Lignin fractionation: Opportunities and Challenges
Lignin is a readily available yet heavily underutilised resource due to its severe degree of diversity and variability related to the plant source and to the processes employed for its isolation. Being in most cases a by-product of technologies targeting other biopolymers, e.g. cellulose, less attention is paid on the physicochemical features of the obtained lignin, which can therefore dramatically vary also on a batch to batch basis. To fully valorise the enormous potential of this material, the development of robust and economically sustainable strategies leading to lignin structures with well-defined and homogenous characteristics is of crucial importance. In this respect, lignin fractionation may represent a valid option, thus is attracting increasing interest from the scientific community. Different methodologies have been established and tested on many lignins in the last years. In this contribution, a critical review of the existing lignin fractionation approaches, in the perspective of the extrapolation of general trends in terms of properties of the extracted cuts is presented. The applications so far investigated are overviewed with a particular focus on the main benefits gained using fractions rather than pristine lignin.