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. Hypochlorite is one such chemical. Another very common bleaching agent used is hydrogen peroxide. In this laboratory, you will learn a simple method to bleach recycled pulp.
Procedure:
Weigh out approximately 7 air dry grams of a colored copy paper. Record the exact mass weighed out. ________g paper
Rip the paper into 2-inch squares and add them to the blender with 1000 mL of warm water.
Calculate the mass of oven-dried fibers in your colored copy paper based on an estimated 90% yield of OD fiber.
OD fibers = (grams copy paper)(90%)
The chemical charge of sodium hypochlorite is 8%. This means that for every 100 grams of OD fiber, you will need 8 grams of sodium hypochlorite Write this ratio as a conversion factor.
Calculate the grams of sodium hypochlorite you will need based on the grams of OD fiber determined in Step 2.
(a) Record the percent sodium hypochlorite of the Clorox you are using. This information should be on the label of the Clorox bottle. The percent sodium hypochlorite may vary from brand to brand.
(b) Rewrite your percent sodium hypochlorite as a conversion factor
Grams sodium hypochlorite
100 g. Clorox
(c) Using the factor label method and percent sodium hypochlorite, convert the grams of sodium hypochlorite determined in Step 4 to grams. Clorox you will have to measure out.
Data Table
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Type of recycled fiber |
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% OD yield |
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Grams OD fiber |
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Chemical charge of Sodium hypochlorite |
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% sodium hypochlorite in CloroxÒ |
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Grams CloroxÒ used |
Weigh out the needed grams of Clorox and add it to the paper and water in the blender. Energize the blender for 5 seconds.
Allow the mixture to sit for 10 minutes, turning on the blender every 2 minutes.
Filter the bleached pulp using filter apparatus provided. Rinse with 1000 ml water.
Allow all the liquid to be pulled from the pulp, forming a thick mat. Turn off the vacuum and discard the liquid as necessary.
Peel the paper towel off the pulp mat. Add this pulp to the blender with about 200 ml of water.
Energize the blender for 5 seconds to make a slurry.
Divide this slurry in half and make 2 handsheets
Questions:
What might be the disadvantages in 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?
Why were you not instructed to refine the pulp before making a handsheet?
Further Experiments: (NOT REQUIRED)
Try the bleaching process on the following types of paper:
Newsprint, unprinted edges.
A corrugated box.
The fluted inner medium of a corrugated box alone.
The outer liner of the corrugated box alone.
Different colors of copy paper.
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 sec 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. Substituting tap water for a portion of the bleaching agent can do this. For instance try the following volumetric ratios of bleaching 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