Biermann Ch. Handbook of Pulping and Papermaking

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INTRODUCTION AND THE LITERATURE

Waste LiquorL^

Recovery

Pulj)

Washing

K— Wash Water

Pulp

Bleaching

Bleaching Chemicals

Pulp

Refining

Paper

Trim

Attrition

And Waste

Paper

Machine

Landfill

or Burn

Paper

Conversion

^ Customer

Fig. 1-4. An overview of chemical pulping and papermaking processes. Courtesy of W. Bublitz.

be outdated; however, it is usually the best

source to get background information in a partic-

ular field.

If one considers articles (and other

references) in specialized fields with applicability

to pulp and paper, such as corrosion, process

control, simulation, and so forth, to be useful,

then the importance of abstract indices to access

the literature becomes obvious. One should not

rely on merely the pulp and paper journals; many

INTRODUCTION TO THE LITERATURE 5

Fig. 1-5. The basic steps to papemiaking. The fiber source is pulped (and bleached for white

papers); the pulp is washed; the pulp is refined to msure the fibers are separated from each other

and to roughen the surface for better fiber bondmg; a paper web is formed from a dilute pulp

slurry letting most of the water dram by gravity; additional water is pressed from the web; and the

remaining free water is removed by evaporation to give the product.

6 1. INTRODUCTION AND THE LITERATURE

important advances to pulp and paper technology

are merely modifications of technologies that are

well established in other disciplines.

On-line computer

searches

Literature searches using computer terminals

is quite common and convenient. Virtually any

computer with a modem can be used from any

location once an account is set up with a vendor.

Most libraries have facilities for doing literature

searches from computers and would probably

know what sources to use for the pulp and paper

industry. This information is also available from

other sources (Steelhanmier and Wortley, 1992).

I recommend that some time be spent with

thorough manual searching of one or two years

with abstract indices when searching a new topic,

especially a topic outside of

ones

normal activities.

This is helpful to learn what key words are most

effective so that important work will not be over-

looked. One should also be familiar with the pulp

and paper literature before getting overly accus-

tomed to using computer-aided searches of the

literature.

1.3 ABSTRACT INDICES

Abstract

Bulletin

the Institute

of Paper

Science

and

Technology

The most complete abstracting service of

research directly related to pulp and paper is the

Abstract

Bulletin,

Institute of Paper Science and

Technology that is published monthly, in addition

to an annual index. It is available on line for

computer searching. Before 1989 it was the Abst-

ract

Bulletin

the Institute

of Paper Chemistry.

Chemical

Abstract

Index

The Chemical Abstract

Index

comprehen-

sive abstract bulletin covering all areas of chemis-

try and chemical engineering. It is extremely

useful for getting current information on all as-

pects of chemical problems affecting the pulp and

paper industry. Author, subject, chemical, and

chemical formula indices are available to find

abstracts. Indices cover a six-month period;

collective indices cover ten volumes, correspond-

ing to five years.

Scientific Citations Index

The principal use of the Scientific Citations

Index is to keep track of the articles cited in the

primary scientific literature. For example, sup-

pose Dr. I. M. First published an article in 1988,

and the citation for that article appeared in the

Literature Cited section of an article published in

Tappi J. in January, 1990 by Ms. U. R. Second.

Under First, I. M. in the 1990

Citations

Index (not

the Source Index), one would find that U. R.

Second cited the article of I. M. First. This is a

useful form of feedback to determine the signifi-

cance of a particular scientific publication. In

some fields there are a few key authors whose

work is usually cited. By determining who cited

these authors, one can find some of the most

recent work.

1.4 TECHNICAL AND TRADE JOURNALS

Nordic Pulp and Paper

Research Journal

This journal publishes about 40 high quality,

fundamental, original research papers per year.

(Arbor Pub. AB, Stockholm, Sweden, appears

quarterly.)

This

journal started

publish research

papers at about the same time (in 1986) the long-

standing

Svensk

Papperstidning,

ceased publishing

research papers.

