Abstract
Agglomeration phenomena of two mixed xerographic toners were investigated using 1-octadecanol as the agglomeration agent and a cationic surfactant as the co-agglomeration agent. One toner carrying no surface charge agglomerated well under most conditions, while the other toner carrying a negative surface charge performed worse. It was found that when mixing these two toners together during pulping and when using 1-octadecanol as the agglomeration agent alone, there was an additive effect on agglomeration. On the other hand, addition of a small amount of cationic surfactant dramatically enhanced the mixed toner agglomeration efficiency and generated an obvious synergistic effect. The particle number after agglomeration was significantly reduced, and the particle size was greatly increased compared to the single toner agglomeration. The optimal amount of the cationic surfactant was close to the optimal cationic surfactant demand of the negatively charged toner. Based on these findings it can be recommended that the cationic surfactant should be added during agglomeration of the mixed office waste paper, and its optimal dosage needs to be chosen to reach the best performance.
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THE SYNERGISTIC EFFECT OF MIXED XEROGRAPHIC TONER AGGLOMERATION
Cuixia Wang,a Yungchang F. Chin,b* and Guolin Tong a
Agglomeration phenomenon of two mixed xerographic toner were investigated using 1-octadecanol as the agglomeration agent and the cationic surfactant as the co-agglomeration agent. One toner that carrying no surface charge agglomerated well under most conditions, while the other toner carried a negative surface charge performed worse. It was found that when mixing these two toners together during pulping and to use the 1-octadecanol as the agglomeration agent alone, an additive effect on the agglomeration existed. Whereas adding a small amount of cationic surfactant dramatically enhanced the mixed toner agglomeration efficiency and generated an obvious synergistic effect. The particle number after agglomeration was significantly reduced and the particle size was greatly increased comparing to the single toner agglomeration. The optimal amount of the cationic surfactant is close to the optimal cationic surfactant demand of the negative charge toner. This finding recommended that the cationic surfactant should be added during agglomeration of the mixed office waste paper and its optimal dosage need to be chosen to reach the best performance.
Keywords: Mixed toner; 1-octadecanol; Cationic surfactants; Agglomeration; Synergistic effect; Surface charge
Contact information: a: Jiangsu provincial Key Laboratory of Pulp and Paper Science and Technology, Nanjing Forestry University, Nanjing 210037, China; b: Special professor of Nanjing Forestry university, Nanjing 210037; *Corresponding author: frankchin2004@yahoo.com.cn
INTRODUCTION
In order to maintain the carbon dioxide balance of the earth, to use less virgin fiber for paper making had become a necessity in many countries. This had led the use of recycled paper as the raw material on paper making. For countries that are short of wood resources, this is even more important for the paper industry. Among all recycled papers, office waste paper is an important grade for recycling which contains quite a lot of bleached fiber. To regenerate pure and clean fiber, contaminants of the recycled paper have to be separated out of it. One of the main contaminants in office waste paper is toner ink. Toners are plastic-based ink used in xerographic copying processes or laser-printing processes. The plate-like ship and wide size distribution of toner particles detached from fibers makes deinking by the conventional methods of washing, flotation, centrifugal cleaning and screening ineffective or inefficient (Zabula et al. 1988; Odada et al. 1991). These difficulties have led to the development of the agglomeration process, by which toner is agglomerated into larger particles using a combination of chemicals, heat treatment and mixing (Synder et al. 1994; Chang et al. 1996; Chen et al. 2004). The larger, more spherical agglomerated particles can be separated from the fiber easily by screening and centrifugal cleaning, yielding a clean, high quality pulp (Borchardt et al. 1997).
Among all agglomeration chemicals, 1-octadeconal has been known as a highly effective agglomerating agent onto the toner ink. However, it had been found that the agglomeration process was ineffective when furnish contained highly sized fibers or starched paper (Synder et al. 1994). The cationic starch was specifically proposed as interfering material if the toner is negatively charged. It will generate negative effect on the 1-octadeconal agglomeration. A positively charge surfactant CTAC (cetyl-trimethyl ammonium chloride) can eliminate the negative effect in a model system (Chen et al. 2004). But, it did not work on conventional printing papers.
