Enhanced Bleachability of Chemi-Thermomechanical Pulp by Hydrogen Peroxide Bleaching in Ethanol-Water Media

Abstract

Hydrogen peroxide (H₂O₂) bleaching in ethanol-water media was used to improve the bleaching efficiency of the chemi-thermomechanical pulp (CTMP). The brightness of CTMP increased and the yellowness decreased when the ethanol ratio was increased to 50%. However, when more than 50% ethanol was added, the brightness decreased, and the yellowness increased. In general, H₂O₂ bleaching in ethanol-water media, except for 100% ethanol, improved the optical properties of CTMP compared to conventional H₂O₂ bleaching. Moreover, the chemical composition of CTMP did not alter significantly. The best bleaching condition for CTMP was observed in 50% ethanol at a bleaching temperature and time of 80 °C and 120 min, respectively. The brightness of CTMP under this condition increased by approximately 22% compared with conventional H₂O₂ bleached CTMP. Principal component analysis (PCA) revealed that the optical properties of bleached CTMP were affected by the structural changes of the aromatic ring and carbonyl group in lignin and carbonyl group in hemicellulose. Consequently, the specific optimal ratio of ethanol that could improve the optical properties of CTMP was determined. The results can serve as a reference for fabricating improved CTMP for its practical application in high-grade papermaking.