Holik H. (ed.) Handbook of Paper and Board

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For sludge and reject incineration in paper mills the following conclusions con-

cerning flue gas emissions are possible:

• Emissions of solid particles, sulfur dioxide, hydrogen chloride, hydrogen fluo-

ride and carbon monoxide are low compared with legal standards. Due to the

high calcium carbonate content of deinking sludge this sludge should not re-

lease all sulfur as sulfur dioxide. State-of-the-art flue gas purification guarantees

that no significant environmental impact arises.

• The emission of heavy metals is very low compared with the legal standards,

especially for emission of cadmium and mercury.

• The emission standard of nitrogen oxides can usually be met by improved com-

bustion control (temperature and oxygen level). Sometimes, the application of

specific measures to remove NOx could be necessary.

• The stringent emission standard of polychlorinated dioxins and furans can be

met without any additional measures in flue gas purification.

10.2.3.2 Composting and Agricultural Utilization

Nearly all types of paper industry waste are suitable for composting. These include

fiber-containing sludges, deinking sludges, bark, wood residues, and biological

sludges from effluent treatment plants. Rejects from recovered paper pulping and

screening operations are not suitable or suitable only to a limited degree. With this

type of waste, the content of plastic and other nonpaper components such as glass

or stones has a detrimental influence.

In all cases, composting of residues from paper manufacturing requires the

application of additives. With the exception of biological sludges, the sludges have

an unfavorable carbon/nitrogen (C/N) ratio for microbial decomposition. They

also have a dense structure that is unfavorable for composting. This requires the

addition of structure-improving materials that are ideally also nitrogen carriers.

Biological waste from households, garden waste, cuttings from trees and plants,

straw, bark, and waste from animal husbandry are suitable as such components.

The composting of fiber sludges and biological sludges, usually with bark, has

been practised on an industrial scale for a long time.

The paper industry also has a long tradition of using sludges in agriculture. This

is true especially for virgin fiber sludges and for biological sludges since the first

biological effluent treatment plants started operation. With the exception of

sludges from biological effluent treatment plants, sludges from the paper industry

have a high carbon/nitrogen ratio and therefore contain only a small proportion of

nitrogen. For this reason, they have only a limited fertilizing effect. The advantage

of their use in agriculture relates to their soil enhancing properties. They not only

contribute to covering the requirements of a humus forming organic substance

but also improve the aeration and cultivation of the soil, increase the water reten-

tion capacity and prevent erosion.

Use of deinking sludges in agriculture is still controversial. In North America,

no objections exist concerning their use as a soil improving material provided the

material does not exceed defined contaminant concentrations or harmful sub-

10 Environmental Aspects442

stance loads. The situation in Germany is different. In general, the contaminant

concentrations of deinking sludges are well below the valid threshold limits for

municipal sewage sludge defined by legislation governing sewage sludge. The Ger-

man Environmental Protection Agency still considers the agricultural use as un-

justifiable for reasons of soil protection, including the irreversibility of numerous

soil contaminants. The agency claims the ecological risk potential of deinking

sludges is not sufficiently known. In the Biowaste Ordinance issued in 1998, the

use of deinking sludges is also not allowable on soil intended for agricultural,

forestry, or horticultural purposes.

10.2.3.3 Use in Other Industries

Rejects, deinking sludges, and combustion ashes of paper mills are used in many

branches of industry for material and energy production purposes. The material

use possibilities for deinking sludges and combustion ashes depend primarily on

the composition of the inorganic components. The inorganic part of the deinking

sludges consists mainly of calcium carbonate and clay. In the combustion ashes of

deinking sludges, calcium oxide and sintered clay are primarily present. The afore-

mentioned inorganic components also have use as raw materials in the construc-

tion industry. The primary use possibilities are therefore the following:

• cement production

• brick manufacturing

• concrete production

• mortar and sand lime brick production

• road construction.

10.2.3.4 Landfilling

Landfilling is the most commonly applied method worldwide for the final disposal

of paper mill wastes. This situation will not change in many more remote regions

of the world in the medium term. In contrast, landfill capacities have already

become very limited in densely populated countries and it is becoming increas-

ingly difficult to obtain authorization to open new landfill sites. Further develop-

ment of landfilling techniques has dramatically increased costs for construction

and operation of landfills. With the current technical state-of-the-art, operating a

landfill site such that any annoyance to the population living nearby or environ-

mental risk due to leakage, odors, fire and explosion risk can be largely elimi-

nated.

