KINETICS OF COLLOIDAL PARTICLE DEPOSITION ON PULP FIBERS .2. DEPOSITION OF CLAY ON FIBERS IN THE PRESENCE OF POLY(ETHYLENIMINE)

The rate of deposition of clay particles on fibers dispersed in water was determined as a function of the amount and the sequence of poly(ethylenimine) addition. The polymer was introduced either to a mixture of fibers and clay or to only one of the components prior to addition of the second one. The primary role of the positively charged polymer was to adsorb onto the negatively charged components, thus modifying their surfaces and consequently promoting their interaction. It has been established that the extent and rate of particle deposition result from an interplay of several kinetic factors, namely the rate of polymer adsorption on fibers and on clay, the rate of collision between clay particles and fibers, and the rate of clay particle aggregation. Under the conditions of low shear rate, the polymer adsorption on fibers is a rather slow process and is comparable to the rate of deposition of dispersed clay particles on fibers. In contrast, polymer adsorption on clay particles proceeds at a faster rate, causing aggregation of the particles. The deposition of aggregates is considerably faster than that of dispersed clay particles.