STABILITY OF GROUND AND PRECIPITATED CACO3 SUSPENSIONS IN THE PRESENCE OF POLYETHYLENE OXIDE AND KRAFT LIGNIN

The behavior of two commercial types of ground and precipitated CaCO3 pigments differ because of different surface characteristics. Ground C aCO3 is treated with a dispersant and, in the absence of salt, it form s a stable suspension because of electrical double layer repulsion. It s stability and surface charge are not affected by polyethylene oxide or sulfonated kraft lignin, added separately or in combination. Destab ilization takes place in the presence of a sufficient amount of salt o wing to the compression of double layers. However in a narrow region o f salt concentration the polyethylene oxide improves stability by an e lectrosterical effect. In contrast; precipitated CaCO3 aggregates at f ast rates, even in the absence of salt, because of insufficient double layer repulsion. Its behavior is not affected by polyethylene oxide a ddition, but the presence of kraft lignin results in stabilizing the s uspension by adsorbing on CaCO3 particles, thus increasing the negativ e surface charge and, consequently, the electrostatic repulsion. (C) 1 998 Elsevier Science B.V.