Cellulose acetate mesophases

Lyotropic Phases. Lyotropic cellulosic mesophases can be observed in a large variety of solvents with derivatives that can be thermotropic (ethylcellulose, hydroxypropylcellulose, acetoxypropylcellulose, etc.) or not (cellulose acetate). 

Cellulose based mesophases have displayed a somewhat steeper inverse dependence of pitch to concentration than that reported by Toriumi (29). A value of x = 3 has been reported for hydroxypropyl cellulose in water (31), for acetoxypropyl cellulose in acetone (32) and for hydroxypropyl cellulose in acetic acid and in methanol (28). Our data for cellulose in NH3/NH4SCN show a reasonably straight line when p l/3 was plotted vs. cellulose concentration (Figure 11), which is in accord with earlier reports (28,29,31,32). 

Cellulose Acetate fCTAi Mesophases. TFA-CH2a2 mixtures are also excellent solvents for CTA. Patel and Gilbert (17) showed the CTA mesophase is cholesteric in nature. They employed various n A-CH2Cl2 ratios. Here, data will be given only for 60 40 ( tv) mixtures. 

Recently, cellulose and its derivatives attracted researchers attention again. Besides the work by Aharoni who confirmed the appearance of the liquid crystalline state for cellulose acetate mentioned above, a number of other works appeared in which liquid crystalline state was established for hydroxypropyl cellulose . Finally, Chanzy et al. have obtained the results indicating the possible transition to the mesophase of cellulose itself, and not only its derivatives. 

Many cellulose derivatives form lyotropic liquid crystals in suitable solvents and several thermotropic cellulose derivatives have been reported (1-3) Cellulosic liquid crystalline systems reported prior to early 1982 have been tabulated (1). Since then, some new substituted cellulosic derivatives which form thermotropic cholesteric phases have been prepared (4), and much effort has been devoted to investigating the previously-reported systems. Anisotropic solutions of cellulose acetate and triacetate in tri-fluoroacetic acid have attracted the attention of several groups. Chiroptical properties (5,6), refractive index (7), phase boundaries (8), nuclear magnetic resonance spectra (9,10) and differential scanning calorimetry (11,12) have been reported for this system. However, trifluoroacetic acid causes degradation of cellulosic polymers this calls into question some of the physical measurements on these mesophases, because time is required for the mesophase solutions to achieve their equilibrium order. Mixtures of trifluoroacetic acid with chlorinated solvents have been employed to minimize this problem (13), and anisotropic solutions of cellulose acetate and triacetate in other solvents have been examined (14,15). The mesophase formed by (hydroxypropyl)cellulose (HPC) in water (16) is stable and easy to handle, and has thus attracted further attention (10,11,17-19), as has the thermotropic mesophase of HPC (20). Detailed studies of mesophase formation and chain rigidity for HPC in dimethyl acetamide (21) and for the benzoic acid ester of HPC in acetone and benzene (22) have been published. Anisotropic solutions of methylol cellulose in dimethyl sulfoxide (23) and of cellulose in dimethyl acetamide/ LiCl (24) were reported. Cellulose tricarbanilate in methyl ethyl ketone forms a liquid crystalline solution (25) with optical properties which are quite distinct from those of previously reported cholesteric cellulosic mesophases (26). 

Marsano E, Bianchi E and Ciferri A (1984) Mesophase formation and poljoner compatibility. 2. Cellulose acetate/(hydroxypropyl)cellulose/diluent system. Macromolecules 17 2886-2889. 

Most work has been concentrated on the formation, structure and properties of ternary systems composed of one cellulose derivative and mixed solvents or other polymer blended solutions. Thus, the liquid crystal properties of ethylcellulose/acrylic acid, ethylcellulose/dichloroacetic acid and ethylcellulose/glacial acetic acid solutions were studied, observing the mesophase behavior when their concentrations exceeded 0.6, 0.3, and 0.35 g/ml, respectively, at room temperature [143]. Also,... 

It should be noted that the cholesteric type of mesophase of polymers is apparently much more common than is generally believed. The presence of rigid-chain or semirigid-chain macromolecules with a chiral center is determining for the realization of this type of structure. The recent communications concerning the detection of the cholesteric mesophase for such long studied polymers as methylamylase [45] and cellulose xanthates, ethyl acetate, and triacetate [46-47] are evidence of the above. 

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