Floatation is a process in which contaminants are preferentially removed from a pulp stock by the attachment to air bubbles. In the flotation process, air is bubbled through the low consistency pulp stock. A foaming agent is added to create foam. Contaminants will attach themselves to the air bubbles rather that remaining in water suspension because of being hydrophobic, having a lack of affinity of water. Pulp fibers do not attach to the air bubbles because of being hydrophilic, having a strong affinity for water. As hydrophobic particles, such as ink, attach to the bubbles and are lifted away from the stock, the bubbles are scraped away as a reject mixture producing cleaner fibers in an accept mixture.
Prelab Questions
Define (a) hydrophobic; (b) hydrophilic.
Referring to the handout "The Chemistry of Making Paper" explain and illustrate the hydrophilic nature of paper fibers
Procedure:
Part 1. Recycling with Deinking
Put 1000 ml of hot tap water in the blender cup.
Tear about 4.5 grams of air-dry copy paper into 2-inch squares. Add the pieces of air-dried paper to the blender.
Cover the blender and blend for 2 minutes.
Add 5-10 drops of foaming agent to the blender.
Carefully fill the blender cup with cold tap water about 0.5 inches to the top.
Put the blender cup only (not the blender motor) in the plastic tray.
Connect the air diffuser with the tubing and the air pump and turn on the pump.
Place the air diffuser into the bottom of the blender cup for 5 minutes. Manually scrape foam off the top into the plastic tray. You may need to add water to the blender to keep the liquid surface near the top. The mixture that is scraped off with the foam is called the "rejects."
The mixture that is left in the blender is called the "accepts." Filter the accepts stock using filter apparatus provided.
When all the material has been poured from the blender, 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 filter paper off the pulp mat. Add this pulp to the blender with about 200 ml of water.
Energize the blender for 5 minutes.
Use all of the slurry to make a handsheets.
Part II. Recycling Without Deinking
Put 1000 ml of hot tap water in the blender cup.
Tear about 4.5 grams of air-dry copy paper into 2-inch squares. Add the pieces of air-dried paper to the blender.
Cover the blender and blend for 2 minutes.
Filter the pulp mixture using the filtering apparatus.
When all the material has been poured from the blender, 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 filter paper off the pulp mat. Add this pulp to the blender with about 200 ml of water.
Energize the blender for 5 seconds.
Use all of the slurry to make a handsheets.
Observations
Compare and contrast the paper you recycled using the deinking process and without the deinking process. Include a sample of each in the table below.
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recycled paper that was deinked |
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recycled paper that was not deinked |
Was the deinking of your recycled paper a success? Why or why not?
Conclusion Questions
Some pulp fiber is scraped away with the foam in the rejects. Why is this undesirable in an industrial process?
Describe ways to modify the flotation experiment to decrease the amount of paper fibers contained in the rejects?
Why would the foaming agent concentration be important? What would be the disadvantage of having too much or too little foam in an automatic continuous system?
Further Experiments
Yield of fibers is very important. Can you develop an experiment that exposes the relationship between yield and removal efficiency?
Can you explain the sensitivity of efficiency time. What is the relationship?
How do different types of wastepaper respond to flotation?
What is the effect of pulping time on the toner particles and the resulting flotation efficiency?