Removal of Lignin-rich Surface Material from Unbleached Kraft Fibres

Abstract

The composition and structure of the surface material of kraft fibres can affect properties of the pulp such as the reactivity in, for example, bleaching processes. In order to study the nature of the surface material, conditions for a gentle removal of fibre surface material from unbleached kraft fibres have been evaluated. An unbleached softwood kraft pulp with a lignin content of 6.2% (kappa number 32) was treated mechanically using three different types of laboratory equipment: a PFI-mill, a high intensity mixer, and a disintegrator. The number of revolutions and the pulp concentration were varied and the removal of surface material was followed by chemical and microscopical analyses. These analyses revealed that there is lignin-rich material present on the fibre surface which can be removed by a mild mechanical treatment. The lignin content of the surface material abstracted was between 2.5 and 4.5 times higher than that of the fibres. The primary fines (obtained by fractionation of unbeaten pulp, 20 ), also originating from the fibre surface, had a lignin content almost 5 times higher than that recorded in the fibres. For analytical studies of the surface material, a mechanical treatment of the kraft fibres in a disintegrator at a pulp concentration of 4.5% and at 20.000-200.000 revolutions is an efficient and suitable treatment for gradual removal of material from the fibre surface.

Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers

“…In order to obtain sufficient amount of surface material, a total of 50 g of pulp (dry weight) was used for each sample. The procedure is based on the study by Heijnesson et al [9] After disintegration, the pulp slurry was treated in a NAF water jet defibrator at a water pressure of 1.8 bars for 5 min. A sieve, PA 71 μm (210 mesh), was mounted in the defibrator, thus retaining the fibers while allowing the fine material to pass through.…”

“…The lignin content on fiber surface has been reported to be more than four times higher than the lignin content in the bulk fiber. [8,9] Since fiber-fiber bonding is important for paper strength, the surface characteristics of pulp fibers play an important role in paper strength development. Increased amount of xylan on the fiber surface generally improves paper strength.…”

Enzyme-Aided Bleaching of Kraft Pulps: Fundamental Mechanisms and Practical Applications

“…It has recently been suggested that pine kraft xylan reprecipitates evenly to all accessible surfaces to the fibre wall (16). In addition to xylan chains, dissolved lignin and covalently bound lignin and xylan have been suggested to reprecipitate to fibre surfaces during cooking (77,18), resulting in relatively high amounts of lignin on the fibre surfaces (19)(20)(21). The amount of xylan readsorbed during cooking depends on the wood species used in pulping.…”

“…Both xylan and lignin are dissolved and partially readsorbed on the fibres during pulping. A rather high content of lignin has been observed both in the primary fines and in the surface material of pine kraft fibres (79,20). Xylanases combined with ESCA have been used to determine the xylan content on the outer surfaces of cellulose fibres.…”

Possible Applications of Cellobiose Oxidizing and Other Flavine Adenine Dinucleotide Enzymes in the Pulp and Paper Industry

“…Since the decrease in Fe(III) reduction was directly related to spruce lignin concentration it may be that this CDH, cellobiose, Fe(III), hydrogen peroxide-system can be used for surface analyses of residual lignin in bleached and unbleached kraft pulps and for lignin in (chemo)thermomechanical pulps (24). Unbleached kraft pulps are known to contain 2.5-4.5 times more lignin on the fibre surface compared with the total amount of lignin in the fibre cell wall (26).…”