1. After steaming at ______ pressure, the chips are brought to the digester pressure of ______ kPa.
a) Low, 500
b) High, 500
c) High, 1000
d) Low, 1000
Discussion
Explanation: After steaming at low pressure, the chips are brought to the digester pressure of 1000 kPa. At LP, turpentine and gases are vented to the condenser. Then they are picked up in a stream of pulping solution and their temperature is raised to 170°C over 1.5 h. After holding at this temperature for a further 1.5 h, the digestion process is essentially complete.
2. Arrange the following processes in the right order from beginning to end in the paper making process.
i. Bleaching
ii. Pulping
iii. Screening
iv. Digestion
v. Washing
a) i,ii,iii,iv,v
b) ii,iv,v,iii,i
c) ii,v,iv,i,iii
d) v,iv,iii,ii,i
Discussion
Explanation: The first step if pulping- mechanical, chemical or semichemical, which is followed by digestion. After digestion, the liquor containing the soluble residue from the cook is washed out of the pulp, which is then screened to remove knots and fiber bundles that have not fully disintegrated. The pulp is then sent to the bleach plant or paper mill.
3. Which of the following is the primary objective of bleaching?
a) To increase strength
b) To maximize yield
c) To increase brightness
d) To remove lignin
Discussion
Explanation: Bleaching is a chemical process applied to chemical and mechanical pulps, primarily to increase their brightness but it also improves the cleanliness of pulp through removing extractives and other contaminants.
4. Which of the following component is majorly responsible for color of the pulp?
a) Cellulose
b) Lignin
c) Hemicellulose
d) Pectin
Discussion
Explanation: Lignin is majorly responsible for color of the pulp. It is the chromophoric groups on the lignin that are largely responsible for the color of the pulp. Cellulose and hemicelluloses are inherently white and do not contribute to color.
5. Bleaching improves the strength of the pulp.
a) True
b) False
Discussion
Explanation: The given statement is false. Bleaching reduces the strength of the pulp. Bleaching involves both the oxidation of colored bodies and the removal of residual encrusting materials (the principal one being lignin) remaining from the digestion and washing stages. This also results in loss of strength.
6. _________ present in lignin is responsible for its color.
a) Chromophores
b) Corona
c) Chomosomes
d) Tonoplast
Discussion
Explanation: Chromophores present in lignin is responsible for its color.The density of Chromophores present in a compound determines its color.
7. ________ is the term used for bleaching of mechanical pulp.
a) Whitening
b) Lightening
c) Chroming
d) Brightening
Discussion
Explanation: Brightening is the term used for bleaching of mechanical pulp. It is done to distinguish it from lignin-removing bleaching methods for chemical pulps. An increase in the brightness of mechanical pulps is achieved by modifying the lignin structures (chromophores) in the pulp furnish.
8. Bleaching by hydrogen peroxide occurs at ____ °C for _____h.
a) 40°C, 2 h
b) 60°C, 2.5 h
c) 40°C, 3 h
d) 10°C, 4 h
Discussion
Explanation: Bleaching by hydrogen peroxide occurs at 40°C for 3 h. It is followed by neutralization and destruction of excess peroxide with SO2. These pulps may be improved in color to only a limited extent since they contain virtually all the lignin from the original wood. Peroxide bleaching allows brightness to be increased by nearly 20%.
9. The residual lignin content in chemical pulp accounts for_______ of the mass.
a) 8%–9%
b) 5%–8%
c) 2%–5%
d) 1%–2%
Discussion
Explanation: The residual lignin content in chemical pulp accounts for 2%–5% of the mass. It is responsible for the dark color of the unbleached pulp. The reagents for full bleaching of chemical pulp are mostly oxidative and since the carbohydrates are also susceptible to oxidation, bleaching must be accomplished under the mildest conditions.
10. The term TCF in chlorine bleaching stands for_________bleaching.
a) Total chlorine free
b) Total cadmium free
c) Total chromium free
d) Total calcium free
Discussion
Explanation: The term TCF in chlorine bleaching stands for total chlorine free bleaching. This has been introduced to enable pulp and paper mills to meet tough new antipollution laws and regulations, and to conserve wood, chemicals and energy.