Liquid phase plasma technology for inkjet separation
Jordan, Alexander Thomas
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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.