DMAc/LiCl, cellulose solutions

In the current study, the aggregated anisotropic phase occurred in solutions prepared from acid hydrolyzed cellulose of dp 35. The higher minimum cellulose concentration for mesophase formation was observed in cellulose solutions richer in NH4SCN (see Figure 6). In these aspects, the cellulose/NH3/NH4SCN system resembles the DMAC/LiCl/cellulose system. 

The relative importance of the hafide anion - HO - Cell interactions can be inferred from application of the Taft-Kamlet-Abboud equation to the UV-Vis absorbance data of solvatochromic probes, dissolved in cellulose solutions in different solvent systems, including LiCl/DMAc and LiCl/N-methyl-2-pyrrolidinone [96]. According to this equation, the microscopic polarity measured by the indicator, Ej (indicator), in kcalmol is correlated with the properties of the solvents by Eq. 1 ... 

As discussed above, solvatochromic data for cellulose solutions in liCl-DMAc indicate that Cl - HO - Cell hydrogen bonding is more important for dissolution than li-cellulose interactions. If decrystalUzation is rate Umiting, and considering that the eqiulibria shown in Eqs. 7 and 8 occur prior to decrys-... 

An additional example is the preparation of gelatinous IPNs of poly(N,N-dimethylacrylamide) (PDMAm) containing 6-25 wt% cellulose, which were obtained in DMAc-LiCl solution as the homogeneous reaction medium for polymerizing DMAm monomer [75]. It was reported that an IPN of CELL = 25 wt % possessed a sixfold higher modulus than a PDMAm control, when compared to their water-swollen state. 

Aqueous salt solutions such as saturated zinc chloride or calcium thiocyanate can dissolve limited amounts of cellulose [131]. Two nonaqueous salt solutions with a lengthy history are ammonium thiocyanate/ammonia and dimethylacetamide/lithium chloride (DMAc/LiCl). Solutions up to about 15% can be prepared with these solvents. DMAc-LiCl has been used for molecular weight determinations of cotton [135] (see Section 1.5.2). 

McCormick et al (12) observed that cellulose concentrations of 10% (w/w) and above in 9% LiCl/DMAC appear lyotropic after slight shearing, but a pure anisotropic phase was not observed even in 15% (w/w) cellulose solutions. 

The preparation of cellulose solutions suitable for SEC analysis in DMAc/LiCl is reasonably straightforward (35,51). The dissolution process requires preswelling of the cellulose in water or its activation in refluxing DMAc. Evidently, it is important that the pH of the cellulose be neutral initially (51) otherwise, considerable degradation may occur before the dissolution process is complete. 

In another vein, a recent report [95] describes the preparation of an all-cellulose composite by dissolving pretreated ramie fibres in DMAc/LiCl and introducing untreated fibres into the ensuing solution. The composites were then isolated by coagulation with methanol and dried. 

The molecular cellulose chains have varying lengths. Measurements of the chain length require that cotton be in solution. Solvents for this purpose include cuprammonium hydroxide solution, phosphoric acid [7664-38-2], nitric acid [7697-37-2], quaternary ammonium bases, cadmium ethylenediamine hydroxide [14874-24-9], cupriethylenediamine hydroxide [111274-71-6] (76), dimethylacetamide [127-19-5]-lithium chloride [7447-41-8] (DMAC—LiCl), and... 

NOC was prepared by stretching a water-swollen cellulose film which had been coagulated from a DMAc /LiCl solution. Dissolution of cellulose and preparation of the template was accomplished by a previously described procedure using a solvent exchange technique (Togawa and Kondo 1999). 

Water-swollen cellulose film from the DMAc/LiCl solution... 

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