1. Introduction to Paper and Pulp

The pulp and paper industry separates useful cellulose fibres from a raw fibrous material, cleans and conditions those fibres, and then reforms them into a continuous sheet with the properties required for writing, printing, packaging, tissue or other applications.

2. Difference Between Pulp and Paper

3. Chemical Nature of Plant Fibres

Most plant-based papermaking materials contain three important structural groups:

• Cellulose: long-chain carbohydrate polymer forming the main useful papermaking fibre.
• Hemicellulose: shorter plant polysaccharides that can contribute to fibre bonding and pulp properties.
• Lignin: complex aromatic polymer that binds plant fibres together and gives rigidity; excessive residual lignin can reduce brightness and long-term colour stability in many paper grades.

4. Raw Materials for Paper Production

The best raw material depends on fibre length, cellulose content, lignin content, availability, cost and the intended paper grade.

5. Sources of Raw Materials

5.1 Forest Sources

Wood is one of the major industrial sources of pulp fibre. Logs are commonly debarked and chipped before pulping.

5.2 Agricultural Sources

Bagasse, cereal straw and other crop residues can supply non-wood fibres and may convert agricultural by-products into useful raw materials.

5.3 Fibrous Plants and Specialty Sources

Bamboo, jute, grasses and traditional bark fibres can be important where locally available. In Nepal, lokta is well known as a traditional handmade-paper fibre.

5.4 Recovered Paper

Old corrugated boxes, office paper, newspapers, magazines and other recovered papers can be repulped. Depending on the intended grade, contaminants and printing ink may need to be removed.

6. Pulping Methods

Pulping separates fibres from one another. The main idea can be achieved mechanically, chemically or by a combination of the two.

6.1 Mechanical Pulping

Mechanical pulping uses grinding or refining energy to separate fibres physically. Much of the lignin remains with the fibre, so fibre yield is high, but paper made from such pulp generally has lower long-term brightness stability and lower strength than well-delignified chemical pulp.

6.2 Chemical Pulping

Chemical pulping uses chemicals and heat to dissolve much of the lignin that binds fibres together.

Kraft / Sulfate Process

A common chemical pulping process digests wood chips in an alkaline cooking liquor containing mainly sodium hydroxide and sodium sulfide. Lignin is dissolved and cellulose-rich fibres are liberated.

Sulfite Process

Sulfite pulping uses sulfite/bisulfite chemistry under acidic or near-acidic conditions to make lignin more soluble and free the fibres.

6.3 Recycled-Fibre Pulping

Recovered paper is mixed with water and mechanically dispersed. Screens, cleaners and—where required—deinking steps remove contaminants before the recovered fibres return to papermaking stock.

7. Stages in the Production of Paper

The exact mill layout varies, but the NEB answer can be organized into the following sequence.

1. Raw-material preparation: debarking, cutting/chipping, sorting and cleaning.
2. Pulping: fibres are liberated mechanically, chemically or through repulping.
3. Washing: spent chemicals and dissolved impurities are removed from chemical pulp.
4. Screening and cleaning: knots, dirt, sand, plastics and oversized particles are removed.
5. Bleaching, where required: residual coloured materials are removed or modified to increase brightness.
6. Refining/beating: fibres are mechanically treated to improve bonding and paper strength.
7. Stock preparation: pulp is diluted and additives such as fillers, sizing agents, dyes or retention aids may be added according to paper grade.
8. Sheet formation: dilute fibre suspension is spread onto a moving porous wire; water drains and a wet fibre web forms.
9. Pressing: the wet web passes through press rolls/felts to remove more water and consolidate the sheet.
10. Drying: heated dryer cylinders evaporate remaining water.
11. Finishing: calendering, coating if required, winding, cutting and packing.

8. Stock Preparation: Refining, Fillers and Sizing

8.1 Refining / Beating

Refining mechanically develops fibre surfaces, increasing flexibility and the ability of fibres to make close contact. Good refining improves bonding and strength, but excessive refining can reduce drainage and alter other paper properties.

8.2 Fillers

Finely divided mineral fillers may be added to improve smoothness, opacity, brightness and print surface. Typical papermaking fillers include calcium carbonate, kaolin clay and related mineral pigments.

8.3 Sizing

Sizing controls the rate at which liquid penetrates paper. Writing and printing paper usually needs enough sizing to prevent ink or water from spreading too rapidly through the sheet.

8.4 Colour and Other Additives

Dyes, optical brightening agents, retention aids, strength additives and other chemicals may be used depending on the required paper grade.

9. Formation of the Paper Sheet

9.1 Headbox and Wire Section

Dilute pulp stock is delivered uniformly from the headbox onto a moving porous wire or forming fabric. Water drains through the fabric while fibres remain and form a wet web.

9.2 Press Section

The web passes through press nips supported by felts. Mechanical pressure removes water and increases fibre-to-fibre contact.

9.3 Dryer Section

The pressed sheet passes over heated cylinders. Remaining water evaporates until the required moisture level is reached.

9.4 Calendering and Finishing

Calender rolls can improve smoothness, thickness uniformity and surface finish. The paper is then wound into reels or cut into sheets.

10. Flow-Sheet Diagram for Paper Production

This is the most important process diagram for Unit 20.

11. Quality of Paper

Paper quality is not a single property. It is a combination of physical, optical, mechanical and surface characteristics chosen for the intended end use.

