Birch lignins, Bonding

More than two thirds of the phenylpropane units in lignin are linked by ether bonds, the rest by carbon-to-carbon bonds. Figure 4-8 shows the principal bonds in lignin. Their proportions are seen from Table 4-1 (spruce lignin) and Table 4-2 (birch lignin). 

Ozonization of lignin forms derivatives of muconic acid that have the unique chemical structure of conjugated double bonds with two carboxyl groups. These derivatives have great potential for chemical modification. The ozonized lignin of white birch was soluble in epoxy resin at 120°C, and the free carboxyl groups were found to react with epoxide. This paper discusses developmental work on the preparation of pre-reacted ozonized lignin/epoxy resins the dynamic mechanical properties of cured resins and preliminary results of the application of these resins as wood adhesives. 

TABLE 4-2. Percentages of Different Types of Bonds in Birch (Betula verrucosa) Lignin (MWL) ... 

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