A steady-state and dynamical rheological study was performed with dilute solutions (1-4%) of high molecular weight cellulose (M, = 350,000). The solutions are strongly viscoelastic. The steady-state viscosity and the first normal stress difference have a power law dependence on the shear rate. T h e power law indices have the same dependence on temperature and concentration. These results as well as the correlation between the steady-state viscosity and the real part of the complex viscosity are in good agreement with the Spriggs model. The 4% concentrated solution shows the beginning of a rubber-like storage modulus plateau, suggesting the existence of an entanglement network.

The polymorphism and morphology of cellulose precipitated from solutions in amine oxide by the slow diffusion of water vapors, was investigated, as functions of the temperature of recrystallization and the degree of polymerization(DP) of the material to be recrystallized. At temperatures around 90°C, low DP cellulose crystallized almost exclusively as cellulose IV II , whereas higher DP material was found in the form of cellulose II. Substantial differences were also found in the morphologies of the various samples: with cellulose II, rod-like crystals were obtained with low DP material while a crystalline fibrillar gel precipitated when high DP samples were recrystallized. In all cases, cellulose IV II was obtained as a granular precipitate.The crystallization behaviour of polysaccharides is influenced not only by their chain conformation but also by the multiple possibilities of inter and intra molecular hydrogen bonding (1,2). This multiplicity, in particular, explains why several polymorphic forms can be obtained when different crystallization conditions are selected for a given specimen.A survey of the various parameters which have a role in directing the crystallization of a given polysaccharide toward one or another polymorph, presents the temperature of crystallization as being the most influential: polysaccharides such as cellulose (3), mannan (4), dextran (5,6), etc. are particularly sensitive to changes in crystallization temperatures as they yield completely different crystals at low or high temperature.In other instances, it is the solvent of crystallization which plays a decisive role in orienting the crystallization toward one or the other polymorph. Such solvent dependant crystallization is well documented in the case of amy lose (7) where minute changes in solvent/precipitant ratio have a dramatic effe ct on shifting the recrystallized amylose among three polymorps: amylose A,Β and V.

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