Application of Photo, Peracetic Acid, and Combination Pre-treatments in Improving Totally Chlorine-Free Bleaching Selectivity

Abstract

The application of totally chlorine-free bleaching (TCF) is well recognised for its environmental compatibility. However, its application is restricted in comparison to a chlorine-based bleaching sequence. TCF bleaching produces pulp with relatively lower brightness and strength properties. Oxygen delignification (O-stage) is commonly used as a first bleaching stage; therefore its selectivity influences TCF bleaching performance. In this study, the selectivity of the O-stage and hydrogen peroxidereinforced O-stage (Op-stage) on tropical hardwood kraft pulp were 0.53 and 0.71, with 37.8% and 55.5% kappa number (Kn) reductions, respectively. The addition of photo pre-treatment prior to the O-stage and Op-stage improved the Kn reduction to 53.7% and 59.2%; consequently the selectivity was enhanced to 1.0 and 0.73, respectively. The Fourier transform infrared spectra showed that photo pre-treatments improved the selectivity by protecting the cellulose from carbonyl-induced degradation. This protective effect was more prominent in the O-stage than the Op-stage. However, the combination of peracetic acid and photo treatment did not further increase bleaching selectivity in either stage. In short, blue light and UV irradiation treatment with or without the prior addition of peracetic acid to ordinary or hydrogen peroxidereinforced oxygen delignified pulp displayed a similar bleaching effect on the resultant pulp.

The effect of treating pine regular kraft pulp with peracetic acid before O2-delignification on the consumption of ClO2 in D0ED1 bleaching

“…The obtained pulp activation using Paa results from the different chemistry of action of this compound with residual lignin in comparison to oxygen in the alkaline environment because it reacts not only with the phenolic rings of the lignin monomeric units but also with the non-phenolic residues of these units (Delagoutte et al 1999;Chong et al 2015). Moreover, it is reported that the treatment of kraft pulps with Paa effectively reduces the content of certain lignin-carbohydrate complexes (Jääskeläinen and Poppius-Levlin 1999) and hexenuronic acids contained in these pulps (Tavast et al 2011;Estaves et al 2020).…”

“…This is because, in addition to the decrease in the residual lignin content of the pulp, the amount of lignin moieties having a degradation activation energy equal or even greater than the degradation process of polysaccharides increases (Karhunen et al 1994;Akim et al 2001). To delignify kraft pulps of low residual lignin content more selectively in bleaching, it has been proposed to use two-stage oxygen delignification of the pulps (Saldivia 2002;Johnson et al 2009) or to pre-treat them with substances that activate the residual lignin moieties of reduced susceptibility for delignification (Fossum and Marklund 1988), such as: performic acid (Hauque et al 2019); peracetic acid (Paa) (Poukka et al 1999;Turner et al 2004;Chong et al 2015;Zeinaly et al 2019;Sharma et al 2020); persulfuric acid (Allison and McGrouter 1995;Jafari et al 2014;Rizaluddin et al 2015); perphosphoric acid (Springer 1997); and salts of these acids (Springer and McSweeny 1993;Allison and McGrouter 1997;Zeinaly et al 2019;Bourchard et al 2000).…”