On the effect of a xylanase post-treatment as a means of reducing the yellowing of bleached hardwood kraft pulp

Catalytic efficiency and stability of tertiary amines in oxidation of methyl 4-deoxy-β-L-threo-hex-4-enopyranosiduronic acid by hypochlorous acid

“…Nowadays, the ageing reactions of either residual lignin or carbohydrates of bleached pulps are the main debatable reason for the reversion (Rosenau et al 2007b;El-Sakhawy 2005). Deposition of models of oxidized carbohydrates or their dehydration products, such as 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (furfural), over different cellulosic substrates have shown the enhancement of chromophore formation upon ageing (Pedroso and Carvalho 2003;Simeonova et al 2007;Brogdon 2009;Rosenau et al 2011). Additionally, the effect of transition metals in ageing reactions has been also confirmed (Granstrom et al 2001;Simão et al 2005;Beyer et al 2006;Lachenal et al 2009).…”

Applicability of Microbial Xylanases in Paper Pulp Bleaching: A Review

“…Xylanase post-treatment of bleached hardwood kraft pulp resulted in significantly reduced yellowing. In spite of the reduction of yellowing, yield could suffer significantly from enzymatic treatment (Simeonova et al 2007). The effects of Pulpzyme HC, a commercial enzyme, were also studied as potential post-treatment enzymes for use after bleaching processes.…”

Enzymatic treatment applied as a final stage in E. globulus kraft pulp bleaching

“…Being chromogenic structures, HexA residues do not deteriorate pulp brightness, but can affect the brightness reversion of bleached pulps . Taking into consideration the structural association between xylan and chromogenic/chromophoric structures, the highly selective removal of this hemicellulose from the fibre surface promotes pulp brightness thus saving bleaching chemicals and reducing environmental impacts . On the other hand, some negative consequences for refining energy and pulp strength can be anticipated as the hydrophilic character and the amorphous state of xylan facilitate fibre swelling and improve interfibre bonding during papersheet formation…”

“…Xylanases can be applied at different stages of the bleaching process, but most applications occur at the brownstock storage tower before or after oxygen delignification . The application of xylanases at the end of the bleaching sequence is scarce and not systematically investigated …”