Optimizing Mixed Waste Paper Properties Through Formamidine Sulfinic Acid Bleaching and Cationic Additive Treatments

This study investigated the synergistic effects of formamidine sulfinic acid (FAS) bleaching and cationic additives on mixed waste paper (MWP) quality. MWP was chemically deinked and bleached with hydrogen peroxide (H₂O₂) or FAS at concentrations of 1–4%. Cationic starch and cationic polyacrylamide (CPAM) were applied as dry-strength additives at 1–3%. FAS bleaching at 4% dosage outperformed H₂O₂, improving brightness by 17% and reducing yellowness by 56%. CPAM showed superior performance in enhancing paper strength properties compared to cationic starch, with an optimal concentration of 2% for both additives. Surface charge analysis demonstrated effective fiber negative charge neutralization by both additives, with CPAM exhibiting higher efficiency. Field emission scanning electron microscopy (FESEM) confirmed significant improvements in fiber surface characteristics, particularly with 2% CPAM and 4% FAS combination. Water retention value decreased with additive application, potentially improving dewatering efficiency. Results indicate that combining FAS bleaching with optimized CPAM dosage can significantly enhance recycled paper quality, potentially narrowing the gap between recycled and virgin pulp properties.