Theoretically, the following possibilities exist for landfilling waste from paper

mills:

• landfilling in monofill dumps for certain types of waste such as ash, sludge, and

bark

• works-owned landfills where all in-plant waste is stored

• landfilling in public dumps where waste from other sources is also stored.

10.2 Solid Waste 443

Depending on local circumstances and the types of waste concerned, pulp and

paper mills sometimes use all three disposal methods. Because the waste from

paper mills is not harmful, using municipal landfills is possible. To minimize

leakage and maintain landfill stability, an extensive dewatering of sludges and

rejects is necessary. Dry solid contents should be above 40 %. The landfill of ashes

from reject and sludge incineration does not require any measures beyond those

governing the dumping of household waste.

10.2.3.5 New Developments

Besides extension of the processes to use waste material described so far, further

possibilities exist for the use of waste from paper mills. These mainly concern

fibrous sludges and deinking sludges. Only a small number of paper mills use

these possibilities, or they have been limited so far to laboratory scale tests and

pilot installations. New developments in the area of sludge use include:

• wet oxidation processes

• fermentation processes

• hydrolysis processes

• production of cat litter and adsorbent materials.

For ash use, filler recovery processes are under development that should permit

the reuse of recovered fillers in the paper industry or other branches of industry.

References

1 C. H. Möbius, Abwasser der Papier- und Zell-

stoffindustrie, 4. Auflage, November 2003

Quelle: http://www.cm-consult.de

2 J. Kappen, W. Dietz, J. Demel, D. Pfaff,

Water use in Germany, Pulp Paper Int.

2003, no. 12, 22–24.

3 I. Demel, J. Kappen, Optimierung

von Wasserkreisläufen, Wochenbl. Papier-

fabrikat. 1999, 127(3), 141–145.

4 L. Göttsching, W. Lüttgen, Organische

Hilfsstoffe als eine Quelle der Wasser-

belastung bei der Papierherstellung, Das

Papier 1978, 32(10 A), V46-V53.

5 U. Hamm, B. Bobek, L. Göttsching, Bio-

logische Abbaubarkeit von Hilfsstoffen der

Papiererzeugung und Papierverarbeitung,

Wochenbl. Papierfabrikat. 1999,127(9),

599–603.

6 F. Zippel, Wasserhaushalt von Papier-

fabriken, Deutscher Fachverlag, Frankfurt,

1999.

7 K. Diedrich, U. Hamm, J.H. Knelissen,

Biologische Kreislaufwasserbehandlung in

einer Papierfabrik mit geschlossenem

Wasserkreislauf, Das Papier 1997, 51(6A),

V153-V159.

8 C. Bülow, G. Pingen, U. Hamm, Complete

water system closure, Pulp Paper Int. 2003,

no. 8, 14–17.

9 U. Hamm, B. Bobek, I. Demel, W. Dietz,

Scheitert die Kreislaufschließung in

Papierfabriken an zu hohen Calcium-

belastungen? ipw 2001, (1), 46–52.

10 D. Pfaff, B. Götz, Aufkommen und Ver-

bleib der Rückstände aus der Zellstoff-

und Papierindustrie – Ergebnisse der

Rückstandsumfrage 2001, Wochenbl.

Papierfabrikat. 2003, 131(17), 1026–

1029.

11 U. Hamm, Final fate of waste from re-

covered paper processing and non-recycled

paper products, in Papermaking Science

and Technology, a series of 19 books,

Book 7: Recycled Fiber and Deinking,

L. Göttsching, H. Pakarinen (Eds.), Fapet

Oy, Helsinki, 2000.

References

444

12 H.-J. Boltersdorf, Zusammensetzung der

groben Rückstände der Papierindustrie,

Bericht der Repa Boltersdorf GmbH,

Brohl-Lützing, 2003.

13 U. Hamm, L. Göttsching, Schwermetall-

pfade bei der Altpapieraufbereitung, Das

Papier 1989, 43(10A), V39-V46.

