(91c) Chemically Modified Lignin Surfactant: Synthesis, Characterization and Their O/W Interfacial Properties
Lignin-based surfactant was prepared through chemical modification. This bio-based surfactant demonstrated to be a good emulsifier for W/O emulsion. Herein, grafting of butyric anhydride (BA), 3-(trimethoxysilyl)propyl methacrylate (MPS) and 2-bromoisobutyryl bromide (BIBB) onto kraft lignin to change its amphiphilicity was conducted. The chemical reactions were confirmed by FTIR, 1H NMR, GPC, TGA analysis, and 31P NMR. Lignin modified with MPS and BIBB could only dissolve partially in organic monomer due to the low grafting ratio. In contrast, over 95% of the hydroxyl group conversion was achieved when butyric anhydride was used. The butyric anhydride modified lignin resultant (lignin-B) was found to be completely soluble in oil monomers. According to the interfacial tension measurement, lignin-B was able to decrease the interface energy between water and styrene from 35 J·m-2 to 15 J·m-2. As expected, stable water-in-oil emulsion was prepared with lignin-B as 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. No separated aqueous phase was observed for 30 days. These results suggest lignin-B has promising potential to be used as a bio-based surfactant or emulsifier.