Journal

of Pulp and Paper

Science

This journal also publishes about 40 high

quality, fundamental, original research papers per

year. (Technical Section, Canadian Pulp and

Paper Association, Montreal, Quebec, appears

bimonthly.)

Tappi Journal

This

journal publishes about 300 high quality,

original research papers per year. It also includes

industry news, summaries of TAPPI conferences,

advertisements, and other topics. (TAPPI,

Norcross, Georgia, appears monthly.)

Because of the sheer number of articles

published, this is often a useful source to collect

some of the current information on a technical

subject. By using the annual index in the Decem-

ber issue, several years of this magazine can be

rapidly checked for articles on a particular subject.

TECHNICAL AND TRADE JOURNALS

References cited in those articles will give further

information, though not necessarily the most

current information.

Other pulp and paper research journals

Pulp and Paper Canada publishes about 70

high quality, original research articles annually in

addition to industry news, feature articles, adver-

tisements, and so forth. (Southam Business Infor-

mation and Communications Group Inc., Don

Mills,

Ontario, published monthly.)

Appita Journal publishes about 40 high quali-

ty, original research papers annually in addition to

industry news, features, advertisements, and so

forth. (Technical Association of the Australian

and New Zealand Pulp and Paper Industry, Inc.,

Parkville, Victoria, appears bimonthly.)

Paperi ja Puu, Paper and Timber publishes

about 60 original research, review, and feature

articles annually along with departments, and other

news items. (Toimitusjohaja, Helsinki, Finland,

10 issues annually.)

Progress in

Paper Recycling appears quarter-

ly since late 1991 and contains research articles

and practical, useful articles in paper recycling.

(Doshi & Associates, Appleton, Wisconsin.)

Other research journals

There are many other journals which have

original research articles on pulping, fiber modifi-

cation and other chemical subjects applicable to

the pulp and paper industry. Some of these

include Journal of

Wood Chemistry

and

Technolo-

gy (Marcel Dekker, Inc., appearing quarterly since

1981),

Wood Science and Technology

(Springer-Verlag, the journal of the International

Academy of Wood Science, appears quarterly).

Wood and Fiber

Science

(Society of Wood Science

and Technology, Madison, Wisconsin, appears

quarterly), Holtzforschung (Walter de Gruyter,

appears bimonthly), Mokuzai Gakkaishi (Japan

Wood Research Society, appears

monthly),

and the

Forest Products Journal, (Forest Products Re-

search Society, Madison, Wisconsin, 10 issues

annually). These journals are essentially confined

to research articles.

Trade journals or magazines

Other pulp and paper journals have industry

news,

feature articles, and advertisements, on a

wide variety of issues in pulp and paper presented

in a relatively non-technical fashion. Many are

available without charge to industry personnel.

Paper Age is published monthly (Global Publi-

cations, Inc., Westwood, New Jersey). Pima

Magazine is published monthly and is designed for

mill management (Paper Industry Management

Association, Arlington Heights, Illinois). Ameri-

can Papermaker (A/S/M Communications, Inc.,

Atlanta, Georgia) is published monthly. It was

published in 4 editions by region of the U.S. from

1987-1992; prior to 1987 it was published as

Southern Pulp and Paper. International

Papermaker IS

published quarterly as of late 1992.

Other magazines include Pulp

and

Paper Magazine

(Stockholm, Sweden, published quarterly) and

Pulp & Paper Journal (Maclean Hunter Ltd.,

Toronto, Ontario, 11 issues per year).

Pulp & Paper (the international version is

Pulp & Paper International, PPT) is published

monthly and is a very good source of current

industry production figures for North America

(Miller Freeman Publications, San Francisco,

California). (In November,

Y)Z6i}sit

Paper Trade

Journal ceased publication and was incorporated

into Pulp & Paper.) It has about six to ten articles

in each issue that focus on one or two topics in

addition to feature articles that might be on any

topic.

