Polymorphs recrystallized cellulose

Polymorphic and Morphological Aspects of Recrystallized Cellulose as a Function of Molecular Weight... 

The crystal structure of cellulose I trinitrate (CTN I), prepared from cellulose I, differed from that of CTN II prepared from cellulose II. Recrystallized CTN I and CTN II were both regenerated to give cellulose II. The unit cell of CTN II is monoclinic, with a = 1.23 nm, b (fiber axis) = 2.54 nm, c = 0.855 nm, and /3 = 91°. The CTN I has a bent chain structure, and CTN II has a bent-twisted type of structure. The relationships of cellulose polymorphs to those of CTN were examined. 

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, whereas higher DP material was found in the form or 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 scimples were recrystallized. In all cases, cellulose was obtained as a granular precipitate. 

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