Differences in rheological properties of solutions of plant and bacterial cellulose in LiCl/N,N-dimethylacetamide

Differences in molecular properties of celluloses from different biological origins were investigated chiefly in terms of the rheological properties of their solutions in 8 wt % LiCl/N,N-dimethylacetamide (DMAc). Cotton unter (CC) and dissolving pulp (DP) were used as cellulose samples derived from plant, and a cellulose from Acelobacter xylimm was also used as a bacterial cellulose (BC). For the three kinds of cellulose solutions, the values of η₀ - η_s (η₀: zero shear rate viscosity of solution, η_s: solvent viscosity) were in proportion to the weight fraction of polymer. Φ_w in the dilute region. On the other hand, they were in proportion to Φ_w ⁴ for the CC and the DP solutions and Φ_W³ for the BC solution in the semidilute or concentrated region. This Φ _w-dependence of η₀ - η_s shows that CC and DP, celluloses from plants, behave as a flexible polymer and that BC behaves as a rodlike polymer, according to several molecular theories. Plateau modulus, G_N, was in proportion to Φ_w² for the CC solution, signifying that network structure by entanglement was formed in the CC solution, as is often observed for solutions of flexible synthetic polymers. On the other hand, the concentrated solution of BC showed the typical small-angle X-ray scattering (SAXS) profile of two-phase systems, which can be well approximated by Debye-Bueche equation. This fact indicates that the structure of the BC solution apparently differs from the network structure.