Pulp and Paper Processes

HISTORY OF PAPER MAKING

Gutenberg Press in 1436

On September 30, 1452 Guttenberg's

Bible was published

The printing press allowed

printed materials to be

produced at a greater rate

thus increasing the demand

for paper

HISTORY OF PAPER MAKING

First North American paper mill in 1690 near

Philadelphia

America's first writing papers were produced by

collecting, separating, and cleaning old cloth

rags

The paper was made in single sheets

HISTORY OF PAPER MAKING

1798, Nicholas-Louis Robert of France

invented a paper making machine that

produced paper on an endless wire screen

Further developed in England by Brian

Donkin

Not put into service until 1804

PAPER

1. A material made of cellulose pulp, derived

mainly from wood, rags, and certain grasses,

processed into flexible sheets or rolls by

deposit from an aqueous suspension, and

used chiefly for writing, printing, drawing,

wrapping, and covering walls.

2. A single sheet of material.

PAPER

Paper is a thin material mainly used for writing

upon, printing upon, drawing or for packaging.

It is produced by pressing together moist fibers,

typically cellulose pulp derived from wood, rags

or grasses, and drying them into flexible

sheets.

PAPER

Paper is a versatile material with many uses.

Whilst the most common is for writing and

printing upon, it is also widely used as a

packaging material, in many cleaning products,

in a number of industrial and construction

processes, and even as a food ingredient –

particularly in Asian cultures.

PAPER

3. One or more sheets of paper bearing writing or printing, especially:a. A formal written composition intended to be published, presented, or read aloud; a scholarly essay or treatise.

b. A piece of written work for school; a report or theme.

c. An official document, especially one establishing the identity of the bearer.

PAPER

Paper, and the pulp papermaking process, was

said to be developed in China during the early

2nd century AD by the Han court eunuch Cai

Lun, although the earliest archaeological

fragments of paper derive from the 2nd century

BC in China

PROPERTIES

Basis Weight (GSM)

The weight or substance per unit area is obviously

fundamental in paper and paper board products. The Basis

weight of paper is the weight per unit area. This can be

expressed as the weight in grams per square metre (GSM or

g/M2), pounds per 1000 sq. ft. or weight in kgs or pounds

per ream (500 sheets) of a specific size. REAM WEIGHT is a

common term to signify the weight of a lot or batch of

paper. Control of basis weight is important as all other

properties are affected. Variations in moisture content in

paper affects the grammage.

DIMENSIONAL STABILITY

An important consequence of the absorption and de-absorption

of moisture by paper is the change in dimension that usually

accompanies changes in moisture content. Such changes in

dimension may seriously affect register in printing processes

and interfere with the use of such items as tabulating cards.

Uneven dimensional changes cause undesirable cockling and

curling. Dimensional changes in paper originate in the swelling

and contraction of the individual fibres. It has been observed

that cellulosic fibres swell in diameter from 15 to 20% in

passing from the dry condition to the fibre saturation point.

It is impossible to be precise about the degree of this

swelling because paper-making fibres differ considerably in

this property, and because the irregular cross-section of

fibres creates difficulty in defining diameter. Change that

occurs in the dimensions of paper with variation in the

moisture content is an important consideration in the use

of paper. All papers expand with increased moisture content

and contract with decreased moisture content, but the rate

and extent of changes vary with different papers.

FOLDING ENDURANCE (DOUBLE FOLDS)

Folding endurance is the paper's capability of withstanding

multiple folds before it breaks. It is defined as the number of

double folds that a strip of 15 mm wide and 100 mm length

can withstand under a specified load before it breaks. It is

important for printing grades where the paper is subjected to

multiple folds like in books, maps, or pamphlets. Fold test is

also important for carton, box boards, ammonia print paper,

and cover paper etc. Folding endurance is a requirement in

Bond, Ledger, Currency, Map, Blue Print and Record Papers.

