Bleaching Basics
After wood chips are pulped, either by chemical or mechanical means, the resulting pulp has a brownish color. In order to create a white or lighter colored final product, the pulp much be bleached. This module provides a brief background on wood fibers and chemical pulping, and then provides information on what bleaching is and how it fits into the papermaking process.
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Course Details
Learning Objectives
• Identify and describe key equipment used in bleaching operations
• Describe the purpose and application of each piece of equipment
• Identify and describe typical bleach stage layouts
• Identify key considerations in selection of pump types
• Describe advantages and disadvantages of different tower types
• Identify and describe safety hazards associated with equipment used in bleaching
Specs
Frequently Asked Questions
What is pulp bleaching?
What is pulp brightness and how is it measured?
What are the chemicals used for pulp bleaching?
What is the difference between “bleaching” and “brightening”?
What does “Selectivity” of a bleaching chemical mean?
Sample Video Transcript
Lignin refers to a group of organic compounds, which are present in the outer layers of the cell walls and between the fibers. It is the glue that holds the fibers together to make wood. To convert wood into paper the lignin that holds the fibers together must be broken down. The lignin content of soft woods is 26 to 32% by weight and for hard woods it is 20 to 28%. Lignin is dark brown in color. Even after most of the lignin has been removed from wood in chemical pulping processes, the pulp fibers are still brown. Lignin is the compound which must be removed or lightened by the bleaching process.
