Butyric anhydride modified lignin and its oil-water interfacial properties

•Lignin-based surfactant was prepared through chemical modification.•The bio-based surfactant proved to be good emulsifier for water-in-oil emulsion.•Chemicals were used to modify lignin and reaction degree was determined by 31P NMR.•Emulsion stability was investigated by sedimentation experiments.

A bio-based surfactant was prepared by chemical modification of kraft lignin. Herein, grafting of butyric anhydride (BA), 3-(trimethoxysilyl)propyl methacrylate (MPS) and 2-bromoisobutyryl bromide (BIBB) onto kraft lignin were conducted to change its amphiphilicity and the chemical reactions were confirmed by FTIR, 1H NMR, GPC, TGA and 31P NMR. The lignin modified with MPS and BIBB was only partially dissolved in organic monomers due to the low grafting ratio. In contrast, over 95% of the hydroxyl group conversion was achieved when BA was used. The BA modified lignin (lignin-B) was found to be completely soluble in the monomers. The interfacial tension measurement indicated the capability of lignin-B to decrease the interface energy between water and styrene from 35 J m−2 to 15 J m−2. As the result, a stable water-in-oil emulsion was achieved using lignin-B as the emulsifier. The average diameters of emulsion droplets were 499.4 nm and 363.9 nm with a lignin-B content of 0.5 wt% and 5 wt% respectively. Due to both steric and electrokinetic effects, the as-prepared water-in-oil emulsion was kept stable over 30 days. These results suggest that lignin-B has a promising potential to be used as a bio-based surfactant.

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