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• Paper is a thin material mainly used for writing
upon, printing upon 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.
Five different fiber classifications include:
– bast or stem fibers, which are the fibrous
bundles in the inner bark of the plant stem
running the length of the stem;
– leaf fibers, which run the length of leaves;
– seed-hair fibers;
– core, pith or stick fibers,
– Grass and all other plant fibers not included
Obtained from the flax plant.
Located inside the stem.
Only 5% usable for
Hemp and jute are other forms
of bast fibers.
Hemp has been used for
cigarette and Bible papers.
It is used for heavy duty
shipping tags and heavy
Seed-hair fibers include;
– and milk weed floss.
Center or pith fibers include;
– and jute.
Seed Hair Fibers—Cotton Plant
• Cotton fibers are
• Used primarily for bank
notes, high grade writing
papers, maps—anything that
strength and durability.
• Wheat Straw
– Absorbs water readily.
– Used to make low grade paper.
• Bagasse fiber
– Made from crushed stalks of sugar cane.
– Used as a source of fuel for Sugar Mills.
• Esparto Plant
– Has very little strength and does not split into fibrils easily.
• Kenaf plant
– Shows great potential
– May produce 5 to 7
times more pulp/acre
– Grows to maturity in
120 days compared to
20 years for most
The remaining fibers include;
seed hulls and
short stem fiber
• 95% of all paper is made from wood
• Deciduous hardwood trees, e.g., Oak,
Gum, Maple, Aspen, etc.
• Coniferous softwood trees, e.g., Pine,
Spruce, Fir, etc. (the softwoods produce a
• It is abundant and replenishable
• It can be easily harvested and transported
to its usage site
• Good tensile strength
• Great affinity for water
• They resist change or degradation by any
chemicals bcoz of this unique
• The objective of pulping is to separate the
wood into individual fibers.
• A pulp mill is a manufacturing facility that
converts wood chips or other plant fiber
source into a thick fiber board which can
be shipped to a paper mill for further
Three broad classifications of pulping
– Mechanical (groundwood)
– Mechanical (refiner)
– Chemical (kraft process)
– Chemical (sulphite process)
– Combination (chemi-mechanical)
– Combination (chemi-thermo mechanical)
– Logs (very occasionally
chips) are pressed into a
turning stone thus
• The bark is removed from the logs.
• Then, the cut logs are forced by hydraulic
or steam pressure against a revolving
grinding stone in the presence of water.
• This treatment converts the wood into a
pulp consisting of minute particles of both
fibrous and non fibrous portions of wood.
• The nonfibrous materials deteriorate when
left for some time in contact with air.
• This type of pulp is not as strong as
• Groundwood pulp has to be mixed with
other pulps, e.g., Newsprint—contains
80% groundwood pulp and 20% chemical
• Low cost and high yield
• This pulp has high bulk and opacity
• Excellent printing, cushioning and ink
– Low strength and brightness
• Refining-Refiner Pulp
– Chips are fed between 2 disks. One disk is always
turning while the other can be fixed or turning.
• Small cylinder or wood chip is placed between
two opposite rotating plastic disc
• Chip disintegrates into coarse fibers
• Compression and decompression of rotating
• Heat generated splits the individual fibers.
• Refiner mechanical pulp also utilizes
waste chips and low grade wood than
• It has the high opacity and yeild
• It is used to isolate fibers from wood
compartment is to remove the lignin
• Delignification is done by degrading the
lignin molecules, bringing them into
solution and removing them by washing
• Also a certain amount of carbohydrates
(cellulose and hemicelluloses) is lost in
• The kraft process (or sulphate process) is
the dominant chemical pulping method
• Which involves cooking the chips in a
solution comprising sodium hydroxide
( NaOH) and sodium sulphide (Na2S), with
OH and HS- as the active anions in the
• The hydrogen sulphide is the main
delignifying agent and the hydroxide
keeps the lignin fragments in solution
• The sulphite process involves dissolving
lignin with sulphurous acid (H2SO3) and
hydrogen sulphite ions (HSO3-) as active
anions in the cooking process
• More recently devolped pulping methods
include the use of organic solvents as
ethanol, methanol and peracetic acid
(CH3CO3H) for delignification .
• To make TMP, wood chips or sawdust are
first softened by steam and then
subjected, under pressure, to the
defibering action of a disk-type refiner.
• This causes the fibers to completely
separate from each other and suffer less
damage than those produced by the
conventional groundwood pulp process.
• TMP is cleaner and stronger when
compared with groundwood pulp.
• TMP is stronger than RMP and stone
groundwood and it eliminate more costly
chemical pulps that are blended with
• It has high yield and high opacity
• It has better runnability on the presses.
• In the chemi-thermo mechanical pulping,
where the wood chips are treated with
mild chemicals prior to the refining
• This mild chemical pretreatment improves
pulp brightness to some extent
• All pulp requires bleaching to remove
residual lignin before papermaking
• The purpose of bleaching is to remove
stains caused by lignin
• There are many different types of
bleaching process, involving different
chemicals and conditions
• Major bleaching agents
– sodium hypochlorite,
– hydrogen peroxide,
– and oxygen
• Chlorine gas is one of the different
bleaching systems that are used to
remove lignin that remains in the pulp.
– Chlorine gas is passed into the pulp-water
– The gas reacts with whatever lignin that is left
and becomes chlorinated.
