Dynamic Mechanical Properties of Polyethylene Melts: Calculation of Relaxation Spectrum from Loss Modulus

Dynamic mechanical properties of several polyethylene melts were investigated using the Weissenberg rheogoniometer. The use of the rheogoniometer for oscillatory shear testing has been discussed. The methods of determining relaxation spectrum from loss modulus based on second‐order approximation of Schwarzl and Staverman, and first‐ and second‐order approximations of Ninomiya and Ferry were found relatively inaccurate in reproducing the original loss modulus and storage modulus data. As a result, the iterative procedure based on Roesler and Twyman's derivation and that based on Tanner's algorithm were employed and found to regenerate accurately the original experimental data. Of all the approximation methods, the one based on the second‐order approximation method of Williams and Ferry was subject to least error in its ability to regenerate the original melt data.