Gloss It is the specularly and diffusely reflected light component measurement against a known standard. Gloss is important for printing such things as magazine advertisements. The level of gloss desired is very dependent on the end use of the paper. Gloss and smoothness are different properties and are not dependent on each other.

Moisture

Most physical properties of paper undergo change as a

result of variations in moisture content. Water has the

effect of plasticising the cellulose fibre and of relaxing and

weakening the interfibre bonding. The electrical resistance

and the dielectric constant of paper both vary with moisture

content. The absorption and reflectance of certain bands of

infrared and microwave radiation by paper are affected by

its moisture content. The amount of water present in a

sheet of paper is usually expressed as a percent. The

amount of water plays an important role in calendaring,

printing and converting process. Moisture control is also

significant to the economic aspect of paper making. Poor

moisture control can adversely affect many paper

properties.

Opacity Opacity is the measure of how much light is kept away from passing through a sheet. A perfectly opaque paper is the one that is absolutely impervious to the passage of all visible light. It is the ratio of diffused reflectance and the reflectance of single sheet backed by a black body. Opacity is important in Printing Papers, Book Papers, etc.

Porosity

Because paper is composed of a randomly felted layer of fibre, it

follows that the structure has a varying degree of porosity. Thus,

the ability of fluids, both liquid and gaseous, to penetrate the

structure of paper becomes a property that is both highly

significant to the use of paper. Paper is a highly porous material

and contains as such as 70% air. Porosity is a highly critical factor

in Printing Papers Laminating Paper, Filter Paper, Cigarette Paper.

Bag Paper and Label Paper. Porosity is the measurement of the

total connecting air voids, both vertical and horizontal, that exists

in a sheet. Porosity of sheet is an indication of absorptivity or the

ability of the sheets to accept ink or water. Porosity can also be a

factor in a vacuum feeding operation on a printing press.

Sizing / Cobb

Because paper is composed of a randomly felted layer of

fibre, it's structure has a varying degree of porosity. Thus,

the ability of fluids, both liquid and gaseous, to penetrate

the structure of paper becomes a property that is both

highly significant to the use of paper. The need to limit the

spreading of ink resulted in "sizing" the paper with

gelatinous vegetable materials which had the effect of

sealing or filling the surface pores. Later, the term "sizing"

was applied to the treatment of paper stock prior to the

formation of the sheet, with water-repellent materials such

as rosin or wax. Resistance towards the penetration of

aqueous solution / water is measured by Sizing or Cobb

values.

Smoothness Smoothness is concerned with the surface contour of paper. It is the flatness of the surface under testing conditions which considers roughness, liveliness, and compressibility. In most of the uses of paper, the character of the surface is of great importance. It is common to say that paper has a "smooth" or a "rough" texture. The terms "finish" and "pattern" are frequently used in describing the contour or appearance of paper surfaces. Smoothness in important for writing, where it affects the ease of travel of the pen over the paper surface. Finish is important in bag paper as it is related to the tendency of the bag to slide when stacked. Smoothness of the paper will often determine whether or not it can be successfully printed. Smoothness also gives eye appeal as a rough paper is unattractive.

Stiffness

Stiffness is the measure of force required to bend a

paper through a specified angle. Stiffness is an

important property for box boards, corrugating

medium and to certain extent for printing papers also.

A limpy and flimsy paper can cause feeding and

delivery problems in larger sheet presses. A sheet that

is too stiff will cause problems in copier machines

where it must traverse over, under, and around feed

rollers. Bond papers also require certain stiffness to

be flat in typewriters etc.

Stretch (Elongation)

Stretch is the amount of distortion which paper

undergoes under tensile stress. Stretchlelongation

is usually expressed, as percent stretch to rupture.

Stretch can be related to the paper's ability to

conform and maintain conformance to a particular

contour, e.g. Copier paper, multicolor offset printing

papers, liquids packing cartons base papers etc. It

is an important property in sack kraft papers which

are used for cement bags etc. Stretch is higher in

cross direction than machine direction.

