Lignins water-insoluble lignin

Figure 11 reveals that the water-insoluble lignin has a broad molar mass distribution with an average molar mass close to Mw = 2000 g/mol. 

Table I. Elemental Composition of the Water-Insoluble Lignin...

Water-insoluble lignin C9H7.4602.47(OCH3)o.83 Milled wood lignin (P. abies) (6) C9H8.8302.37(OCH3)o.96... 

It is assumed that the water-insoluble lignin is a polymerization and oxidation product of a Cio monomer, C9Hn03(0CH3). The brown color may be the result of loss of 0.17 methyl groups and hydrogen atoms during the formation of a quinonoid structure and loss of 0.7 moles of water. 

Figure 10. Lignins dissolved on heating spruce wood meal with dioxane-phosphate buffer (60 40% v/v) for 16 h at 150°C (A) Lignins dissolved (B) Water-insoluble lignin. Column Spherisorb ODS. Elution Gradient elution with phosphate buffer-methanol.

Figure 11. Water-insoluble lignin. Column Sephadex G-50. Eluent 0.5 M NaOH.

Figure 12. IR-spectra of the water-insoluble lignin and a MWL preparation of Pinus sylvestris (obtained by courtesy of Dr. Bo Hortling).

The water-insoluble lignin amounted to about one-third, and the hexane-dioxane soluble lignins (which were mostly monomers) to about 20%, of the lignins dissolved. 

Hiittermann, A. Gel permeation chromatography of water-insoluble lignins on controlled pore glass and sepharose CL-6B. Holzforschung 32, 108-111 (1978)... 

The significance of phenoxy anions is well recognized in the isolation of kraft and other water-insoluble technical lignins by acid precipitation. The ioniza tion of phenoHc hydroxyl groups coupled with the reduction of molecular size renders native lignin soluble in the aqueous pulping solution, thus enabling its separation from the polysaccharide components of wood. 

Lignin is water-insoluble and it contains only a few hydrophilic functionalities (primarily the phenolic groups). In order to increase its solubility, aqueous pulping processes therefore seek either to introduce water solubilising groups, or to reduce the degree of polymerisation or both. 

Chlorination of pulp is usually carried out at fairly low consistency and its function is to convert the residual insoluble lignin in the pulp to compounds which are water or alkali soluble. Chlorine reacts very rapidly with pulp and most of it is consumed within a few minutes. 

The role of LCC s in living plant tissues is presumed to be related to the prevention of water-soluble hemicelluloses from dissolving out of the cell wall by the formation of micelles or aggregates that immobilize sugar chains, and the solubilization of water-insoluble material such as lignin, thereby enabling it to move to any place in the cell. 

The similarity of the two spectra in Figure 12 confirms the lignin nature of the water-insoluble substance. 

Alkaline-extracted/acid hydrolysis (AH/NaOH) lignin samples were prepared by subjecting aspen wood flour to a one hour cook at 120°C in 0.05N sulfuric acid (22), followed by mixing the clarified supernatant with 1% w/w NaOH at 25°C with a Waring blender. The insoluble lignins were precipitated by addition of acid and water washes (32% yield). 

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