Improved Strength of Peroxide-Bleached Deinked Pulp after TEMPO-Mediated Oxidation at Medium Consistency

Deinked pulp was pretreated using the 4-acetamido-2,2,6,6,- tetramethyl-pipelidine-1-oxyl radical (TEMPO)/NaBr/NaClO system and then bleached using hydrogen peroxide to achieve a medium pulp consistency. The effect of the amount of oxidant NaClO addition on the peroxide bleaching of deinked pulp was studied. The treated pulp was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The characterization of XRD and SEM showed that the treated pulp had a higher degree of crystallinity and more fibrillation than untreated pulp. Fiber quality analysis also revealed that the treated pulps had more fines and shorter fiber length than the untreated pulp. A handsheet test showed that the deinked pulps pretreated with the TEMPO system exhibited high tensile index values. The tensile index of the TEMPO pretreated pulp was 17% higher than that of the pulp bleached by hydrogen peroxide alone