Wet End Chemistry – Papermaking Process Additives
Chemical additives are used in the papermaking process for many different reasons, and they are often divided into two groups. Functional chemicals directly improve properties of the sheet, while process chemicals affect operations on or near the paper machine. This module covers the second group – process chemicals. It discusses the purpose of some of the more common process additives used on paper and board machines, and describes how they work.
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Learning Objectives
• Describe the composition of papermaking furnishes • Differentiate between the two classes of papermaking additives • Describe the composition of “anionic trash” • Describe the purpose and function of common paper and board machine process additives, including pH control chemicals, charge neutralizers, retention and drainage aids, pitch control additives, biocides, and foam control additives
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, Polish |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
How do papermaking process additives differ from functional papermaking additives?
Process additives affect process operations on or near the machine, while functional additives directly improve properties of the sheet.
Where does “anionic trash” come from?
Anionic trash can enter the papermaking process in several ways. It can enter with the incoming fresh water, broke pulp, or purchased pulp, or with virgin slush pulp as residuals from pulping or bleaching operations.
Why is good retention important?
Improved retention decreases the fines concentration in the white water, improves drainage, decreases press felt filling, reduces sheet two-sidedness, improves additive efficiencies, and improves overall machine cleanliness.
What is the best pitch control additive for my machine?
In acid systems, alum can be used to attach pitch to fibers. In alkaline systems, dispersants can be used to prevent pitch from precipitating, or fillers can precipitate the pitch onto the furnish. Lowering calcium and magnesium levels, or adding chelating agents, can also help. The best approach must often be determined by trial and error.
What is the difference between a defoamer and an antifoamer?
A defoamer works by breaking down the foam, while an antifoamer prevents the foam from forming.
Sample Video Transcript
In Acid Systems, Alum can be used to attach pitch to fibers. In Alkaline Systems, dispersants can be used to prevent the pitch from precipitating. Or fillers like Talc can be added to precipitate the pitch on to the furnish so it is carried out with the sheet. Alternatively, calcium and magnesium levels can be reduced or key lading agents can be used to deactivate them in order to prevent the precipitation of pitch. The best approach for a given mill and machine must often be determined by trial and error.
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