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

✍ Scribed by M. Marx-Figini; F. Rex Gonzalez

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 401 KB
• Volume: 38
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.1989.070380202

✦ Synopsis

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 < DPq < 7000 and shear rates ( q ) between 100 s-l < 7 < 2000 s-'. The results show a strong dependence of the transition Newtonian to non-Newtonian behavior on the three variables 7, DP, and c, similar t o that found recently on solutions of synthetic polymers. Emphasis has been put on the critical concentrations corresponding to the standard shear rate loo0 s-' to correspond to the standard conditions (i. = 1000 s-'; 0.3 < [s] . c < 0.6; DS = 2.90 i 0.02) proposed for the determination of the intrinsic viscosity [ q ] of cellulose nitrates. I t 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 t o i. = 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 [ q ] 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 D P = 1O00, is not a consequence of the applied shear rate but rather of the molecular properties of the solutes themselves.