the composition. Figures 3.6 and 3.7 show the behaviour of different palm stearins. PMF shows crystallisation exotherms which overlap into several peaks, while its melting thermogram shows one main endotherm with a shoulder, finally melting... 

The sample investigated was amorphous to X-rays. Its crystallisation is represented by the sharp exothermic peak centred at 492 C. During crystallisation, the residual species trapped in the amorphous network (water (m/z=18) and a small peak of CO2 - its magnification marked as A in the inset in the figure) were evolved. The amount of the carbon released during the crystallisation of the zirconia aerogel amounts to 0.007 mass%. 

On cooling the heated samples, exothermic peaks, due to the crystallisation of hard segment domains, were seen in the DSC curves. Again, the higher exothermic peak temperature suggested the existence of larger size hard segments for HER elastomer. 

Figure 1.9 shows an example of detecting a glass transition beneath a cold crystallisation exotherm. The total heat flow corresponds to a conventional DSC experiment. It is not possible from inspection of the distorted peak in this curve to conclude that it is formed from an exotherm (from the crystallisation of PET) superimposed on a glass-rubber transition (from the polycarbonate). The additional signals of MTDSC make this interpretation clear. In this case, the crystallisation acts like a chemical reaction once formed the crystals remain as the temperature increases through the peak. Thus, the process is non-reversing. 

In the author s opinion there is ample evidence for the existence of smaller, less perfect lamellae which form in the constrained amorphous phase between primary lamellae. It is perfectly reasonable that this would be so - since secondary crystallisation occurs in a constrained amorphous phase. Accordingly the second interpretation is favoured. However, it is also true that melting and recrystallisation occur during a heating scan and so the small LTMP may represent more of the lamella size distribution than the small size of the peak would suggest. In cold-crystallised samples there may be a lot more small lamellae than the size of the LTMP indicates (because melting is accompanied by a simultaneous crystallisation exotherm) and indeed the clearest evidence for the melting-recrystallisation interpretation comes from cold-crystallised materials. 

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