A method for producing functionalized lignin, wherein: the functionalized lignin comprises: an acyl content of about 1 to about 45 per 100 Ar; an ethoxyl content of about 1 to about 45 per 100 Ar; and at least one of: 1) a phenolic OH content of less than about 70; and 2) a β-O-4 content of at least about 10; the method comprising: providing a residue comprising lignin and cellulose; subjecting the residue to a liquid comprising an organic compound, thereby forming a first mixture; wherein the subjecting is performed at a first temperature of about 100 °C or less and for a time of less than about 225 minutes; wherein the first mixture comprises: a first liquid fraction comprising solubilized functionalized lignin functionalized with the organic compound; and a first solid fraction comprising cellulose; and wherein the residue is obtained by a process comprising: extracting a least a portion of hemicellulose from a lignocellulosic biomass using a first fluid comprising water, thereby forming a second mixture comprising: a second liquid fraction comprising hemicellulose; and a second solid fraction comprising treated lignocellulosic biomass; wherein the first fluid has a second temperature of at least about 110°C and a second pressure of at least 10 bar; exposing the treated lignocellulosic biomass to a second fluid comprising water, thereby forming a third mixture comprising: a third liquid fraction; and a third solid fraction comprising the residue; wherein the second fluid has a third temperature of at least about 350°C and a third pressure of at least about 180 bar. the functionalized lignin comprises: an acyl content of about 1 to about 45 per 100 Ar; an ethoxyl content of about 1 to about 45 per 100 Ar; and at least one of: 1) a phenolic OH content of less than about 70; and 2) a β-O-4 content of at least about 10; the method comprising: providing a residue comprising lignin and cellulose; subjecting the residue to a liquid comprising an organic compound, thereby forming a first mixture; wherein the subjecting is performed at a first temperature of about 100 °C or less and for a time of less than about 225 minutes; wherein the first mixture comprises: a first liquid fraction comprising solubilized functionalized lignin functionalized with the organic compound; and a first solid fraction comprising cellulose; and wherein the residue is obtained by a process comprising: extracting a least a portion of hemicellulose from a lignocellulosic biomass using a first fluid comprising water, thereby forming a second mixture comprising: a second liquid fraction comprising hemicellulose; and a second solid fraction comprising treated lignocellulosic biomass; wherein the first fluid has a second temperature of at least about 110°C and a second pressure of at least 10 bar; exposing the treated lignocellulosic biomass to a second fluid comprising water, thereby forming a third mixture comprising: a third liquid fraction; and a third solid fraction comprising the residue; wherein the second fluid has a third temperature of at least about 350°C and a third pressure of at least about 180 bar. providing a residue comprising lignin and cellulose; subjecting the residue to a liquid comprising an organic compound, thereby forming a first mixture; wherein the subjecting is performed at a first temperature of about 100 °C or less and for a time of less than about 225 minutes; wherein the first mixture comprises: a first liquid fraction comprising solubilized functionalized lignin functionalized with the organic compound; and a first solid fraction comprising cellulose; and a first liquid fraction comprising solubilized functionalized lignin functionalized with the organic compound; and a first solid fraction comprising cellulose; and wherein the residue is obtained by a process comprising: extracting a least a portion of hemicellulose from a lignocellulosic biomass using a first fluid comprising water, thereby forming a second mixture comprising: a second liquid fraction comprising hemicellulose; and a second solid fraction comprising treated lignocellulosic biomass; wherein the first fluid has a second temperature of at least about 110°C and a second pressure of at least 10 bar; exposing the treated lignocellulosic biomass to a second fluid comprising water, thereby forming a third mixture comprising: a third liquid fraction; and a third solid fraction comprising the residue; wherein the second fluid has a third temperature of at least about 350°C and a third pressure of at least about 180 bar. a second liquid fraction comprising hemicellulose; and a second solid fraction comprising treated lignocellulosic biomass; wherein the first fluid has a second temperature of at least about 110°C and a second pressure of at least 10 bar; exposing the treated lignocellulosic biomass to a second fluid comprising water, thereby forming a third mixture comprising: a third liquid fraction; and a third solid fraction comprising the residue; wherein the second fluid has a third temperature of at least about 350°C and a third pressure of at least about 180 bar. a third liquid fraction; and a third solid fraction comprising the residue; wherein the second fluid has a third temperature of at least about 350°C and a third pressure of at least about 180 bar.