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THE STUDY OF THE POSSIBILITY OF THE AQUASOL PROCESS TO DEINK ONP AND MOW
A. Khalafi, M. Faezipour, M. Khatibzadeh, M.M. Nazhad and A. Pirjani
In this study, the Aquasol process was used to deink ONP (Old Newsprint) and MOW (Mixed Office Waste). An aqua-solvent and surfactants mixture was applied to dissolve, disperse and remove ink. The efficient dislodging of ink requires optimized conditions of retention time, temperature, solvent type and print age (i.e. aging). Finally, the contaminants, ink particles in particular, were removed along with the solvent by decantation.
The results indicated that the maximum brightness was achieved using 4 hours retention time, 60oC temperature, with the print age of 6 months for both ONP and MOW.
Xylene is better than dichloromethane; dichloromethane cannot be used with conventional devices. The simultaneous increase of retention time and temperature, and decrease of print age will cause an increase in brightness. Besides, separate increase of retention time and temperature led to an increase in brightness. The lower the print age, the higher the final brightness achieved throughout the process. In this case, the majority of brightness loss occurred during 6 months after printing and then the effect of aging on brightness is less significant.
The interactive and independent influences of the variables are discussed illustratively and thoroughly.
Aquasol, Deinking, Print age, Old Newsprint, Mixed Office Waste, Surfactant, Organic solvent, Aging
Around 80% of total recovered paper can be obtained from three different sources: Cartons, Newsprints and Mixed Office Waste. Fewer than 20% of recovered papers were deinked in order to use in production of newsprint, tissues and other white papers (2). These data show the significance of old newsprint and mixed office waste and it requires research and survey to process these kinds of raw material.
In 1991, 32MT of newsprint were produced worldwide, of which 8.5MT were recycled fibre (11). In this case, the proportion of recycled fibre in the production of newsprint was predicted to be threefold and reach 30MT in 2005(12).
Mixed office waste is a proper alternative to chemical wood-free pulp to manufacture high quality and high yield pulp (about 60-70%) (6). In Iran, the Latif Paper Co. is deinking mixed office waste by flotation to manufacture tissues.
The first use of organic solvents in deinking was in the 1930s when hydro-emulsion of chlorinated hydrocarbons was used (8). Chlorinated hydrocarbons dissolve the resinous content of ink and remove it (3, 4, 5 and 9). However, solvents are not expected to dissolve all kind of contaminants and to be a complete replacement for water in the deinking process.
It was also reported that the Riverside Paper Co. has used hot chlorinated solvents to remove wax and polyethylene from bleached board and it was successful in deinking (5).
Solvents can deink special printed paper, which cannot be deinked by the conventional deinking process, and give dry pulp that can be shipped or stored. In addition, solvents would not result in water contamination and the level of fibre swelling in this process would be below 10 % (1).
Solvents have the most efficient effect, when the paper is coated and the least efficient one, when the paper is not coated so that a higher amount of ink penetrated into the paper.
2. Materials and method
1) Raw material (recovered paper)
In this study two types of paper were used as follows:
1.1- Old Newsprint (ONP)
These ONPs were collected from Ettelaat newspaper central office. The delivery dates of these samples were 2000, 2001 and 2003 when the print age of them were 0.5, 1 and 2 years respectively. These samples had been stored in an archive room where they were not subjected to severe sunlight, undesirable heat or moisture.
1.2- Mixed Office Waste
These samples were collected from the yard and deinking line of Latif Paper Co. In collecting these samples a special attempt was focused on selecting papers with an exact print age of 0.5, 1 and 2 years. These papers were recovered from the agricultural ministry, local agricultural offices, police offices, insurance institutes, natural resources offices and other individual companies.
2.1- Xylene (C6H4 (CH3))
3. Sample preparation
These samples were collected from the printed section of ONP and MOW (and processed without chemicals) and were torn to 1.5cm×1.5cm by hand. Solid matter content and MC of samples were determined.
These samples were collected from the printed section of newsprint and office waste and were torn to 1.5cm×1.5cm by hand. Solid matter content and MC of samples were determined. The mix of main samples was: 100%ONP, 100%MOW and 50%ONP: 50%MOW.
4. Deinking procedure
After sample preparation, the deinking was conducted using Xylene, DCM and surfactants as follows:
4.1. Soaking (retention time)
In this stage, the samples were soaked in the solution of anionic surfactant for 1, 2 and 4 hours and in 20, 40 and 60 ºC and neutral pH. Specified mass of samples were weighed and put into the prepared solution of anionic surfactant and the consistency was adjusted to 3.5%. Then the solution was put in a hot water bath for a specific time.
4.2-cationic surfactant addition
0.3 %( based on dry weight of fibre) of the cationic surfactant added to the solution while agitating gently to make it homogenous.
