Boosting the cationization of bamboo pulp fines via ultrasonic-alkaline pretreatment

Cationic etherification is valuable for imparting advanced functionality to lignocellulosic fibers, but its practical application is constrained by high reagent demand and a low reaction efficiency. This study developed an ultrasonic-alkaline synergistic pretreatment to enhance the cationic etherification of the fine fraction from bamboo chemi-mechanical pulp (BMP). To elucidate its underlying mechanism, this study employed ultrasonic pretreatment and NaOH pretreatment in two separate processes to generate control groups. Cationic etherification modification of fines was conducted with the gradient dosages of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC), and the superiority of synergistic pretreatment was verified comparatively. Furthermore, the mechanism of the ultrasonic-alkaline pretreatment was elucidated by systematically tuning parameters (ultrasonic duration, ultrasonic power, and aqueous sodium hydroxide concentration) and examining how these variables influence the fine fraction. The results show that this pretreatment significantly improved the degree of substitution (DS) to a maximum of 41%. This enhancement is attributed to the cleavage of the ester bonds in hemicellulose and lignin, promoting their removal and disrupting the crystalline regions of cellulose. Collectively, these changes markedly increase the exposure of active hydroxyl groups, which in turn promotes the etherification reaction significantly. These findings indicate that ultrasonic-alkaline pretreatment offers an efficient and green strategy for boosting the cationic modification efficiency of lignocellulosic materials. Consequently, the cationized fines at 6% addition improved the paper strength of bamboo and wood pulps by over 20%.