Pulp and Paper Multiple Choice Questions on “Pulp Bleaching”.
1. Bleaching is the treatment of wood (and other lignocellulosic) pulps with chemical agents to decrease their brightness.
a) True
b) False
Answer: b
Clarification: Bleaching is the treatment of wood (and other lignocellulosic) pulps with chemical agents to increase their brightness.
2. Bleaching of chemical pulps is achieved by lignin addition.
a) True
b) False
Answer: b
Clarification: Bleaching of chemical pulps is achieved by lignin removal.
3. _________ removal in chemical pulps leads to higher fiber-fiber bonding strength in paper, but the strong chemical pulps decrement in the length of cellulose molecules, resulting in weaker fibers.
a) Softwood
b) Hardwood
c) Lignin
d) Pulp
Answer: c
Clarification: Lignin removal in chemical pulps leads to higher fiber-fiber bonding strength in paper, but the strong chemical pulps decrement in the length of cellulose molecules, resulting in weaker fibers.
4. Bleaching mechanical pulps is called _________ to distinguish it from bleaching of chemical pulps.
a) Brightening
b) Bloating
c) Blackening
d) Branding
Answer: a
Clarification: Bleaching mechanical pulps is called brightening to distinguish them from the bleaching of chemical pulps.
5. Brightness is a term used to describe the _________ of pulp or paper, on a scale from 0 to 100.
a) Whiteness distribution
b) Whitness obstructivness
c) Coquettes
d) Bleach
Answer: a
Clarification: Brightness is a term used to describe the whiteness distribution of pulp or paper, on a scale from 0 to 100.
6. _________ is the yellowness of pulps on exposure to air, light, heat, and fungi due to modification of residual lignin forming chromophores.
a) Colour reversion
b) Colour addition
c) Oxidation
d) Exposure
Answer: a
Clarification: Colour reversion is the yellowness of pulps on exposure to air, light, heat, and fungi due to modification of residual lignin forming chromophores.
7. _________ pulps are susceptible to colour reversion.
a) Chemical
b) Mechanical
c) Dithionite
d) Hydrousulfite
Answer: b
Clarification: Mechanical pulps are particularly susceptible to colour reversion, though chemical pulps may experience this when exposed to high temperatures.
8. _________ pulps are not susceptible to colour reversion.
a) Chemical
b) Mechanical
c) Dithionite
d) Hydrousulfite
Answer: b
Clarification: Mechanical pulps are particularly susceptible to colour re-version, though chemical pulps may experience this when they are exposed to high temperatures.
9. Bleaching stages are carried out consistencies for pulp bleaching are from _________%.
a) 8-10
b) 3-20
c) 3-10
d) 4-15
Answer: b
Clarification: Bleaching stages are carried out under consistencies from 3-20%. Higher consistencies of 10-20% are used with chemicals such as oxygen, peroxide, and HOCl, which react with lignin slowly.
10. Higher bleaching stages are carried out in consisitencies of range____________
a) 8-10
b) 10-20
c) 15-20
d) 3-10
Answer: b
Clarification: Bleaching stages are carried out consistencies from 3-20%. Higher consistencies of 10-20% are used with chemicals such as oxygen, peroxide, and hypochloride, which react with lignin slowly.
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