- •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
11.3 Dissolving Grade Pulp
of the yarn. On the other hand, the presence of resins considerably improves the
accessibility of reagents to the cellulose substrate (e.g., alkali cellulose) due to lowered
surface tension. The amount of extractives in the dissolving pulp is determined
by both the wood species used and the pulping and bleaching operations.
Acid sulfite cooking is rather sensitive to wood that is rich in resins. The major
problems arise with phenolic extractives originating from pine, larch, Douglas fir
and other extractive-rich wood species, which tend to undergo condensation reactions
with reactive lignin structures. The formation of high molecular-weight resinous
products may cause uncontrollable pitch problems in subsequent operation
steps. These may be largely overcome by applying a two-stage process with an initial
bisulfite or neutral sulfite stage. Thereby, the most reactive groups of lignin
are protected by sulfonation. Hardwoods are generally better suited for acid sulfite
pulping than softwoods. In the case of some resinous hardwoods, such as birch or
some aspen species, the delignification of parenchyma cells with a high content
of resins remains incomplete. Subsequent chlorine-free bleaching sequences –
particularly those containing ozone stages – contribute significantly to reducing
the resin content. Additionally, the short parenchymal cells may be removed by
fractionation, though this is connected with high yield loss.
Kraft cooking is less sensitive to wood raw materials that are rich in resins
because most acidic extractives, together with part of the neutral lipophilic compounds,
are dissolved in the cooking liquor, leaving little resin in the unbleached
pulp. However, if the fraction of unsaponifiable compounds is high (as with many
hardwoods), the fatty acid soaps formed do not possess sufficient micellar-forming
properties to carry less polar compounds into solution. During PHK pulping
of Eucalyptus globulus L., nearly all polyphenols, phenols, fatty acids are dissolved.
Two-thirds of the neutral compounds are left in the unbleached pulp, while twothirds
consists of b-sitosterol [26]. During bleaching, the unsaponifiables are modified
to more polar compounds containing carboxyl groups; these compounds, together
with other polar extractives such as fatty acids, are favorable as surface
active agents in the viscose process and account in part for good filtration of the
viscose prepared from this pulp [27,28].
Resins derived from pulps of high resin content – and particularly those containing
higher amounts of nonpolar neutral substances such as hydrocarbons and
waxes – show a tendency to accumulate in the spinnerets. The deposits of resin
inside the holes in the spinnerets increase the adhesion of precipitated zinc sulfide,
and this ultimately leads to clogging of the spinnerets [29]. In times of conventional
bleaching, chlorination of extractives caused viscose turbidity, which
was closely associated with spinning jet clogging [30]. The introduction of hydrophilic
groups by means of oxidation during bleaching operations (O, D, Z, P)
improves the dispersibility of pulp resin in sodium hydroxide [30].
Viscose quality was greatly affected by the ozone charge during the course of
TCF bleaching (O-A-Z-P) of an aspen PHK pulp [31]. A step-wise increase in
ozone charge from 1.0 to 3.3 kg odt–1 significantly decreased the content of acetone
extractives while improving viscose quality, characterized as the relationship
between the average particle volume and viscose filterability (Fig. 11.9).
1031
11 Pulp Properties and Applications
0.20 0.15 0.10 0.05
0
20
40
300
400
500
Centricleaning
(3.3)
(1.9)
(1.0)
Particle Volume [ppm] PVC Filter value
PVC Filter Value Particle Content in Viscose
Acetone Extractives [% od]
Fig. 11.9 Relationship between the content of
acetone extractives of a TCF-bleached aspen-
PHK pulp and viscose quality [31]. The reduction
of acetone extractives was achieved by
increasing charges of ozone and additional
post cleaning with a centricleaner. Pulping
according to the VisCBC process: P-factor 750,
H-factor 600, EA concentration in cooking
liquor 0.875 g L–1; TCF-bleaching according to
O-A-Z-P to achieve brightness >91% ISO.
10 100
0
1
2
3
4
5
6
[5]
[4]
[3]
[2]
[1]
[5] 3.3 kg O
3
/odt and postcleaning
[4] 3.3 kg O
3
/odt
[3] 1.9 kg O
3
/odt and postcleaning
[2] 1.9 kg O
3
/odt
[1] 1.0 kg O
3
/odt
frequency
Particle Diameter [μm]
Fig. 11.10 Particle size distribution of viscose samples made
from aspen PHK pulps of varying ozone charges and additional
post cleaning operations [31]. Pulping conditions
according to Fig. 11.9.
1032