abstract
Two industrial elemental chlorine free (ECF) bleaching sequences, D(0)(EOP)D(1)(EP)D(2) and OQ(PO)DP, are compared with respect to the bulk content of lignin, carboxyl, hexeneuronic acids (HexA), and reducing groups after each bleaching stage. HexA groups contribute significantly to the total content of carboxyl groups, and their degradation during chlorine dioxide bleaching is reflected by a decrease of the carboxyl content. The higher degradation using an enhanced use of oxygen-based bleaching chemicals is associated with a higher fiber charge reduction, mainly due to xylan depletion. Additionally, the effect of process variables of a laboratory final hydrogen peroxide stage on the chemical composition of the fully bleached pulp (D(0)(EOP)D(1)P and OQ(PO)DP) is studied. The ability of final peroxide bleaching to raise the content of carboxyl groups is dependent on the operating conditions and pulp bleaching history. A balance between carbohydrate oxidation and dissolution of oxidized groups determines the effect on fiber charge. The effect of hydrogen peroxide stabilizers added into the final stage on the content of carboxyl groups is also reported.
keywords
HEXENEURONIC ACID GROUPS; HEXENURONIC ACID; CHLORINE DIOXIDE; KAPPA-NUMBER; OXIDIZABLE STRUCTURES; RESIDUAL LIGNIN; CARBOXYL GROUPS; PART 1; FIBER; CHROMOPHORES
subject category
Materials Science
authors
Loureiro, PEG; Domingues, EF; Evtuguin, DV; Carvalho, MGVS
our authors
Dmitry Evtyugin
Associate Professor with Aggregationacknowledgements
Portucel Soporcel group and Celbi mill are acknowledged for supplying the pulps and FCT (Portuguese Foundation for Science and Technology) is acknowledged for the Doctoral degree grant of Loureiro (SFRH/BD/29690/2006).