Shear rate dependence of the viscosity of cellulose nitrate solutions in the dilute concentration regime revisited

Authors

  • M. Marx-Figini,

    Corresponding author
    1. Polymer Division-INIFTA, Faculty of Exact Sciences, National University of La Plata, Argentina
    • Polymer Division-INIFTA, Faculty of Exact Sciences, National University of La Plata, Argentina
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  • F. Rex Gonzalez

    1. Polymer Division-INIFTA, Faculty of Exact Sciences, National University of La Plata, Argentina
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  • Postal address: C. C. (P.O.B.) No. 16, Suc. (Filial) No. 4, 1900 La Plata, Argentina.

Abstract

A detailed rheological study of cellulose nitrate in ethylacetate had been carried out in the dilute concentration (c) regime, covering a degree of polymerization (DP) range between 300 < DPη < 7000 and shear rates (equation image) between 100 s−1 < equation image < 2000 s−1. The results show a strong dependence of the transition Newtonian to non-Newtonian behavior on the three variables equation image, DP, and c, similar to that found recently on solutions of synthetic polymers. Emphasis has been put on the critical concentrations corresponding to the standard shear rate 1000 s−1 to correspond to the standard conditions (equation image ≅ 1000 s−1; 0.3 < [η] · c < 0.6; DS = 2.90 ± 0.02) proposed for the determination of the intrinsic viscosity [η] of cellulose nitrates. It is shown that solutions with concentrations adjusted according to the above given conditions still exhibit Newtonian behavior, up to the highest range of DP. It follows, therefore, that applying the standard conditions, an extrapolation to equation image = 0 as has been proposed often for the intrinsic viscosity determination of cellulose nitrate is not advisable and results in considerable error. Considering the relationship between [η] and DP, the present results indicate that the decrease of the exponent (a) from a = 1.0 to a = 0.76, taking place above a DP ≅ 1000, is not a consequence of the applied shear rate but rather of the molecular properties of the solutes themselves.

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