FLOW OF MELTS OF HIGH-DENSITY POLYETHYLENE AND ITS MIXTURES WITH WAX NEAR THE MELTING TEMPERATURE

The flow of high-density polyethylene, polyethylene waxes, and their m ixtures in a capillary viscometer was studied near the melting tempera ture under the conditions when the crystalline phase in these systems was partially retained. The limiting degree of crystallinity where the flow still takes place was 10% for high-density polyethylene and 30% for wax. Yield stresses and an abnormal decrease in viscosity were obs erved with an increase in shear stress. The extremely high viscosity a nd apparent activation energy of viscous flow occurring with a decreas e in temperature is explained by cross-linking of the polymer chains b y crystallites and the formation of macromolecular aggregates with hig h apparent masses.