Lignin Distribution within the Lignocellulose Cell Wall and the Topochemistry of Delignification by Thermochemical Treatment

Abstract

Lignocellulosics are attracting attention as an alternative resource to fossil fuel towards a sustainable society. Among its cell wall components, lignin, which is the second most abundant natural polymer next to cellulose, is expected as a feedstock for the value-added materials. Thus, the development of efficient extraction from the cell wall and its utilization are highly required. Thermochemical treatment such as super- and sub-critical fluid treatment have an effective delignification property and its delignification mechanism has been studied. However, the structure and concentration of lignin vary among the taxonomical species, cell types and morphological region, and the delignification behavior is not uniformly occurred within the cell wall. Thus, in this article, the heterogeneous distribution of lignin in lignocellulosics cell walls will be introduced in the order of moiety, interunit linkages, pendant structure and concentration in each morphological region. Then, the latest research on the topochemistry of delignification during thermochemical treatment will be presented, in particular using super- and sub-critical fluids treatments.