DMAC-LiCl system, cellulose

Two different procedures may be used to dissolve cellulose in the DMAC-LiCl system. The first proceeds via solvent exchange of cellulose soaked in water, to DMAC through ethanol, followed by stirring in 8% DMAC-LiCl at room temperature. The second one requires heating of a cellulose-DMAC suspension at 165 °C for 30 minutes, whereupon LiCl is added to the cellulose suspension at about 100 °C during the course of cooling, to adjust to 8% DMAC-LiCl (Fig. 27). 

Cellulose acetate was produced by the room temperature homogeneous acetylation of cellulose with acetic anhydride in the presence of amines in DMSO-H2CO systems Cellusose acetate was also prepared by adding 7ml acetic anhydride to 100ml of a solution of 5 percent cellulose in DMAc-LiCl to which had been added 0.5ml of 71 percent perchloric acid solution. The solution was allowed to stand for one day at room temperature and was then heated at 40°C for 2 hrs. before the ester was precipitated from the solvent by the addition of methanol. Cellulose and chitin have also been esterified and carbanylated at room temperature by the addition of phenyl isocyanate and pyridine to a solution in DMAc-LiCl systems. 

NaOCl. With increasing of NaOCl concentration from 1 to 10 vol% tensile strength and elongation values increased from 40 to 56 N/mm and from 10.3 to 24.6%. Kennedy et al. reported that the treatment used to removed lignin in wood pulps created voids and a wide distribution of pores [29]. Such microporous structure eases the penetration by activation liquids and solvent used in DMAc/LiCl system. Therefore, the fibers could interact more with the solvents. This could increase the interactions between cellulose fibers in the case of the bleached fibers. 

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. 

Cotton fibers are single cells composed primarily ( 96%) of the polymer cellulose. In our laboratory (5), cotton fibers were dissolved directly in the solvent DMAC-LiCl. This procedure solubilizes fiber cell wall components directly without prior extraction or derivatization, processes that could lead to degradation of high MW components. MW determinations have been carried out by a size-exclusion chromatography (SEC) system using commercial columns and instrumentation with DMAC-LiCl as the mobile phase. Incorporation of viscometry and refractive index (RI) detectors (6) allowed application of the universal calibration concept (7) to obtain MW distributions (MWDs) based on well-characterized narrow-distribution polystyrene standards (5). The universal calibration concept used by incorporation of dual detectors bypasses the need for cellulose standards. There are no cellulose standards available. Polystyrene standards for a wide range of MWs dissolved readily in DMAC-0.5% LiCl with no activation necessary. 

Henniges U, Schiehser S, Rosenau T, Potthast A (2009) Cellulose solubility dissolution and analysis of problematic cellulose pulps in the solvent system DMAc/LiCl. In Liebert TF, Heinze TJ, Edgar KJ (eds) Cellulose solvents for analysis, shaping and chemical modification. ACS symposium series, vol 1033. American Chemical Society, Washington, pp 165-177... 

If polymer samples with a certain desirable molecular weight are not directly available, like with some biopolymers, fractionation is often the only way to achieve such produrts. Eckelt and Wolfr have recently given an overview concerning the fractionation of biopolymers by means of CSF. This chapter describes the direct fractionation of native cellulose in the solvent-nonsolvent system DMAc+LiCl/acetone. How the CSF method can be applied for the polysaccharides pulluian and dextran is outlined by Eckelt et al. ... 

Cellulose activation has been achieved by heating the polymer with dry LiCl, at 110 °C, under reduced pressure, 2 mm Hg, followed by addition of DMAc. It is important to introduce the solvent while the system is maintained under reduced pressure, in order to avoid hornification [56]. As expected, the activation conditions employed were found to be dependent on cellulose structure, samples with high DP and high Ic required pre-treatment, i.e., mer-cerization (cotton linters), and/or longer activation time. This solubilization... 

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 ... 

Recently, use of LiCl/DMAc and LiCl/l,3-dimethyl-2-imidazolidinone as solvent systems for acetylation of cellulose by acetic anhydride/pyridine has been compared. A DS of 1.4 was obtained the substituent distribution in the products synthesized in both solvents was found to be the same, with reactivity order Ce > C2 > C3. Therefore, the latter solvent system does not appear to be better than the much less expensive LiCl/DMAc, at least for this reaction. It appears, however, to be especially efficient for etherification reactions [178]. It is possible, however, that the effect of cellulose aggregation is more important for its reaction with the (less reactive) halides than with acid anhydrides this being the reason for the better performance of the latter solvent system in ether formation, since it is more efficient in cellulose dissolution. 

The solubility of chitin is remarkably poorer than that of cellulose, because of the high crystallinity of chitin, supported by hydrogen bonds mainly through the acetamido group. Dimethylacetamide containing 5-9% liCl (DMAc/IiCl), and N-methyl-2-pyrrohdinone/LiCl are systems where chitin can be dissolved up to 5%. The main chain of chitin is rigid at room temperature, so that mesomorphic properties may be expected at a sufficiently high concentration [67,68]. 

Miyamoto et al. [165] observed a more uniform acetylation among different hydroxyl groups in LiCl dimethylacetamide (DMAC) as compared to heterogeneous reactions (Table 3). Cellulose dissolved in DMSO-PF is known to form methylol derivatives, especially for the 6-OH group. Acetylation of cellulose in this system [174-176] was shown to occur preferentially at the methylol hydroxyl group generated in situ. 

Most of the investigations to obtain LC cellulose were undertaken to achieve high-performance films or fibers from anisotropic solutions. The development of stable cellulose LiCl/dimethylacetamide (DMAC) systems led to an attempt to produce anisotropic solutions [36, 37]. Evidence was found of mesophase formation at 10-15% by weight depending on the salt concentration, with some problems due to limited solubility at high concentration (>15%). Measurements of the persistence length of cellulose in a dilute solution of this system indicate that the cellulose chains are stiffer than those of cellulose derivatives [38], and therefore lower the critical concentration for... 

McCormick [6] discovered that Af,Af-dimethylacetamide (DMAc) (Figure 10.3) and lithium chloride (LiCl) would dissolve the cellulose. He and his coworkers also observed cholesteric lyotropic mesophases of cellulose in this solvent system [7,8], which formed at cellulose... 

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