Effect of polyethylene oxide and kraft lignin on the stability of clay and its deposition on fibers

The mechanism by which PEO (polyethylene oxide) operates in the retention of clay was investigated. Two potential mechanisms were considered : (a) flocculation of suspended clay particles, with the resultant flocs captured in the forming web of fibers ; and (b) direct deposition of clay particles on fibers. Neither PEO alone nor in combination with a cofactor (sulfonated kraft lignin, SKL) flocculated clay in the absence of salt (CaCl 2 ). Indeed, the cofactor SKL acted as a dispersant, stabilizing the clay suspension. Thus floc capture is an unlikely mechanism for clay retention. However, when PEO alone was added to mixtures of fiber and clay, deposition of clay onto fibers was observed. This action was enhanced by the presence of SKL Asymmetric polymer briding is proposed as the mechanism for deposition and retention of clay on fibers. The bridge, however, is transient without the presence of a cofactor, implying that the cofactor strengthens the polymer bridge. Application : this paper describes the mechanism of polyethylene oxide-assisted retention of clay.