The focus of a given month does not

change much from year to year, so this is often an

excellent source for general, up to date informa-

tion on a given topic. In 1995, the topics were:

Month Focus

JAN Outlook'95; Capital spending

FEB CEO Profiles; Recycling

MAR Process Control; Non-chlorine bleaching

APR Papermakingchemicals ;Forming/Pressing

MAY Coating; Recycling; Environmental;

Papermaking

JUN Stock Preparation; Quality Management;

Mechanical Pulping

JUL Mill Maintenance; Woodyard

AUG Process Support Equipment; Market Pulp

SEPT Engineering; Anatomy of a Startup

OCT Chemical pulping/bleaching; Finishing

and converting

NOV Power/recovery; transportation

DEC Mill Manger's Report; Pulping/bleaching

8 1. INTRODUCTION AND THE LITERATURE

1.5 REFERENCE BOOKS

PaperWorld

This highly recommended, five volume

reference (in addition to the General Index and

World Atlas) covers the international pulp and

paper industry. Each volume is divided into five

parts covering 1) Pulp and Paper Industry, 2)

Exporters and Importers, 3) Suppliers (for exam-

ple,

machines and chemicals), 4) Associations, and

5) Trade Press. Names, addresses, and phone

numbers are given in most cases. (Birkner® &

Co.,

Hamburg, Germany.).

Lockwood-PosVs

Directory

The

Lockwood

Post's Directory lists

pulp

and

paper mills, converting mills, and suppliers with

information on personnel, types and amounts of

products produced, water, wood and power usag-

es,

equipment, etc. by state or province for the

United States and Canada, respectively. It is

updated annually.

(1990

Lockwood-Post

Direct-

ory, Miller Freeman Publications, Inc., New

York, N.Y. 1990.)

Pulp & Paper Fact Book

This 426 page reference book

lists

production

by grades, sales, prices, and historical trends of

companies for each grade. It is updated annually.

{1990

North American Fact

Book,

Miller Freeman

Publications, Inc., San Francisco, CA 1990.)

Tappi

Test

Methods,

Tappi

Useful Methods

This two-volume set contains standardized

test procedures for everything from wood chips to

containers and coated paper including many raw

materials used in these processes. Volume 1

covers fibrous materials, pulp testing, and paper

and paperboard testing. Volume 2 covers

nonfibrous materials, container and structural

materials testing, and testing practices. These test

methods are used throughout the industry to insure

quality control and comparability of

results.

Other

countries have similar sets of testing procedures

that are mentioned later. (Tappi Test Methods,

TAPPI, Atlanta, Georgia, 1991. In 1992 it was

published as a single volume.) Tappi Useful

Methods is a supplement of additional methods that

have not been as thoroughly reviewed as the

official test methods.

Tappi

Technical Information Sheets

This three-volume set contains data sheets on

densities of solutions, troubleshooting and other

guides, inspection reports, tables, figures, glossa-

ries,

etc.

(Technical Information

Sheets, TAPPI,

Atlanta, Georgia, 1989.)

Standard Testing Methods

This contains a series of standardized test

methods and data sheets of use to the pulp and

paper industry. It is similar to the two previously

listed references put out by TAPPI Press, but

contains tests of the CPPA. (Standard Testing

Methods, Technical Section, Canadian Pulp and

Paper Association, Montreal, Quebec.)

Pulpwoods of

the United States

and Canada

This two-volume set (Volume 1, conifers;

Volume 2, hardwoods) lists tree species, their

silvics, wood properties, and general pulping

characteristics with references. It includes the

commercial species of North America. This

information is increasingly important as pulp mills

look to alternate species as wood fiber supplies

become more difficult to obtain. (Pulpwoods of

the United

States

and Canada, 3rd edition. Insti-

tute of Paper Chemistry, Edited by Isenberg, I.H.,

revised by Harder, M.L., and L. Louden,

Appleton, Wisconsin, 1981.)

