Liquid phase plasma technology for inkjet separation
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Jordan, Alexander Thomas
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Abstract
Currently most deinking technologies are dependent upon flotation and dissolved air flotation
(DAF) technology in order to separate inkjet ink from fiber and water. Much of this
technology is based on ink that is extremely hydrophobic. This made flotation and DAF
very easy to use because the ink in the water would very easily move with the air in flotation
and be brought to the surface, after which the ink can be skimmed and the pulp can
be used.
Now that small scale printing has become the norm, there has been a move to high
quality, small scale printing. This involves the use of a hydrophilic ink. Hydrophilic ink
cannot be easily separated from water and fiber the same way the hydrophobic ink can be.
With low concentrations of hydrophilic ink in the process water stream, it can be absorbed
into the process but as the hydrophilic ink concentration rises alternative methods will be
needed in order to separate inkjet ink from water.
One solution is to find a method to effectively increase ink particle size. This will
enable the ink particles to be filtered or to have an increase ecacy of removal during
flotation. In this thesis, one solution is discussed about how electric field and electric
plasma technologies can be used to increase particle size and help purify process water in
recycle mills.
This plasma treatment can very effectively bring ink particles together so that they may
be separated by another method. There are two methods by which this may take place. One
is polymerization and the other is electro-coagulation. These processes can work side by
side to bring ink particles together.
This plasma treatment process creates free radicals by stripping off hydrogen atoms
from surrounding organic matter. These free radicals then react with the high alkene bond
content within the ink to create a very large covalently bonded molecule. This is the new
mechanism that is being investigated in this thesis. The other action that is taking place is electro-coagulation.
Plasma treated ink can be filtered out using a cellulose acetate or cellulose nitrate membrane
or they can be filtered using paper or fiber glass filters as well. The extent at which
these can be filtered out is dependent on the size of the pores of the filter. In this study, it
was shown that the plasma treatment was able to clean water with a fairly small amount
of energy. It was also found that treatment time and concentration had very little eect on
the outcome of the treatment ecacy. One factor that did have an effect was the pH. At
very high pH values the process became noticeably less eective. The high pH essentially
eliminated the electro-coagulation aspect of the treatment process and also hurt the polymerization
aspect as well because of lower amount of hydrogen atoms available for the
plasma to create free radicals.
A model of the process was used to try to give the reader an idea of the ecacy that the
process would have in an industrial scale process. The model assumes that two types of ink
particles exist. One is ink that has a radical and another in which the ink does not have a
radical. The model also assumes that if ink is at all polymerized, ink is filtered out with the
0.8 micron filter. The model assumes three reactions; initialization, propagation and partial
termination. The partial termination is a result from the general chemical structure of ink.
Ink has many double bonds in its general structure which makes termination very unlikely
to occur, so the model assumes that on average when two radials interact that only one is
eliminated. This model is only supposed to give the reader an idea of the ecacy of the
process. The numbers provided in the model will change very significantly in a different
system.
The evidence behind polymerization aspect of the process comes from two main sources.
One is the small molecule analysis from methanol after being exposed to the plasma and the
other from the plasma being exposed to allyl alcohol. The small molecule analysis shows
that the process generates free radicals on organic molecules. Methanol was exposed to
the plasma and then the resulting GC/MS analysis showed that 1,2-ethanediol was present, this showed that the electric discharge process was able to create free radicals on organic
molecules in the liquid phase.
Using a similar process the plasma discharge process was exposed to a mixture of allyl
alcohol, water and propanol and water in two separate experiments. The difference between
these two molecules is an alkene bond that is between the carbon two and carbon three
atoms. The particle size of both samples was then analyzed and it was shown that the
solution with allyl alcohol had an average particle size about an order of magnitude larger
than the solution with propanol in it.
Because of all the evidence discussed here and in the rest of the thesis we believe that
the plasma treatment of ink has both polymerization and electro-coagulation aspect. This
process could also be a potential solution to the water soluble ink problem that will soon
face the recycling industry.
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Date
2013-01-31
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