Abstract
A protocol for the fractionation of lignin with 1-butanol as solvent has been proposed in order to improve the utilization of industry alkali lignin. 1-butanol soluble lignin (BSL) was used as a building block for temperature-sensitive hydrogel with N-isopropylacrylamide (NIPAAm) through graft polymerization. The result shows that 1-butanol fractionation is an effective method to improve the molecular weight homogeneity of lignin (PDI, 2.5 to 1.83) and increase the hydroxyl group content (0.585–1.793 mmol/g). The incorporation of BSL into the temperature-sensitive hydrogel can enhance the thermal stability and increase the hydrophobicity of the gel, which leads to a decrease in lower critical solution temperature (LCST). In addition, the compression strength, swelling ratio, and pore size of the gel can be adjusted by the dosage of lignin. This stimuli-responsive gel, with an LCST around 32 °C, is expected to be applied in the agricultural field as a pesticide carrier by stimulating release and absorption properties based on the change in natural environmental temperature.
Highlights
Lignin, the second most abundant natural terrestrial polymer on earth after cellulose, is considered the most promising raw material to replace petrochemical-based feedstock in light of its antioxidant and antimicrobial properties and its high carbon content [1,2,3]
1-butanol (δ = 11.3, ∂d = 16, ∂p = 5.7, ∂h = 15.8), containing an alkane chain that consists of four carbon atoms and a polar hydroxyl group, is used as a solvent
Lignin monomer contains an alkane side chain with three carbon atoms and a hydroxyl group [2], which is similar to the chemical structure of 1-butanol
Summary
The second most abundant natural terrestrial polymer on earth after cellulose, is considered the most promising raw material to replace petrochemical-based feedstock in light of its antioxidant and antimicrobial properties and its high carbon content [1,2,3]. Most lignins are burned as a cheap source of energy to meet domestic energy consumption, and only a small amount of industrial lignins have been used to develop high-valued products, due to their intrinsic structural heterogeneity, poor solubility in common solvents, and wide distribution of molecular weights. The heterogeneity of lignins has become more severe in chemical pulping processes due to the incomplete impregnation of the chemicals in feedstock, which poses a challenge for applications where a constant molecular size is required [6,7,8] To circumvent this problem, solvent fractionation was proposed by scientific researchers based on partial solubility of polymers into solvents. The water absorption, thermal property, interior morphology, and the mechanical properties of the obtained gel were investigated in detail
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