A method of fractionating lignin, comprising: (i) removing hemicellulose sugars from a biomass, thereby obtaining a lignin-containing remainder, wherein the lignin-containing remainder comprises lignin and cellulose; (ii) contacting the lignin-containing remainder with a lignin extraction solution to produce a lignin extract and a cellulosic remainder; wherein the lignin extraction solution comprises a limited-solubility solvent, an organic acid, and water, wherein the limited-solubility solvent and water form an organic phase and an aqueous phase; and (iii) separating the lignin extract from the cellulosic remainder; wherein the lignin extract comprises lignin dissolved in the limited-solubility solvent; further comprising one, two or three additional step(s) selected from: (iv) distilling or flash evaporating the lignin extract, thereby removing the bulk of the limited-solubility solvent from the lignin extract to obtain a solid lignin; (v) heating the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin; and (vi) applying a vacuum to the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin;. and further comprising: (vii) contacting a sample comprising the solid lignin with an organic solvent to form a resulting biphasic mixture, wherein the mixture comprises: a) a remainder solid designated as solvent insoluble (SI) fraction comprising a first fraction of the lignin; and b) a liquid solution comprising the solvent and a second fraction of the lignin, wherein the second fraction is designated as solvent soluble (SS) lignin fraction; and (viii) spatially separating the (SI) lignin fraction from the (SS) lignin fraction; wherein the first fraction of lignin and second fraction of lignin have different glass transition temperatures. (i) removing hemicellulose sugars from a biomass, thereby obtaining a lignin-containing remainder, wherein the lignin-containing remainder comprises lignin and cellulose; (ii) contacting the lignin-containing remainder with a lignin extraction solution to produce a lignin extract and a cellulosic remainder; wherein the lignin extraction solution comprises a limited-solubility solvent, an organic acid, and water, wherein the limited-solubility solvent and water form an organic phase and an aqueous phase; and (iii) separating the lignin extract from the cellulosic remainder; wherein the lignin extract comprises lignin dissolved in the limited-solubility solvent; (iv) distilling or flash evaporating the lignin extract, thereby removing the bulk of the limited-solubility solvent from the lignin extract to obtain a solid lignin; (v) heating the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin; and (vi) applying a vacuum to the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin;. (vii) contacting a sample comprising the solid lignin with an organic solvent to form a resulting biphasic mixture, wherein the mixture comprises: a) a remainder solid designated as solvent insoluble (SI) fraction comprising a first fraction of the lignin; and b) a liquid solution comprising the solvent and a second fraction of the lignin, wherein the second fraction is designated as solvent soluble (SS) lignin fraction; and a) a remainder solid designated as solvent insoluble (SI) fraction comprising a first fraction of the lignin; and b) a liquid solution comprising the solvent and a second fraction of the lignin, wherein the second fraction is designated as solvent soluble (SS) lignin fraction; and (viii) spatially separating the (SI) lignin fraction from the (SS) lignin fraction; <EOS>