Surface Modification Of Precipitated Calcium Carbonate And Its Application In Paper-making Process

Substituting part of virgin fibers in paper stock with mineral filler has been practiced in paper-making industry for many years. However, the increase of the filler content in papers has been determined by the process cost, optical properties, formation,printability. Increasing the filler content decreases the fiber-filler and filler-fiber bonding and reduces the paper's strength, bulk and stiffness, abrasion and dusting during paper making. The surface modification of calcium carbonate of an available approach to improve the strength of the filled paper. Recent years, many related work have been carried out.To maximize the efficiency and reduce the papermaking problems using filler in papermaking conditions,many approaches have been reported for modified calcium carbonate including different pulp and filler combinations, preflocculation of the filler, incorporation of starch in the sheet, lumen loading. Unfortunately, none of these technologies has delivered a practical solution in paper mills. In this research, modified calcium carbonate using fatty acid or fatty acid salt/starch is to increase filler-fiber bonding, to improve the filler retention and the paper strength.In the first stage of this study, modification of calcium carbonate using fatty acid or fatty acid salt/starch was investigated. Firstly, according to the breaking length, burst and tearing index, we can determine the optimum modifier agent. Then orthogonal experiments were conducted to determine the effects, including starch dosage, sodium oleate dosage, starch gelatinization temperature, gelatinization time and the time at max temp on filler modification. Secondly, we characterized the modified product by Zeta potential and conductivity. At last, the topography of calcium carbonate was analyzed by optical and scanning electron microscopy (SEM). The results show that stearic acid/starch is the best agents for modified precipitated calcium carbonate (PCC), but sodium oleate/starch is fit for modified ground calcium carbonate. After modified, Zeta potential and electrical conductivity of the filler changed obviously. Using optical and scanning electron microscopy (SEM), it is found that the dispersion performance of modified calcium carbonate is better, and no aggregation occurred obviously.In the second part of experiment, we used dynamic drainage jar and turbid meter for the retention of filler and investigated the effete of modified filler on physical and optical properties. At last, the topography of calcium carbonate was analyzed by optical and scanning electron microscopy (SEM). In the study, we knew that the single pass retention of modified filler was higher than the unmodified, and the SEM photographs of handsheet also show the conclusion is right. The physical properties of filled handsheets were improved clearly. In addition, compared with the unmodified, the brightness and opacity of handsheets decreased, but the adsorption of modified filler on fibers was efficient and enhance fiber- fiber bonding, also indicating superior retention property.