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SYNOPSISChemical structures of cellulose and chitosan dissolved in trifluoroacetic acid (TFA) and those of cellulose and chitosan films cast from their TFA solutions were studied by 13C-NMR and infrared ( IR) spectroscopy. Cellulose is trifluoroacetylated selectively at the C6-hydroxyl groups in the TFA solution, and chitosan is dissolved in TFA by forming amine salts with TFA a t the CP-amine groups. IR analyses of cellulose films cast from its TFA-acetic acid solutions showed that partly trifluoroacetylated cellulose in the solution state turns to partly acetylated cellulose in the solid state during evaporation of the solvents in air by the ester interchange. Chitosan films cast from its TFA-acetic acid solutions still have the amine salts with TFA. These acetyl groups in cellulose films and TFA in chitosan films are removable by soaking the films in 1N NaOH at room temperature for 1 day.

SYNOPSISInteractions between cellulose and chitosan molecules in cellulose-chitosan blend films, prepared using trifluoroacetic acid as a cosolvent for the two polysaccharides, were studied by X-ray diffraction and Raman analyses and by measurements of mechanical properties of the blend films. Crystallinity of cellulose in the blend films decreased with an increase in chitosan content. The blend films had tensile strengths of 45-100 MPa and Young's moduli of 2-7.5 GPa in dry states. These values had the maximum around 30% chitosan content in the blend films. These results suggested the presence of interactions between cellulose, chitosan, and water molecules in the films. However, Raman analysis suggested that cellulose and chitosan molecules in the blend films seemed to have the same secondary structures as those in 100% cellulose and 100% chitosan films, respectively. Thus, these results indicate the presence of interactions in the interfacial region between small domains of cellulose and chitosan. The presence of chitosan molecules may lead to decrease in the domain size of cellulose, and to increase in the interfacial region between cellulose and chitosan domains.

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SYNOPSISA thin membrane of bacterial cellulose (BC) obtained from Acetobacter culture was tested for its performance as a dialysis membrane in aqueous systems. The BC membrane showed superior mechanical strength to that of a dialysis-grade regenerated cellulose membrane, allowing the use of a thinner membrane than the latter. As a result, the BC membrane gave higher permeation rates for poly(ethy1ene glycols) as probe solutes. The cutoff molecular weight of the original BC membrane, significantly greater than that of regenerated cellulose, could be modified by concentrated alkali treatments of the membrane. The nature of the change at the ultrastructural level caused by the alkali treatments was studied by X-ray diffraction and scanning electron microscopy. 0 1993 John Wiley & Sons, Inc.I NTRO D U CT 1 0 N Acetobacter xylinum, a Gram-negative bacterium, produces cellulose extracellularly. This cellulose is formed as gel-like mass (pellicle) at the surface of the medium and can be purified by proper chemical treatments. This material has high crystallinity and large surface area and has been attracting attention as a new form of cellulosic material. The proposed application includes an acoustic vibrator taking advantage of its high elastic modulus's2 and an insoluble thicker/binder for foods and sheetlike mater i a l~.~ When a purified pellicle is dried on a flat substrate, a thin translucent cellulose membrane is formed. This membrane is expected to have unique properties because it consists of fine and continuous crystalline microfibrils, not like paper sheets or regenerated cellulose films. One possible application is molecular filtration such as dialysis or ultrafiltration. It has been proposed to use the bacterial cellulose as a dialysis membrane in nonaqueous syst e m~.~ On the other hand, regenerated cellulose membranes have been widely used as a dialysis membrane in aqueous systems, where chemical stability and low toxicity of cellulose are preferable properties, especially in applications for labile biological systems. This study aimed at elucidating the basic characteristics of bacterial cellulose membrane as molecular separation medium in aqueous conditions, together with modifying the structure of the membrane by chemical treatments for controlling its molecular permeation characteristics. The tests were conducted in the dialyzing mode, i.e., without pressurizing the primary-side solution, by using a series of poly (ethylene glycols) [ poly (ethylene oxide) ] as probe solutes. EXPERIMENTAL Bacterial Cellulose (BC) MembraneThirty milliliters of sterilized Schramm-Hestrin medium4 was placed in a plastic Petri dish (inner diameter, 87 mm) and was inoculated with Acetobacter xylinum ( ATCC 23769 ) . Immediately after inoculation, the medium was gently but thoroughly mixed by swirling the dish so that the cells were distributed uniformly. The culture was statistically incubated at room temperature for 5-7 days, until the liquid medium was filled with cellulose pellicle.The harvested pellicle was rinsed with...