Lithium chloride/N , N-dimethylacetamide Research Articles

Influence of the carbohydrate composition on the molecular weight distribution of kraft pulps

The molecular weight distribution (MWD) of hardwood kraft pulps and softwood kraft pulps dissolved in lithium chloride/ N, N-dimethylacetamide (LiCl/DMAc) have a different shape. Two fairly well separated distributions of hardwood kraft pulps are obtained by size exclusion chromatography whereas the MWDs of softwood kraft pulp is more complex. Since these two pulps contain different types of hemicelluloses, the neutral carbohydrate composition of different cuts of the MWDs was examined. The results indicate that the two distributions observed for hardwood kraft pulps originate from cellulose and xylan, respectively. In contrast, the hemicellulose of softwood kraft pulps elute over the entire molecular weight range. The carbohydrate analysis of the collected fractions shows that glucose is the major component in all fractions. The relative concentration of mannose decreases during elution, i.e. with decreasing molecular weight ( M) whereas galactose, xylose and arabinose increases during elution, i.e. with decreasing M. The coelution of cellulose and glucomannan may be due to association properties, which gradually decrease with increasing amount of galactose substituents. The difference in elution behaviour between hardwood and softwood kraft pulp xylans may be due to different amounts of glucuronic acid groups and/or how these groups are distributed along the main chain. It is thus more difficult to interpret differences in the MWDs of softwood kraft pulps than of hardwood kraft pulps.

Chemical modification of chitin and chitosan 1: preparation of partially deacetylated chitin derivatives via a ring-opening reaction with cyclic acid anhydrides in lithium chloride/ N, N-dimethylacetamide

Derivatives of partially N-deacetylated chitin (DAC) were prepared via ring-opening reactions with various cyclic acid anhydrides in lithium chloride/ N, N-dimethylacetamide (LiCl/DMAc) system. Some cyclic acid anhydrides such as succinic, maleic, glutaric, and phthalic anhydrides gave successfully water-soluble DAC derivatives. From the enzymatic studies, the glycosyl bond of succinyl and maleoyl DAC-20 (20% DAC) was rapidly degraded by lysozyme or chitinase, though that of phthaloyl DAC-20 was not. The ester linkage of succinyl DAC-20 was stable against lipase for five days at room temperature.

SIZE EXCLUSION CHROMATOGRAPHY OF LIGNINS USING LITHIUM CHLORIDE/N,N-DIMETHYLACETAMIDE AS MOBILE PHASE. II. DISSOLVED AND RESIDUAL PINE KRAFT LIGNINS

Dissolved and residual pine kraft lignin samples were isolated from different delignification phases of kraft flow–through cooks. The molecular weight distributions (MWDs) were studied by size exclusion chromatography using lithium chloride/N,N-dimethylacetamide (LiCl/DMAc), not previously applied to isolated softwood lignin samples before. The MWDs were compared with results obtained using tetrahydrofuran (THF) or lithium chloride/N,N–dimethylformamide (LiCl/DMF) as mobile phase. Some important characteristics of the isolated lignin samples including the MWDs are reported and compared with a previous study on birch wood kraft lignins. The molecular weight of the lignins was changed in a similar way irrespective of mobile phase used. The molecular weight of the dissolved lignin increased during the cook. By contrast, the change in molecular weight of the residual lignin samples did not show a clear trend with respect to cooking time. One explanation for this irregular change may be the low efficiency of the acid dioxane extraction of the pine kraft pulp obtained early in the cook as this pulp contains a large amount of lignin. Apart from this sample, the size of the residual lignin sample decreases and resembles that of the dissolved lignin at the end of the cook. For all samples, the MWD was positioned at higher molecular weight range when LiCl/DMAc was used as the mobile phase compared with THF. The explanation for this behaviour seems to be that the polystyrene standards elutes later from polystyrene-divinylbenzene columns compared to the lignin samples when a mobile phase of higher polarity is used. The shapes of the distributions were also different between LiCl/DMAc and THF, whereas LiCl/DMAc and LiCl/DMF gave similar distribution profiles. These results emphasize the importance of using the same mobile phase and column packing material when comparing MWD and size of different lignins and also when comparing lignins and carbohydrate polymers in pulp.

