Lignin fragments

The exploitation of lignin fragments in macromolecular materials can be divided into three different approaches (i) as additives in physical blends [57]  

The chemical participation of lignin macromonomers in polymerization or copolymerization reactions has been focussed mostly on the reactivity of both types of OH groups, and hence in the synthesis of polyesters, polyurethanes and polyethers, although some research has also dealt with their intervention through the unsubstituted aromatic sites in different formaldehyde-based resins in partial replacement of phenol [58, 59]. 

Recent additions to the search of lignin-based polymers include the use of lignin oligomers and vegetable oils to elaborate paper hydrophobic coatings [65] and the preparation of epoxy networks derived from lignosulfonate and glycerol [66]. 

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LiP catalyze several oxidations in the side chains of lignin and related compounds [26] by one-electron abstraction to form reactive radicals [27]. Also the cleavage of aromatic ring structures has been reported [28]. The role of LiP in ligninolysis could be the further transformation of lignin fragments, which are initially released by MnP. 

Figure 3.3 Partial structure (16 aromatic units) of a spruce lignin fragment.

Figure 6.12 A mechanism for the generation of lignin phenoxy radicals due to direct oxidation by laccase and a mediation process involving colloidal lignin fragments, according to Felby etal. (1997b).

Crawford and co-workers were the first to study in detail the action of two streptomyces, S. badius 252 and S. viridosporus T7A, on lignocellulose from different sources. Their work led to the conclusion that the bacterial action on aqueous suspensions of these lignocellulosics resulted in the solubilization of lignin fragments which precipitate upon acidification Acid Precipitable Polymeric Lignin (APPL) (1-10). 

Carbohydrate moiety linking non-glycosidically to lignin fragment... 

Polymers from Degradation Products and Lignin Fragments... 

From a practical viewpoint, perhaps diphenylmethane derivatives are formed at the extremities of lignin fragments in alkaline pulps. The derivatives might then react as shown in Scheme II, forming colored products such as AA, in which R represents the remainder of the lignin fragment. 

Hydrogenolysis and hydrogenation may occur in the absence of a catalyst but for rapid stabilization of, or effective addition of hydrogen to, the primarily formed lignin fragments, the application of a suitable catalyst is necessary The only exception to this principle are hydrogen-generating reactions which occur when primary alcohols and alkali are heated to temperatures in the vicinity of 350 °C... 

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