Wood Handbook

This is a general handbook on the physical,

mechanical, electrical, thermal and other proper-

ties of wood and wood composites. {Wood

Hand-

book:

Wood

as an

Engineering

Material.

Agricul-

ture Handbook number 72, Washington, DC: U.

S. Dept. of Agriculture; revised 1987.)

1.6 TEXTBOOKS

Handbook for

Pulp

and Paper

Technologists

This resource of pulp and paper technology

includes numerous illustrations. It is weak in the

theoretical and practical sides of the field and

slightly dated, but strong on the equipment aspect.

(Handbook for Pulp and Paper Technologists,

Smook, G.A., Joint Textbook Committee of the

Paper Industry, CPPA, Montreal, Quebec or

TAPPI, Atlanta, Georgia, 1982. 395 p.)

TEXTBOOKS

Pulp and Paper:

Chemistry

and

Chemical

Technology

This four-volume set gives a comprehensive

look at the chemistry of pulp and paper technolo-

gy. It is not heavily illustrated, nor does it give

much detail on equipment descriptions, but neither

of these detract from its purpose. It is a useful

reference book, a good starting point for detailed

information on many topics in pulp and paper.

{Pulp and Paper:

Chemistry

and

Chemical

Tech-

nology, Casey, J.P., Ed., Wiley-Interscience,

New York, N.Y. 1980, 1980, 1981, 1983 vol.

1-4, respectively. 2609 p. total) Topics, not book

titles,

are:

Wood chemistry, pulping and bleaching

Papermaking and environmental control

Chemical additives, paper properties and

analysis

Coating and converting

Wood

Chemistry:

Fundamentals and Applications

This book is a fundamental volume on wood

chemistry of very high relevance to the pulp and

paper industry. It covers the chemistry of wood

and bark components, pulping and bleaching

chemistry, chemistry of cellulose plastics and other

derivatives (derived from dissolving pulp), and

carbohydrate chemistry. {Wood

Chemistry:

Fun-

damentals and Applications, Sjostrom, E., Aca-

demic Press, New York, 1981. 223 p.; 2nd

edition, San Diego, 1993.)

Textbook

Wood Technology

Volume l~structure, identification, uses, and

properties for the commercial woods of the United

States and Canada-is very useful. Extensive

micrographs and descriptions by wood species also

make it an important reference book. Since the

cost of wood is now about 20-40% of the final

product (although quite variable) and can be

expected to increase as a percentage with more

competition for this resource, knowledge about

wood becomes very important.

{Textbook

of Wood

Technologyy Vol 1, 3rd edition, Panshin, A.J.,

and C. deZeeuw, McGraw-Hill Book Company,

New York, N.Y., 1970. 705 p.)

Others

Other textbooks are still useful if somewhat

dated. These include Pulping Processes,

Rydholm, S.A., Interscience, New York, 1965

(corrected version, 1967) 1269 p.; Handbook of

Pulp and Paper Technology, Britt, K.W.,

Reinhold, Publishing Corp., New York, 1964,

537 p.; the two-volume set Pulp and Paper

Science and Technology, Libby, C.E.,

McGraw-Hill, New York, 1962, 436 and 415 p.,

respectively; Paper

and

Paperboard,

Kline, I.E.,

Miller Freeman, San Francisco, 1982, 232 p. (2nd

ed., 1991, 245 p. and, except for updated statis-

tics,

very similar to the first edition); Pulp Tech-

nology and

Treatment

for Paper, Clark, J.d'A.,

Miller Freeman, San Francisco, 1978, 751 p. (2nd

ed., 1985, 878 p., which includes nominal updat-

ing of some fundamentals like mechanical pulp-

ing);

and the three-volume set Pulp and Paper

Manufacture, 2nd ed., MacDonald, R.G., Ed.,

McGraw-Hill, New York, 1969, (769, 542, and

655 p., respectively) listed below.