Tearing Resistance

Tearing resistance indicates the behaviour of paper in

various end use situations; such as evaluating web

runnability, controlling the quality of newsprint and

characterising the toughness of packaging papers where

the ability to absorb shocks is essential. fibre length and

interfibre bonding are both important factors in tearing

strength. The fact that longer fibres improve tear strength is

well recognised. The explanation is straight forward; longer

fibres tend to distribute the stress over a greater area, over

more fibres and more bonds, while short fibres allow the

stress to be concentrated in a smaller area.

Temperature and Humidity: Conditioning of Paper

Conditioning of paper is also of importance in many printing

and converting operations. In addition to the effect of moisture

content on physical properties, it also determines the build up

of static of the paper sheet subjected to pressure and to

friction. The tendency for paper to develop static becomes

greater with increasing dryness. Cellulosic fibres are

hygroscopic i.e. they are capable of absorbing water from the

surrounding atmosphere. The amount of absorbed water

depends on the humidity and the temperature of the air in

contact with the paper. Hence, changes in temperature and

humidity, even slight changes, can often affect the test results.

So, it is necessary to maintain standard conditions of humidity

and temperature for conditioning.

Thickness

Thickness or Caliper of paper is measured with a

micrometre as the perpendicular distance between

two circular, plane, parallel surfaces under a

pressure of 1 kg./ CM2. Caliper is a critical

measurement of uniformity. Variations in caliper, can

affect several basic properties including strength,

optical and roll quality. Thickness is important in

filling cards, printing papers, condenser paper,

saturating papers etc.

PAPER TYPES

Abrasive Kraft Used For : Abrasive Kraft is used for making sand paper used in roughening applications.

Absorbent Kraft Used For : Used for Laminates, tube making and defence applications.

Alkaline Paper Paper having pH values greater than 7 made by an alkaline manufacturing process.

Anti Rust Paper Paper which has the property of protecting the surfaces of ferrous metals against rust.

Antique Paper Printing paper having good bulk and opacity with rough or matt surface.

Art Paper Normally, china clay (kaolin) coated on both sides of the paper. This finish of both the sides is same, be it glossy or matt.

Used For : Brochures, calendars, magazine covers, magazine text, where high quality printing is required

Azurelaid Paper A laid paper usually bluish green in colour having a good writing surface.

THE MODERN PAPER MAKING PROCESS

The process of making paper begins far from

the paper mill itself

Clearcut in Oregon's Coast Range

THE MODERN PAPER MAKING PROCESS

Paper Making Process Overview [Chesterton, 2004]

THE MODERN PAPER MAKING PROCESS

THE MODERN PAPER MAKING PROCESS

1) Mechanical Pulping

2) Chemimechanical

3) Thermomechanical

4) Chemimechanical and Thermomechanical

Pulping (CTMP)

5) Chemical Pulping

Five Methods of pulping

MECHANICAL PULPING

There are two major mechanical pulps, thermo

mechanical pulp (TMP) and groundwood pulp (GW). In

the TMP process, wood is chipped and then fed into

large steam-heated refiners where the chips are

squeezed and made into fibres between two steel

discs. In the groundwood process, debarked logs are

fed into grinders where they are pressed against

rotating stones and made into fibres

MECHANICAL PULPING

Mechanical pulping does not remove the lignin,

so the yield is very high, >95%, but also causes

paper made from this pulp to yellow and

become brittle over time. Mechanical pulps

have rather short fibre lengths and produce

weak paper. Although large amounts of

electrical energy are required to produce

mechanical pulp, it costs less than chemical

pulp.

LIGNIN

Lignin or lignen is a complex chemical compound

most commonly derived from wood, and an integral

part of the secondary cell walls of plants[1] [2] The

term was introduced in 1819 by de Candolle and is

derived from the Latin word lignum,[3] meaning

wood. It is one of the most abundant organic

polymers on Earth, exceeded only by cellulose,

employing 30% of non-fossil organic carbon,[4] and

constituting from a quarter to a third of the dry

mass of wood.

