Deinking is the process of separating ink particles from the fiber by using different methods like washing or flotation. The methods mostly depend on the size of the ink particles.
Enzymatic deinking involves the use of enzymes for controlling reactions in the pulp. Whereas, in chemical deinking, a large number of chemicals are used.
Chemical deinking is a traditional deinking process that is adopted by the majority of paper mills.
Both enzymatic deinking and chemical deinking have their own set of advantages and disadvantages.
Let us discuss the pros and cons of both types of pulp deinking processes.
Enzymatic Deinking
What are enzymes? Enzymes are substances that act as catalysts for regulating the process of chemical reactions.
Enzymatic deinking is the process in which enzymes are for removing the ink stains and particles from the pulp. The enzymes get altered themselves in the process.
Some of the common enzymes like endoglucanase, cellulase, and xylanase are mainly used in the papermaking process for removing the ink particles from the fibers.
Enzymes can either act directly on the fibers or the ink film. These substances are capable of removing small fibrils from the surface of the ink particles which facilitates their separation in the flotation/washing steps.
Enzymatic deinking is advantageous to deink high-quality wastepaper of which reuse is usually limited by the high content of non-contact inks (toners).
Some of the popular enzymes used for enzymatic deinking are –
- Xylanase
- Viscozyme
- Celluclast
- Buzyme
- Pentopan mono
- AXC
- Novozym
- IOGEN cellulase
- SAFISYM
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Enzymatic Deinking Process
How is enzymatic deinking done? Suspend the pulp in distilled water and disintegrated for 10-15 minutes. Enzymes are added to the mixture in appropriate quantities as per the quantity of the pulp. The enzymatic preparations are diluted to achieve better dispersion.
The solution is allowed to sit for 30 minutes for the reactions to occur. The high consistency of the pulp prompts fiber-to-fiber attrition favoring in the ink detachment process.
After 30 minutes, the pulp suspension is boiled to inactivate the enzymes and stop the reaction.
The released ink is immediately separated from the fibers to avoid redeposition. The fibers are afterward recovered for testing.
Chemical deinking
Chemical deinking is done by treating the pulp with chemicals for separating the ink and stain particles from the fibers. Chemical deinking is less expensive as compared to enzymatic deinking.
However, unlike enzymatic deinking, it has some harmful effects on the environment.
Some of the popular chemicals used for enzymatic deinking are –
- Agalite or Talc
- Chlorine Dioxide
- Dolomite
- Guar Gum
- Hydrogen Peroxide
- Lime Stone
- Magnesium Bisulfite
- Polyvinyl Alcohol (PVA)
- Salt Cake
- Sodium Aluminate
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Chemical Deinking Process
How is chemical deinking done? The chemical deinking process is carried out in much similar way to the enzymatic deinking process. Chemicals are added to the pulp instead of chemicals.
The only difference is that, unlike enzymes, the chemicals don’t need to be stopped from reacting. The chemicals get dissolved into the pulp.
Therefore, the final mixture is not boiled and the ink stains get successfully separated from the fibers.
Chemical Deinking vs Enzymatic Deinking
Chemical deinking is a traditional deinking process that involves a large number of chemicals that may prove harmful to the environment. This method is expensive and highly environmentally damaging.
Whereas, on the contrary, the biological deinking treatment is in favor of detaching the ink particles from the fibers without causing a lot of pollution or discharge of hazardous substances.
The chemical products increase the strength index and decrease the drainage properties. Some of the chemicals favor the swelling and consequently increase the fiber bondings potentially by enhancing the flexibility, conformability, and surface area.
The enzymatic deinking process is as efficient as the chemical deinking process.
Conclusions
We can use the enzymes as it is a competitive strategy for deinking recycled pulp. However, special attention should be paid while selecting the suitable enzymes as per the raw material.
Thorough process optimization is needed to achieve a good quality end product. It is important to know that different type of pulp reacts differently to similar deinking protocols of both chemicals as well as enzymatic.
The effectiveness of the enzymatic deinking process depends critically on the furnishing properties than chemical ones. Enzymatic deinking is preferable more in the operation where more industrial waste paper is included.
According to some researchers, more ink removal was obtained by treating the pulp with chemicals and the strength of the material was not affected as much. Enzymes favor ink removal as well, however, their action significantly affects the paper strength properties.
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