Adsorption of Modified Starches on Pulp Fibers

The adsorption of amylose and amylopectin, the two components of starch, on pulp fibers was investigated. It was found that there is a preferential adsorption of amylose on fibers. Both cationic starch and hydroxyethyl ether starch show low-affinity Langmuir-type isotherms, but the adsorption capacity of hydroxyethyl ether starch on fibers as well as its affinity to fibers is much less than that of cationic starch. However, before reaching steady state, the cationic starch adsorption goes through a maximum, ascribed to a competition between adsorption and desorption of starch clusters and individual starch molecules. The steady-state cationic starch adsorption follows the expected trend when the electrolyte concentration is changed; that is, the adsorption first increases with the salt concentration and subsequently decreases. Adsorption of hydroxyethyl ether starch does not depend on electrolyte concentration, except for a small decrease at high ionic strength, ascribed to the shrinking of pores in the fiber wall.