Dioxane lignin, preparation

Chum HL, Ratcliff M, Schroeder HA, Sopher DW (1984)Electrochemistry of biomass-derived materials. I. Characterization, fractionation, and reductive electrolysis of ethanol-extracted explosively depressurized aspen lignin. J Wood Chem Technol 4 505-532 Crozier TE, Johnson DC, Thompson NS (1979) Changes in a southern pine dioxane lignin on oxidation with oxygen in sodium carbonate media. Tappi 62 107-111 Ekman K, Enkvist T (1955) Some determinations of weak and strong acids in various lignin preparations and pulps. Pap Puu 37 369-382... 

Table 8.3.2. Number-average molecular weights of spruce dioxane lignin fractionated by preparative size exclusion chromatography (Pla and Robert 1974a, Froment and Robert 1977)...

Fig. 2 Apparent MWDs representing homologous series of an aspen kraft lignin preparation secured by fractionation/desalting through Sephadex LH-20 in aqueous 35% dioxane after incubation of parent preparation at 203 g/L in 1.0 M ionic strength aqueous 0.40 M NaOH for (1) 7215 hr, (2) 4600 hr, (3) 1930 hr, (4) 1116 hr, (5) 542 hr, and (6) 252 hr, and at 0.10 g/L in aqueous 0.10 M NaOH for (7) 74 hr, (8) 382 hr, (9) 1167 hr, and (10) 2728 hr. Sephadex G-lOO/aqueous 0.10 M NaOH elution profiles monitored at 320 nm.

However, in 1939 this difficulty was obviated by Brauns extraction of about 3% lignin from spruce wood by means of the solvent, ethyl alcohol, at room temperature (9). He termed this preparation native lignin. It was found to be soluble in methanol, ethanol, dioxane, dilute sodium hydroxide and pyridine, and insoluble in water, ether, petroleum ether and benzene. Chemically it behaved the same as lignin as it exists in woody tissues. It also reduced Fehling s solution and gave a strong... 

Figure 5. Effect of lignin content on mechanical properties of HPC/OSL blends prepared by injection molding (—), dioxane casting (—), and pyridine casting (— —).

Organosolv lignin-PEG was synthesized using a procedure similar to that used for the lignin model compounds. A 20% dioxane solution of 0.4 M NaOH was prepared. To 6 mL of this solution, 0.6 g of the chloroform soluble fraction of organosolv lignin... 

Besides cellulolytic enzyme lignin, the so-called Bjorkman lignin, alternatively referred to as "milled wood lignin" (MWL) is the best preparation known so far, and it has been widely used for structural studies. When wood meal is ground in a ball mill either dry or in the presence of nonswelling solvents, e.g., toluene, the cell structure of the wood is destroyed and a portion of lignin (usually not more than 50%) can be obtained from the suspension by extraction with a dioxane-water mixture. MWL preparations always contain some carbohydrate material. 

The purification procedure can be modified by omitting the last addition of chloroform (Lundquist and Kirk 1980). This results in a somewhat less efficient removal of carbohydrates but separation of the organic layer is easier. The precipitation in ether included in the preferred method removes residual extractives and other contaminants but also causes losses of ether-soluble lignin constituents. Purification procedures involving gel permeation chromatography (Kirk and Lundquist 1970, Bardet et al. 1985) should be considered when there is an interest in retaining the latter type of materials. Ether solubles from a preparation of spruce MWL have been examined (Lundquist et al. 1977). Hydrophilic constituents of dioxane-water extracts from milled spruce wood have recently been investigated (Lundquist et al. 1990). 

A weighed amount of lignin is dissolved or suspended in dioxane-methanol (9 1, v/v) and one drop of water/2ml solvent (approximately 5 mg of lignin ml-1 of solvent). Diazomethane is added to the solution under a stream of nitrogen over a 5-min period at room temperature. (The reaction should be conducted in a well-ventilated hood.) The diazomethane is conveniently prepared from N-methyl-N-nitroso-p-toluenesulfonamide (Merck-Schuchardt, Aldrich, Fisher, Fluka, and others) in a special reaction flask as described by Schlenk and Gellerman (1960). After a reaction time of approximately 20min, the procedure is repeated and diazomethane is again added over a 5-min period. The pro-... 

The enzymatic hydrolysis of milled wood with an enzymatic cellulase/hemi-cellulase complex is very useful for isolation of LCC preparations [31-33]. Partial enzymatic hydrolysis of the milled wood with an endoglucanase followed by wet chemistry separation allows for the isolation of various LCC fractions from wood and pulps [22]. The complete enzymatic hydrolysis of milled wood results in a preparation called milled wood enzymatic lignin (MWEL) [20] (Eig. 2). The extraction of MWEL with aqueous dioxane produces soluble CEL preparations [33]. Another variant of CEL preparations are those isolated by enzymatic hydrolysis of the residue after extraction of MWL [21]. 

Spectroscopic method - Approximately 0.2 g lignin of known moisture content was dissolved in 50 mL dioxane (96%) and the solution was diluted 1 10 in dioxane and then 1 1 in water and the pH was adjusted to 13 by addition of 1 mol. NaOH. A control was prepared with the same dilution but with the pH adjusted to 1 by addition of 1 mol. HCl. The average lignin value was used to calculate the percent phenolic OH. 

A fraction analogous to BjOrkman lignin (39) was obtained when a portion of finely-powdered suberin polymer from the periderm of 5. tuberosum was solubilized with dioxane. This soluble fraction, however, was not enriched in either aromatic or aliphatic components over the insoluble residue (unpublished results). Other procedures from lignin chemistry - including refluxing in HCl/dioxane or HCl/dimethylformamide, and dioxane treatment at 160 C and high pressure (268, 396) - resulted in 20 o to 50% solubilization of the suberin preparation, but with each method the insoluble material contained the majority... 

Initial studies, primarily done on suberin from the periderm of S. tuberosum give additional indication of the secondary structure of the polymer. Enriched preparations of suberin always contain high levels of carbohydrate (as much as 50 o). Obviously the suberin-enriched preparations contain covalently attached cell wall carbohydrates and the linkages between suberin and carbohydrate may be similar to those proposed for the attachment of lignin to carbohydrate (132, 268). Chemical studies on the polymer have shown that very few of the hydroxyl groups of cu-hydroxy acids are free and that the polymer has very few (< 5%) free aliphatic carboxyl moieties (230). Fractionation of S. tuberosum suberin by partial solubilization with 1 % HCl/dioxane has indicated that the aliphatic components may be in separate domains, for polymeric fractions that contained a larger proportion of fatty acids and fatty alcohols but a lower proportion of cu-hydroxy acids and dicarboxylic acids have been isolated. These fatty acids and fatty alco-... 

---