After retention time, a specified amount of Xylene or DCM was added to the system, and agitated intensively using a glass bar in order to make the solvent interface with the paper surface and dissolved ink and other contaminants. In this stage it was observed that after agitation the solvent was darkened indicating the ink dissolved.
After agitation, the suspension maintained stagnant then decantation was conducted. To be sure of efficient decantation, this stage was repeated several times until the total solvent washed away.
The suspension was repulped using a kitchen blender (SUNNY blender). The consistency was adjusted to 5%. The repulping time was 7 minutes (this duration was got by accomplishing several pre-tests).
4.6-handsheet making and brightness measurement
Handsheets were made using a laboratory handsheet maker with the basis weight of 60gr/cm2 and the brightness (ISO %) of them was measured.
4.7- type of experimental design and statistical analysis method
The experimental design of this study was a completely randomized incomplete mixed factorial design. The results were analyzed and the charts were drawn using SAS and SPSS software and GLM variance analysis method. The means were compared using Duncan's mean comparison test (in the level of 5%).
The variables and their level are shown in table 1.
Table 1. Variables and their levels in this study
The independent variables are anionic and cationic surfactant dose (0.3% and 0.4% respectively) and pH (about 7.5)
3. Results and discussion
Brightness is the most important optical property of paper which has worldwide use in industries, universities and research institutes.
The brightness is often measured on both side of the paper (top and wire sides).
The control samples were repulped without chemical processing, handsheets were made and the brightness of top and wire sides was measured. These results are presented in table 2.
Table 2. Brightness (ISO%) of top and wire sides of control samples
The results of GLM variance analysis presented in table 3.
Table 3. Summary of GLM variance analysis for comparison independent and interactive effects of variables
t:Retention Time T:Temperature a: Print Age P: Paper Type
**-significant in the level of 1%
*- significant in the level of 5%
1- Independent effects
I) retention Time
The brightness reached the highest level in 4 hours (fig.1). This can be attributed to the increase of water-surfactants solution penetration into paper, due to the swelling of fibres, and weakening the attachment between ink and fibres as well.
The reason for the dramatic loss of brightness in 2 hours retention time is not clear.
Fig 1. Independent effect of retention time on brightness (ISO %) top and wire side
The same results were reported in the literature that brightness got to the highest level in 4 hours retention time and there is no difference between 1 and 2 hours. It was also shown that in the retention time of range of higher that 4 hours the chromophore groups will appear.(10)
One of the factors which facilitate the chemical reaction rate is temperature. In this study the effect of this factor was not significant statistically (table 2).
There is no difference between 20 and 40oC and brightness value decreases slightly in 40oC, for which its reason is not clear (fig 2).
Fig 2. Independent effects of temperature on brightness
Temperature influences wetting rate, defibration rate and dispersion of ink and other contaminants. It also decreases the viscosity of water and makes it penetrate into the fibre network rapidly and deeply. The higher the temperature, the lower the time of repulping (7). It has been reported in the literature that temperatures near 60oC during all stages of deinking would lead to increase of brightness higher than 25 and 95oC. The reason that brightness value decreases at 95oC is attributed to the raise of temperature above glass transition temperature(Tg) of ink(10).
III) Print age
Aging is defined as the interval between printing and time of experiment (in case of ink) and interval between paper production and time of experiment (in case of paper). Brightness was expected to decrease dramatically with increase of print age in this study, but it was found that at the excessive print age of 6 months the brightness would decrease steadily and the majority of aging occurs during 6 months print age. Therefore the brightness loss after 1 and 2 years were 4.09% and 3.85% respectively.
The other point that should be mentioned here is that the higher the brightness gain in different print ages shows the high efficiency of the aquasol process.
Fig 3. Independent effects of print age on brightness
The same result was reported in the literature indicating that the majority of aging occurs during 5 months after printing and after that, there is not a significant difference in brightness values (10).
IV) Paper type
As expected, the office waste and ONP pulps got the highest and lowest brightness values respectively (fig 4). Comparing these data and the data deriving from table 1, the brightness improvement is 6.25%, 4.75% and 2.68% for ONP, ONP: MOW and MOW respectively.
The major part of the MOW from Latif Paper Co. were laser and copy printed papers and a small proportion of them were offset printed books, carbonless papers and carbon printed papers. The samples collected from the mentioned paper contained carbon printed papers. Solvent cannot dissolve the laser and copy toner, so the 2.675% of improvement in MOW can be contributed to the dissolved ink and other contaminants from the carbon printed papers in solvent.
As the ink used in offset newsprint was oil based, it can be concluded that solvents have the most efficient effect in processing of ONP.
Fig 4. Independent effect of paper type on brightness
MOW is made of chemical wood free bleached pulp with high brightness value while ONP is composed of high lignin content mechanical pulp, therefore, the difference between two brightness values was justified.
The mix of ONP and MOW got the brightness value of 70% which is between ONP and MOW.
