TEMPERATURE AND FREQUENCY-ANALYSIS OF THE DYNAMICAL VISCOELASTIC PROPERTIES OF HIGH-DENSITY POLYETHYLENE

The behaviour of the dynamical visco-elastic functions in high-density polyethylene (HDPE), which carries the trade mark 'Bulen', in the region of gamma and beta relaxation transitions was studied. The method of forced torsion vibrations was used to obtain curves for the storage modulus (G'), loss modulus (G2) and loss tangent (tg delta) in the temperature interval (-180 to +20)-degrees-C and torsion frequency (0.1 to 100) rad/s. The maximum values of the storage modulus, the temperature at which these maximums appear and the full width at half maximum show an increase with the increase in the torsion frequency, but the most outstanding and prominent change is in the interval (0.1 to 10) rad/s. This fact is explained with reference to the processes of the deformational orientation of the macromolecular chain segments leading to changes in the intensity of the anelastic intermolecular interactions, the frequency response of the kinetic elements responsible for the realization of the gamma relaxation transitions, etc. The analogical frequency dependencies, derived from the loss tangent curves, show that the greatest changes take place in the same frequency interval (0.1 to 10) rad/s, although certain differences can be seen, and some of them are explained by the greater sensibility of tg delta changes in the physical kinetics of the gamma transition. The specific region in PE characterizing the local minimum of the mechanical losses is also discussed.