Our previous study showed that some xerographic toner that carrying no surface charge agglomerated much better than the negative surface charged toner under either neutral or alkali conditions. Actually, the negatively charged toner did not agglomerate at all under alkaline conditions. The addition of a cationic surfactant greatly improved the agglomeration of the negatively surface charged toner but had relatively negative effect on the toner that carrying no surface charge (Wang et al. 2011). Our other study also confirmed that some negatively charged laser toner agglomerated well under neutral conditions, but it did not agglomerated under alkali condition. Adding proper type of cationic surfactants would greatly improve the agglomeration efficiency (Jiang et al. 2012).
It is thus clear that different toners have different agglomeration characteristics and the neutral pulping condition generates less agglomeration problems. Since available sources of post-consumer office paper contain many different types of toners, it was of interest to examine the results of 1-octadecanol agglomeration performed with more than one toner present. Although an effective co-agglomeration system had been proposed by using Nonylphenol Polyethylene Glycol Ether (HLB=8.9) together with 1-octadecanol to agglomerate the combinations of two different type of toners, the mixed toner agglomeration system has not been studied thoroughly (Welf et al. 2001). The effect of cationic surfactant onto the mixed toner agglomeration was also not studied before.
This study mainly focused on the agglomeration effect of cationic surfactants onto a two mixed toners system. It is hoped to give more understanding and help to improve some agglomeration problems in mixed office waste de-inking systems.
EXPERIMENTAL
Materials
The copy paper used was a commercial product “GOLD BALL”, made by APP Co., China. Photo-copied paper was printed from the same original by using two different Japanese xerographic copy machines and copied with toners made by the same company: Kyocera KM-1635 (Toner A) and Canon iR 6000 (Toner B). Toner A carried no surface charge and Toner B carried slightly negative charge. All other chemicals were purchased locally. Detailed information for these materials is listed in Table 1.
Table1. List of Materials
Pulping
These two photo-copied papers were torn to 1cm×1cm pieces separately and mixed with different weight percentage before pulping. A home-made 1.0 L stainless steel pulper with a screw type rotor driven by a variable speed motor was used for pulping and agglomeration. Before pulping, 465 ml of distilled water was added to the pulper and heated up to 70oC by partially submerging the pulper in a water bath maintained at a little bit higher than 70 oC. 1-octadecanol (0.6 g, 2% based on paper) and different amount of surfactants were added and mixed at 300 rpm for three minutes to ensure that the 1-octadecanol was molten. To the pulper, 30 O.D. grams of mixed photo-copied paper was added and disintegrated at 800 rpm for 15 minutes. After 15 minutes, the rotor speed was reduced to 440 rpm for 45 minutes for toner agglomeration. After pulping, the pulp slurry was transferred to a plastic bag and cooled down in tab water. Six handsheets, each with basis weight of 60 g/m2, were made according to TAPPI Standard Method T205 OM-8. The handsheets were air dried for 24 hours and evaluated by image analysis system with a Canon LiDE100 Scanner. The software used was Autospec V4.0 Image Analysis System (State Key Laboratory of Pulp and Paper Engineering; South China University of Technology). Each experiment was conducted twice to verify the experimental error.
Surface Charge of Toners
Blank transparency films were copied through Kyocera KM-1635 and Canon iR 6000 copiers to transfer their toner onto the film surface. The printed toner was then scraped and collected from the film surface by a stainless steel perpendular. The collected toner was then screened to sizes between 50 and 100 meshes. Screened toner (0.1 g) was added to a 150 ml glass beaker with 40 ml of distilled water. The beaker was then put on an electric heater with automatic temperature control and mixed with a speed controlled Teflon rotor for 60 minutes at 70 oC.
