De-inking removes ink and adhesive from recycled paper through a pulp washing and flotation process. Paper recycling causes less pollution than producing paper from raw materials. The deinking process varies in North America and Europe, with washing being superior for removing small ink particles and flotation providing a higher percentage of original fiber. Despite the ecological benefits, deinking can be expensive, and techniques to improve and economize the process are needed.
De-inking is an industrial process that removes ink and adhesive material from recycled paper. A pulp washing process removes small ink particles by rinsing with a mixture of water and dispersants, which are used to break down the oils. Larger particles and adhesives are removed in a flotation process. Surfactants, chemicals used to aid in cleaning, are combined with air and injected into a slurry of pulp. This causes contaminants to come loose and float to the surface, where they can be removed.
Paper recycling causes 35 percent less water pollution and 74 percent less air pollution than producing paper from raw materials. Printed materials discarded after use, such as newspapers, magazines and office waste, make up a significant percentage of all recyclable paper. The treatment of this material plays an important role in efforts towards pollution control and sustainability. For printed matter, this entire recycling process is sometimes referred to as deinking.
The sorted waste paper is cut into small pieces by a pulper. Area of water and chemicals added to adjust pH level, aid in bleaching, and act as an emulsifying agent. The material leaves the pulper as a thick slurry directed to a centrifugal cleaning device. The rotational force of this machine expels contaminants larger than the pulp fibers through the screens.
The literal deinking step follows and relies on two main processes including washing and flotation. The scrubbing process is most often used in North America to make toilet paper products. The pulp slurry is rinsed with water and dispersants which remove fine ink particles as the water is driven out of the slurry. Up to 80% of the original paper fiber is recovered. This method has also been used successfully in processing old newspapers for new newsprint stock.
In Europe, the most widely used deinking process is foam flotation. Chemical surfactants are added to the pulp slurry. These chemicals form a foamy layer on top of the slurry. Air bubbles are injected into the mix, bringing the ink to the surface, where it is trapped in the foam layer. When this process is used on old newsprint, about a third of the total mix will be old magazines added to reinforce them.
Of the two processes, the washing method is superior in removing smaller sized ink particles. The flotation method provides the highest percentage of original pasta fiber. This process also produces less contaminated water. A combination of both processes is often used in high-quality deinking of office waste. The deinked fiber can go through a further stranding stage before being used in papermaking.
Despite the ecological benefits of paper recycling, the higher cost of deinking can be prohibitively expensive. The two processes are also less successful at dealing with products than some modern printing methods. Techniques to improve and economize deinking can be useful to encourage the process.
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