No abstract

Direct dye with a high affinity for cellulose substrate was utilized as a cellulose anchor to promote retention of paper strengthening additives under various conditions associated with the wet end of a paper machine. Direct Red 28 (DR) was covalently linked to anionic polyacrylamide (A-PAM) via a condensation reaction using water-soluble carbodiimide. The DR-conjugated A-PAM (DR-A-PAM) demonstrated good retention efficiency, resulting in strength enhancement of handsheets. Anionic trash showed no interference with the performance of DR-A-PAM in the wet end, while the additive performance was sensitive to calcium ions. Surface plasmon resonance analysis gave useful information on the cellulose-anchoring ability of DR-A-PAM. Dye molecules were irreversibly adsorbed onto the cellulose substrate under aqueous conditions, while A-PAM possessed no significant affinity for cellulose. These results suggest that anionic DR moieties in DR-A-PAM molecules served as a cellulose-anchor, possibly due to multiple CH-π interaction between hydrophobic face of cellulose substrate and π-conjugated system of dye molecules. Such a unique interaction of direct dye and cellulose provides a new insight into the wet end system, and does not depend on conventional electrostatic attraction.

Cellobiose-pendant polymers were synthesized by radical polymerization and their affinity for a cellulose matrix was investigated by quartz crystal microbalance (QCM). A 2-(methacryloyloxy)ethylureido cellobiose (MOU-Cel) macromer was synthesized by coupling cellobiosylamine with 2-(methacryloyloxy)ethyl isocyanate followed by polymerization in an aqueous radical reaction system. The interaction of the resulting poly(MOU-Cel) with a pure cellulose matrix in water was evaluated by QCM analysis. Poly(MOU-Cel) was strongly adsorbed to the cellulose substrate, whereas neither cellobiose nor MOU-Cel macromer exhibited an attractive interaction with cellulose. This specific interaction was not inhibited by the presence of ionic contaminants, suggesting that multiple cellobiopyranose moieties in each polymer molecule might cooperatively enhance its affinity for cellulose. Moderate insertion of acrylamide units into the polymer backbone improved the affinity for cellulose, possibly due to an increased mobility of sugar side chains. Polymers such as these, with a high affinity for cellulose, have potential applications for the surface functionalization of cellulose-based materials, including paper products.