The interpretation of the results in this section was very complicated and in some sections the authors just present the results. Three dimensional plane charts were used to show the trends accurately.
I) retention time and temperature
Retention time and temperature are important factors; the highest level of brightness was gained in 4 hours retention time and 20 and 60oC and the lowest one was gained in 2 hours retention time and 40oC (the reasons are not clear) (figs 5 and 6). In high temperatures and long retention time, the surfactants have the opportunity to enter into the fibre network, swell fibres and wet the print which leads to the detachment of the fibre-ink bond and finally the solvent dissolves the ink particles in order to remove them.
Fig 5. Interactive effects of retention time and temperature on brightness (top side)
Fig 6. Interactive effects of retention time and temperature on brightness (wire side)
II) Retention time and print age
Brightness is decreasing and increasing with increase of print age and decline in retention time respectively, with the exception of 2 hours retention time and 2 years print age (the reasons are not known) (figs 7 and 8).
Fig 7. Interactive effects of retention time and print age on brightness (top side)
Fig 8. Interactive effects of retention time and print age on brightness (wire side)
III) Temperature and print age
The brightness got to the highest level at 20oC with different print age and at 60oC with 2 years print age (the reasons are not known) (figs 9 and 10).
Fig 9. Interactive effects of temperature and print age on brightness (Top side)
Fig 10. Interactive effects of temperature and print age on brightness (wire side)
IV) Temperature, print age and paper type
Brightness in ONP and MOW increase and decrease with simultaneously increase of print age and temperature (figs 11, 12, 14, 15).
In the mix of MOW: ONP increase of print age and temperature would lead to decline of brightness (figs 13 and 16 )
Fig 11. Interactive effects of temperature and print age on brightness (top side) in MOW
Fig 12. Interactive effects of temperature and print age on brightness (top side) in ONP
Fig 13. Interactive effects of temperature and print age on brightness (top side) in mix of MOW: ONP
Fig 14. Interactive effects of temperature and print age on brightness (wire side) in ONP
Fig 15. Interactive effects of temperature and print age on brightness (wire side) in OMW
Fig 16. Interactive effects of temperature and print age on brightness (wire side) in mix of MOW: ONP
V) Print age, retention time and paper type
Simultaneously increase of retention time and print age would increase and decrease brightness respectively in both ONP and MOW (figs 17, 18, 19, 20) and decrease and increase of brightness in mix of ONP: MOW (figs 21, 22).
Fig 17. Interactive effects of retention time and print age on brightness (top side) in ONP
Fig 18. Interactive effects of temperature and print age on brightness (wire side) in ONP
Fig 19. Interactive effects of temperature and print age on brightness (top side) in MOW
Fig 20. Interactive effects of temperature and print age on brightness (wire side) in MOW
Fig 21. Interactive effects of temperature and print age on brightness (top side) in the mix of MOW: ONP
Fig 22. Interactive effects of temperature and print age on brightness (wire side) in the mix of MOW: ONP
VI) Temperature, retention time and paper type
In MOW simultaneous increase of temperature and retention time, increase and decrease the brightness respectively (figs 25, 26).
In ONP, higher brightness was gained in short retention times and high temperatures and lower brightness was achieved in long retention time and low temperatures (figs 23, 24).
In the mix MOW: ONP simultaneous increase of temperature and retention time, decrease the brightness value(figs 27, 28).
Fig 23. Interactive effects of retention time and print age on brightness (top side) in ONP
Fig 24. Interactive effects of retention time and print age on brightness (wire side) in ONP
Fig 25. Interactive effects of retention time and print age on brightness (top side) in MOW
Fig 26. Interactive effects of retention time and print age on brightness (wire side) in MOW
Fig 27. Interactive effects of retention time and print age on brightness (top side) in the mix of MOW: ONP
Fig 28. Interactive effects of retention time and print age on brightness (wire side) in the mix of MOW: ONP
1. The best treatment variables - Using Duncan's mean comparison test, the best treatment variables are: Retention time of 4 hours, temperatures of 60C, Print age of 0.5 year and paper type of ONP.
2. Separate increase of retention time and temperature and decrease of print age results in improvement of optical properties.
3. Simultaneous increase of retention time and temperature and decrease of print age increase brightness.
4. Majority of aging occurs during 6 months print age and in excessive print age; the brightness loss will not be significant.
5. Aquasol can be used to deink carbon printed papers.
6. Increase of retention time in low temperatures (room temperatures) has no significant effect on brightness.
7. As the mix of MOW and ONP got the brightness value of 69.5%, thus a mix of them can be used to manufacture medium quality papers.
8. Dichloromethane (DCM) cannot be used in the Aquasol process with conventional tools and for using DCM it requires a specially designed machine.
9. The Aquasol process is efficient in the removal of stickies, which are present in mixed office waste.
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