Effect of pH on the aggregation stability of microcrystalline cellulose dispersions in aqueous 0.1 m NaCl solutions

Effect of pH on the coagulation kinetics of microcrystalline cellulose dispersions in an aqueous 0.1 M NaCl solution is studied by the flow ultramicroscopy. The lowest coagulation rate is observed at pH 4.9. A decrease or an increase in pH gives rise to the coagulation rate approaching the rate of fast coagulation (according to Smoluchowski) at pH 1.0. Results of calculating the particle pair interaction energy in terms of the DLVO theory with allowance for only the molecular and ion electrostatic components suggest the dominance of attraction forces at any interparticle distances and cannot explain the data of experimental methods. The allowance for the structural component, which arises upon the overlap of water boundary layers surrounding hydrophilic particles of microcrystalline cellulose, makes it possible to treat the experimental results and estimate possible values of the K and I parameters of the equation for the structural component.