After being cooling to room temperature, cationic polyelectrolyte (0.001 mol/L HCA, 5 mL) was added to the mixture and allowed to react for 30 minutes. After the reaction, the filtrate was separated from the slurry with a 200 mesh ceramic filter to collect the filtrate. The filtrate was then back-titrated using an anionic polyelectrolyte titrant (PVSK) to determine the surface charge of each toner. The end point was determined by a particle charge detector (PCD-03 Mütek, BTG).
RESULTS AND DISCUSSION
Single Toner Agglomeration
Experiments for single toner agglomeration were conducted to understand each toner’s agglomeration performance and characteristics. Toner A and Toner B had quite a different agglomerating performance as shown in Table 2. When using 1-octadecanol as the agglomeration agent, Toner A performed well. The number of ink particles per square meter (NPM) was reduced by more than 96% (from 491,000 to 19,000) and the average particle size was increased by seven times, from 0.03 mm2 to 0.23 mm2. Toner B, on the other hand, agglomerated poorly. The reduction of NPM value was only 54% (from 433,000 to 197,000) and the average ink particle size was unchanged. Furthermore, visual observation clearly showed that not only the particle size but also the particle shape were different between these two agglomerated toners. After agglomeration with 1-octadecanol, the ink particle of Toner A was spherical, whereas those of Toner B were flat. These differences in size and shape can greatly affect the screen efficiency (Carr 1991; Borchardt et al. 1997). These results also consist with earlier studies (Chen et al. 2004; Wang et al. 2011).
From previous studies, it was clear that chemically-aided toner agglomeration is influenced by toner charge characteristics (Chen et al. 2004; Wang et al. 2011; Jiang et al. 2012). A charge titration test was conducted to determine the surface charge of the toners. It was found that Toner A has non-detectable surface charge; whereas, Toner B has a slightly negative surface charge of -0.002 mEq/g. These results were consistent with the agglomeration performance of each toner (Table 2).
It was also shown that some of cationic surfactant such as CTAB can greatly improve the agglomeration of the toner carrying a negative surface charge in our previous studies. As shown in Figs. 1 and 2, CTAB is very effective for Toner B’s agglomeration, which dramatically reduced the NPM number and enlarged the average ink particle size. When the dosage of CTAB reached 0.08%, the value of NPM reached the minimum value (41,000) and the average ink particle size reached to the maximum value (0.22 mm2). When the dosage of CTAB exceeded 0.08%, the agglomeration efficiency became lower. In the case of Toner A, the story was different. Adding CTAB as the co-agglomeration agent had an adverse effect on both the NPM value and the average ink particle size. Although the adverse effect happened to Toner A, the agglomerated ink particle shape maintained spherical and most of them can be screened out by a 0.15 mm slot screen. This phenomenon has been found and discussed in detail at previous studies (Wang et al. 2011; Jiang et al. 2012).
Thus, it is clear that different types of toners have different agglomeration performance. For Toner A, 1-octadecanol alone was enough to perform a good agglomeration. But the CTAB was needed for Toner B to get similar result.
Table 2. Performance of 1-octadecanol Agglomeration
Fig.1. Effect of CTAB on NPM after agglomeration with 2.0% 1-octadecanol
Fig.2. Effect of CTAB on average ink particle size after agglomeration with 2.0% 1-octadecanol
Agglomeration of the Two-Toner System via 1-Octadecanol
Experiments were conducted to explore the effect of 1-octadecanol onto the combination of two different toners agglomeration. This was achieved by agglomerating a pulp stock that contained paper printed with Toner A and paper printed with Toner B mixed with different weight percentage.
