Oxlignin: A Novel Type of Technical Lignin from Kraft Pulp Mills.

Lignin, a bio-originated polymer, is being explored as an alternative to nonrenewable fossil resources. It is obtained from biomass during pulping and is mostly burned for energy. In most kraft pulp lines, residual lignin in the pulp is oxidized and solubilized during an oxygen delignification step. This study proposes an isolation method for lignin solubilized during oxygen delignification, which we refer to as "oxlignin", and explores its structural characteristics and properties. The study found acid precipitation to be an effective method for partially isolating oxlignin from the oxygen delignification step. Various analytical methods were employed, including UV-vis absorption analysis, 31P NMR spectroscopy, FT-IR spectroscopy, SEC, and TGA. In addition, the solubility of the lignin was studied in four different solvents and compared to the commercial kraft lignins. The study found that oxlignin is a promising substitute for lignosulfonates in certain applications due to its hydrophilicity and high solubility in water, methanol, and ethanol. Compared to kraft lignins, oxlignin has a lower phenolic group content but higher carboxylic acid content.