Lignin as a potential source of high-added value compounds: A review

Biorenewable polymers from different natural sources have attracted the attention of the research community in different fields such as food, biomedicine, cosmetic, and polymer composite industries. Lignin, as the second most abundant natural polymer in the world and mainly produced as a residue from the pulp and paper industry and ethanol production, is an attractive material for the development of ecofriendly, low-cost, and biodegradable products. During the last decades, different applications of lignin have been investigated, using it as a macromolecule or depolymerizing it for the production of fuels and low molecular weight chemicals. This review article assesses these investigations into the different applications/uses of lignin. Different lignin transformation processes are described, together with the main resulting products. First, the isolation processes or types of produced lignin are outlined together with the current lignin-producing companies. Then, information is provided about the analytical methods used to characterize it. Finally, this review presents the current products/applications of lignin as a macromolecule and current efforts focused on lignin depolymerization, motivating new catalysts being tested today.