Pulp and Paper – A Detailed Study
PULP AND PAPER
COMPONENTS OF WOOD:
It is made by polymerization of glucose in the shape of a very long chain of cells. These contents should be in higher quantity for a suitable raw material.
The complex polymer in plant cell walls that gives the plant rigidity and strength, and is the major component of wood. It is a binding material for cells. Its ratio should be lower and there should be minimum lignin for suitable raw material.
If a number of joined molecules is less in the chain that is called hemicellulose and better than cellulose. Hemicellulose is unlike cellulose dissoluble in water. This should also be in less quantity.
These are actually mineral of soil taken up by plants through roots with soil moisture. They impart coloration to paper. They should not be more than 10% otherwise more chemicals will be required to whiten the paper, which is not economical.
This fraction termed extractive is composed of a variety of material that generally is not considered a part of the cell wall. These organic extraneous compounds may be included low molecular weight. They should also be in less quantity or amount.
A substance consisting of wood fiber isolated from wood by mechanical or chemical means and used for the manufacturing of paper called Pulp. The process of isolating wood fiber is called Pulping.
CHARACTERISTICS AND CLASSIFICATION OF IMPORTANT FIBROUS RAW MATERIALS:
- Hardwood: in Sulphite pulp
- Softwood: in Kraft pulps
- The whole bagasse (dry refuse left after the juice has been extracted from sugar cane, grapes, or sugar beets. Use: fuel, cattle feed, making paper) are used for pulping. For the production of higher quality of paper which requires the removal of pith, which constitutes 25% of the dry material.
- Seasonal and limited because mills itself use it.
- Cannot be stored due to having sugar content which changes into alcohol in summer and thus danger of fire.
- Its fiber is longer than grass and hard cores.
- But not very good due to more ash contents.
- Bamboo is from grass family and there are about 1000 spp in different parts of the world.
- Limited supply as used as fodder.
- Low yield about 40%
- The expensive paper is manufactured from wheat straw
- In Pakistan Kai, Fritaiss, and Berveza are used for papermaking.
- Before pulping roots and other extraneous are removed.
- It is preferable to cut a 1-inch length
- Nowshera paper mill is based mainly on grasses.
- In China, Taiwan, Egypt, Spain, Indonesia, Thailand, used
- Rice has great extraneous matter such as node, leaves grain, debris and fines.
- These matters are removed by cutting the straw into 1-3 inches length followed by passing through cyclones or screens by machine.
- Rice straw has ash content 14 to 20%
- Rice straw has a very high silica content
- Used in many of the Pakistani pulp and paper mills for pulp manufacturing
- Soda, Kraft, and NSSC processes are most usual.
- Fibers consist of quite pure cellulose
- Cotton linens are shorter fibers, seed hairs
- Used for dissolving pulps
- Alkaline processing of linters from seed.
- Ramie (a lustrous soft durable fiber obtained from the bark of a bush. Use: fabric, rope OR; a perennial bush whose bark yields ramie. Native to Asia. Latin name: Boehmeria nivea)
- Plants are grown in sub-tropical countries
- Produce largest fibers used in papermaking
- They have outstanding strength and are used for especially applications
- Filter paper, saturating papers, condenser tissues, and tea bags are an example of such uses.
- Used robe has been one of the sources.
Characteristics of Raw materials:
- It should contain less ash content
- Materials contain fewer extractives
- Contain less lignin (removal of lignin is called pulping)
- Contain less hemicellulose
- Contain maximum cellulose
- Woods with less wall thickness are preferred
- More lumen width, good pulping properties
- Long fiber are preferred (because of more strength)
CRITERIA FOR SUITABILITY OF A SPECIES TO BE USED FOR PULP MANUFACTURING:
In order to obtain best quality pup and ultimately the paper, and to make the pulp and paper industry more economical, profitable and successful, besides many other factors imperatives, it is also essential that before using a particular wood species in the manufacture of pulp its suitability should be properly checked. This suitability checking is based on Physical, Anatomical, and Chemical analysis of wood.
Physical Analysis or Study:
Under this head, we study the basic density and color of the wood.
- Basic Density:
- Generally, density is defined as, “mass per unit volume of a substance.”
- In case of wood, we use the term Basic Density which is defined as, “Dry weight per green volume of wood.”
- Basic Density of a wood simple is worked out in the laboratory which involves following steps:
- Soak the wood sample in water
- Remove the extra water from the wood surface with the help of a tissue paper.
