Volume 2, Issue 9 (October 2005)
Characterization of Sulfonated Lignin Dispersants by Hydrophobic Interactive Chromatography
Organic surfactants can be produced by sulfonation of lignin that naturally occurs in the structural tissue of plants. These sulfonated lignins often exist as a heterogeneous mixture that is difficult to analyze by conventional means. It is believed that molecular weight and degree of sulfonation impact the hydrophobic balance and subsequent performance of lignin dispersants, but analytical measurements of these properties typically report an average value and give little or no detail about heterogeneity. Each component of this mixture will impart a unique quality to the dispersant and its subsequent effect in the formulation. Hydrophobic Interactive Chromatography (HIC) is useful in separating and characterizing various components of lignin dispersants based on hydrophobic response. For example, Borresperse NA (BNA-6.0) has a high percentage of hydrophilic material that elutes quickly from the column. In contrast, Lignosperse AGO-300 (OXY-2.6) elutes much later and has a strong hydrophobic peak. Both have overlapping middle peaks. These two dispersants are completely water soluble, although their dissolution rates differ. However, significant portions of OXY-2.6 are not soluble in 32-0-0 liquid fertilizer. The fractional percentage of dispersant that remains insoluble in 32-0-0 is predicted by HIC.