11.1 Quality Depends on End Use

12. Recycling of Paper

Recovered paper can be used again as a fibre source. A simplified recycling process is:

1. Collection and sorting.
2. Repulping with water.
3. Screening and cleaning.
4. Deinking when required.
5. Fibre treatment and blending.
6. Stock preparation and papermaking.

13. Environmental Aspects of Pulp and Paper Production

Pulp and paper manufacture uses water, energy, fibres and process chemicals. Responsible production focuses on efficient raw-material use and pollution prevention.

Main Environmental Concerns

• Unsustainable fibre harvesting if forest resources are poorly managed.
• High water use in washing, pulping and sheet preparation.
• Wastewater containing dissolved organic matter, suspended solids and process chemicals.
• Energy consumption for pulping, evaporation and drying.
• Solid residues, screening rejects and sludge.
• Air emissions and odour from some chemical pulping operations.

General Control Measures

• Sustainable forestry and greater use of suitable recovered/non-wood fibres.
• Water recycling and closed-loop process improvements.
• Effluent treatment before discharge.
• Recovery and reuse of pulping chemicals where industrial processes allow.
• Efficient energy use and recovery of process heat.
• Responsible handling of bleaching and other chemicals.

14. High-Yield Summary Table

15. Common Exam Mistakes

16. Worked Examples

17. Important Exam Questions

Short-Answer Questions

1. Define paper and pulp.
2. Differentiate pulp and paper.
3. What is the main fibre-forming polymer in paper?
4. State the roles of cellulose and lignin in plant material.
5. Name four raw materials used for paper manufacture.
6. Name two non-wood fibre sources.
7. Why is bamboo important as a paper raw material?
8. What is lokta paper?
9. How is waste paper used as a raw material?
10. What is mechanical pulping?
11. What is chemical pulping?
12. State the principle of the Kraft process.
13. Why is pulp washed after chemical pulping?
14. What is the purpose of screening and cleaning?
15. Why is pulp bleached?
16. What is refining or beating?
17. What is the function of fillers in paper?
18. What is sizing?
19. What happens in the wire/forming section?
20. What is the function of the press section?
21. Why is paper dried?
22. What is calendering?
23. Define grammage.
24. What is opacity?
25. Why is paper smoothness important?
26. State any five qualities of good paper.

Long-Answer Questions

1. Explain the raw materials and sources of raw materials used in paper production.
2. Differentiate mechanical, chemical and recycled pulping.
3. Describe all major stages in the production of paper.
4. Draw and explain the flow-sheet diagram of paper production.
5. Explain stock preparation and the functions of refining, fillers and sizing.
6. Describe sheet formation, pressing, drying and finishing in a paper machine.
7. Explain the important physical, mechanical, optical and surface properties used to judge paper quality.
8. Write a short note on paper recycling.
9. Write a short note on environmental issues in pulp and paper manufacture.

Diagram Questions

1. Draw raw material → pulp → paper.
2. Draw the plant-fibre composition diagram.
3. Draw the fibre-source classification diagram.
4. Draw mechanical vs chemical vs recycled pulping.
5. Draw stages of paper production.
6. Draw stock preparation diagram.
7. Draw forming → pressing → drying → finishing.
8. Draw the complete paper-production flow-sheet.
9. Draw the paper-quality concept map.
10. Draw the recycling loop.

18. One-Minute Revision

• Paper is a sheet mainly made from interlaced cellulose-rich fibres.
• Pulp is the separated fibrous mass used to make paper.
• Cellulose is the principal useful fibre polymer.
• Lignin binds plant fibres and is partly or largely removed in chemical pulping.
• Raw materials include wood, bamboo, bagasse, straw, jute, lokta, cotton/rags and waste paper.
• Softwood generally supplies longer fibres; hardwood generally supplies shorter fibres.
• Mechanical pulping separates fibres physically and retains more lignin.
• Chemical pulping uses chemicals and heat to dissolve much of the lignin.
• Kraft pulping uses strongly alkaline cooking liquor.
• Recovered paper is repulped, screened, cleaned and sometimes deinked.
• Raw-material preparation includes debarking, chipping, sorting and cleaning.
• Pulp is washed and screened after pulping.
• Bleaching is used when a brighter pulp is required.
• Refining develops fibre surfaces and improves fibre bonding.
• Fillers can improve opacity, smoothness and print surface.
• Sizing controls penetration of water and ink.
• The wire section forms the wet paper web.
• The press section mechanically removes water.
• The dryer section evaporates remaining water.
• Calendering improves smoothness and finish.
• Main paper-quality groups: mechanical, optical, structural and surface/fluid properties.
• Important quality terms: grammage, thickness, strength, brightness, opacity, smoothness, porosity and absorbency.
• Required paper quality depends on end use.
• Recycling allows recovered paper to become a fibre source again.
• NEB flow-sheet: raw fibre → preparation → pulping → washing/cleaning → bleaching → refining/stock preparation → forming → pressing/drying → finishing.

19. Diagram Practice

Students should practice these labelled diagrams for the NEB examination:

1. Fibrous raw material → pulp → paper.
2. Cellulose, hemicellulose and lignin concept map.
3. Sources of papermaking fibres.
4. Mechanical, chemical and recycled pulping.
5. Full stages in paper production.
6. Stock-preparation additives.
7. Forming, pressing, drying and finishing sections.
8. Complete NEB paper-production flow-sheet.
9. Paper-quality property map.
10. Recovered-paper recycling loop.