At the end of this module, you will be able to:
- Define the terms "pulp," "paper" and "paper grades"
- Describe the major milestones in the history of papermaking
- Differentiate between hardwood and softwood fibers
- List in order the major operations for pulping and papermaking
- Differentiate between mechanical, chemical, and semichemical pulping
- Describe the screening, bleaching and refining steps in pulp processing
- Define and order the major sections of a paper machine
The following key questions are answered in this module:
How are softwood and hardwood fibers different from each other?
Softwood fibers tend to be long and flexible, which contributes to the strength characteristics of paper. Hardwood fibers tend to be short and stiff, which contributes to the bulk, smoothness, and opacity of paper.
Why is paper that is made from mechanical pulp called "wood-containing paper"?
Mechanical pulps contain all of the constituents of wood, including the lignin, and so they are referred to as "wood-containing."
What is the "liquor" that is used in chemical pulping processes?
"Liquor" is the name of the water-based chemical solution that is used to cook wood chips in chemical pulping processes.
What happens to the chemicals in the cooking liquor after the pulping process?
The chemicals are washed out of the pulp and then they are recovered so that they can be reused.
Pulping and papermaking processes require a lot of steam heat. Where does this steam come from?
As part of the chemical recovery process, many organic compounds from the wood are burned to produce steam.
Below is a transcript of the video sample provided for this module:
The two major chemical pulping processes are sulfite and kraft or sulfate. In both processes, wood chips are cooked in a chemical solution called liquor to remove the lignin and separate the cellulose fibers from each other. Because lignin and some other wood components are dissolved and removed, these pulps are referred to as wood-free. One major disadvantage of chemical pulping processes is that they have yields in the range of 40 to 50%, whereas mechanical pulping yields run around 95%. The main advantages of chemical pulps are that the fibers are longer and stronger, and they can be bleached to a high brightness.
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