The Pulping of Wood

Control, Secondary Fiber, Structural Board,

Coating

Papermaking and Paperboard Making

Work on the 3rd edition of the Pulp and

Paper

Manufacture SQiits {with

7 x 10 in. format)

began in 1983. While generally informative, they

often lack continuity, making them difficult for

newcomers to use. The titles are as follow:

Properties of Fibrous Raw Materials and

Their Preparation for Pulping, 1983, 174 p.

Mechanical Pulping, 1987, 281 p.

Secondary Fiber and Nonwood Pulping,

1987,

266 p.

Sulfite Pulping and Technology, 1985, 352 p.

Alkaline Pulping, 1989, 637 p.

6. Stock Preparation and Nonfibrous Additives,

1992,

316 p.

Paper Machine Operations, 1991, 693 p.

8. Coating, Converting and Specialty Processes,

1990,

386 p.

9. Mill Control and Control Systems: Quality &

Testing, Environmental, Corrosion, Electri-

cal,

1992, 386 p.

10.

Process Control & Information Systems,

1993.

10 1. INTRODUCTION AND THE LITERATURE

1.7 CHEMISTRY REFERENCE BOOKS

Merck Index

The Merck Index contains data on over

10,000 chemicals, drugs, and biologicals with

information on synonyms, formula, structure,

elemental composition, commercial manufacture,

toxicity, uses, physical properties, and solubilities

in various solvents. It is updated approximately

every eight years, with the 11th edition appearing

in 1989, and available on-line for computer

searches. There are also tables on subjects such

as pH indicators and buffer solutions, conversion

factors, abbreviations, and names of organic

chemistry reactions. (The Merck Index, eleventh

edition, Merck & Co., Inc. Rathway, N.J., 1989.)

Handbook of

Chemistry

and Physics

This is a widely used, extensive collection of

information that is revised annually. It is divided

into sections containing mathematical tables,

properties of the elements, inorganic compounds,

and organic compounds, general chemistry, and

physical constants. (Handbook of

Chemistry

and

Physics, 70th edition, 1989-1990, Weast, R.C.,

Ed., CRC Press, Boca Raton, Florida, 1989.)

Lange's Handbook of

Chemistry

The Handbook of Chemistry contains tables

of mathematical and statistics, fundamental con-

stants,

conversion factors, atomic and molecular

structures, physical constants of inorganic and

organic compounds (crystalline form, refractive

index, melting and boiling points, density, and

selected solubilities), analytical chemistry (activity

coefficients, equilibrium constants, pH measure-

ments, gravimetric factors, etc.), electrochemistry,

spectroscopy (X-ray, NMR, IR), thermodynamic

properties (enthalpies and Gibbs free energies of

formation, entropies, and heat capacities of com-

pounds and elements), and physical properties

(solubilities, vapor pressures, melting and boiling

points, viscosity, dipole moments, etc.). This

handbook is revised approximately every six

years.

(Lange's Handbook of Chemistry, thir-

teenth edition. Dean, J.A., Ed., McGraw-Hill

Book Co. New York, N.Y., 1985.)

Perry's

Chemical

Engineers'

Handbook

Although most of the information covered in

this extensive reference is related to engineering

rather than chemistry, this is an extremely useful

reference book for topics such as thermodynamics,

corrosion, reactor design, distillation, process

control, and evaporation in the area of chemical

engineering. Information on virtually any unit

operation used by the pulp and paper industry can

be found in this book. (Perry's Chemical Engi-

neering Handbook, sixth edition. Perry, R.H. and

D.W. Green, editors, McGraw-Hill Book Co.,

New York, N.Y., 1984.)

1.8 OTHER REFERENCES

This list of references does not include the

many books, bibliographies, conference proceed-

ings,

and other sources of information available in

specific areas of pulp and paper. To locate these,

one should obtain a Publications Catalog from

TAPPI Press (Atlanta, Georgia), a Bibliographic

Series

List from the Institute of Paper Science and

Technology [Atlanta, Georgia and formerly the

Institute of Paper Chemistry (Appleton, Wiscon-

sin)],

a list of Pulp and Paper Technical Books

available from the Technical Section of the Cana-

dian Pulp and Paper Association, or similar re-

sources.

