Lignin topological structure

Experimental data on hydrodynamic properties of natural and biosynthetic lignins in dilute solutions are reviewed. The results of viscometric, translational diffusion, and sedimentation studies provide evidence for the macromolecnles of lignin having a complex topological structure. The benefits and limitations of the theoretical approaches used to describe the topology of lignin macromolecular chains are discussed. The relationship between hydrodynamic characteristic and fractal properties of lignin is considered. 

One of the promising methods for studying the topological structure of lignin involves computer simulation, which is advantageous over statistical methods in that there is no need to introdnce any assumptions concerning the distribution of elements in the system and information about intramolecular cyclisation can be obtained from the modelling. 

Comparison of the fractal dimensionalities of lignins and the dehydropolymers revealed that the bulk DHP biosynthetic analog provides an adequate model of the topological structure and polymer properties of the native soluble lignins. 

By using conventional methods of polymer science to analyse the topological structure of lignin polymers, a number of important parameters of this structure were reliably determined. 

Lignin is synthesised in plants from monomeric molecnles, whose functionality varies from two to four. Thus, both branched chain and the crosslinked structure may be formed. In plant tissue, the polymer chains of lignin are snrronnded by macromolecules of noncellulosic polysaccharides, with which they form an amorphous lignocarbohydrate matrix. The experimental methods that allow the stndy of the complex topology of macromolecules in a multicomponent solid composite are very limited. Therefore, most of the data are interpreted using theoretical methods developed from polymer chemistry. 

Gravitis, J., Erins, P. Topological and conformational structure and macroscopic behaviour of lignin. J. Appl. Polym. Sci. Appl. Polym. Symp. 37, 421-440 (1983)... 

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