Properties and Characterization of Porous Material Prepared by Hydrothermal Treatment of Kaolin
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uniformity of appearance and printability [3,5]. As a filler, kaolin is used to extend fiber and improve opacity, brightness and other desirable characteristics [1,6]. Opacity is one of the most important optical properties and stems from the light scattering ability of the pigment. Both refractive index (pigment-air interface) and particle size contribute to light scattering. Although the existing kaolin pigments offer good opacity, development of highly opacifying and bulking pigments is important from the stand point of producing lighter weight coated paper. Attempts have been made to aggregate kaolin particles and create voids to increase light scattering. Various reagents, such as, Na-silicate [7,8], organosilicate compounds [9], Na-aluminate [7,10], polyacrylic acid [11] and quaternary ammonium and diallylammonium polymer salts [12,13] have been used for aggregation. Shi et al. [14] have shown that the hydrothermal digestion of kaolin slurry in NaOH and/or KOH also aggregates the kaolin particles via surface modification and obviates the need for adding the direct crosslinking agents. The objective of this work was to characterize the properties of the chemically aggregated materials prepared by hydrothermal treatment of kaolin in the presence of various concentrations of NaOH and KOH. EXPERIMENTAL Feed Material The kaolinite used in this study was Kaofine 90, a fine (98%
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