Lignin linkages

As seen, lignin structure and composition differs from plant to plant, means that lignin obtained from one source may need to be handled differently than lignin from another.

Plant lignins can be broadly divided into three classes: softwood (gymnosperm),  hardwood (angiosperm) and grass or annual plant (graminaceous) lignin.

Lignin abundance generally decreasing in the order of softwood, hardwoods and grasses

Lignins have in commons lots of different linkages. The linkages of lignin, individually depicted in Figure 1, include b-O-4, 5-5, b-5, 4-O-5, b-1, dibenzodioxocin, spiridienone, a-O-4 and b-b linkages, of which the b-O-4 linkages is dominant, consisting of more than half of the linkage structure of lignin. The relative abundance of the various linkages in softwoods (i.e. spruce) and hardwoods (i.e. birch), are given in Table 1

Fig. 1 Bonds in Lignin

Table 1. Linkages found in softwood and hardwood lignin 

References:

W. Boerjan et al., Annu. Rev. Plant Biol.54 (2003) 519

J. Zakzeski, P.C.A. Bruijnincx et al., Chem. Rev. 110 (2010) 355

2P. T. Patil et al., Energy Fuels, 25 (2011) 4713