BLEACHING
Quiz
Complete these exercises at your leasure and mail me with your score. Good Luck!
What two types of bleaching can be used for the bleaching of mechanical fibre?
- Elimination and reduction
- Oxidative and reductive
- Oxidation and elimination
- Passive and active
What brightness might be expected from a Kraft pulp?
- 0-15
- 15-30
- 30-45
- 45-60
What is responsible for the colour of lignin?
- Conjugated double bonds
- Sulphonate groups
- Sulphate groups
- Heterocyclic rings
What chemical is used in reductive bleaching?
- Dithionite
- Hydrogen peroxide
- Oxygen
- Sulphur dioxide
What is the optimum consistency for reductive bleaching of mechanical wood pulp?
- 2%
- 4%
- 6%
- 8%
What is the typical pH for reductive bleaching of mechanical wood pulp?
- 3-4
- 5-6
- 9-10
- 9-10
What is the typical time for reductive bleaching of mechanical wood pulp?
- 10-30 minutes
- 20-40 minutes
- 30-50 minutes
- 40-60 minutes
Why is the bleaching consistency critical when using dithionite?
- If the consistency is too high, dithionite will react with dissolved oxygen
- If the consistency is too low, dithionite will react with dissolved oxygen
- If the consistency is too low, production rates will be uneconomical
- If the consistency is too high, dithionite will damage the fibres
At what consistency is oxidative bleaching of mechanical wood pulp carried out?
- 5-15%
- 10-20%
- 15-30%
- 20-25%
What is the typical pH for oxidative bleaching of mechanical wood pulp?
- 5-6
- 7-8
- 9-10
- 10-11
What is the typical time for oxidative bleaching of mechanical wood pulp?
- 1-3 hours
- 2-4 hours
- 3-5 hours
- 4-6 hours
In oxidative bleaching of mechanical wood pulp using H2O2, what other chemical is used?
- AKD
- ASA
- EDTA
- PDMC
What letters are used to describe the six stages of chemical bleaching?
- A, B, C, D, E, F
- C, D, E, H, O, P
- C, E, H, K, P, Y
- D, E, H, M, P, Y
What test is used to determine residual lignin?
- Bleach number
- Chlorine number
- Gamma number
- Kappa number
How is the reaction stopped when determining the residual lignin?
- By adding sulphuric acid
- By adding a mix of potassium iodide and iodine
- By adding iodine
- By adding potassium iodide
What type of titration is used?
- Automatic titration
- Back titration
- Direct titration
- Double titration
What consistency is used for oxygen bleaching?
- 10-20%
- 20-30%
- 30-40%
- 40-50%
Why has the use of chlorine for bleaching been reduced
- Because of damage to the earths ozone layer
- Because of the production of dioxin
- The cost of chlorine has risen sharply
- Chlorine damages the fibres