Wet-end interaction of celluloseaffinity molecules as retention promoter

Wet-end application of direct dye and cello-oligo-saccharide with a high affinity for cellulosic substrate was investigated with regard to retention behavior of polymer additives under various wet-end conditions. Either Direct Red 28 (DR28) or cellobiosylamine (CB) was covalently introduced into anionic polyacrylamide (A-PAM); called DR-A-PAM or CB-A-PAM, respectively. The DR-A-PAM added to paper furnish exhibited a high retention efficiency, resulting in the physical enhancement of paper sheets. Anionic trash showed nearly no interference with the DR-A-PAM functions, although Ca²⁺ ions remarkably reduced the additive retention. The CB-A-PAM also performed well both for its retention and the paper strength in a clean wet-end system. Surface plasmon resonance analysis provided useful information for cellulose-anchoring ability of DR28 and CB moieties. The DR28 was irreversibly adsorbed onto cellulosic substrate. On the other hand, cellobiose and A-PAM had no specific interaction with cellulose, although the CB-A-PAM was tightly adsorbed on the cellulose surface. It was presumed that multiple numbers of β-1, 4-glucan units in one CB-A-PAM molecule synergistically enhanced the affinity for cellulose. These cellulose anchors would perform as a retention promoter based on the novel wet-end interaction.