Characterization and properties of lignocellulosic fibers with thin-film deposited cationic precursor

Abstract

Cationic pulp has been prepared by depositing ultra-thin films of a cationic silane precursor on the pulp surface. The deposited thin film has been characterized by relative measurement of film thickness and also by determining the charge behavior of the modified fiber surface in an aqueous suspension by streaming current, ionic mobility and charge density measurements. Although the calculated film thickness was found to be less than 30 Å, a significant difference in the calculated thickness values between X-ray photoelectron spectroscopy and ellipsometry was observed. Streaming current measurements confirmed that the cationic charge carrying capacity of cellulosic fibers depends on the hydrophobicity of the fibers. The charge density of the cationic fibers was found to be lower than conventional polyelectrolytes that are used as flocculants in wet-end papermaking. Effect of pH on the ionic mobility of the precursor deposited fibers demonstrated the more pH tolerant character of the cationic fibers compared to the unmodified fibers. Effect of precursor concentration on cationic charge behavior of cellulose, stoned ground wood and thermomechanical pulp demonstrated that, for most of the cation modified fibers, there was a marginal increase in charge with higher precursor concentration. Temperature and pH have little effect on charge properties. A partial replacement of anionic fiber by silane deposited cationic fiber in a fiber slurry improved fines and filler retention properties. Microscopic analyses of floc structure suggested that the improved retention properties exhibited by the cationic fibers could be due to the formation of smaller but stronger flocs at higher shear rates.