Adding Value to Lignin by Oxidation in Supercritical Carbon Dioxide

BODY: The properties of lignins as emulsification agents in systems composed of water and oil are presented. Laboratory and industrial Kraft lignins were characterized in terms of surface activity and phase behavior in equilibrated Lignin−Oil−Water systems. Lignin−based emulsions were obtained for oil fractions of different Equivalent Alkane Carbon Number. The properties of emulsions obtained after changing systematically their formulation and composition was investigated in terms of emulsion drop size, viscosity and stability. The type of oil as well as the nature of the aqueous phase (salinity and pH) has a marked effect on the effectiveness of lignin to stabilize the respective emulsion. The experimental results were organized in two−dimensional maps of the type Formulation−water fraction which clearly demonstrate that lignin emulsions behave according to the behavior anticipated for conventional surfactants. Lignin−based emulsifiers were able to form highly−stable macro emulsions with up to 80% oil and relatively small drop size (1−10 microns). Finally, the possibility for an extensive use of lignins as alternative to expensive synthetic surfactants is discussed.