Background: Some contaminants defy removal by any physical type of separation process. For instance, contaminants that are absorbed or exist in the fiber wall may be very difficult to remove. Dyes in particular are one such contaminant. Another contaminant inherent in the fiber is lignin. To remove or destroy dyes or lignin one must resort to chemical attack. A bleaching agent is used to destroy the "chromophores" responsible for making fibers dark. Sodium hypochlorite is one such chemical. Another very common bleaching agent used is peroxide. In this laboratory, you will learn a simple method to bleach recycled pulp.

1. Obtain an 8.5 by 11 inch piece of colored copy paper.
2. Cut the paper in half. Set aside one-half of the sheet of paper as a control. Rip up the other half of the paper into approximately 2 inch squares and add to 1000 ml of hot water in a blender cup.
3. Blend for 30 seconds.
4. Filter the pulp through a Buchner Funnel. You may use either a piece of filter paper or some cheese cloth as the filtering material. Peel the filter paper (or cheese cloth) off of the pulp mat. Put the pulp mat into an approximately 250 ml glass bottle or jar.
5. SAFETY: Always use caution when using bleach. It is a chemical that should be treated with respect. Avoid contact with skin. Avoid splashes. Use safety glasses when handling the bleach. The bleach will destroy clothing. Add enough common household sodium hypochlorite bleach to cover the pulp mat, approximately 50-100 ml. Use a stirring rod to mix the bleach and the pulp.
6. Stir for about 10 seconds approximately every 3 minutes. Observe if there is any color change over a time period of about 10 minutes.
7. After the bleaching, dilute the contents with 500 ml of water.
8. Make a filter pad using the filtering apparatus, this time leaving the filter paper on the pad.
9. SAFETY: Always use caution with a laundery iron. Do not leave a hot iron where it could be incidentally contacted or dropped off a table. Make sure the electric cord is not in a position to be snagged accidently. Make sure to turn off the iron when finished using.Put the filter paper and pad between two sheets of premium kitchen paper towel tissue. Dry the filter pad with a laundry iron until dry. Peel off the filter paper after dry.
10. Qualitatively compare the original colored copy paper with the bleached sample. Make observations.

What might be the disadvantages of using too much bleach?

Do you think changing the consistency of the pulp would change the bleaching process?

How might time or temperature change the efficiency of the bleaching process?

What may have been needed in the bleaching process if some parts of the pulp are bleached and others are not?

Try the bleaching process on the following types of paper:

1. Newsprint, unprinted edges.
2. A corrugated box.
3. The fluted inner medium of a corrugated box alone.
4. The outer liner of a corrugated box alone.
5. Different colors of copy paper.
6. A high quality coated brochure.

*How does each of the above respond to the bleaching process?

*Try the bleaching process on moderately heavily printed toner paper. Make sure to pulp for 30 seconds or less. Does the bleaching process have any effect on the toners? Why or why not?

*For one of the types of wastepaper that does bleach (e.g. a colored copy paper or a corrugated box) try to determine how much bleaching agent is needed to effectively bleach the wastepaper pulp. This can be done by substituting tap water for a portion of the bleaching agent. For instance try the following volumetric ratios of bleach to water: 100/0, 75/0, 50/50, 25/75, 10/90, 5/95, 1/99.

*Peroxide is a common bleaching agent. Try to bleach any of the types of wastepaper that does bleach with hypochlorite with peroxide available from a grocery or drug store. What is your result? Why did or it did not work?

Last Modified: