The Effect Of Filler Physical-Chemical Properties On Retention Behavior

More than fourty kinds of fillers are collected in the study, including calcium carbonate, talc, clay and titanium dioxide. The filler physical-chemical properties such as: moisture, combustion loss, particle size distribution, particle shape, pH, conductivity, zeta potential, surface charge, oil absorption, settling rate etc were studied .The dynamic drainage device was used to study the effect of the mixing of pulp and filler, retention additives and filler and mixing ratio of different fillers on dynamic filler retention. It was found that the filler led a good retention by a higher temperature, longer mixing time of the filler and pulp. Results also show that filler species, average particle size, blend ratio of different kind of filler have different effect on filler retention. The different retention aids and shearing affect greatly on the filler retention too. Average particle size is the most important property which affect the filler retention rate without retention addtives. Filler particle size has great effect with filler retention. Mechanical entrapment is the main mechanism for filler retention without retention aids, but absorption is the main mechanism with the presence of retention aids. The retention aids have greater effects on the fine filler particle than the coarse particle. The type of filler is another important factor to affect the filler retention.The absorption ability of filler is also studied in this thesis, including the adsorption of fillers by pulp and the adsorption of starch by fillers. The adsorption of clay particles by the outer surfaces of pulp has been measured during the turbulent mixing of suspensions. A new dynamic drainage method is established to study the absorption characteristics of clay on fibers, including the fine content, shearing, mixing time, retention aids, furnish temperature and pH etc. Absorption is one of the most important mechanisms on filler retention; the specific surface area of the fiber has great effect on the filler absorption rate on the fiber; the retention additives usage and their adding order have obvious effect on it. In addition, the temperature and stirring speed were closely related to the absorption.The absorption properties of cationic starch and native starch by filler and pulp are studied. Results show that, for the same type of filler, the specific surface area is increased with the descreasing of the particle size. Surface charge affect the adsorption of cationic starch by filler. Cationic starch absorption by pulp is greater than the absorption by filler. The absorption of cationic starch is stronger than that of native starch by kaolin and titanium dioxide, but the absorption of native starch on talc and calcium carbonate is larger than that of cationic starch.The Al₂O₃ coated GCC were prepared in this study. The modified GCC has higher retention than the unmodified filler, thus saved retention aids.