- Measure the volume of the wood in this condition
- Dry the wood sample in the oven up to the time when its weight becomes constant.
- Weight oven dry wood. So the ratio of this weight with volume obtained in soaked condition will give the basic density.
- For making pulp the basic density of wood should be b/w 400 – 650 kg/m3
- Wood with basic density beyond these limits can be converted into pulp, but this will not be standard pulp and require many processes.
- The density of wood is 60% a genetic character.
- Up to 40%, we can alter the density of a species with Silviculture practices such as increasing rotation age, best management, spacing, fertilization, etc.
- Density varies from tree to tree, species to species, locality to locality and also influenced by chemical composition from top to bottom of the tree.
- The color of the wood:
- The color of wood also plays an important role in its suitability for pulping.
- Darker is the wood color implies more lignin presence so more chemical requires for pulping and bleaching which means more environmental pollution and vice versa if the color is light.
Anatomical Analysis or Study:
Under this head, our concern is with the length of the fiber, the wall thickness of fiber, lumen width, and rinkle ratio.
- Length of fiber:
- Greater the length of fiber more it will be resistant to tearing and lower is length means more susceptible to tearing.
- Wall thickness of fiber:
- The thicker the fiber wall more difficult to be pressed and result in the creation of voids/ pores.
- On the other hand, thinner the wall more easily it pressed and ovoid creation of voids/ pores in the paper.
- Lumen width:
- More will be suitable if lumen width (the cavity within a plant cell wall) is more because it yields in the smooth surface due to easily pressing.
- These properties give rise a relation known as Rinkle Ratio:
- If RR < 1 it will be suitable
- If RR > 1 it will not be suitable.
Chemical Analysis or Study:
Wood is composed of organic and inorganic components.
- A major portion of wood is cellulose. Both soft-wood and hard-wood have 30 – 50% cellulose which is found in the cell wall of fiber
ie C6 H12 O6 + C6 H12 O6 à (C6 H10 O5)2 – H2O
- More is cellulose in a wood species more suitable it will be for pulping.
- It is the 2nd major component which serves as binding or cementing material b/w cellulose chains.
- Actually pulping is nothing, but the removal of lignin to obtain fiber.
- Therefore, as low will be lignin as much as it will be suitable for pulping because less chemical is required for processing.
- The trees have their defense system called extractives which fight against the disease.
- These are coloring matters.
- Shisham looks brown due o presence of high extractives, while poplar light color due to low extractives. So high extractive containing species are not suitable for pulping because their bleaching requirement will be more.
MAJOR CONSTRAINTS OF PULP AND PAPER IN PAKISTAN AND SUGGESTION:
INTRODUCTION & HISTORY:
According to tradition, the paper was first made in ad 105 by Ts’ai Lun, a eunuch attached to the Eastern Han court of the Chinese emperor Ho Ti. The material used was probably the bark of the mulberry tree, and the paper was made on a mold of bamboo strips. The earliest known paper still in existence was made from rags about ad 150. For approximately 500 years the art of papermaking was confined to China, but in 610 it was introduced into Japan and into Central Asia about 750 as a result of the attack of the Arabs to China. Paper made its appearance in Egypt about 800 but was not manufactured there until 900.
The use of paper was introduced into Europe by the Moors, and the first papermaking mill was established in Spain about 1150 and the man behind was Tariq Bin Zeyyad. In succeeding centuries, the craft spread to most of the European countries. The introduction of movable type about the middle of the 15th century made book printing practical and greatly stimulated papermaking. The first paper mill in England was established in 1495, and the first such mill in America in 1690.
The increasing use of paper in the 17th and 18th centuries created shortages of rags, which were the only satisfactory raw material known to European papermakers. As a result, many attempts were made to devise substitutes, but none was commercially satisfactory. At the same time, attempts were made to reduce the cost of paper by developing a machine to supplant the hand-molding process in paper manufacture. The first practical machine was made in 1798 by the French inventor Nicholas Louis Robert. Robert’s machine was improved by the British stationers and Brothers Henry Fourdrinier and Sealy Fourdrinier, who in 1803 produced the first of the machines that bear their name. The solution of the problem of making paper from cheap raw material was achieved by the introduction of the groundwood process of pulp making about 1840 and the first of the chemical pulp processes approximately ten years later.
With the discovery of America by Christopher Columbus (1451-1506), the technology then moved to the US where it flourished to its peak and it became the leading country in Paper industry not only it’s manufacturing but also in its consumption (350 kg paper per capita consumption) presently, whereas for the case of Pakistan the rate of consumption is about 4 kg paper per capita consumption.
