Alkali lignin, preparation

UV spectra of neutral solutions of ALCELL lignins exhibited maximum at 205-210 nm and at 275-281 nm which are characteristic of other lignin preparations. Alkali-neutral difference spectra exhibited three maxima at about 252-254 nm, 296-300 and 363-366 nm which indicate the presence of aromatic hydroxyl, a-conjugated hydroxyls, and conjugated carbonyl groups. The latter includes carbonyl groups in the a-position as well as those in cinnamaldehyde units mentioned above. The alkali-neutral difference spectrum of ALCELL lignins reduced with sodium borohydride shows an almost complete elimination of the peak at 360-366 nm and an increase... 

Nahum LS (1969) Estimation of double bond content in lignin from the results of the oxo reaction of wood and lignin model compounds Tappi 52 712-714 Pew JC, Connors WJ (1971) Color of coniferous lignin Tappi 54 245-251 Redinger L (1961) Alkali lignin, its condensation products with phenols, and preparation of curable resins Monatsber Dtsch Akad Wiss (Berl) 3 571-578 Richtzenhain H, van Hofe C (1939) A stilbene derivative from the sulfite waste liquor Chem Ber 72 1890-1892... 

Acidic condition. Acidic hydroxymethylation occurs mainly at the C2 or C6 position of aromatic nuclei which may be phenolic or etherified units. It is used in the preparation of wood adhesives. The influence of lignin structure on reactivity and performance of the resulting resin product is still not entirely understood, as discussed by Nimz [3951. Van der Klashorst [396-398] reported the acidic condensation of alkali lignin and lignin model compounds with formaldehyde. Initial hydroxymethylation was faster with syringyl units... 

Alkali lignin, which is prepared by treating the wood with aqueous solutions of sodium hydroxide, in the presence of sodium sulfide (sulfate lignin) is a more appropriate object for structural studies. This polymer is not a polyelectrolyte and has a high molecular mass. In dimethylsulfoxide (DMSO), the macromolecules of sulfate lignin are compact particles, which are characterised by [r ] varying from 7.4 (M = 1.3 x 10 ) to 13.3 cm /g (M = 38.7 X 10 ) and the log [p] versus log M plot with the slope b = 0.15 [45, 46]. 

Alkali lignin is used as a binding agent in the cellulose industry to prepare hard-board made from wood and cellulose. It is used as a stabilizer in asphalt emulsion. 

Preparation from Waste Sulfite Liquors. The starting material for vanillin production is the lignin present in sulfite wastes from the cellulose industry. The concentrated mother liquors are treated with alkali at elevated temperature and pressure in the presence of oxidants. The vanillin formed is separated from the byproducts, particularly acetovanillone (4-hydroxy-3-methoxyacetophenone), by extraction, distillation, and crystallization. 

Scalbert A, Monties B (1986) Comparison of wheat straw preparations. II. Straw lignin solubilization in alkali. Holzforschung 40 249-254... 

Phenol and substituted phenols can be obtained from lignin by pyrolysis, alkali fusion, and hydrogenolysis (165-167). This methodology could be used to prepare an adhesive starting material, presently obtained from petroleum sources, from a renewable source, although technical difficulties require solution through further research. 

Chemical modification reactions continue to play a dominant role in improving the overall utilization of lignocellulosic materials [1,2]. The nature of modification may vary from mild pretreatment of wood with alkali or sulfite as used in the production of mechanical pulp fibers [3] to a variety of etherification, esterification, or copolymerization processes applied in the preparation of wood- [4], cellulose- [5] or lignin- [6] based materials. Since the modification of wood polymers is generally conducted in a heterogeneous system, the apparent reactivity would be influenced by both the chemical and the physical nature of the substrate as well as of the reactant molecules involved. 

Cellulose is insoluble in most solvents including strong alkali. It is difficult to isolate from wood in pure form because it is intimately associated with the lignin and hemicelluloses. Analytical methods of cellulose preparation are discussed in the section on Analytical Procedures. ... 

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