Viscosity, sedimentation, diffusion, and osmotic behavior of long‐chain nitrocellulose molecules
Authors: Newman Seymour , Loeb Leopold , Conrad Carl M. 
Published: April 2003

Viscosity, sedimentation, diffusion, and osmotic pressure measurements in ethyl acetate are reported on four unfractionated nitrocellulose polymers containing about 13.5% nitrogen and varying in molecular weight from 0.93 to 15 x 105.

Detailed viscosity determinations in buret viscometers in the concentration range 0.025 to 0.300 g./dl. and over a range of velocity gradients from about 500 to 5000 sec.‐1 are presented. Viscosity data adjusted to fixed shear rates fitted closely the relation ηsp/C = [η] + a2C + a3C2. Plots of ηsp/C vs. C at different shear rates were found to diverge rapidly with increasing concentration. For the nitrate of highest molecular weight, the viscosity was strongly shear‐dependent and the intrinsic viscosity appeared to vary from 52 at 3000 sec.‐1 to 80 or more at 0 sec.‐1. The other samples displayed these tendencies less markedly with decreasing molecular weight. Other extrapolation procedures are also discussed. The intrinsic viscosity data accumulated at 500 sec.‐1 could be represented by the relation [η] = KMα; α = 0.99; the molecular weights were those obtained from sedimentation‐diffusion measurements on the unfractionated nitrocelluloses. Assuming for practical purposes α = 1, then Km (\documentclass{article}\pagestyle{empty}\begin{document}$\[= \overline {{\rm DP}} /[{\rm \eta ]}\]) is found to have the value 80 ± 3. Assuming a negligible depolymerization during nitration, the analogous factors required for cupriethylenediamine and for cuprammonium were found to be 170 and 230, respectively. The effect of varying shear rate on these factors is illustrated.

The sedimentation constants obtained were readily extrapolated to infinite dilution with an expanded sedimentation‐concentration relation, S = S0/(1 + K2C + K′s C2). Diffusion constants were obtained following the second moment method and mathematically extrapolated to zero concentration according to Gralén. Molecular weights were computed with the Svedberg equation. Number average molecular weights were obtained osmotically.

Some consideration of the data in terms of the theories of Debye‐Bueche and Kirkwood‐Riseman is given. It is found that both K‐R's and D‐B's theories predict the variation of intrinsic viscosity with molecular weight within twice the standard deviation of the observed slope from the frictional coefficient‐molecular weight data. In both viscosity and sedimentation the polymer appears, therefore, to behave in an approximately equally “free draining” fashion. For the calculated intrinsic viscosity of a sample of intermediate molecular weight a reasonable value is obtained from the latter theory only; but it is not uniformly successful in predicting all [η]'s, particularly those corresponding to low molecular weights.

The relation between Ks, the first interaction coefficient in sedimentation and molecular dimensions, is briefly discussed. Also considered are the interaction coefficients in viscosity, especially as regards their dependence upon velocity gradient.