- •Pulp Purification Herbert Sixta
- •9.2.2.1 Introduction
- •Introduction
- •10.4 Emissions to the Aquatic Environment
- •Is converted into carbon dioxide, while the other half is converted into biomass
- •Into alcohols and aldehydes; (c) conversion of these intermediates into acetic acid and
- •10 Environmental Aspects of Pulp Production
- •In North America, effluent color is a parameter which must be monitored.
- •It is not contaminated with other trace elements such as mercury, lead, or cadmium.
- •10.6 Outlook
- •Increase pollution by causing a higher demand for a chemical to achieve identical
- •In addition negatively affect fiber strength, which in turn triggers a higher
- •Introduction
- •2002, Paper-grade pulp accounts for almost 98% of the total wood pulp production
- •Important pulping method until the 1930s) continuously loses ground and finds
- •Importance in newsprint has been declining in recent years with the increasing
- •Isbn: 3-527-30999-3
- •Virtually all paper and paperboard grades in order to improve strength properties.
- •In fact, the word kraft is the Swedish and German word for strength. Unbleached
- •Importance is in the printing and writing grades. In these grades, softwood
- •In this chapter, the main emphasis is placed on a comprehensive discussion of
- •1010 11 Pulp Properties and Applications
- •Is particularly sensitive to alkaline cleavage. The decrease in uronic acid content
- •Xylan in the surface layers of kraft pulps as compared to sulfite pulps has been
- •80% Cellulose content the fiber strength greatly diminishes [14]. This may be due
- •Viscoelastic and capable of absorbing more energy under mechanical stress. The
- •11.2 Paper-Grade Pulp 1011
- •Various pulping treatments using black spruce with low fibril
- •In the viscoelastic regions. Fibers of high modulus and elasticity tend to peel their
- •1012 11 Pulp Properties and Applications
- •11.2 Paper-Grade Pulp
- •Viscosity mL g–1 793 635 833 802 1020 868 1123
- •Xylose % od pulp 7.3 6.9 18.4 25.5 4.1 2.7 12.2
- •11 Pulp Properties and Applications
- •Inorganic Compounds
- •11.2 Paper-Grade Pulp
- •Insight into many aspects of pulp origin and properties, including the type of
- •Indicate oxidative damage of carbohydrates).
- •In general, the r-values of paper pulps are typically at higher levels as predicted
- •Is true for sulfite pulps. Even though the r-values of sulfite pulps are generally
- •Is rather unstable in acid sulfite pulping, and this results in a low (hemicellulose)
- •11 Pulp Properties and Applications
- •Ing process, for example the kraft process, the cellulose:hemicellulose ratio is
- •Increases by up to 100%. In contrast to fiber strength, the sheet strength is highly
- •Identified as the major influencing parameter of sheet strength properties. It has
- •In contrast to dissolving pulp specification, the standard characterization of
- •Is observed for beech kraft pulp, which seems to correlate with the enhanced
- •11.2 Paper-Grade Pulp
- •11 Pulp Properties and Applications
- •Is significantly higher for the sulfite as compared to the kraft pulps, and indicates
- •11.2 Paper-Grade Pulp
- •Xylan [24].
- •11 Pulp Properties and Applications
- •11.2 Paper-Grade Pulp
- •11 Pulp Properties and Applications
- •Introduction
- •Various cellulose-derived products such as regenerated fibers or films (e.G.,
- •Viscose, Lyocell), cellulose esters (acetates, propionates, butyrates, nitrates) and
- •In pulping and bleaching operations are required in order to obtain a highquality
- •Important pioneer of cellulose chemistry and technology, by the statement that
- •11.3 Dissolving Grade Pulp
- •Involves the extensive characterization of the cellulose structure at three different
- •Is an important characteristic of dissolving pulps. Finally, the qualitative and
- •Inorganic compounds
- •11 Pulp Properties and Applications
- •11.3.2.1 Pulp Origin, Pulp Consumers
- •Include the recently evaluated Formacell procedure [7], as well as the prehydrolysis-
- •11.3 Dissolving Grade Pulp
- •Viscose
- •11 Pulp Properties and Applications
- •11.3.2.2 Chemical Properties
- •11.3.2.2.1 Chemical Composition
- •In the polymer. The available purification processes – particularly the hot and cold
- •11.3 Dissolving Grade Pulp
- •In the steeping lye inhibits cellulose degradation during ageing due to the
- •Is governed by a low content of noncellulosic impurities, particularly pentosans,
- •Increase in the xylan content in the respective viscose fibers clearly support the
- •11.3 Dissolving Grade Pulp
- •Instability. Diacetate color is measured by determining the yellowness coefficient
- •Xylan content [%]
- •11 Pulp Properties and Applications
- •Xylan content [%]
- •11.3 Dissolving Grade Pulp
- •11.3 Dissolving Grade Pulp
- •Is, however, not the only factor determining the optical properties of cellulosic
- •In the case of alkaline derivatization procedures (e.G., viscose, ethers). In industrial
