IN-SITU CELLULOSE FIBRES LOADING WITH CALCIUM CARBONATE PRECIPITATED BY DIFFERENT METHODS

In-situ loading of cellulose fibres is meant at maximizing filler retention, which is one of the most difficult problems in the production of printing papers with high filler content. Three methods for in-situ precipitation of calcium carbonate [CaCO3] into the lumen and in the wall of the cellulose fibres were investigated (IS-PCC): a) calcium hydroxide [Ca(OH)(2)] formation by the reaction of calcium chloride [CaCl2] and sodium hydroxide [NaOH] in a fibre suspension, followed by CaCO3 precipitation with carbon dioxide [CO2]-carbonation; b) CaCO3 precipitation by a double-exchange reaction between CaCl2 and sodium carbonate [Na2CO3] in a fibre suspension; c) CaCO3 precipitation through cellulose fibre saturation with a Ca(OH)(2) solution, followed by a carbonation reaction. The effectiveness of the in-situ precipitation methods was evaluated on pulp filter pads and paper handsheets, obtained on a standard lab former, by various analyses and investigations: calcium carbonate content, X-ray diffraction, SEM images, optical and mechanical properties of the paper sheets. The analyses proved that, whichever in-situ precipitation method was used, calcium carbonate precipitated both into the lumen and wall pores of fibres, particulates presenting a typical calcite diffraction pattern. However, significant differences were noticed among the in-situ precipitation methods concerning the yield of calcium carbonate precipitated into the fibre structure and particle sizes, and their distribution in the fibre wall and lumen, which influence the optical and mechanical properties of paper.