Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Pulping, Digestion and Bleaching”.
1. ______ is the process after pulping.
a) Rolling
b) Bleaching
c) Digestion
d) Sheeting
Answer: c
Clarification: Digestion is the process after pulping. The digestion process essentially consists of treating wood in chip form in a pressurized vessel under controlled conditions of time, liquor concentration and pressure/temperature.
2. Which of the following is the primary function of digestion?
a) To separate the fibers
b) To produce a well cooked pulp
c) To bleach the pulp
d) To increase the strength of the pulp
Answer: b
Clarification: The primary function of digestion is to produce a well cooked pulp, free from the non-cellulosic portions of the wood (i.e., lignin and to a certain extent hemicelluloses). It’s other functions are- to achieve a maximum yield of raw material (i.e., pulp from wood) commensurate with pulp quality and to ensure a constant supply of pulp of the correct quality.
3. 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
Answer: d
Clarification: 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.
4. 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
Answer: b
Clarification: 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.
5. 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
Answer: c
Clarification: 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.
6. Which of the following component is majorly responsible for color of the pulp?
a) Cellulose
b) Lignin
c) Hemicellulose
d) Pectin
Answer: b
Clarification: 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.
7. Bleaching improves the strength of the pulp.
a) True
b) False
Answer: b
Clarification: 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.
8. _________ present in lignin is responsible for its color.
a) Chromophores
b) Corona
c) Chomosomes
d) Tonoplast
Answer: a
Clarification: Chromophores present in lignin is responsible for its color.The density of Chromophores present in a compound determines its color.
9. ________ is the term used for bleaching of mechanical pulp.
a) Whitening
b) Lightening
c) Chroming
d) Brightening
Answer: d
Clarification: 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.
10. 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
Answer: c
Clarification: 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%.
11. The residual lignin content in chemical pulp accounts for_______ of the mass.
a) 8%–9%
b) 5%–8%
c) 2%–5%
d) 1%–2%
Answer: c
Clarification: 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.
12. 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
Answer: a
Clarification: 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.
13. The term ECF in chlorine bleaching stands for _________ bleaching.
a) Elemental chromium free
b) Estimated chlorine free
c) Essential chlorine free
d) Elemental chlorine free
Answer: d
Clarification: The term ECF in chlorine bleaching stands for elemental chlorine free bleaching. Chlorine bleaching was identified as the major source of polychlorinated dioxins and dibenzofurans compounds. In addition to dioxins and furans, a host of other chlorinated organic compounds (known collectively as adsorbable organic halides or AOX) are formed during chlorine bleaching. Strict regulations now limit the production of these chlorinated compounds, resulting in a move away from molecular chlorine bleaching to chlorine dioxide, so-called ECF or elemental chlorine free bleaching.
14. ________ is the mostly used chemical for bleaching of chemical pulp.
a) Sodium Hydroxide
b) Potassium Iodide
c) Hydrogen Peroxide
d) Sodium Disulphite
Answer: c
Clarification: Hydrogen Peroxide (H2O2) is the mostly used chemical for bleaching of chemical pulp. The reaction typically requires 3 h at 40°C and is followed by neutralization and destruction of excess peroxide with SO2. Peroxide bleaching allows brightness to be increased by nearly 20%.
15. Recycled paper requires more chemicals and causes more harm to environment than new paper.
a) True
b) False
Answer: b
Clarification: The given statement is false. Recycled paper uses lesser chemicals than new paper. Recycling of paper is an example of the sustainable use of resources. Recycled or secondary fibers are an important raw material in terms of volume and utilization for the paper industry in many countries, due to market pressures resulting from government legislation, increasing public awareness of issues like sustainability and a dwindling supply of virgin fibers in some regions.