Exploitation of the Hexagonal Phase in Polyethylene

Another way to disentangle linear polyethylenes, and thus to control the interphase without the need of using a solvent, is to anneal the polymer in the hexagonal phase. Bassett has discussed the role of the hexagonal phase in the crystallization of polyethylene extensively in an earlier chapter in this book. Briefly, polyethylene exhibits a number of different crystal structures, with the hexagonal phase being observed in hnear polyethylenes at elevated pressure-temperature in isotropic samples or at ambient pressure in oriented samples. For this reason, we have to distinguish between these two situations, namely isotropic and oriented polyethylene, however, we will focus only on isotropic polyethylene and will refer readers to reference [18, 19] for an overview of oriented polyethylene. 

For isotropic polyethylene, the hexagonal phase is usually observed at elevated pressure and temperature, in fact, above the triple point Q located at 3.4 kbar and 220°C according to the pioneering work of Bassett et al. [20] and 

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