Chapter 7 (2) Final

Question 1

What is the main goal of chemical pulping?

Answer 1

To dissolve the non-cellulose and non-fibrous components of the wood, primarily lignin, to separate cellulose fibers.

Question 2

What are the two main types of chemical pulping processes?

Answer 2

Sulphate process (Kraft) and Sulphite process.

Question 3

Discuss general process of Chemical pulping

Answer 3

1. Logs are first chopped in wood chips.
2. Then cooked with chemicals under high pressure. Cooking removes lignin and separates the wood into cellulose fibers.
3. The resulting slurry contains loose but intact fibers which maintain their strength.
4. During process, half of the wood dissolves into black liquor.
5. The cooked pulp is then washed and screened.
6. The black liquor is separated out from the pulp before the bleaching process.

Question 4

Why is the cooked pulp washed and screened in chemical pulping?

Answer 4

To remove black liquor and any remaining impurities before the bleaching process.

Question 5

What happens during the cooking stage of chemical pulping?

Answer 5

Wood are cooked with chemicals under high pressure, which removes lignin and separates the wood into cellulose fibers.

Question 6

What is the main advantage of the Kraft (Sulphate) process?

Answer 6

It produces high-strength pulp and efficiently recovers chemicals, making it environmentally friendly.

Question 7

What is the main disadvantage of the Kraft process?

Answer 7

It produces sulphur by-products, which can create odor problems.

Question 8

What is the main difference between chemical and mechanical pulping?

Answer 8

A: Chemical B: Mechanical
1. Yield- A: Low 40-70% B: High 90-80%
2. Cellulose purity- A: High, lignin dissolved B: Low, lignin remains
3. End Uses- A: Dissolving pulp, High quality paper, Reinforcement pkg. B: Low quality, High volume paper, 4. Molded products
Raw material sensitivity- A: Low B: High

Question 9

Pulping Quality Parameters

Answer 9

A: Chemical B: Mechanical
Strength - A: High (fibers intact) B: Low (fibers remains)
Bulk - A: Low (more and flexible fibers) B: High (few and less flexible fibers)
Optical - A: Dark but bleachable, Poor light scattering B: Bright but hard to bleach, Good light scattering.
A: Good-long fibers, few fines B: Poor-short fibers, many fines.

Question 10

Which pulping method produces stronger fibers?

Answer 10

Chemical pulping produces stronger fibers because the fibers remain intact, whereas mechanical pulping damages the fibers.

Question 11

What is the primary use of chemical and mechanical pulp?

Answer 11

• Chemical pulp is used for high-quality paper, dissolving pulp, and reinforcement packaging.
• Mechanical pulp is used for low-quality paper products like newsprint.

Question 12

What is the main advantage of chemical pulping in terms of fiber flexibility?

Answer 12

Chemical pulping produces more flexible fibers, which improves paper strength and quality.

Question 13

What is the purpose of refining/beating in papermaking?

Answer 13

To increase the surface area of fibers for better hydrogen bonding and to unravel fibers for improved paper strength.

Question 14

What is the purpose of calendering in paper finishing?

Answer 14

To compress dry paper to give it a smooth and glossy finish.

Question 15

What is the difference between plywood and laminated wood?

Answer 15

• Plywood is made of layers of wood with grains running at right angles,
• while laminated wood has layers with grains running parallel.

Question 16

What are the four main operations in papermaking?

Answer 16

Refining, sheet forming, pressing, and drying.

Question 17

What is the main disadvantage of urea-formaldehyde adhesives?

Answer 17

Their bonds break under wet or moisture conditions.

Question 18

What is phenol formaldehyde (PF) used for in wood composites?

Answer 18

It is used as an adhesive in construction plywood and oriented strand board due to its boil-proof bonds and resistance to wet conditions.

Question 19

What is melamine formaldehyde (MF) used for in wood composites?

Answer 19

It is used in plastic laminates, decorative laminates, and paper coatings due to its durability and low formaldehyde emissions.

Question 20

What are bioadhesives?

Answer 20

Natural polymeric materials that act as adhesives, often derived from biological monomers like sugars, used for bonding wood and other materials.

Question 21

What is a wood composite?

Answer 21

A material made from natural wood or wood combined with other materials like plastics or metals, bonded together using adhesives, heat, and pressure.

Question 22

What are the main types of wood composites?

Answer 22

Plywood, laminated wood, core boards, sandwich boards, fiberboards, and particleboards.

Question 23

What is plywood, and how is it made?

Answer 23

Plywood is made of three or more thin layers of wood (veneers) bonded together with adhesive, with each layer’s grain running at right angles to the adjacent layer for strength and stability.

Question 24

What is laminated wood?

Answer 24

A built-up product made of wood layers (laminae) with their grain running parallel, glued or fastened together, used in furniture, construction, and sports goods.