Modified Lignins

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

C. D. Williamson. Chemically modified lignin materials and their use in controlling fluid loss. Patent GB 2210888, 1989. 

Figure 2. A general scheme of various ways to modify lignin and its low molecular weight degradation products.

To conclude the above methods of incorporation of modified lignin in polymer networks and blends opens new promising possibilities for the technical use of lignins and makes it competitive with other raw materials for engineering plastics. 

Modified lignin materials may serve as components in (semi)conducting systems. All heterogeneous and amorphous polymeric complexes are now of interest for possible future employment in electrically conducting materials. 

High hydrolytic resistance against aqueous acid and base The modified lignins were found not to consume more alkali than the parent lignin (i.e., 50-80 mg KOH/g of derivative as compared to 85 mg KOH/g of parent lignin) ... 

Continuous improvements of chlorophosphazene-modified lignins, allowing the evaluation of a wide range of applications. 

Some results of the modification of lignin sulfonate Ultra B002 by reaction with terephthaloyl chloride are summarized in Table VI. The total hydroxyl content of the lignosulfonates as well as their derivatives are presented in Table VII. The hydrolytic resistance of selected products is evaluated in Table VIII. The results presented in Tables VI-VIII stress several advantages of the derivatives with terephthaloyl chloride. The modified lignin sulfonates were insoluble, or only very slightly soluble, in organic solvents. They were, however, soluble in dimethyl sulfoxide. Ordered structures were identified by X-ray studies (16,17). 

Modified Lignins as the Carriers for Controlled Release Preparations... 

If toughness is not the limiting consideration, then the simple addition of PEG soft segment appears to offer an attractive route to the production of polyurethanes with 25 to 30 wt.% lignin. It is important to note that both of the studies considered here have employed modified lignins. The relative advantage of hydroxypropylation (16) over fractionation (19) would depend on the relative cost of either procedure. 

Areas of uncertainty in this method of analyzing modified lignins include the problem that little more than one-third of the lignin is converted to volatile products by the hydrogenolysis reaction the non-volatile fraction cannot be analyzed by VPC/MS. This will constitute a difficulty only if the... 

Hydrochloric add, on being boiled with lignin, turn red, and ultimately brown. In the solid state, it be-. comes black, but does not dissolve in the acid. When this substance is washed and dried, it burns with flame, bowing that it is only modified lignin, and not entirely carbonized. Fused potossa, or a strong solution of this alkali, changes a portion of the matter into oxalic and acetic acide, which combine with the base the alkaline liquor, when treated with acids, ports with a modified lignin which is blued by iodine. 

These data indicate that mechanical, chemical, and biological attack of lignin create radical centers. We turned our attention next to an EPR analysis of chemically modified lignins. Reducing a number of samples (23) with NaBH4 seemed to have very little effect on the spin content. However, when samples were converted to their metal salts, a marked increase in free radical centers was observed. Acidification of the salts returned the spin content to its original level. 

Thus, a small concentration of ortho- or parabenzoquinone species in an environment of phenolic functions could explain the radical enhancement upon basification. The residual spin content of the neutral or acid form of lignin is almost nil in whole wood, very small in native lignins, but significant in kraft and other chemically modified lignins. Such a stable free radical could be attributed to (a) the small equilibrium concentration of I in Equation 1, (b) a semiquinone polymer patterned after synthetic models (4y 25) containing donor and acceptor groups, or (c) radicals entrapped and stabilized in a polymeric matrix (5,15). 

The quinonemethide content of chemically modified lignins may be much higher. If quinonemethide precursors (—e.g. structures of type III) are present in high yield pulps in residues of condensed lignin attached to the fibers, attempts to bleach the pulps with oxidizing agents may lead... 

Figure 2.5. Schematic representation of the modified lignin theory of humus formation. Adapted with permission from Stevenson, F. J. (1994). Humus Chemistry Genesis, Composition, Reactions, 2nd ed. John Wiley and Sons, New York.

Chlorination or chlorine dioxide treatment is almost always followed by a caustic extraction. Alkaline extraction neutralizes the pulp and removes the lignin rendered more soluble by chlorine treatment. Removal of this modified lignin opens up the cell wall and allows for milder delignification to be used in later bleaching steps. Caustic extraction is generally performed with most chlorinated chemical pulps at 50-60° with 0.5-5% NaOH for 1 to 2 hr. Consistencies are usually quite high (12 to 16%) to reduce the amount of water and minimize energy requirements. 

The Kraft process that is widely used in wood pulping leaves behind 5% to 8% by weight of residual modified lignin in the pulp. This residual is responsible for the characteristic brown color of the pulp and is commercially removed by the use of bleaching agents such as chlorine and chlorine oxides [32], Bleaching operations produce dark-brown effluents that contain toxic and mutagenic chlorinated products that constitute an environmental... 

Although the free phenolic structures are oxidized faster, chlorine dioxide also destroys nonphenolic phenyl propane units and double bonds present in the pulp chromophores. After cleavage of the benzene ring various di-carboxylic acids are formed, such as oxalic, muconic, maleic, and fumaric acids in addition to products substituted with chlorine (Fig. 8-10). As a result of depolymerization and formation of carboxyl groups the modified lignin is dissolved during the chlorine dioxide treatment and in the sodium hydroxide extraction stage that usually follows. 

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