Calcium carbonate deposition on cellulose

Cellulose powder was found to be a substrate favoring the deposition of calcite crystals from stable supersaturated solutions at pH 8.50 and at 25 degrees C, Kinetic analysis of the initial rates showed that they were proportional with the relative supersaturation with respect to calcite. Analysis of the dependence of the induction periods on the initial solution conditions showed that the number of ions forming the critical nucleus was 5. The second-order dependence of the rate of precipitation of calcite on cellulose on the solution supersaturation suggested a surface controlled mechanism. The surface energy of the calcite nuclei growing on cellulose was calculated to be 46 mJ m(-2) from the dependence of the induction time on the solution supersaturation, The overgrowth of calcite on cellulose was done selectively on the macromolecules possibly through active sites formation at ionizable functional groups (-OH), The nucleating capability of cellulose was found to be comparable with that of sulfonated polystyrene and significantly lower in comparison with sulfonated polystyrene divinyl benzene copolymer on which vaterite was formed. This fact together with the selective growth of the most stable calcite suggested that stereochemical factors are very important in determining both the kinetics and the nature of the polymorph formed. (C) 2000 Academic Press.