Cationic Starches of High Degree of Functionalization: 12. Modification of Cellulose Fibers toward High Filler Technology in Papermaking

Modification of cellulose fibers via adsorption of highly functionalized 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch) with a degree of substitution (DS) in the range from 0.25 to 1.54 was investigated by electrokinetic measurements and filler retention tests. It was found that the amount of cationic HPMA starch adsorbed at the isotherm plateaus depends on two parameters: the DS of the starch derivative and, more remarkably, the amylose/amylopectin ratio. All studied HPMA starches allow significant improvement of kaolin particle retention in comparison to untreated fibers and fibers modified with low-substituted commercial starch. We suggest that, because of the local overcharging of the cellulose surface through the adsorption of starch macromolecules, the filler retention capacity is enhanced even at low and moderate degrees of coverage when the surface has a net-negative charge. Taking into account the efficiency and cost of starch cationization, the optimum DS of the HPMA starch for cellulose modification in papermaking was found to be in the range 0.6-0.7, where a degree of filler loading of 500 mg/g can be reached at a level of HPMA starch addition of 0.5-0.6%.