The current and emerging sources of technical lignins and their applications

Technical lignins are bulk feedstocks. They are generated as byproducts from pulping or cellulosic ethanol production. As lignin undergoes significant structural changes as a result of chemical and physical treatments, all technical lignins are unique in terms of chemical structure, molecular weight, polydispersity, and impurity profile. Kraft lignin is potentially the largest source of technical lignin as new isolation technologies have been implemented on an industrial scale in recent years. Lignosulfonate has been an integral product in sulfite pulping biorefineries. It has a well established market in the construction industry. Organosolv-like lignin production is increasing as cellulosic ethanol has been promoted as a substitute for fossil fuel. It may have unique applications because it has low molecule weight and is free from sulfur. Technical applications of lignin are expected to expand as its characteristics are improved with fractionation or chemical modification. The application of technical lignin has been focusing on developing products equivalent to those made by petroleum chemicals. Recent developments in technical lignin supply should increase its market share as an additive in polyurethanes and as a substitute for phenol-formaldehyde adhesives. Quality improvement of technical lignin may also encourage the study of lignin as an alternative feedstock for carbon fiber. Moreover, technical lignin depolymerization has been extensively explored to provide renewable aromatic chemicals. Starting from controlled pyrolysis and thermal liquefaction as the baseline technologies, many different chemical depolymerizations have been invented with a wide range of underlying chemical principles. (c) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd