EVALUATION OF CORRECTIONS IN RHEOLOGICAL MEASUREMENTS OF POLYETHYLENE.PART II.POWER LOW INDEX,RABINOWITSCH CORRECTION

摘要

The results of investigation of the effect of Rabinowitsch correction on the courses of flow curves and viscosity curves for two polyethylene grades (PE-LD and PE-MD) as well as their blend in the ratio 1:1 were presented (Table 1,Fig.1-6).Rheological investigations were performed in the real conditions of extrusion process,using extrusion rheometer and cylindrical dies of circular cross-sections and various L/D ratios (Table 2 and 3).Power low index n was found to vary from 0.28 to 0.86 (Table 5),dependently on the system investigated.The differentiation in power low index values is due to different values of shear stress tau_w and various ranges of uncorrected shear rate during the polymer flow through the die of defined length and diameter.The application of real n-values in evaluation of the Rabinowitsch correction factor,related to changes of viscosity in the range of 75 % relative to non corrected values,reveals in a significant viscosity curves shift.Experimentally determined rheological values (power low index,Rabinowitsch correction,shear stress,corrected shear rate,apparent viscosity and corrected viscosity) are given in Tables 5-7.