Determination of viscosity average molar masses of polyethylene in a wide range using rheological measurements with a harmless solvent

Rheological measurements of polyethylene solutions in a novel nontoxic solvent were used to determine the Mark-Houwink parameters for PE of widely different molecular weights to assess the viscosity average molar mass for PE of several millions of g.mol⁻¹. Solutions of high density polyethylene that had been previously characterized by size exclusion chromatography were prepared in a harmless naphthenic oil. The intrinsic viscosities were obtained by varying the concentrations of the different calibration samples solutions using a rotational rheometer equipped with a Couette cell. The intrinsic viscosities were determined by both Huggins and Kraemer descriptions of the viscosity variations with concentration. Subsequently, a calibration curve of intrinsic viscosities versus the molar mass was plotted, and the parameters of the Mark-Houwink-Sakurada equation were obtained for polyethylene in naphthenic oil. Using this equation and the newly estimated parameters, the viscosity average molar mass of a high molar mass polyethylene and a commercial ultra high molar mass polyethylene were been determined by measuring their respective intrinsic viscosities. Finally, the method has been validated by comparing these results to values obtained by standard viscosimetry in 1,2,4-trichlorobenzene and to the values given by the supplier, obtained by other methods.