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Precipitated calcium carbonate (PCC) is a filler that is widely used for papermaking, and lime sludge is a special type of PCC recovered from the black liquor from kraft pulping. There has been some concern that lime sludge may interfere with the development of paper's hydrophobicity in comparison with commercial PCC and ground calcium carbonate (GCC) due to the presence of impurities when alkyl ketene dimer (AKD) is used as the sizing additive. In this work, fillers with different particle size distributions were prepared, and the effects of particle composition on surface chemistry of fillers, adsorption for AKD, sizing degree of final paper sheets, and retention behavior of fillers were evaluated. The results showed that, through matching different particle size distributions for lime sludge fillers, the negative zeta potential decreased from -26.2 mV to -20.8 mV, the specific surface area decreased from 15.0 m²/g to 9.1 m²/g, and total pore volume decreased from 0.037 cm³/g to 0.026 cm³/g, which was favorable for the low adsorption for AKD. Consequently the sizing effect of filled paper was improved. Moreover, the retention rate also was increased by changing the particle size distribution of lime sludge. [ABSTRACT FROM AUTHOR]

The penetration of ink into paper affects the final appearance of printing and the amount of ink usage. In this work, UV-curing fluorescent rose ink was used to investigate the penetration and distribution of the ink pigments as well as their correlation with the surface topography of paper. The ink penetration and distribution were characterized with Confocal Laser Scanning Microscopy (CLSM), whereas the microstructure of the paper surface was observed using Atomic Force Microscopy (AFM). The AFM results showed that the surface of the paper coated with kaolin layer was the smoothest among the samples. Also the pore size of the calcium carbonate coating layer was smaller than that of the kaolin coating layer. Meanwhile, the pore size distribution of the calcium carbonate coating layer appeared to be relatively narrow, compared with other samples. The results of CLSM images indicated that the depth, size, and arrangement of pores affected the penetration depth and distribution of ink pigment on coated paper. The large pores led to deeper penetration of ink pigments, and uniform ink absorption occurred when the pore distribution was uniform. The UV-curing ink pigments not only set on the surface of the uncoated paper, but also they penetrated into the paper interior and adhered to the fiber surface. [ABSTRACT FROM AUTHOR]