There are many reports of the U.S. Depart-

ment of Agriculture Forest Product Laboratory

(FPL) in Madison, Wisconsin that are not well

known. The early summary publication that

includes bibliographies of FPL reports and journal

publications of the FPL staff is useful to access

much of the early work of this laboratory. The

reference to this information is Report No. 444,

List of publications on pulp and paper, August,

1960,

58 pp. Semiannual lists are available as

well on the work done at the FPL. Some of these

reports contain pulping and papermaking studies

on wood species that may become commercial in

the future as fiber becomes more and more diffi-

cult to obtain.

1.9 ANNOTATED BIBLIOGRAPHY

On-line literature searches using computers

Steelhammer, LC. and B. Wortley, The

computer connection, PIMA Mag. 75(5):40-

ANNOTATED BIBLIOGRAPHY H

41(1992). This brief article lists several of

the vendors of computer literature searches

with their addresses and phone numbers.

History of

the

industry

Clapperton, R.H., The Paper-making Ma-

chine, Its

invention,

Evolution

and Develop-

ment, Pergamon Press, New York, 1967,

365 p. (Out of print.) This work is easy

reading and made interesting by the diagrams

and photographs. A section includes biogra-

phies of early papermakers including L.

Robert, L. Didot, J. Gamble, H. Fourdrinier,

J. Hall, J. Dickinson, Escher Wyss and J.

Voith. As I read this, I soon find myself

vicariously looking over the shoulders of the

great inventors as they first design and as-

semble their machines. This was an impor-

tant source of information for the text above

and is my favorite reference on the history of

the paper machine.

Smith, D.C., History of

Papermaking

in the

United States (1691-1969), Lockwood Pub.

Co.,

New York, 1970. 693 p.

Hunter, D., Papermaking, The History and

Technique of an Ancient Craft, 2nd ed.,

Alfred A. Knope, New York, 1943. 611 p.

with over 317 photographs and diagrams.

Dard Hunter came from a long line of paper-

makers and printers. His writings on the

history of papermaking are well known, and

a papermaking museum, once housed at the

Massachusetts Institute of Technology, but

now at the Institute of Paper Science and

Technology, is named after him.

5. Hunter, D.,

Papermaking Through Eighteen

Centuries, William Edwin Rudge, New

York, 1930. 358 p. This work deals with

early methods of papermaking and includes

numerous sketches and pictures of old tech-

niques.

6. Rudlin, B.,

Making

Paper - A Look into the

History of an Ancient Craft, Vallingby,

Sweden, 1990, 278 p. with 16 color plates (8

leaves) of contemporary, artistic, handmade

papers using a variety of vegetable fibers.

This work covers both handmade paper and

machine-made paper.

EXERCISES

Sources

information

In 1981 and 1982 some articles on carbohy-

drate analysis came out of the laboratory of

G. D. McGinnis. Using the Chemical Ab-

stracts find one or two citations for these

articles.

Once again, using the Chemical Abstracts,

find the references for some recent articles

on silylation (trimethylsilylation) of carbohy-

drates (monosaccharides). How would you

find some of the more important references

in this field without looking through every

single

Chemical

Abstract index over the last

30 years?

In 1985 an article in Analytical Chemistry

cited the following article: C.J. Biermann,

T.P. Schultz, and G.D. McGinnis, titled

Rapid steam hydrolysis/extraction of mixed

hardwoods as a biomass pretreatment. /.

WoodChem. Tech., 4(1), 111-128 (1984).

Using the Science Citations Index find the

article in

Analytical

Chemistry.

Is anthraquinone considered toxic? How is it

manufactured? (Merck Index)

What is the boiling point for H2S? (CRC

Handbook

Chem/Phys)l

6. Name a journal that appears in the Current

Contents (not previously discussed in this

chapter) that might have articles of interest to

a wood chemist.