PROBLEMS OF PULP AND PAPER IN PAKISTAN:
A number of factors are responsible for the tribulations of Pulp and Paper and its thriving in Pakistan. These are discussed as under:
Low Forest Cover:
The condition of forest cover in Pakistan is derisory which is about 5.2% and the canopy cover counseled for any country supposed to be greater than 20%. Majority of these forests lie in our important catchment areas which, in any circumstance, cannot be felled. The only trees available for paper production are from agroforestry.
Of all the factors responsible for the depletion of forest cover; deforestation is the major one and that is 1.5%. According to a report of IUCN if this rate of deforestation persisted we will be having no forest cover after 16 years.
Population, as it is said, is one of the main rationales behind the depletion of forest covers. If it is so then why forest cover in China and India is not dwindling instead of escalating.
Afforestation can be helpful in upsurge the forest cover in the country. Yet again we are lacking two important resources, explicitly water and land, which are essential in this regard. Majority of the country is in Sub-Tropical Eco-region where land is of Xerosere nature and drought prevails for most of the year. And rest of the major part (6.2 million hectare which is about one-third area of the country) is facing the problem of salinity and waterlogging.
The planting of salt tolerant trees like Eucalyptus spp is the best step in this direction. Since it is a salt tolerant species even it can tolerate a pH of 10 so it will not only help in solving the problem but also it is one of the best species used in the production of paper.
Less number of mills:
The number of paper manufacturing mills is very much less and these few mills cannot meet the demands of the paper utilizing industries. Besides, the operational mills in the country are all small-scale mills. These mills are obviously low capacity mills and were established to meet the demand of the paper utilizing industries of the previous times.
Presently 50 mills of pulp and paper are working in Pakistan which cannot go through with the demands of the country. Besides the machines are small and old having very low efficiency. The operating efficiency is 60 %. For the case of America, if the operating efficiency of any machine comes below than 80% it is closed down. The reason behind is the proportionality between the cost and efficiency of the machine. Greater the efficiency of the machine, lower will be the costs and vice versa.
On account of above reasons, Pakistan is importing about 50% of its paper requirements which costs about Rs. 13 billion annually which are the 7th biggest import, so it is a substantial pressure on our foreign exchange.
Shortage of Raw Materials:
Paper can be produced by non-woody products and wood products. As mentioned earlier Pakistan has a very low forest cover which either lies on imperative catchment areas or of protected or reserved legal status. The only predilection is the use of non-woody products. This by no means cannot substitute the wood products.
Use of Non-Woody Products as Raw Materials:
In Pakistan non-woody products ie wheat straws, grasses, etc are used for papermaking as raw materials. These products cannot be a substitute to the woody raw materials owing to the following reasons.
- If we check out the word paper industries, 90% of the market is based on woody products while only 10% rely on non-woody products, which is reversed for the case of Pakistan.
- The collection of non-woody products is intricate and overpriced while the collection of woody products is simple.
- The storage of wood products is best and long termed while non-woody products cannot be stored for longer time having poor storage.
- The number of mills in the country should be increased.
- The private sector should be allowed and must be given incentives so that they can invest with ease of mind.
- New advanced technologies should be adopted and sophisticated types of machinery to be imported to establish large-scale mills to get the high-quality paper at lower costs.
- Fast growing tree spp should be planted on farmlands through social forestry programmers so that woody raw material is easily available for the paper industry.
- Woody raw material should be used for the manufacturing of paper instead of non-woody raw material as the former is of high quality.
Pakistan is expending a large amount of money on foreign exchange if this amount is utilized in Afforestation on saline and waterlogged areas it will not only full fill our paper demands but also play an imperative role in improving the livelihood of people by creating job opportunities for instance.
MANUFACTURING OF PULP BY CHEMICAL METHODS:
The pulp is manufactured by using Chemicals ie
- Sodium hydroxide (NaOH)
- Sodium sulfide (Na2S)
Both these chemicals have advantages as well as disadvantages in using them. NaOH dissolves the lignin content up to 15 – 20% only while Na2S dissolves about 98% lignin. NaOH weakens the fibers of wood; subsequently, the paper will not be of good quality. Some of the cellulose material gests dissolve, weakening the fiber. Na2S when reacts with lignin forms organt sulfur compounds which is slightly polluting to the environment. But most of the pulp is manufactured by using sodium sulfate, called Sulphate Pulping. Sodium hydroxide pulping is also used called Soda Pulping or alkaline pulping.
