Ultrasonic-assisted ionic liquid treatment of chemithermomechanical pulp fibers

Enhancing the swelling of chemithermomechanical pulp is essential for improving its physical properties and thus broadening its end-use applications. In this work, ionic liquid (IL) using 1-allyl-3-metheylimidazolium chloride ([Amim]Cl) was used for reducing hydrogen bonding within the fiber wall, and ultrasonic treatment was used for improving the performance of IL treatment. Mixing IL with pulp fibers at 5 ml/g concentration decreased the Canadian standard freeness (CSF) of pulp from 760 to 570 ml at room temperature, and the pretreatment with ultrasonic treatment for 20 min reduced its CSF to 545 ml. The ultrasonic-assisted IL treatment improved the tensile, tear and burst indices as well as the folding endurance of the cellulosic network by 41, 36, 12 and 150%, respectively. The surface charge density and area of fibers were improved, but the lignin and hemicellulose contents of the fibers were reduced via ultrasonic-assisted IL treatment.