– The chlorinated lignin is then removed when
treated with the caustic soda NaOH (Sodium
Mechanical pulp bleeching
• After the refining process, the resulting fibers
do not have the brightness required for most
paper applications. Bleaching is therefore
• For the mechanical pulp, hydrogen peroxide,
sodium hydrosulphite or formamide sulphuric
acid are used for bleeching
• Chlorine was widely used in the past but few
mills use it today.
Chemical pulp bleeching
• In chemical pulping, the majority of the
lignin has been removed in the pulping
• In general kraft or sulphate process
requires more bleeching than sulphite
• Sodium hypochlorite or hydrogen peroxide
may be used for brightening chemically
• Once the pulp has been screened,
cleaned and bleached it is ready for the
• It involves many operations, including
stock blending, refining, broke
management, operation of the several
system, and mixing and blending of wetend additives.
• All these are important operations in
determining the quality of paper and paper
• The pH is controlled and various fillers,
such as whitening agents, size and wet
strength or dry strength are added
• Additional fillers such as clay, calcium
carbonate and titanium dioxide to
Fibers & non fibers
• Fiber - Selected for properties & cost
• Non-fibrous Additives - Selected to
obtain properties not inherent in fiber
– Strengthening Agents (Starch)
– Fillers (Clay, CaCO3, TiO2, etc)
– Internal Sizing Agents (Rosin,etc.)
– Coloring agents
• Pulp is pumped through a sequence of
tanks that are commonly called chests.
• Chests may be either round or rectangular
made with special ceramic tile faced
reinforced concrete, mild and stainless
steels are also used
• Pulp slurries are kept agitated in these
chests by propeller like agitators near the
pump suction at the chest bottom.
• Production level
– To break down the raw material into individual
– to separate fibers and contaminants,
– to separate fibers/solids and water,
– to treat the fibers, and
– to treat the residual contaminants.
• Recovery level
– where fibers and other solids, and water are
recovered from the rejects of the separation
processes applied in the production level.
Again fibers and contaminants as well as
solids and water have to be separated.
• Discharge level
– for ecological and economic reasons the
final rejects are separated into wastewater
and residues with high dry content.
• High Hemicellulose content - Easy to
refine, strong & dense sheet.
• High Lignin - Difficult to refine, and
• High Carboxylic Acid Content – Causes
fiber swelling, and ease in refining
• pH - Easier at high pH, but difficult to
Fillers are applied to the paper mainly;
• To improve the optical properties, such as
brightness and opacity
• To improve the smoothness of the sheet
surface (i. e. decreased roughness,
especially after calendering)
• To improve the sheet formation by filling
the voids between the fiber matrix
• To enhance printability in the various
printing processes due to a more uniform
paper surface, higher opacity and better
• The latter resulting in reduced printing ink
penetration, wicking and ink strike-through
to the opposite side of the sheet
• To improve the dimensional stability of the
paper as most fillers remain inert when
wetted, unlike the natural fibers usually
used in papermaking.
• To improve the permanence of the paper
(alkaline papermaking, calciumcarbonate
• Sizing makes the fiber hydrophobic and
thus prevents or reduces the penetration
of water or other aqueous liquids into the
• Sizing prevents the spreading and strike
through of ink or printing colors.
• Papermaking fibers have a strong
tendency to interact with water.
• A high absorbency is important for a few
paper grades such as toweling and tissue.
• Also corrugated medium paper must be
“absorbent” to a certain degree to convert
properly in the corrugating process.
• On the other hand such properties are
disadvantageous for many paper grades
e. g. liquid packaging, top layer of
corrugated board, writing and printing
papers and most of the specialty papers.
• The water and liquid absorbency can be
reduced by the addition of sizing agents to
the paper stock and/or by their application
to the paper surface.
• Sizing is usually performed in a size press
or a film press.
• In a size press, the web is passed through
a pond of the sizing agent, which is
located above a roll nip.
• As a result of both capillary action in the
pond and the hydraulic pressure in the roll
nip, the paper web absorbs the sizing
• The amount of size pick-up and the
degree of penetration depend upon the
– the concentration and viscosity of the size,
– the absorption behavior (porosity, moisture
content, temperature, etc.) of the paper web,
– and the nip pressure and nip length.
– Control of the size pick-up is mainly by
variation of the size concentration, but also by
variation of the nip pressure.
• This process is called internal dyeing and
is the most widely used paper dyeing
• Because of clean working conditions and
the most efficient usage, the dyes are now
mostly added continuously and fully
automatically into the stock flow.
• choice of dye and the fixing and dyeing
conditions largely depend on the raw
materials used in papermaking (recycled
fibers, stone groundwood, TMP, CTMP,
unbleached or bleached chemical pulp,
type and portion of filler) and on its
• Eg. higher degree of beating of the pulp
results in a deeper coloring
• Fillers increase the required amount of
dyes because they absorb dyes and, at
the same time, reduce the coloration
• Addition of dye is determined by a few
e. g. high consistency dyeing at a stock
consistency of 3–4 % (before mixing with
white water ahead of the headbox)
• Alternatively low consistency dyeing at a
stock consistency of 0.5–1.5 % (in front of
the mixing pump or pressure screens).
• The pH conditions are very important.
• The addition of aluminum sulfate usually
promotes the absorption of dyes and
yields less colored waste water and
• In general, there is a trend towards paper
production in the neutral or alkaline pH
range. These conditions need dyes with a
very good affinity to the paper stock in a
neutral medium and/or very effective
fixatives and retention aids.
Advantages and disadvantages
• Batch addition has the advantage of
thorough mixing of the additives with the
paper stock and optimal fixation due to
longer contact time between the fiber and
• The disadvantages are that the time
required for color correction and color
change is relatively long (loss of