References

445

Paper and Board Grades and Their Properties

Otmar Tillmann

11.1

The Material Paper: a Survey

11.1.1

Introduction

The term paper refers to sheet material that is made essentially from fibers of plant

origin. The characteristic feature of this nonhomogeneous material is its fiber

network, which is usually arranged in layers containing pores of varying size. The

properties of paper differ substantially from those of the fiber resources. These

differences are illustrated in Table 11.1, which shows some selected material prop-

erties of wood, as the most important fiber source, in comparison with paper. As a

result of the physical and chemical properties and the highly ordered state of wood

fibers, wood is unsuitable for direct production of sheet material which could serve

as writing material. The construction of paper, i. e., sheet material with properties

that are optimal for writing, printing or packaging, is possible only after the break-

down of wood into its elemental fiber building blocks, their modification in the

pulping process, and their controlled bonding in the papermaking process. Paper

Table 11.1 Comparison of selected properties of wood and

paper.

Property Wood Paper

density, g cm

–3

0.3–0.5 0.5–1.5

Young’s modulus, GPa 1.3 1.8–4.3

tensile strength, MPa 90–200 20–200

breaking length, km 7–30 1–8

strain to rupture, % 0.6–0.8 0.8–4

fiber alignment ordered random

Handbook of Paper and Board. H. Holik (Ed.)

ISBN: 3-527-30997-7

446

can be made with an extremely wide range of properties by varying the construc-

tion parameters: type of wood, pulping process, stock preparation, and papermak-

ing process. This is illustrated in Table 11.2.

The wide range of paper and board properties that result from the construction

parameters mentioned above can be increased still further by the use of additives

such as mineral and chemical aids. For instance, the smoothness and brightness

of printing paper can be increased by addition of inorganic pigments (fillers) [1].

Many special demands made on paper can be met by using suitable chemical

additives, e.g., wet strength by using wet-strength additives or printability by using

sizing agents [2]. However, paper produced with all these aids will never meet all

conceivable requirements at a time. In each case only a few paper properties that

are particularly important for the intended purpose can be optimized, as far as the

other properties are concerned, concessions must be made.

11.1.2

Material Properties

The specific characteristic features of paper vary widely, depending on the type of

paper. Nevertheless, there are a number of properties that are characteristic of all

papers. These are inhomogeneity, hygroscopicity, anisotropy, and viscoelasticity.

Paper is an inhomogeneous material made from homogeneous elements: fibers,

fillers, and air-filled pores. The homogeneous regions extend over a few microme-

ters (a few millimeters in the longitudinal fiber direction), corresponding to the

characteristic dimensions of these particles.

A sheet of paper also exhibits other inhomogeneities, which can have character-

istic dimensions of a few millimeters or centimeters. These are known as cloudi-

ness and result from undesired fiber flocculation in the sheet forming process [3].

In this way, variations in caliper and density develop, and this leads to correspond-

ing variations in transparency, the “clouds”. Finally, the production process can

also give rise to inhomogeneities, e.g., due to stock pulsations in the headbox and

in the sheet forming section [4]. Only betaradiographic measurements can give

exact information about local mass differences. The existence of inhomogeneities

must be taken into account in paper testing, e.g., by choosing the appropriate size

of sample.

The most important characteristic of paper is its hygroscopicity, i. e., its ability to

absorb or release moisture, depending on the ambient climate, until an equilib-

rium is reached. It is significant whether the state of equilibrium is established by

absorption or desorption of water [5]. The equilibrium moisture contents of some

types of paper at various levels of relative humidity are listed in Table 11.3.

As a result of the hygroscopicity of paper, physical paper properties, such as

sheet dimensions, basis weight, tensile strength, strain to rupture, folding

strength, bending stiffness, etc., are dependent on the ambient conditions [6]. With

a change in the ambient climate, the full attainment of a new equilibrium mois-

ture content of paper is a process which takes several hours. However, the change

in the physical properties of the paper starts almost without delay and occurs very

11.1 The Material Paper: a Survey 447

Table 11.2 Selected properties of some grades of paper and

board.