- •11.3 Dissolving Grade Pulp
- •Viscose
- •Viscose
- •In order to bring out the effect of mwd on the strength properties of viscose
- •Imitating the regular production of rayon fibers. To obtain a representative view
- •11 Pulp Properties and Applications
- •Viscose Ether (hv) Viscose Acetate Acetate
- •Xylan % 3.6 3.1 1.5 0.9 0.2
- •1.3 Dtex regular viscose fibers in the conditioned
- •11.3 Dissolving Grade Pulp
- •Is more pronounced for sulfite than for phk pulps. Surprisingly, a clear correlation
- •Viscose fibers in the conditioned state related to the carbonyl
- •1038 11 Pulp Properties and Applications
- •In a comprehensive study, the effect of placing ozonation before (z-p) and after
- •Increased from 22.9 to 38.4 lmol g–1 in the case of a pz-sequence, whereas
- •22.3 To 24.2 lmol g–1. The courses of viscosity and carboxyl group contents were
- •Viscosity measurement additionally induces depolymerization due to strong
- •11 Pulp Properties and Applications
- •Increasing ozone charges. For more detailed
- •11.3 Dissolving Grade Pulp
- •Is more selective when ozonation represents the final stage according to an
- •11.3.2.3 Supramolecular Structure
- •1042 11 Pulp Properties and Applications
- •Is further altered by subsequent bleaching and purification processes. This
- •Involved in intra- and intermolecular hydrogen bonds. The softened state favors
- •11.3 Dissolving Grade Pulp
- •Interestingly, the resistance to mercerization, which refers to the concentration of
- •11 Pulp Properties and Applications
- •Illustrate that the difference in lye concentration between the two types of dissolving
- •Intensity (see Fig. 11.18: hw-phk high p-factor) clearly changes the supramolecular
- •11.3 Dissolving Grade Pulp
- •Viscose filterability, thus indicating an improved reactivity.
- •11 Pulp Properties and Applications
- •Impairs the accessibility of the acetylation agent. When subjecting a low-grade dissolving
- •Identification of the cell wall layers is possible by the preferred orientation of
- •Viscose pulp (low p-factor) (Fig. 11.21b, top). Apparently, the type of pulp – as well
- •11 Pulp Properties and Applications
- •150 °C for 2 h, more than 70% of a xylan, which was added to the cooking liquor
- •20% In the case of alkali concentrations up to 50 g l–1 [67]. Xylan redeposition has
- •11.3 Dissolving Grade Pulp
- •Xylan added linters cooked without xylan linters cooked with xylan
- •Viscosity
- •In the surface layer than in the inner fiber wall. This is in agreement with
- •11 Pulp Properties and Applications
- •Xylan content in peelings [wt%]
- •Xylan content located in the outermost layers of the beech phk fibers suggests
- •11.3.2.5 Fiber Morphology
- •11 Pulp Properties and Applications
- •50 And 90%. Moreover, bleachability of the screened pulps from which the wood
- •11.3.2.6 Pore Structure, Accessibility
- •11.3 Dissolving Grade Pulp
- •Volume (Vp), wrv and specific pore surface (Op) were seen between acid sulfite
- •11 Pulp Properties and Applications
- •Irreversible loss of fiber swelling occurs; indeed, Maloney and Paulapuro reported
- •In microcrystalline areas as the main reason for hornification [85]. The effect of
- •105 °C, thermal degradation proceeds in parallel with hornification, as shown in
- •Increased, particularly at temperatures above 105 °c. The increase in carbonyl
- •In pore volume is clearly illustrated in Fig. 11.28.
- •11.3 Dissolving Grade Pulp
- •Viscosity
- •11 Pulp Properties and Applications
- •Increase in the yellowness coefficient, haze, and the amount of undissolved particles.
- •11.3.2.7 Degradation of Dissolving Pulps
- •In mwd. A comprehensive description of all relevant cellulose degradation processes
- •Is reviewed in Ref. [4]. The different modes of cellulose degradation comprise
- •11.3 Dissolving Grade Pulp
- •50 °C, is illustrated graphically in Fig. 11.29.
- •11 Pulp Properties and Applications
- •In the crystalline regions.
- •11.3 Dissolving Grade Pulp
- •Important dissolving pulps, derived from hardwood, softwood and cotton linters
- •11.3 Dissolving Grade Pulp 1061
- •Xylan rel% ax/ec-pad 2.5 3.5 1.3 1.0 3.2 0.4
- •Viscosity mL g–1 scan-cm 15:99 500 450 820 730 1500 2000
- •1062 11 Pulp Properties and Applications
150 °C for 2 h, more than 70% of a xylan, which was added to the cooking liquor
(isolated from a eucalyptus pulp), was retained on the cellulose surface at a residual
effective alkali concentrations of approximately 10 g L–1, and still more than
20% In the case of alkali concentrations up to 50 g l–1 [67]. Xylan redeposition has
been demonstrated unequivocally by carbohydrate and GPC analysis (Fig. 11.24).
The xylan distributions across the fiber wall of TCF-bleached acid sulfite and
PHK dissolving pulps, obtained from both spruce and beech wood, were investigated
employing a new enzymatic peeling technique [69,70]. A general characterization
of the pulp substrates subjected to enzymatic peeling is provided in
Tab. 11.11.