The results are shown in Figs. 3 and 4. As can be seen on both figures, the additive effect of the two toners agglomeration existed. On Fig. 3, the NPM was slightly higher than the theoretical value when the percentage of Toner A paper was lower than 60%. This might be caused by the reduction of the effective collision between Toner A and 1-octadecanol when the highly dispersed ink particle of Toner B existed. Although the negative interference existed, the impact to the system was small. As shown on Fig. 4, the agglomerated ink particle size was almost not affected and was consistent with the theoretical value. Here the measured actual NPM and average ink particle size after pulping was defined as actual value (AV for short). The theoretical value of different paper toner combination (TV for short) was calculated as following equations:
Where, “NPM of Toner A or B” means the NPM value of pure Toner A or B agglomeration
“PPM of Toner A or B” means the PPM value of pure Toner A or B agglomeration
It is clear that when two different toners were present during the agglomeration stage, the presence of a second toner, which possessed different agglomeration characteristics, had very little influence to each other. An additive effect of the agglomeration was basically existed.
Fig.3. Effect of 2.0% 1-octadecanol on NPM after agglomeration of two toners mixed with different percentage
Fig.4. Effect of 2.0% 1-octadecanol on average ink particle size after agglomeration of two toners mixed with different percentage
The Effect of Cationic Surfactant on the Two-Toner System
In order to investigate the effect of the cationic surfactant on agglomeration efficiency of the two-toner system, a small amount of cationic surfactant, 0.08% CTAB, was added together with 2.0% 1-octadecanol. The results are shown in Figs. 5 and 6. The theoretical values of mixed toners agglomeration based on single toner agglomeration results with the same amount of 1-octadecanol and CTAB were also plotted in the same figures for comparison.
Fig. 5 shows the effect of the addition of CTAB on NPM after agglomeration of two different toners mixed with different weight percentage. As shown in Fig. 5, the NPM after pulping was much lower than the theoretical value in all the range of mixing ratio. When increasing the percentage of the Toner A paper in the mixed paper, the NPM gradually decreased and appeared to reach a minimum (11,000). Comparing to theoretical value of the percentage of Toner A paper at 80%, the NPM reduction was 80% (from 55,000 to 11,000). Above this percentage, the NPM value appeared to increase. It should also be noted that the minimal NPM value is even better than the best agglomeration result of single toner agglomeration either with or without the cationic surfactant (Fig. 1).
The effect of the CTAB on agglomeration of the two-toner system was further manifested by the average ink particle size, as shown in Fig. 6. The average ink particle size increased from 0.22 mm2 to a maximum of 0.39 mm2 when optimal percentage (80%) of the Toner A paper was added. Above this percentage, the average ink particle size was rapidly reduced from 0.39 mm2 to 0.09 mm2. Although the average ink particle size reduced quickly, the size was still bigger than the theoretical value. Furthermore, the optimal average particle size of 0.39 mm2 is more than three times larger than the theoretical value of 0.11 mm2 and was also much larger than that of single toner agglomeration (Fig. 2).
Thus, it is clear that the 1-octadecanol and the cationic surfactant CTAB can form a synergistic agglomerate system on mixed toners deinking. Even though adding CTAB as the co-agglomeration agent had an adverse effect for Toner A, it seemed the 1-octadecanol and the surfactant CTAB system induced complete agglomeration of all the toner particles and thus formed the largest ink particle size. Actually, adding a small amount of Toner B paper would generate this synergistic effect and made the agglomeration efficiency higher. Although the reason is unclear, it was hypothesized that with the help of CTAB the agglomerated Toner B had very high agglomerating ability and thus promoted the overall agglomeration efficiency.
