Fiber properties of de-inked old newspaper pulp after bleaching with hydrogen peroxide

Abstract

Hydrogen peroxide was applied to bleach recycled de-inked pulp from old newspaper (ONP) in this study. Following single-stage bleaching, the fiber properties of the pulp (viz. brightness, yield, fiber length, fiber charge, and strength properties) were determined. Finally, the crystal structure of cellulose, fiber surface morphology, and functional groups of the control pulp and the bleached pulp using hydrogen peroxide were analyzed by XRD, SEM, and FT-IR, respectively. The single-stage peroxide bleaching applied to the de-inked ONP pulp could produce a high brightness pulp of 58% ISO at a yield of 92%. Fiber length decreased after bleaching treatment. The crystallinity index of cellulose of de-inked ONP pulp during bleaching or rinsing treatment increased due to the dissolution of cellulose in amorphous regions and/or the dissolution or loss of non-cellulosic constituents (hemicelluloses and lignin). Hydrogen peroxide bleaching resulted in fibrillation and longitudinal tearing of the fiber surface due to delignification, which led to an increase in the paper strength. FT-IR data showed that the content of carboxylic acid groups decreased during peroxide bleaching. The main chromophore (conjugated carbonyl groups) and the guaiacyl units of the pulp were damaged after bleaching resulting in delignification.