1048
11.3 Dissolving Grade Pulp
3 4 5 6 7
0.0
0.3
0.6
0.9
1.2
Xylan added linters cooked without xylan linters cooked with xylan
dW/d(logM)
log Molar Weight
Fig. 11.24 Molar mass distribution of cotton linters after
cooking for 2 h at 150 °C with a residual EA-concentration of
10 g L–1 in the absence and presence of xylan [67]. The xylan
was isolated from a eucalyptus kraft pulp. GPC measurements
were made according to [68].
Tab. 11.11 Characterization of TCF-bleached dissolving pulps
made from spruce and beech wood produced by acid sulfite and
prehydrolysis kraft (PHK) cooking procedures [70].
Pulp type Bleaching
sequence
Bleached yield
[%]
Viscosity
[mL g–1]
Brightness
[% ISO]
Xylan
[%]
Glucomannan
[%]
Beech-S (E/O)-Z-P 39.7 573 91.4 3.3 0.6
Beech-PHK O-A-Z-P 38.1 465 91.1 6.4 0.4
Spruce-S (E/O)-Z-P 42.3 526 90.0 1.8 2.4
Spruce-PHK O-A-Z-P 38.5 439 83.4 2.3 1.3
The enzyme treatment causes a peeling effect which removes fiber material,
starting from the fiber surface. An analysis of the removed material by capillary
zone electrophoresis (CZE) revealed fundamental differences in the radial distributions
of hemicelluloses, as shown in Fig. 11.25. These differences may account
for some of the differences in dissolving properties of acid sulfite and PHK pulps.
The results show that all dissolving pulps investigated have a higher xylan content
In the surface layer than in the inner fiber wall. This is in agreement with
results obtained from paper-grade pulps [70,71]. The enrichment, however, is
1049
11 Pulp Properties and Applications
1 10 100
0
2
4
6
8
Sulfite: Spruce Beech
PHK: Spruce Beech
Xylan content in peelings [wt%]
Peeled carbohydrates [wt%]
Fig. 11.25 Radial distribution of xylan in TCF-bleached spruce
and beech sulfite and PHK dissolving pulps, according to
Tab. 11.11. Xylan content determined in aliquots of the hydrolyzate
(mass % of carbohydrates), collected after 1, 3, 10 min
and 48 h of enzymatic peeling, and after total hydrolysis [70].
highly dependent upon both the process and the wood species used. The high
Xylan content located in the outermost layers of the beech phk fibers suggests
that xylan precipitation occurs in the final kraft cooking phase, as shown for cotton
linters in Fig. 11.24. Beech sulfite dissolving pulp, however, shows a comparable
even cross-sectional concentration profile, as was determined for paper-grade
pulps [71]. For spruce PHK and acid sulfite dissolving pulps, only a very thin outermost
surface enrichment of xylan is found. But again, xylan is more enriched at
the surface of the PHK fibers as compared to the acid sulfite fibers. It is known
from practice that sulfite pulp behaves satisfactorily during the manufacture of
cellulose acetate, whereas kraft pulp with a similar (average) chemical analysis
does not. The enrichment of hemicellulose in PHK pulps may be one reason for
the impaired properties. Therefore, it is important to know if the pronounced
xylan profile through the cell wall can be leveled out by reinforced purification
conditions. Indeed, the enrichment of xylan was shown to decrease considerably
when prehydrolysis conditions were gradually intensified (increasing P-factor)
while the kraft cooking conditions were kept constant (Fig. 11.26).
A general characterization of the beech PHK pulps subjected to enzymatic peeling
is provided in Tab. 11.12.
1050
11.3 Dissolving Grade Pulp
50 500 1000 2000
0
10
20
30
40
50
60
Average Xylan Content [%]
at a peeling rate of 10 mass %
Xylan Enrichment on Surface [%]
P-factor
xylan enrichment
0
5
10
15
20
average xylan content
Fig. 11.26 Xylan enrichment on surface at a peeling rate of
10 mass % of beech PHK pulps prepared by increasing P factors
while Visbatch® cooking conditions were kept constant.
For enzymatic peeling conditions, see Fig. 11.25.
Tab. 11.12 Characterization of TCF-bleached beech PHK pulps
prepared according to the Visbatch® process comprising four
different levels of P-factor [72].
Pulp type Bleaching
sequence
Bleached yield
[%]
Viscosity
[mL g–1]
Brightness
[% ISO]
Xylan
[%]
Glucomannan
[%]
50 O-A-Z-P 44.4 466 90.7 15.6 0.6
500 O-A-Z-P 38.1 465 91.1 6.4 0.4
1000 O-A-Z-P 34.7 488 91.2 3.9 0.3
2000 O-A-Z-P 30.4 470 89.0 2.3 0.2
The decrease in surface xylan concentrationmay be explained by both the enhanced
removal of xylan from the outermost surface layers through reinforced prehydrolysis
conditions, and the diminished reprecipitation of xylan from solution during the
final phase of cooking due to a significant reduction in xylan concentration.