Lignin chemical degradation

The next question is which criteria are suitable to indicate unequivocally similarities or distinctions betw een lignin preparations. In practice, physical, analytical and chemical degradative techniques are used to characterize lignins. 

Pyrolysis of biomass is defined as the chemical degradation of the biopolymers (cellulose, lignin and hemicellulose) constituting the wood fuel which initially requires heat. As can be seen in Figure 51, all reaction pathways making up the pyrolysis are not endothermic, which implies that some of the pyrolysis reactions generate heat. However, overall the pyrolysis process is endothermic. 

Modem concretes often incorporate a mixture of chemical and mineral admixtures, each of which may interact with the various constituents of cements and influence cement hydration reactions. The admixture-cement interactions may in fact be viewed as the reaction between two complex chemical systems - the multicomponent, multiphasic inorganic materials in the cement and the organic compounds of multicomponent admixture systems. For example, lignosulfonate water-reducers are intrinsically complex mixtures of chemical compounds derived from the chemical degradation of lignin, while synthetic admixtures such as superplasticizers contain species with a broad distribution of molecular weights, reaction products, or other chemicals added for a specific purpose [125]. The performance of an admixture in concrete is highly dependent on many... 

Lignin is the third most abundant structural polymeric material found in plant cell walls typically comprising up to 20-30% of woody biomass, from which most lignin is sourced as a by-product of papermaking. Lignin binds hemicellulose and cellulose together in plant cell walls and shields them from enzymic and chemical degradation. 

Burdon542 has surveyed the current hypotheses for the structure of humic substances and has concluded that the various products from chemical degradations and NMR data are all consistent with their being mixtures of plant and microbial materials and their microbial degradation products. The examination of soil carbohydrates, proteins, lipids, and aromatics supported this view the presence of colour, fluorescence, ESR signals, mellitic acid, and other features do not contradict it. Regarding the Maillard reaction, some free monosaccharides and the necessary amino species are present in soil, so it may proceed, but only to a small extent it is not a major process. However, in marine environments, the relative abundance of carbohydrates and proteins makes them more probable precursors of humic substances than lignin or polyphenols. 

Although the periodate oxidation and aminolysis methods provide quantitative data on the frequency with which of phenolic hydroxyl groups occur in lignin, they do not reveal the structural environment in which they occur. Such information may be obtained by other means, e.g., UV spectroscopic or chemical degradation methods (Adler 1977). 

Nakano et al. [404] observed that approximately 90% of an acid hydrolysis lignin residue from white birch became soluble after treatment with 3% sodium sulfite at 2(X)°C. Reactivity of the hydrolysis lignin was improved by milling, which was assumed to increase accessibility, and may also induce some chemical degradation. 

The complex polycyclic molecular frameworks of lignin comprise phenol and alkyl phenyl ether derivatives as major structural units. Chemical degradation and more or less... 

The purposes of this chapter are twofold. The first is to provide an overview on the significance and comparative performances of the most commonly used chemical degradation methods, especially with regard to screening, informative, and quantitative capabilities. The second purpose is to provide lignin structural information based on the use of these methods, with a special focus on thioacidolysis. Since the detailed laboratory procedures are beyond the scope of this chapter, the reader is advised to consult the corresponding original papers mentioned in the reference section. 

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