LIGNIN

CHEMICAL PULPING

To make pulp from wood, a chemical pulping process

separates lignin from cellulose fibers. This is

accomplished by dissolving lignin in a cooking liquor,

so that it may be washed from the cellulose fibers.

This preserves the length of the cellulose fibers. Paper

made from chemical pulps are also known as wood-

free papers–not to be confused with tree-free paper.

This is because they do not contain lignin, which

deteriorates over time

CHEMICAL PULPING

The pulp can also be bleached to produce

white paper, but this consumes 5% of the

fibers. Chemical pulping processes are not

used to make paper made from cotton, which is

already 90% cellulose.

PRODUCING PAPER

The pulp is fed to a paper machine where it is formed

as a paper web and the water is removed from it by

pressing and drying.

Pressing the sheet removes the water by force. Once

the water is forced from the sheet, felt (not to be

confused with the traditional felt) is used to collect the

water. When making paper by hand, a blotter sheet is

used.

Drying involves using air and or heat to remove water from the paper sheet. In the earliest days of papermaking this was done by hanging the paper sheets like laundry. In more modern times, various forms of heated drying mechanisms are used. On the paper machine, the most common is the steam-heated can dryer. These dryers can heat to temperatures above 200 °F (93 °C) and are used in long sequences of more than 40 cans. The heat produced by these can easily dry the paper to less than 6% moisture.

FINISHING

The paper may then undergo sizing to alter its physical

properties for use in various applications. Sizing is used

during paper manufacture to reduce the paper's tendency

when dry to absorb liquid, with the goal of allowing inks and

paints to remain on the surface of the paper and to dry

there, rather than be absorbed into the paper. This provides

a more consistent, economical, and precise printing,

painting, and writing surface.

FINISHING

Paper at this point is uncoated. Coated paper has a thin layer

of material such as calcium carbonate or china clay applied to

one or both sides in order to create a surface more suitable for

high-resolution halftone screens. (Uncoated papers are rarely

suitable for screens above 150 lpi.) Coated or uncoated papers

may have their surfaces polished by calendering. Coated

papers are divided into matte, semi-matte or silk, and gloss.

Gloss papers give the highest optical density in the printed

image

FINISHING

The paper is then fed onto reels if it is to be

used on web printing presses, or cut into

sheets for other printing processes or other

purposes. The fibres in the paper basically run

in the machine direction. Sheets are usually cut

"long-grain", i.e. with the grain parallel to the

longer dimension of the sheet.

CLASSIFICATION OF PAPER

Paper may be classified into seven categories:[14]

Printing papers of wide variety.

Wrapping papers for the protection of goods and merchandise. This

includes wax and kraft papers.

Writing paper suitable for stationary requirements. This includes ledger,

bank, and bond paper.

Blotting papers containing little or no size.

Drawing papers usually with rough surfaces used by artists and designers,

including cartridge paper.

Handmade papers including most decorative papers, Ingres papers,

Japanese paper and tissues, all characterized by lack of grain direction.

Specialty papers including cigarette paper, toilet tissue, and other industrial

papers.

THE MODERN PAPER MAKING PROCESS

The chemical method is the most popular because it

produces a higher quality paper than mechanical

pulping

The most popular method of pulp production is the

Kraft process, producing nearly 85% of all pulp in

the United States

This will be the focus of the pulping description

THE MODERN PAPER MAKING PROCESS

Chesterton Pulp Digester [Chesterton, 2004]

THE PROBLEMS AND SOLUTIONS

The pulp and paper industry came into its own during a period when the environmental effects of chemical plants were not well understood, and discharges were not well regulated

The operation of a pulp and paper mill creates many environmental concerns

THE PROBLEMS AND SOLUTIONS

One of the very first

impacts of the paper

industry was the

deforestation of large

tracts of land in the early

1900s

Today the paper

companies practice a

process of sustainable

forestry

Brush Creek, Private Land, Oregon

THE PROBLEMS AND SOLUTIONS

The Sustainable Forest Initiative program was developed in 1994 by the American Forest & Paper Association to ensure forests are protected

