Spectrophotometric and flow ultramicroscopic study of the aggregation and sedimentation stability of aqueous dispersions of sulfate lignin in a pH range of 12.0–2.3

Abstract

The aggregation and sedimentation stability of low-concentrated (10 mg/l) aqueous dispersions of sulfate lignin are studied by the spectrophotometry and flow ultramicroscopy methods in a wide pH range (12.0–2.3). Initial solution of sulfate lignin (pH 12.0) is shown to be a polydisperse system stable with respect to aggregation and sedimentation. As pH decreases up to 3.2, the sedimentation stability is retained, whereas a loss of aggregation stability resulting in an enlargement of initial fine particles invisible with a flow ultramicroscope and their transition into the visible size range are observed even at pH 11.0. In the course of time, the formed visible particles aggregate with a concomitant decrease in their total concentration. This process is even more pronounced at pH 10.0. At pH 2.3, the system loses its sedimentation and aggregation stability, and the visible particle concentration increases by tens of times compared to pH 12.0 then, the particles aggregate that results in a decrease in the total particle concentration. At any pH value, the systems studied are polydisperse that is most pronounced at pH 2.3.