Different methods are used in chemical Pulping:
- Sulfite Process:
- Sulfate Process or Kraft Process
- Soda Process:
A digester having dia of 16ft and height of 50ft is used. Wood chips are put in the digester and steam is done at 150-170 OC. Sodium Sulphate and water are also introduced in it. Cooking is done for 4-5 hours. If pulp of more good quality is needed, time and amount of chemicals are increased. After cooking when the value is opened, whole material falls in blow tank below digester. Blow tank has the capacity to accommodate material form 3 digesters. The bottom surface of the blow tank is porous, so pulp is filtered. When pulp from digester falls in blow tank, due to its mechanical energy, fibers are separated. After blow tank pulp is washed. After washing black liquor goes to drain and pulp goes to knotter. From knotter pulp goes to the screener where larger particles are separated. After screening, we get fine pulp which is used for paper manufacture.
Recovery of Black Liquor:
Black liquor causes water pollution, so its recovery is essential.
Sulfate Process or Kraft Process:
Chemical pulping is done by Kraft Pulping process. Kraft is the name of a German scientist Dhal Kraft.
Advantages of the kraft pulping process:
There are several advantages of this process which are as follows:
- Any wood species either softwood or hardwood can be used for pulp.
- This is a self-sufficient pulping process.
- A number of by-products like vanilla, turpentine, rosin, etc are formed.
- Pulping time is very short.
- Recovery of the chemicals at the end.
- Strength properties of paper are very good. Papers used for writing, printing, photographic films, cellulose acetate asters; etc can be formed of good quality.
Disadvantages of kraft pulping:
The chemical pulping process is highly polluting because Organo-sulphur compounds are formed, which are highly toxic.
Steps for manufacturing of pulping:
Various steps in the manufacturing of pulp are as follows:
Logging operation and debarking:
The logging operation is done in the forest. In order to decrease the transportation cost, mills should be established near or in the center of the forest. Debarking can also be done in the forest on the spot. The bark contains the dead cells; it is of no use in the making of pulp but contains food reserves which are beneficial for the fertility of the soil. Debarking can be done by;
- The labor, but in industrialized countries, labor cost is high, so automatic debarking is done.
- Biological method ie barks can be ruptured by the action of sunlight, fungus, and moisture.
- Special roller/ drums are used to remove the bark. The logs are put into the drums and the drums are rotated. After collisions, the bark becomes easy to remove.
Chipping of logs:
Logs are first converted in a specific size and are placed in an automatic chipper, which converts it into small size chips and is further processed to the paper mills.
Screening of wood chips:
Screening is done in order to get a uniform chip size. The oversize chips are removed by screening. Knots are also removed by this process.
Boiling and digestion:
The wood chips after screening are boiled in the boilers, to soften the wood chips and then convert them into pulp which is further processed for paper manufacturing. The boiled pulp is then transferred to digesters. NaOH and Na2S along with water are poured into the drum containing the pulp. Sulfur will dissolve the lignin up to 98% and pulp will be formed. Sodium carbonate Na2CO3 and Calcium carbonate CaCO3 is also added. The drum is rotated so that the ingredients mix up and pulp is separated. Pulp floats on the top while at the bottom, black liquor settles, containing the inorganic un-reacted chemicals, extractive, 28% lignin and hemicelluloses.
Washing of Pulp liquor:
Black pulp liquor which settles down at the bottom is a source of many chemicals ie hemicellulose, lignin 28%, extractives, turpentine oil, etc. it is a source of energy which increases the internal energy required for the pulping process and this is how chemical pulping is a self-sufficient process.
MANUFACTURE OF PULP BY MECHANICAL PROCESS:
In the mechanical pulping process, only mechanical energy is used to separate fibers of the wood. For this purpose, stones are used which grind the wood. While grinding, due to friction that energy is produced and temp increases up to 170-1800C which is sufficient to melt lignin and fibers which is sufficient to melt lignin and fibers which is the binding material of fibers, so fibers are separated. Water is also applied on stones to reduce temp to prevent logs from burning and surface of the stone is also washed.
- In Mechanical Pulping all ingredients of wood remain in the pulp so yield is high ie 98-99%.
- High electric energy is required.
- It is used in newsprint paper manufacture
- Fibers are torn cell wall (the majority of fibers) and disintegrated into pieces.
Mechanical Pulping in Pakistan:
Mechanical pulping is not done in Pakistan because;
- The raw material is not available
- Electric power is not available in required quantity.
