Modification Of Ground Calcium Carbonate And Its Application In Papermaking

Filler applications in paper can significantly reduce paper costs, improve paperoptical properties and reduce energy consumption. Filler can also be used as functionaladditives for the production of functional paper. Therefore, filler has importantapplication value. In paper filler applications, there exist problems, such as damagingthe strength properties of paper due to interfering with the formation of hydrogenbonding among fibers, reducing filler retention with the increase in the amount of addedfiller, causing sizing obstacles, limiting the optical performance of filler and sometimesincreasing the abrasion of paper machine. The study on paper filler focused on theapplication problems has important practical significance. In this paper, ground calciumcarbonate (GCC) was modified with starch/alkyl ketene dimer in order to improve theperformance of filler when added on paper, thus reducing the adverse effects of fillerson the strength properties, sizing development of paper.The surface modification of filler with AKD/starch are basically composed of thefollowing four aspects:(1) the surface modification of calcium carbonate with AKD,(2)the modification of AKD coated GCC with starch,(3) combination of unmodifiedground calcium carbonate with AKD coated filler according to the different mixing ratioto investigate the influences of modified to unmodified filler ratio on the strength andwater-resistance properties of paper, such as sizing degree and contact angle,(4)combination of gelled starch with unmodified ground calcium carbonate as well asAKD coated filler according to the different mixing ratio to investigate the influences ofstarch addition on paper properties.Results show that the papers filled with modified GCC have improved tensilestrength, bursting strength and sizing degree compared with that filled with theunmodified GCC. The higher the added amount of modified GCC, the higher theimprovement on paper strength and water resistance. However, the contact angle ofpaper is not proportional to the ratio of modified GCC. Higher contact angles areobtained at40%and100%of charge ratio of modified fillers. For paper filled withcationic starch modified GCC, the tensile strength is improved while the brightness islowered with increasing the content of the cationic starch while higher added with theincrease of the cationic starch content. Adding starch modified GCC instead ofunmodified GCC enhances filler retention. Modified starch is better than unmodifiedstarch in coating fillers. The paper filled with modified starch coated filler has higher tensile strength, the larger contact angle and sizing degree than the paper filled withconventional starch coated filler.