On the mechanism of low temperature glass transition in low density polyethylene films

The low temperature phase transition Tg of unirradiated low density polyethylene (LDPE) films was subjected to intensive investigations using both FTIR and FT-Raman techniques while cooling from room temperature to the liquid nitrogen temperature and re-heating. Cooling unirradiated LDPE film near Tg leads to the appearance of two IR bands at about 1642 cm-1 and 3350 cm-1. These two IR bands are reported herein for the first time, appearing on cooling the unirradiated film at 158 K and their intensities are found to increase remarkably with further decrease of temperature to liquid nitrogen temperature. Also, these two IR bands disappear while heating from liquid nitrogen temperature to room temperature at about 203 K, which is thought to be Tg. These two IR bands are not detected for the γ-irradiated LDPE films. The role of the so-called local ordering is thought to be essential for the appearance of the two newly appearing IR bands. (author)