Crystallization and annealing of polyethylene

The kinetic theory of nucleation and crystal growth rather well predicts the thickness of polyethylene single crystals isothermally crystallized from melt but fails with crystals grown from dilute solutions. The latter case is in better agreement with the theory of thermodynamic stability of single crystals. Density variation of bulk samples during annealing above the temperature of crystal formation is the consequences of adaptation of the density deficient surface layer of the every single crystal from the smaller thickness corresponding to crystallization to the larger one of annealing temperature and by a linear thickness increase with log t. The thickening rate increases with higher temperature and smaller molecular weight. The same effects also explain the slow density increase during secondary crystallization from melt and the small deviations of primary crystallization from A VRAMI 's theory.