Theory of Mechanical Pulping:
- Due to friction among stone and log surface heat energy is produced which is sufficient to melt lignin which is a binding material, so fibers are isolated.
Methods of Mechanical Pulping:
Stone groundwood pulp:
- First of all, logs are debarked then put in a machine
- A stone is moving and rubbing against the logs and convert them into pulp.
- The surface of the stone is continuously sprayed with water to keep the abrasive surface clean.
- Boil up to near the boiling point.
- In the mechanical process, no chemical composition occurs in the wood.
- The majority of the fibers are separated by the slight change.
- Conifers and low density of hardwood is used
Refiner mechanical pulp:
- Principles of RMP is like those of Chacki (water mill)
- First of all logging; then debarking; taking two disc one with grooves and is stationary and the other disc moving by electricity but with no grooves.
- Biter pulp is formed than the former one method because here there are fewer disturbances in the fiber length and is modern and has high yield percentage while stone groundwood pulp is an old method.
- Heat + Force (force is required comparatively less)
- Here logs are debarked; chips are formed by chipping; heating by a stream in digester for softening; then by two discs as in RMP process.
- High yield pulp (80 – 90%)
- Most modern method
- The superior quality of pulp among all mechanical pulp
Species used in Mechanical Pulping:
Spp having lower density eg conifers and other woods are suitable of a mechanical pulping, hence much energy is not required or less power is required eg following is the energy requirement for mechanical pulping of poplar and spruce.
Poplar needs 3300 kwh/ ton
Spruce needs 12000 kwh/ ton
Problems in Mechanical Pulping:
- Specific dia of logs is required in Mechanical Pulping.
- 70-80% mechanical pulp is used in newsprint 20-30% chemical pulp is used which is costly and increases the cost of paper to increase strength.
MANUFACTURE OF PULP BY CHEMI-MECHANICAL PROCESS:
- In this process, the fabrication of wood is accomplished by mechanical means.
- The chemical treatments are used to improve the physical properties.
- Such treatments are steaming, or mild digestion with water, bi-sulfite, neutral sulfite, caustic soda or Bi-carbonate.
- Following processes are included in this category:
- Cold soda pulp process
- Chemi groundwood pulping process
- Hot sulfite pulp process
- Groundwood pulp process
Cold soda pulp process:
The wood chips are treated with diluted caustic solution (2 to 6%) at room temperature and softened the chips are reduced to pulp by disc machine.
Chemi groundwood pulping process:
In this process, high-density hardwood is digested in neutral sulfite liquor and then reduced to pulp by grinding. It is not successful to obtain the ground wood from the hardwood; however, a wide range of pulp can be obtained by taking some chemical treatment.
Hot sulfite pulp process:
The use of hot neutral or bi-sulfite liquor in the treatment of chips prior to the mechanical fibrising type of treatment produce of while treating colored pulp from softwood which is comparatively stronger than groundwood.
Ground wood pulp process:
For the manufacturing of structure board wood is mechanically de-fiberized to a fiber pulp after steaming at a high temperature and pressure.
In thermo-mechanical pulping, thermal energy is also used in addition to mechanical energy. First, the chips are heated with steam. Due to steaming fibers become soft and the pulping process becomes easy. Furthermore, good quality pulp is produced.
- Quality of pulp is good due to less dust formation because fibers are soft.
- Only 5% chemical pulp is used
- Yield is 80 – 85%
- The coloration of fibers takes place. For discoloration, bleaching is to be done with chemicals. So we have to apply additional chemical energy. Hydrogen peroxide is used for bleaching.
- Due to the use of chemicals pollution hazards are increased.
Methods of T.M. Pulping:
- Bauer Process:
- Defibrator Process:
- Saund Process:
This is a storage tank in which chips are stored. From this storage chips are conveyed to the digester through a conveyor which is run by power digester is a tube-like structure which is insulated outside to check the loss of heat. It is provided with a screw which moves with power. Chips are passed through a digester and it takes 10-20 minutes to pass through digester. Steaming takes place during this period and fibers become soft.
From digester material taken to the refiner no 1 where deliberation is done. For deliberation, the material is taken to the 2nd refiner.
In this process, chips from storage go to screw feeder. From screw, feeder chips go to the digester. Digestion in this process is vertical in position. Chips move form up to the downward direction and steam moves upward. It takes 10-15 minutes to pass chips through digester. Steaming occurs during this period and fibers become soft.
After this material goes to the first refiner where deliberation is done under the same steam pressure. After deliberation, the material goes to refiner no 2 for defibrillation.
