DYNAMIC-MECHANICAL SPECTROSCOPY OF THE OR IENTED FILMS OF HIGH-DENSITY POLYETHYLENE

Dynamic mechanical properties of the oriented films based on HDPE prep ared by multistep zone annealing with draw ratios lambda = 4.7, 9.9, 2 1.2, and 28 were studied at a frequency of 3.5, 11. 35, or 110 Hz and in a temperature range from -150 to + 120 degrees C. Intensities of th e gamma-relaxation and alpha-relaxation transitions were shown to decr ease with increasing lambda. For the samples with maximum lambda, the corresponding temperature dependence of loss tangent shows an intense beta-relaxation peak at -37 degrees C (frequency 3.5 Hz), which is vir tually not observed far the oriented HDPE and ultrahigh-molecular-weig ht PE. Maximum tear energy of the samples with lambda = 28 is indicati ve of enhanced interfibrillar affinity, in particular, at the expense of densification of interfibrillar amorphous regions, The molecular mo bility in these regions may be responsible for the appearance of the a bove beta relaxation peak. Temperature-frequency superposition of mech anical losses was carried out. Minimum values of the apparent activati on energy are characteristic of the samples with maximum values of lam bda, which indicates a less pronounced cooperative character of relaxa tion processes under these conditions.