SIZE EXCLUSION CHROMATOGRAPHY OF LIGNINS USING LITHIUM CHLORIDE/N,N-DIMETHYLACETAMIDE AS MOBILE PHASE. I. DISSOLVED AND RESIDUAL BIRCH KRAFT LIGNINS

The molecular weight distributions (MWDs) of dissolved and residual lignins from different delignification phases during flow-through kraft cooking of birch have been studied. The fundamental characteristics of the isolated lignin samples were evaluated and the lignins were characterised by size exclusion chromatography using lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) not used for isolated lignin samples before. The MWDs of underivatized and acetylated samples were compared with the MWDs of acetylated samples obtained by using tetrahydrofuran (THF) as mobile phase in a similar chromatographic system. The results indicate that removal of pulp lignin during the initial phase of kraft cooking of birch is restricted partly because of the large size of the lignin polymer. However, at the end of the cook no such restrictions remain. The apparently larger molecular size obtained with the LiCl/DMAc-system compared to the THF-system, may be due to interactions between the polystyrene standards and column matrix in combination with a more extensive conformation of the lignin polymer and/or a higher degree of swelling of the polystyrene-divinylbenzene matrix. Although differently accentuated, the residual lignin samples show a bimodal MWD in both solvents. Possible explanations for this phenomenon may be due to structural heterogeneity in the residual lignin, different molecular conformation due to the polarity of the solvent and/or different degrees of associations between lignin fragments in the two solvents.

Cellulose esterification with fatty acids and acetic anhydride in lithium chloride/N,N‐dimethylacetamide medium

AbstractHomogeneous esterification of cellulose with saturated fatty acids (n‐octanoic to n‐octadecanoic) was accomplished with acetic anhydride co‐reactant in lithium chloride/N,N‐dimethylacetamide (LiCl/DMAc) medium. Cellulose mixed triesters (CMT) were obtained after 5 h at 130°C with an average of 2.2 acetyl groups and 0.8 fatty substituents per anhydroglucose unit. A mixed acetic‐fatty anhydride, formed in situ, accounts for the grafting of the fatty moiety. The purified products were characterized and compared to the analogous cellulose simple fatty triesters (CST) that were synthesized from fatty acid chlorides in pyridine medium. Dynamic contact angle with water, glass transition, and storage moduli were correlated with the length of the fatty substituents. The CMT proved to be highly hydrophobic and more mechanically resistant than the CST.

Non-catalytic photo-induced graft copolymerization of methyl methacrylate onto O-acetyl-chitin

O-Acetyl-chitin was prepared in a lithium chloride- N,N-dimethylacetamide (LiCl/DMAc) system with high yield. The degree of acetylation was controlled with the amount of acetic anhydride. The obtained O-acetyl-chitin swelled not only in polar organic solvents, such as N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO), but also in water. O-Acetyl-chitin powder was graft-copolymerized to methyl methacrylate without catalyst. Graft copolymerization was initiated by the photolysis of the O-acetyl-group and the polymerization in a Quartz tube proceeded easier than in a Pyrex tube. The addition of DMSO in the reaction system did not always accelerate the graft copolymerization. Effects of various factors such as monomer concentration, degree of substitution of the O-acetyl-group and polymer concentration were also investigated.

Preparation of chitin- p-toluenesulfonate and deoxy(thiocyanato) chitin

Chitin- p-toluenesulfonate(tosyl-chitin) was prepared homogeneously in lithium chloride-N,N-dimethylacetamide (LiCl/DMAc). In this solvent system, the side reaction of O-acetylation often occurred by solvolysis of p-toluenesulfonyl(tosyl) chloride. The utilization of strong base either triethylamine or 4-dimethylaminopyridine, leads to highly tosylated chitin, with minimal incorporation of an O-acetyl group. Similar results were found in the substitution of N-methylpyrroridone (NMP) for DMAc. Chitin-4(methylamino)butylate was obtained with a pyridine catalyst. The degree of tosylation increased with increasing amount of tosyl chloride and became constant above 1. Tosyl-chitin obtained at high reaction temperature was highly chlorinated. The tosyl-chitin with high degree of substitution was readily soluble in various polar organic solvents such as dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF). By X-ray analysis, it was observed that the crystallinity of tosyl-chitin became low as the reaction proceeded. Treating tosyl-chitin with potassium thiocyanate in DMSO produced deoxy(thiocyanato)chitin.