7. The

American Men

and

Women

Science

a handy reference for learning about many of

the scientists with Ph.D. or M.D. degrees-

for example, someone who will interview

you for a research position. Using this find

out where some scientists you know or C. J.

Biermann was educated.

12 1. INTRODUCTION AND THE LITERATURE

8. Use the Lockwood-Post's directory to find

out how many pulp and paper mills are

operating in your state or province.

9. Use the Abstract Bulletin of IPST to find a

recent reference to an article on one of the

following current topics. After you have

read the article, write your own one page

sunmiary of the article. Be sure to give the

article citation in your sunmiary so your

reader may locate this article.

A. The use of anthraquinone in pulping.

Oxygen delignification.

C. Use of chlorine dioxide in pulping.

Dioxin in paper or mill effluent.

10.

Use Pulp and Paper to find out last month's

production by grade of paper for the United

States.

11.

Using Lange

Handbook of

Chemistry,

find

the value for the first acid dissociation con-

stant of aluminum ion in water. Try to

calculate the pH of 0.01 M

AICI3

in water.

Using the literature

12.

Of course, the literature comes from people

who are willing to write. This is an impor-

tant skill that takes time and practice to de-

velop.

It is useful to write essays from one

or two paragraphs to one or two pages

throughout the course. Some suggested

topics are as follows:

A. Select a mill in your vicinity and write

a two paragraph synopsis of pulping

method(s) used, the grades of paper

produced, the names of the mill manag-

er and technical director, and other

information necessary to brief your

"supervisor" who is going to visit the

mill next week.

Write an essay describing the difference

between heat and temperature.

C. A one to two page essay on a topic of

you own choosing.

13.

Which would you use the Abstract Bulletin of

IPST or the Chemical Abstracts to quickly

find an article on dioxin in pulp mill effluent?

Why? Which would you use to find the

latest information on the long term toxicity of

dioxin? Why?

14.

You have an interview with Dr. John Paper

for a research position. You want to find

some information about him and his research

work. Give two resources that might be

suitable for this.

WOOD AND FIBER FUNDAMENTALS

2.1 WOOD AND BARK

Bark

Bark (Fig. 2-1) is the outermost layer of tree

trunks and branches that protects the tree from its

environment. It comprises about 10%-20% of the

tree stem and has complex anatomy and chemistry.

Bark is a contaminant in the wood supply used for

making pulp because it decreases the quality of

pulp proportional to its level of contamination.

There is very little usable fiber in bark (mostly

due to the very small size of the fibers in bark),

and it consumes chemicals during pulping and

bleaching stages; furthermore, it causes dark

specks in the final paper product. The relatively

high level oinonprocess

elements

(impurities) such

as silica and calcium interfere with chemical

recovery

processes.

For the pulp industry, typical

bark tolerances in wood chips are 0.3 to 0.5%,

although the kraft process is more tolerant than the

other pulping processes. Bark removed from

wood is usually burned as a fiiel. Whole tree

chipping in the forest (a practice some argue will

become important in the future as it gives a higher

yield of wood chips) requires cleaning of

the

chips

before pulping to remove bark, dirt, needles or

leaves, twigs, etc.

Chemically, bark typically consists of about

10-30%

extractives (depending on the species and

extraction procedures), 15-45% cellulose, 15-40%

lignin, and the remainder is other carbohydrates

(termed polyoses that are similar to the hemi-

celluloses) and tannins (condensed polyphenolic

compounds). Bark, especially the outer bark, may

contain waxy materials called suberin and cutin,

which are polyesters of dicarboxylic acids with

Cig

to C24 structures and bifimctional alcohols among

other molecules.

Fig. 2-1. The anatomy of Douglas-fir bark including three dimensional view of whole bark (left),

cross section of bark (upper right), and isolated fibers Oower right). Courtesy of R. L. Krahmer.