The effect of wood supply and bleaching process on pulp brightness stability

Abstract

One hundred different 5.5-year-old Eucalyptus grandis x Eucalyptus urophylla wood clones were cooked to kappa number 15-17.5 and the resulting kraft pulps oxygen-delignified to kappa 9.5-11.5 under fixed conditions, except for chemical charges. Thirteen samples showing large variations in effective alkali requirement, pulp yield and O-stage efficiency and selectivity were selected for brightness reversion studies. These samples were bleached to 90-91% ISO by DEDD and DEDP sequences and their brightness stability and chemical characteristics determined. Heat reversion of the eucalyptus kraft pulps was strongly influenced by the wood supply, with brightness loss varying in the range of 2.1-3.6 and 0.8-1.7 %ISO for ODEDD and ODEDP bleached pulps, respectively. Pulps bleached by the ODEDP sequence showed reversion values 1.3-1.9 % ISO lower than those bleached by the ODEDD sequence. Pulp carbonyl content decreased by 35-40% during the final peroxide bleaching stage. Carbonyl and carboxyl groups correlated positively with brightness reversion, as did permanganate number and acid soluble lignin. Pulp final viscosity and metal and DCM extractives contents showed no significant correlation with brightness reversion. Pulping, oxygen delignification and ECF bleaching performances also showed no correlation with brightness reversion.

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

“…In general, the residual chromophores are difficult to analyze due to their minute presence (ppm or even ppb range) in fully bleached pulps (Oliveira et al 2006;Schedl et al 2017). The analysis of chromophores in bleached pulps after ageing may involve their extraction and chemical characterization.…”

Efeito da extração alcalina na redução do número Kappa no branqueamento ECF

“…Segundo Oliveira et al (2006) e Colodette e Gomes (2015), o processo de branqueamento é um dos fatores que mais influência na estabilidade da alvura, sendo que tratamentos alcalinos são muito eficientes na remoção de extrativos e lignina residual, diminuindo assim o efeito negativo dos mesmos na reversão de alvura.…”

A influência dos ácidos hexenurônicos no rendimento e na branqueabilidade da polpa kraft

“…Isto se deve a maior estabilidade dos grupos presentes na celulose quando são branqueados com peróxido de hidrogênio em meio alcalino. 21 Embora a implementação do estágio ácido tenha causado um decréscimo na viscosidade de 13,6%, a diferença entre a viscosidade final das duas seqüências, OD(E+P)DD e OA HT D(E+P)DD, foi de apenas 5,3 pontos percentuais. Deve-se notar, ainda, que a viscosidade final da seqüência OA HT D(E+P)DD foi de 19,7 mPa.s, a qual se apresenta dentro dos padrões de qualidade exigida.…”