“responsible environmental practices and sound business practices can be integrated to the benefit of landowners, shareholders, customers and the people they serve” [aboutsfi, 2004]

THE PROBLEMS AND SOLUTIONS

For every tree harvested

today, the paper

companies are planting five

seedlings

There is now more

forestland than in 1970

The Sustainable Forest

Initiative has been a

success

THE PROBLEMS AND SOLUTIONS

Many environmental concerns surround water

usage

Release of Hydrogen Sulfide (H2S)

and Sludge

THE PROBLEMS AND SOLUTIONS

Hydrogen Sulfide

Hydrogen sulfide is a toxic gas that smells like rotten eggs

At elevated levels, it can irritate the eyes and respiratory system

It can be deadly at very high levels (greater than 500,000 parts per billion)

THE PROBLEMS AND SOLUTIONS

No current Federal Limits on H2S

In January 2000, EPA issued a Federal

Register notice announcing H2S is one of

the chemicals for which EPA is developing a

health assessment

Individual States are setting limits

THE PROBLEMS AND SOLUTIONS

Reduction of Wastewater

Reduce the demand for the high quality

bright-white paper

For “lower quality” papers use a combination

of other chemicals in the bleach process

(oxygen for example)

Do a better job of pulping the wood

Machine and Cross Direction

Paper has a definite grain direction due to greater

orientation of fibres in the direction of travel of the

paper machine. This grain direction is known as

machine direction. The cross direction is the direction

of paper at right angles to the machine direction. Some

of the properties vary with the MD and CD and hence

the values are reported in both the directions. While

sheeting the paper, machine and cross direction are to

be kept in mind and the sheet cutting to be done to

suit the end use requirements

Examples: 1. All printing papers are to be cut in

long grain (The biggest dimension in the grain

direction). 2. Book papers fold better and the book

stays open better if the sheets are out so that the

machine direction runs up and down the pages. 3.

Wrap around labels for metal cans and bottles are

to be cut with the machine direction vertical to

obtain greater flexibility about the can. Long grain

and Short grain : The sheet is in long grain if the

larger dimension is parallel to grain (MD) direction.

The sheet is said to be in short grain if the larger

dimension is parallel to cross direction (CD).

THE PROBLEMS AND SOLUTIONS

Ash and smoke, byproducts of burning the black liquor and fuel in the recovery boiler and power boiler, escapes thru the smoke stacks

THE PROBLEMS AND SOLUTIONS

Improved electrostatic precipitators are being installed to help prevent the release of ash and smoke into the atmosphere

The process of concentrating the black liquor has been improved

Use cleaner burning fuels

HOPE FOR THE FUTURE

Still have a long way to go to prevent any

environmental impact

Operating a paper mill is a balancing act

Cost

Quality

Environment

Time

HOPE FOR THE FUTURE

“responsible environmental practices and sound

business practices can be integrated to the benefit of

landowners, shareholders, customers and the people

they serve”

Raw Materials

Probably half of the fiber used for paper today comes from wood that has been purposely harvested. The remaining material comes from wood fiber from sawmills, recycled

newspaper, some vegetable matter, and recycled cloth. Coniferous trees, such as spruce and fir, used to be preferred for papermaking because the cellulose fibers in the pulp of

these species are longer, therefore making for stronger paper. These trees are called "softwood" by the paper industry. Deciduous trees (leafy trees such as poplar and elm) are

called "hardwood." Because of increasing demand for paper, and improvements in pulp processing technology, almost any species of tree can now be harvested for paper.

Some plants other than trees are suitable for paper-making. In areas without significant forests, bamboo has been used for paper pulp, as has straw and sugarcane. Flax,

Most paper is made by a mechanical or chemical process.

hemp, and jute fibers are commonly used for textiles and rope making, but they can also be used for paper. Some high-grade cigarette paper is made from flax.

