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The De-inking Process
Before paper is recycled to make
white paper, the ink must be removed from the paper through
a process called, intuitively enough, the de-inking process.
This process involves physiochemical means that gradually clean
and recover the fiber that is later taken to a papermachine
that creates the final product. In some cases, even the pulp
recovered from the process is in turn itself de-inked and sometimes
bleached to produce paper such as graphic paper. Other types
of paper that are made from de-inked, recycled paper include
newsprint, tissue paper, office paper, and writing paper.
Two major processes are exploited
in the de-inking process: washing and flotation. First, the
recovered paper is deposited into a pulper
drum, where it is mixed with water, washed and rinsed. Some
of the smaller contraries(contaminants) are screened out at
this stage, then the mixture is then made into a slurry. Surfactants
are added and air is bubbled through the mixture. The larger
ink particles that were not removed in the washing process are
removed here and trapped at the top. The foam that results from
the entrapment is then quickly removed, as the foam-trapped
ink will be reabsorbed into the pulp if not removed in a timely
fashion.
When old newsprint(ONP) grade paper is de-inked,
a small percentage of used magazines(about 30%) are added to
the mix of paper. The reason for this is that the coatings used
contain clay which attracts and attaches to the ink more readily,
increasing the efficiency of the de-inking process. Technology
has greatly affected exactly how paper is de-inked and the quality
of the process depends on the equipment and chemicals used.
Challenges abound in the de-inking
field, such as the thermochemical effect called the Summer Effect,
caused by tremendous heat which accelerate the paper's aging
process while it is in transit aboard trucks and trains in the
hot summer months. The increase in heat causes the inks in the
paper to bind more tightly, making the process of de-inking
more difficult. Research has gone into the use of enzymes, various
chemical surfactants, and a variety of washing techniques, such
as hyperwashing.
After the pulp is de-inked, it is
ready to be run through a paper machine to produce the final
paper product. Subsequently, after the paper is finally produced
and thoroughly inspected both visually, using a magnifying glass,
and mechanically, using a brightness meter. The resultant paper's
mechanical properties(e.g. wet strength, tear strength) are
also assessed to insure that the desired paper quality is achieved.
De-inking mills have been increasing
in recent history, and now there are around 420 de-inking mills
worldwide.
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