Selected properties of

some grades of paper

and board

Property LWC,

Mechanical

paper

Newsprint Wood-free

offset

printing

paper

Bag paper SC-A,

Super-

calendered

mechanical

uncoated

magazine

paper

Boxboard

basis weight, g m

–2b

54–55 45–49 81.4 69.7 45–60 286

caliper, mm

45–46 62–80 110 106 39–54 453

density, g cm

–3c

1.25–1.3 0.61–0.74 0.74 0.66 1.15–1.23 0.63

specific volume cm

–1c

0.8–0.78 1.35–164 1.35 1.52 0.8–0.9 1.59

tensile strength, N

MD 36–40.9 26.5–30 64.5 78.5 36–42 245.5

CD 14.6 12.6 25.1 53.5 80.5

elongation,%

MD 1.0–1.2 0.8–0.9 1.6 2.8 1.2–1.3 2.0

CD 1.6 1.8 3.0 6.2 3.2

breaking length, km MD 4.5–4.95 3.30 5.25 7.50 5.75

CD 1.75 1.55 2.05 5.15 1.85

tear growth resistance,

mNm m

–1e

MD 180 120 340 640 1200

CD 250 170 410 630 200–230 2440

bursting strength

(Mullen), kPa

100 50 150 350 550

Smoothness (Bekk)

fs 633–2460 71.4 18.2 6.1 22.9

ws 600–2430 63.4 8.6 4.4 2.9

smoothness

(PPS, 1 MPa)

, mm

0.7–0.8 1.0–1.2

roughness (Bendtsen), fs 22 90 273 702 113

mL min

–1h

ws 20 114 469 838 > 500

specific bending

stiffness, Nmm

MD 0.06 0.12 0.37 0.39 37.8

CD 0.03 0.04 0.19 0.18 13.1

brightness,%

fs 73.1 (76)

55.9 84.6 66–67 81.5

ws 72.3 (76)

56.3 84.6

opacity, %

92–92.7 96.5 90.5 88–93 88–93

MD = machine direction; CD = cross machine direction; fs = felt side;

ws = wire side; b, ISO 536; c, ISO 543; d, ISO 1924; e, DIN EN 21974,

SCAN/P11:96; f, ISO 5758–01; g, DIN 53 107–00; h, 8791/2–90; I,

5629; j, 2470; k, ISO 2471; l, ISO 8791; m, brightness D65 R457 (UV).

11 Paper and Board Grades and Their Properties448

quickly at the beginning and slows down later. For this reason, paper should be

processed in rooms in which the climatic conditions are favorable for the partic-

ular paper property required. The paper must be in equilibrium with the climate in

the room and the climatic conditions must be kept largely constant. The testing of

paper requires the establishment of testing climatic conditions (standard climate:

23 °C, 50 % relative humidity, cf. Section 11.2.2.1).

Paper is an anisotropic material with regard to many physical properties. This

anisotropy is due to the anisotropic properties of the individual fibers, which result

from the fibrillated microstructure of the fiber rather than the fiber shape [7]. As a

result of the fibrillated structure, the fiber can accept, for example, high tensile

forces in the direction of the fiber axis with low elongation; however, even small

tensile forces acting perpendicular to the fiber axis cause high elongations.

During drying the fiber shrinks in the axial direction by only about 1 to 2%. In

comparison, shrinkage in the direction perpendicular to the fiber axis (radial direc-

tion) reaches about 30%. If the fibers in a paper sheet were completely randomly

oriented sheet shrinkage in all directions would be equal and mainly governed by

the low longitudinal fiber shrinkage. The more the fibers in a sheet are oriented in

one direction the higher sheet shrinkage will occur in the direction perpendicular

to the main fiber orientation. This is due to the increased influence of the larger

radial fiber shrinkage. The fibers in a paper produced on a paper machine are not

aligned randomly, the machine direction is usually preferred (anisotropy of fiber

orientation). Furthermore the fiber mat is passed through the paper machine un-

der tension, which prevents free shrinkage of the fibers during drying, mainly in

the machine direction. Restraining forces in the cross machine direction are lower

and nonuniform across the width, being smaller at the edges. This results in a

nonuniform cross machine profile of shrinkage.

Both fiber alignment and shrinkage restraints are responsible for the anisotropy

of the moisture expansion of finished paper, which is generally far lower in the

machine direction than in the cross machine direction, the latter being nonuni-

form across the width. Both the above factors also affect the load – deformation

Table 11.3 Moisture content of selected types of paper in

equilibrium with various levels of humidity at 23 °C.

