VISCOSITY OF CONCENTRATED-SOLUTIONS OF ETHYLENE-VINYLACETATE COPOLYMERS IN PARAFFIN AT 3 MOLECULAR-WEIGHTS AND AT 3 TEMPERATURES

Measurements of the viscosity η of concentrated solutions of the ethylene-vinyl-acetate copolymer (EVA) in paraffin were carried out at a temperature 80°C; 120.5°C; 150°C, at molecular weights of the EVA, M2 = 150 000; 200 000; 250 000, and at concentrations c2 up to 11 g/100 cm3 solution. The equation of Bueche and Kelley and its extension to the lower concentrations (both related to the free-volume theory) and the semiempirical equations of Onogi et al. and of Weissberg et al., were considered with the aim of correlating the values of η vs. c2 in the most general way possible. The numerical elaboration of the data made it possible to calculate the value of Δη (root-mean-square deviation between calculated and experimental ln η) in the various cases, and it emerged that when curves ln η vs. c2 are considered at T and M2 constant, the best interpolation is obtained with Bueche's equation with three parameters (β,f1,f2), while if all the experimental points are considered with T and M2 variable Weissberg's equation gives the best interpolation. The behaviour of Onogi's equation is intermediate, however the master curves at T = constant make it possible to assemble the data with limited dispersion. The comparison of our viscosity data with the ones calculated by means of the free-volume theoretical expressions leads to the conclusion that the paraffin-EVA system has been studied in a concentration region below the critical value of the polymer concentration above which the chain entanglements prevail. © 1979 Dr. Dietrich Steinkopff Verlag.