Lignin bonded chemical distribution

By taking apart the cell wall of a modified wood specimen and separating the cell wall components from one another, it is possible to determine the distribution of bonded chemicals in the cell wall polymer. It is more difficult to delignify modified wood than unmodified wood, which means that the lignin has been substituted 122, 127, 128). This is true for wood reacted with both acetic anhydride and methyl isocyanate. Table IX shows that the lignin component is always more substituted than the holocellulose components 128). This would indicate that the lignin is either more accessible for reaction than holocellulose or that it is more reactive than holocellulose. Lignin was found to be more reactive than cellulose toward acetylation 129). 

Bonding methyl, ethyl, propyl, and butyl isocyanates to wood gives good decay resistance at weight gains above about 20%. Determination of the distribution of bonded chemical with methyl isocyanate in southern pine shows that 60% of the lignin hydroxyls are substituted and 12% of the holocellulose hydroxyls are substituted at the point where resistance to biological attack occurs. 

In the cell walls of higher plants,178 hemicelluloses are found in close association with cellulose and lignin, and evidence for the distribution of these three main components in the various parts of the wall has been obtained by staining techniques.179 It is not certain, however, whether the close association of these substances can be accounted for entirely in terms of physical entanglement and secondary forces (van der Waals and hydrogen bonding) or whether primary chemical bonds unite some of the components. 

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