Reversible Melting of Semi-crystalline Polymers Frequency dependence of the reversible melting enthalpy |
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Authors: | Cser F Rasoul F Kosior E |
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Institution: | (1) CRC for Polymers Pty. Ltd., 32 Business Park Dr., Notting Hill VIC, 3168, Australia |
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Abstract: | Modulated DSC (MDSC) has been used to study the heat flow during melting and crystallisation of some semi-crystalline polymers
i.e. different grades of polyethylene (LDPE, LLDPE and HDPE), and polypropylene (PP).
The heat capacities measured by MDSC are compared with the hypothetical complex heat capacities of Schawe and it is shown
that numerically they are equivalent; nevertheless, the concept of the complex heat capacity is problematic on a thermodynamic
basis.
A reversing heat flow (proportional to the experimental heat capacity of the material) was present at all conditions used
for the study. In the melting zone of the polymers it depends on the modulation frequency and on the amplitude. Higher amplitude
and frequency of modulation reduce the ratio of the reversing heat flow to the total heat flow, the latter is nearly independent
on these parameters.
The reversible component of the melting enthalpy of polymers depends on the modulation frequency, the modulation amplitude
and the type of the polymer. It increases by increasing the branching in polyethylene.
The existence of the reversible heat flow during the crystallisation and melting is contrary to the current hypotheses and
theories of polymer crystallisation.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | crystallisation heat capacity MDSC melting polymers |
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