ANISOTROPIC EFFECTS OF THE GLASS-TRANSITION IN ORIENTED POLYETHYLENE

The influence of orientation on the glass transition of semicrystallin e polyethylene was investigated using Brillouin spectroscopy. Orientat ion was achieved by drawing the sample to 6.55 times its original leng th. The temperature range covered was 100-300 K. By performing the sec ond logarithmic derivative of the longitudinal sound velocity vs, temp erature graph the glass transition is found by a pronounced minimum. I n the isotropic sample it takes place at T-g = 234.8 +/- 1.7 K. This c urve nearly coincides with that found from longitudinal sound velocity in chain direction of the oriented sample. Perpendicular to the chain s no effect shows up. As is discussed, thermal expansion can be ruled out as an explanation of this strong anisotropic effect.