Fig.5. Effect of 0.08% CTAB on NPM after agglomeration of two toners mixed with different percentage at 2.0% 1-octadecanol
Fig.6. Effect of 0.08% CTAB on average ink particle size after agglomeration of two toners mixed with different percentage at 2.0% 1-octadecanol
Amount of Cationic Surfactant
The charge of surfactant relative to the OD paper weight also impacts agglomeration performance. It was interesting to determine if different amount of CTAB would affect the synergistic effect of the mixed toners agglomeration. The 0.04%, 0.08%, and 0.10% CTAB were added by pulping two mixed toners paper at the weight ratio of 1:1 with 2.0% 1-octadecanol, respectively. The results were shown in Figs. 7 and 8. As shown in Fig. 7, when 0.04% CTAB was added, the agglomeration efficiency was poor. The NPM after pulping (79,000) was close to the theoretical value (78,000) and thus only additive effect occurred. When increasing the dosage of CTAB to 0.08%, the agglomeration reached to its best performance. The NPM after pulping was reduced by 67% comparing to the theoretical value (from 50,000 to 16,000). It should be mentioned that this dosage was also the best agglomeration conditions for the pure Toner B. When CTAB dosage further increased to 0.10%, the NPM after pulping reduced by 69% comparing to the theoretical value (from 91,000 to 28,000). Although the synergistic effect maintained similar to that of 0.08% CTAB, the agglomeration efficiency became worse (from 16,000 to 28,000).
Fig.7. Effect of CTAB on NPM after agglomeration of two toners mixed by the ratio of 1:1 with 2.0% 1-octadecanol
Fig.8. Effect of CTAB on average ink particle size after agglomeration of two toners mixed by the ratio of 1:1 with 2.0% 1-octadecanol
Above results was further manifested by the agglomerated ink particle size (Fig. 8) which had very similar trend. Thus, it could be concluded that the agglomeration efficiency was affected by the amount of the cationic surfactant added. The optimal amount of the cationic surfactant is close to the optimal cationic surfactant demand of the negative charge toner.
Different Type of Cationic Surfactants
In order to further examine the effect of different cationic surfactants on agglomeration of mixed toners. It was used that the another cationic surfactant, LDBAC, which consists of a C12 alkyl group and carries a phenol group for comparison. The pulping conditions were same as above by mixing two toners paper at the weight ratio of 1:1 with 2.0% 1-octadecanol. Since the best agglomeration performance of LDBAC occurred at 0.06% for Toner B (data not shown), we choose this condition to compare with the dosage of 0.08% CTAB. As shown in Figs. 9 and 10, not only CTAB but also LDBAC could generate the synergistic effect. Actually, the NPM synergistic effect of LDBAC (from 59,000 to 19,000, 67%) was close to that of CTAB (from 50,000 to 16,000, 67%), and the agglomerated ink size synergistic effect of LDBAC (from 0.08 to 0.24, 3 times) was higher than that of CTAB (from 0.15 to 0.32, 2 times). The synergistic effect of LDBAC was better than CTAB.
It can thus be concluded that the synergistic effect is valid for more than one type of cationic surfactants.
Fig.9. Effect of LDBAC and CTAB on NPM after agglomeration of two toners mixed by the ratio of 1:1 with 2.0% 1-octadecanol
Fig.10. Effect of LDBAC and CTAB on average ink particle size after agglomeration of two toners mixed by the ratio of 1:1 with 2.0% 1-octadecanol
CONCLUSIONS
- Adding a small amount of cationic surfactant together with 1-octadecanol will greatly improve the agglomeration of the toner carrying a negative charge but have a slightly negative effect on that of the toner carrying no surface charge.
- The additive effect of the mixed toner agglomeration existed when only 1-octadecanol was used.
- Adding a small amount of cationic surfactant together with 1-octadecanol will enhance the mixed toner agglomeration efficiency and generate a significantly synergistic effect.
- The synergistic effect is affected by the amount of the cationic surfactant added. The optimal amount of the cationic surfactant is close to the optimal dosage of the negative charge toner agglomeration.
- It is recommended that the agglomeration deinking of mixed office waste paper with 1-octadecanol should be carried out under neutral conditions with the addition of appropriate amount of the cationic surfactant.
ACKNOWLEDGMENTS
The financial support from the scientist foundation of the Nanjing Forestry University (G2010-02) and PAPD of Jiangsu Higher Education Institutions are appreciated.
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Article submitted: April 6, 2012;