F I B E R M O R P H O L O G Y :

Lw Fiber Length Distribution

Freq

uen

cy (%

)

Fiber Length (mm)

220 / Chapter VII

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52: Southern Bleached Softwood Kraft (SBSK)Mercerized

Fiber Length Lw (mm): 1.67Britt Jar Fines (%): 2.99Curl Index: 0.369Coarseness (mg/100m): 42.1Population (million fibers/g): 2.03

Surface of Handsheet (Low Magnification)

A P P R O P R I A T E A P P L I C A T I O N S :Mercerized softwood is sold globally to all producers of filter media. There probably are not any air or oil filters that are

not made with either a mercerized or similar pulp. The very demanding capacity specifications (flow-through properties)

require an openness and high porosity that can only be achieved by one of the specialty pulps such as this one. Some latex

saturators of heavy board have also found that a small amount of mercerized softwood is helpful in opening the base stock

to allow the resin to saturate completely. If a satisfactory in-feed system is available, mercerized softwood is also very

beneficial in high-loft air-laid nonwovens.

W O O D S P E C I E S :Slash pine

D I S T I N C T I V E A T T R I B U T E S :This is one of the more sophisticated specialty pulps (as well

as one of the highest priced). Fully mercerized softwood

pulps exhibit exceptional bulk and porosity. The pulp has a

hand feel similar to that of a ball of cotton. After steeping

in caustic for a carefully controlled amount of time and

drying to 104% Air Dry, the pulp exhibits a Frazier porosity

as high as 480 seconds (for the most advanced grade).

Prior to mercerization, the pulp has only 10% of this

porosity. Mercerized softwood pulp has such a high degree

of crystallinity (cross-linked hydroxyl groups) and low

hemicellulose level that there is no point in refining it. Not

only would refining destroy the bulk and porosity, but

almost no increase in strength properties would be realized.

H A N D S H E E T P R O P E R T I E S :

PFI CSF Scattering Coefficient Density Bulk Tear Index Stretch TEA Breaking Length Zero Span Brightness

Revolutions ml m2/kg g/cm3 cm3/g mNm2/g % J/m2 km km %

0 779 23.7 0.290 3.44 1.52 1.42 0.43 0.066 7.26 83.7

5000 763 22.0 0.429 2.33 14.2 1.12 6.79 1.32 10.2 82.6

10000 712 21.1 0.465 2.15 17.5 2.13 22.6 2.18 10.9 82.7

15000 466 22.6 0.540 1.85 20.3 3.17 53.8 3.92 11.0 81.9

20000 268 21.6 0.569 1.76 15.4 3.63 69.2 4.01 11.5 83.1

Atlas of Market Pulps / 221

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Surface Cross Section

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

CSF (x 20, ml) Tear Index (mNm /g)

Scattering Coefficient (m /kg) Breaking Length (km)

Bulk (x 0.1, cm /g)

PFI Mill Refining (x 1000, revolutions)

Pulp 52

Rel

ativ

e Sc

ale

1.70

1.90

2.10

2.30

2.50

2.70

2.90

3.10

3.30

3.50

0 1 2 3 4 5

Tensile Breaking Length, km

Pulp 52

Tear

Ind

ex,m

Nm

2/g