Cotton and linen rags are used in fine-grade papers such as letterhead and resume paper, and for bank notes and security certificates. The rags are usually cuttings and waste

from textile and garment mills. The rags must be cut and cleaned, boiled, and beaten before they can be used by the paper mill.

Other materials used in paper manufacture include bleaches and dyes, fillers such as chalk, clay, or titanium oxide, and sizings such as rosin, gum, and starch.

The Manufacturing

Process

Making pulp

1 Several processes are commonly used to convert logs to wood pulp. In the mechanical process, logs are first tumbled in drums to remove the bark. The logs are then sent to

grinders, which break the wood down into pulp by pressing it between huge revolving slabs. The pulp is filtered to remove foreign objects. In the chemical process, wood chips from

de-barked logs are cooked in a chemical solution. This is done in huge vats called digesters. The chips are fed into the digester, and then boiled at high pressure in a solution of

sodium hydroxide and sodium sulfide. The chips dissolve into pulp in the solution. Next the pulp is sent through filters. Bleach may be added at this stage, or colorings. The pulp is

sent to the paper plant.

Beating

2 The pulp is next put through a pounding and squeezing process called, appropriately enough, beating. Inside a large tub, the pulp is subjected to the effect of machine beaters.

At this point, various filler materials can be added such as chalks, clays, or chemicals such as titanium oxide. These additives will influence the opacity and other qualities of the

final product. Sizings are also added at this point. Sizing affects the way the paper will react with various inks. Without any sizing at all, a paper will be too absorbent for most uses

except as a desk blotter. A sizing such as starch makes the paper resistant to water-based ink (inks actually sit on top of a sheet of paper, rather than sinking in). A variety of

sizings, generally rosins and gums, is available depending on the eventual use of the paper. Paper that will receive a printed design, such as gift wrapping, requires a particular

formula of sizing that will make the paper accept the printing properly.

Pulp to paper

3 In order to finally turn the pulp into paper, the pulp is fed or pumped into giant, automated machines. One common type is called the Fourdrinier machine, which was invented in

England in 1807. Pulp is fed into the Fourdrinier machine on a moving belt of fine mesh screening. The pulp is squeezed through a series of rollers, while suction devices below

the belt drain off water. If the paper is to receive a water-mark, a device called a dandy moves across the sheet of pulp and presses a design into it. The paper then moves onto the

press section of the machine, where it is pressed between rollers of wool felt. The paper then passes over a series of steam-heated cylinders to remove the remaining water. A

large machine may have from 40 to 70 drying cylinders.

Finishing

4 Finally, the dried paper is wound onto large reels, where it will be further processed depending on its ultimate use. Paper is smoothed and compacted further by passing through

metal rollers called calendars. A particular finish, whether soft and dull or hard and shiny, can be imparted by the calendars. The paper may be further finished by passing through

a vat of sizing material. It may also receive a coating, which is either brushed on or rolled on. Coating adds chemicals or pigments to the paper's surface, supplementing the sizings

and fillers from earlier in the process. Fine clay is often used as a coating. The paper may next be supercalendered, that is, run through extremely smooth calendar rollers, for a

final time. Then the paper is cut to the desired size.

Environmental Concerns

The number of trees and other vegetation cut down in order to make paper is enormous. Paper companies insist that they plant as many new trees as they cut down.

Environmentalists contend that the new growth trees, so much younger and smaller than what was removed, cannot replace the value of older trees. Efforts to recycle used paper

(especially newspapers) have been effective in at least partially mitigating the need for destruction of woodlands, and recycled paper is now an important ingredient in many types

of paper production.

The chemicals used in paper manufacture, including dyes, inks, bleach, and sizing, can also be harmful to the environment when they are released into water supplies and nearby

land after use. The industry has, sometimes with government prompting, cleared up a large amount of pollution, and federal requirements now demand pollutionfree paper

production. The cost of such clean-up efforts is passed on to the consumer.

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