In this process chips from storage come in conveyer from where they go in a digester which is horizontal instead of vertical. After digester wood chips come in a cyclone where steam is exhausted and chips go to the refiner. Twin disc refiner is used in this case.
It is a Dutch word which means to fade the color. So bleaching means to fade the color and increase brightness.
The brightness of the paper required varies with the use of paper. Eg brightness sufficient for newsprint is 50% but for a textbook is 80%.
Color in the paper is due to lignin which has a yellow color. Complete removal of lignin from the pulp is not possible. About 2-3% of lignin bleaching is done.
First sunlight soap was used as a bleaching agent. Then NaOH was introduced. Now there are many chemicals which can be used for bleaching.
Chemicals for Bleaching of Mechanical Pulp:
For mechanical pulp, lignin preserving chemical are sued. The chemical covertly lignin into acids which don’t give color.
- Hydrogen peroxide P
- Dithionite Y
- Oxygen O
- Ozon Z
Chemicals for bleaching of Chemical Pulp:
These chemicals dissolve the logs:
- Chlorine C
- NaOH E
- Sodium Hydrochloride H
- Chlorine dioxide D
Factors affecting color:
- Residual lignin
- Resin content
- Manganese, copper, iron impact color.
- Quality of wood eg poplar gives bright color than eucalyptus.
MANUFACTURE OF PAPER:
Manufacture of Paper can be divided into two processes:
- Sheet Formation:
To obtain paper or paperboard from the pulp is called Sheet Formation. Different operations during sheet formation can be classified as under:
- Stock Preparation:
- Sheet Formation:
Stock preparation includes following operations:
For beating a beater known as Hollower is used. It consists of a steel tank with sound edges which lie at a partition wall in the center. Thus a channel is formed around the partition wall in which pulp flows on one side of the partition wall. On the channel a solt equipped with knives. Directly below the solt is a bed plate which also consists of the stationary ball. During beating pulp is forced to pass in b/w bars of revolving solt and bed plats.
Another refiner is used called as Jordan engine. It is a conical shell which is provided with bars which are stationary. Inside of the shell is a moving core which consists of bars. The pulp is beaten b/w these bars.
Like wood, the paper has the power to absorb water from the atmosphere. So when the paper goes in the market it is destroyed by absorbing water. To check absorption of water by paper, sizing is done. Sizing are the chemical which when mixed with paper, they check absorbing of water. For this purpose, the resin is used.
Fillers are also the chemicals which are used to fill the spaces among fiber spaces. Following chemicals are used as fillers:
- Titanium dioxide
- Barium sulphate
The cheap one is China clay.
Coloring of paper can be done in a beater or by the surface application after manufacture of paper.
After preparation of stock, this stock is sent to head box. This stock contains ½% fibers. Then stock flows from head box to the bronze wire screen by force of gravity. The pulp fibers remain on the screen while the water drained. While moving forward, the screen also shakes in a sideward direction to orient the fibers to distribute fibers uniformly, thus increasing the strength of paper. While still on screen, the material passes through the suction box which sucks water from the material. Then this material passes under a dandy roll which gives the material a smooth top surface. At this stage, materials contain 8% moisture. Rubber deckles straps travel along the screen at the same speed to form edges of the sheet.
Now sheet from screen goes to press section. In press section first felt blanket carries the sheet through a number of rolls. Here more water is removed and the sheet is given a uniform shape.
After passing through press rolls, the sheet is removed by second felt blanket which carries it through series of drying rolls. Then it is rolled through drying rolls, the paper becomes dry and sizing may be added at this stage.
After drying sheet enters the calendar stack which is a series of smooth heavy steel rods which give final shape to the paper. After ironing paper is mound on reels.
Paper is wound on a reel in its full machine width. Paper machines are 1-8 in wide. These sheets are then cut in finishing room and packed into a pile of 500-1000 and is called ream which are sent in the market.
For correction and improvements please use the comments section below.
4 thoughts on “Pulp and Paper – A Detailed Study”
my dear Naeem
assalam o alaikum
hope it finds you happy and healthy inshaAllah. your inputs are always very useful and valuable. may you please add references in your reviews/articles etc. for further convenience.
Muhammad Khurram Shahzad
PFI session (1997-2001)
SRO (Forest Management)
Walekum Assalam Sir
Your feedback is really valuable and I’ll keep these guidelines in mind. Regards
Thanks for sharing the information with us, it was very informative
You’re welcome 🙂