Type of paper Basis weight, g m

–2

Relative humidity, %

20 50 75

newsprint 50 6.5 8.5 10.0

gravure printing 65 6.0 8.0 9.2

offset, mechanical 80 5.2 6.4 7.9

offset, wood-free 80 5.0 6.3 7.5

art paper, mechanical 120 4.1 5.7 6.9

art paper, wood-free 120 3.8 5.3 6.5

11.1 The Material Paper: a Survey 449

properties (strain-to-stress) of paper, which are therefore also anisotropic (cf. Table

(11.2)).

Many papers exhibit an anisotropy with respect to their composition in the nor-

mal direction (z-direction). The process technology of production on the four-

drinier wire is responsible for this phenomenon. On the wire side, substances

(fillers and fines) that can pass through the wire are washed out, while on the other

side, they are retained by the fiber mat. This results in different smoothness prop-

erties on the two sides of the paper, also known as the two-sidedness of paper. Two-

sidedness of paper can be minimized by twin wire formers. A further anisotropy in

the z-direction results from frozen stresses during nonsymmetrical drying of the

web at the top and bottom sides. As a result of the in-plane anisotropy of the sheet,

the machine direction must be considered and marked when taking samples for

testing anistropic properties, such as strength. Two-sidedness is important in the

testing of printability, for example. Therefore top and bottom sides have to be

marked as well.

Finally, paper has viscoelastic properties [8, 9], i.e., it can be elastic like a solid or

viscous like a thick liquid. The viscoelasticity is also a result of the superimposition

of the properties of the individual fibers and those of the fiber network. The vis-

cous flow of the individual fibers is caused by the sliding of fibrils at high tensile

loads. The individual fibers exhibit elastic behavior at low tensile loads. In the fiber

structure of paper, the sliding of fibers at fiber intersections results in a flow effect

and the paper undergoes plastic deformation. A characteristic feature of viscoelas-

ticity is the dependence of the onset of flow on the loading rate. Small loads acting

over long periods of time result in flow, whereas large intermittently acting loads

cause only elastic deformation. Therefore, in the determination of the tensile

strength of paper, the time is fixed within which the tensile stress applied causes

the paper to break.

11.1.3

Summary

The material paper has essentially four characteristic features: inhomogeneity, hy-

groscopicity, anisotropy, and viscoelasticity. These features must be taken into con-

sideration in the testing of paper (cf. Table (11.4)). The magnitude of these features

depends on the type of fiber, the fiber raw material, the pulping process, and on the

process techniques used in stock preparation and papermaking. Consequently,

there are a large number of variables in papermaking and many degrees of free-

dom are involved in the adjustment of the desired paper properties. Therefore,

several different paths can usually be followed to obtain papers with comparable

technical properties. This is of importance in the standardization of paper proper-

ties. Only the technical characteristics may be stipulated in each case, but not the

process used to realize these characteristics, otherwise, there would be the danger

of excluding new technologies and impeding technical progress.

11 Paper and Board Grades and Their Properties450

11.2

Types of Paper, Board and Cardboard [10]

Paper and board are planar products made essentially from fibers that are mostly

of plant origin, and different portions of fillers. Fillers are mainly inorganic sub-

stances, their content in the product may vary from zero to about 40%. Paper and

board are formed by draining a fiber suspension through a sieve. The resulting

fiber web is subsequently compacted and dried.

There are approximately 3000 kinds of paper and board products [11]. Most

products with a basis weight up to 225 g m

are defined as paper. Above 225 g m

these products are usually called board, but the naming overlaps.

Depending on their use the paper and board grades can be divided into four

main groups:

1. graphic papers

2. packaging paper and board grades

3. hygienic papers

4. specialty paper and board grades.

This classification has also been largely adopted by the Statistisches Bundesamt

(Federal Statistical Office) of Germany in Chapter 48 of the “Commodity index for

foreign trade statistics” [12]. The basis of this systematology is a “harmonized

system for the marking and coding of merchandise” of the “council for tariff co-

operation”.

11.2.1

Graphic Papers

The term graphic papers refers to a large range of different papers that are suitable

for printing and writing and are made from virgin or recycled fibers or mixtures of

them.

Table 11.4 Characteristic material properties and their effect on

testing conditions.

Property Effect

inhomogeneity sample dimensions, number of measurements

anisotropy testing direction

two-sidedness tested side

hygroscopicity relative humidity, temperature

viscoelasticity duration of test

11.2 Types of Paper, Board and Cardboard 451