- •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
For over 80 years, regenerated fibers of high quality and special uses have also
been spun from a cuprammonium solution (cupram), a metal complex solvent for
cellulose. Less than 2% is estimated for cuprammonium rayon within the world
rayon production. The high demand on processability and pulp quality requires
the use of high-purity cotton linters which, compared to the viscose process, is not
a decisive cost factor.
Table 11.5 provides a rough overview of the raw material sources, dissolving
pulp technologies and main applications.
Tab. 11.5 Overview of different applications of dissolving pulps.
Product Simplified reaction scheme Raw material Pulping
processes
Bleaching
processes
Viscose
Staple CellOH _I_ NaOH__CellONa B, E, S, H, P*) AS, PHK ECF, TCF
Textile filaments CellONa _ CS2 _ Cell_OCSSNa_0_4_0_5 E, S, H, P*) AS, PHK ECF, TCF
Technical Filament H__Zn2__Na_ __CellOH _II_ P*),MHWPHK (CCE) ECF
Cuprammonium
Rayon
CellOH _I_ Cu__NH3 _4 _OH_2_ __CellOH _II_ CL,S SO, AS ECF
Lyocell
Textile CellOH _I_ NMMO _H2O __CellOH _II_ E, P*), H AS, PHK TCF, ECF
Non-Wovens B, E, S, H, P*) AS, (PHK), K TCF, ECF
Ethers
MC CellONa _ CH3Cl _ Cell_OCH3_x S, E, P, H, MHW,CL AS, (PHK), SO ECF
MHPC CellONa _ CH3Cl PO__
Cell__OCH2CHOCH3_x_OCH3_y_
S, E, P, H, MHW,CL AS, (PHK), SO ECF
HEC CellOH _ EO OH_ __
Cell__OCH2CH2O_x_CH2CH2O_y_
S, E, P, H, MHW,CL AS, (PHK), SO ECF
CMC CellONa _ ClCH2COO_ _
Cell__OCH2COONa_x
S, E, P, H, MHW,CL AS, (PHK), SO ECF
1025
11 Pulp Properties and Applications
Tab. 11.5 Continued.
Product Simplified reaction scheme Raw material Pulping
processes
Bleaching
processes
Acetate
Tow CellOH _ _CH3CO_2O H_ __
Cell_OCOOCH3_2_3
MHW,H, S, E, P AS (CCE),
PHK (CCE)
ECF,
CONV
Plastics P, CL PHK-CCE, SO ECF,
CONV
Nitrocellulose (NC)
High-N-NC (x = 3) CellOH _ HNO3
H_ __Cell_ONO2_x CL SO CONV
Low-N-NC (x = 2) CL, S SO, AS CONV,
ECF
Microcrystalline
Cellulose (MCC)
CellOH H_ __CellOHcryst MHW,H, S, E, P (AS), PHK ECF
Raw Material:
B (beech), E (eucalypt), S (spruce), H (hemlock), P (pine), MHW(mixed hardwood), CK (cotton linters)
*) sulfite cooking with pine and other resinous wood requires different pH profile → two-stage
processes, or measures to remove the resins
Pulping Purification Processes:
AC (acid sulfite), PHK (prehydrolysis kraft), CCE (cold caustic extraction), SO (soda).
Products:
EO = ethylene oxide, PO = propylene oxide
MC (methylcellulose), MHPC (methylhydroxypropylcellulose), HEC (hydroxyethylcellulose).
11.3.2.2 Chemical Properties
11.3.2.2.1 Chemical Composition
Organic Compounds
Hemicelluloses (short-chain alkali-soluble carbohydrates)
One of the main objectives of dissolving pulp production is the removal of noncellulosic
carbohydrates which constitute the major part of the short-chain material
In the polymer. The available purification processes – particularly the hot and cold
caustic extraction processes – contribute to a considerable increase in production
costs, mainly due to high yield loss and high chemical charges (see Sections 8.3
and 8.4). Therefore, the extent of purification is adjusted to the demands on the
particular further processing. However, even small amounts of alien polysaccharides
may influence the processability and properties of the final product.
During steeping, the first step of alkaline processing of dissolving pulps for
the viscose and etherification procedures, alkali-soluble hemicelluloses are
removed to an extent depending on pulp quality, the process conditions and the
1026