Fractionation

Fiber fractionation generally follows the probability mechanism of separation.

Despite the limitations placed on fractionation efficiency by currently available

screening and cleaning equipment, fractionation applications are gaining increasing

attention and the prospects of value-added, tailor-made fibers have stimulated

the imagination of product developers.

With regard to paper-making properties, pulps containing long and thick-walled

fibers generally produce a higher tear index. Pulps with thin-walled fibers, and

those containing fines, have better optical properties, higher tensile strength,

internal bond strength, elongation and density [23,27].

The different fractions can be separately refined or treated otherwise, and may

then be recombined, or not. A market pulp producer with two dewatering

machines may fractionate his pulp to increase the long fiber content of the furnish

sent to one machine in order to produce a high-value reinforced pulp. A

paper producer with a multi-layer headbox may direct the shorter fibers to the surface

layers to improve sheet smoothness and optical properties, while placing the

longer fibers in the core to provide strength [10]. Besides strength, fiber fractionation

can also substantially improve the porosity of a pulp by removing the short

fibers and fines that reduce porosity [28].

In total, the fractionation of pulp creates a multitude of new opportunities for

the alternative utilization of the fiber raw material. Nevertheless, fractionation is

practicable only in mills which can make use of all the obtained fractions.

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