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Summary:
Lumen loading is a method that retains colloidal pigments into the porous structure of cellulosic fibers. It has been reported that lumen loading can provide better paper properties compared with loading by direct addition of pigments into the papermaking furnish. The paper properties, including optical, physical, surface and structural, can in turn affect the paper printability. The objectives of this research are: to load calcium carbonate pigments into the fiber pores as much as possible, to compare the lumen loading results from a mechanical method and a chemical method, and to evaluate the properties of the handsheets made from lumen loaded fibers. Calcium carbonate pigments are studied because of the current interest in the acid-to-alkaline conversion of the papermaking chemistry. Experimental results indicate that the greatest lumen loading levels are 10.8% by the mechanical method and 13.0% by the chemical method. Lumen loading with the mechanical method are mainly affected by mixing speed, mixing time, and the particle size of calcium carbonate. However, lumen loading with the chemical method are primarily controlled by the dosage level of the precipitating chemicals, sodium carbonate and calcium hydroxide, and the molar ratio of the two chemicals. Compared with the direct addition handsheets at equivalent loading levels, the lumen loaded handsheets have significantly higher brightness, opacity, and tear resistance. However, the lumen loaded handsheets reveal lower smoothness, gloss, and bursting strength.