Mechanical Relaxation in Polyethylene Crystallized With Various Degrees of Lamellar Orientation

The mechanical relaxation behavior of a set of well-characterized samples of polyethylene crystallized with different degrees of lamellar orientation is reported. The various samples ranged in morphology from unoriented isotropic samples to ones which showed a high degree of orientation of the b-axis along the sample growth direction. The mechanical measurements were made using a torsion pendulum apparatus of standard design, the direction of shear being normal to the b-axis for the oriented samples. The temperature range covered was from 100 to 400 °K. No definite effects attributable to orientation were observed for either the γ or β relaxation process, whereas for the α relaxation results for G″ indicate that a slight decrease in peak height resulted from the presence of lamellar orientation, particularly on the high temperature side of this peak. Data for the real and imaginary parts of the complex shear compliance are also discussed.