Milan, for supplying some samples and many useful suggestions and to Dr. M. Dell'Eva and Mr. A. Tealdi for valuable help. This investigation was supported by the Italian Research Council through its "Chimica Fine e Secondaria" project.
Light scattering and viscosity measurements on diluted and moderately concentrated solutions of several cellulose samples dissolved in MJV-dimethylacetamide (DMAc) containing 5% or 7.8% (w/w) LiCl are reported. Cellulose samples include regenerated cellulose, sulfate pulps, and HC1 hydrolyzates having DP between 60 and 760. Solubilization without chain degradation was achieved by using a method reported in the patent literature involving activation of cellulose by DMAc at the reflux temperature followed by addition of LiCl. Cellulose was dissolved either as a molecular dispersion (I) or as stable aggregates (II) consisting of ca. 7 fully extended cellulose molecules with a side-by-side organization. Concentration-dependent association equilibria (III) involving single molecules or aggregates were also observed. The occurrence of said situations depends upon the concentration, Cp, of stock solutions prepared with the method indicated above, the concentration, c, to which stock solutions are diluted, the LiCl concentration, the DP, and the treatment performed by the producer. In particular, acid hydrolysis favors situation II. This complex situation is considered in the accompanying paper in order to establish a relationship between the size of polymer particles and the critical concentration for mesophase formation.
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