Comprehensive evaluation of deinking performance o

Comprehensive evaluation of deinking performance of waste paper deinking agents

at present, most dip production lines in China use imported soap deinking agents. With the variety of inks, the probe is 7993 series, which belongs to positive voltage power supply mode. With the decline of waste paper quality, the requirements for deinking agents are also increasing. We should vigorously develop new and efficient compound deinking agents, non-ionic deinking agents and biological enzyme deinking agents to meet the needs of the domestic market. At present, there are different evaluation methods and means for deinking agents. For flotation deinking technology, which requires that the molecular weight of thermoplastic used for thermoforming should not be too low. The deinking performance of deinking agents should be comprehensively evaluated from two aspects: pulping and flotation

1 pulping

pulping is the first step of waste paper treatment. Its purpose is to maintain the original strength of the fiber to the greatest extent and effectively peel the ink from the fiber without changing the shape of various impurities as far as possible. Usually, the pulping effect is evaluated by the combined residual ink concentration (Eric junction), over washing whiteness and total effective residual ink concentration (Eric total) of the pulped pulp (hereinafter referred to as post pulping pulp)

1.1 combined effective residual ink concentration

combined effective residual ink concentration (Eric junction) value reflects the ink concentration that has not been stripped on the fiber. The smaller Eric knot, the better the effect of ink peeling from the fiber. Its determination 6. The method of bending steel bars in the steel bar bending experimental machine is: take a certain amount of crushed pulp, place it in the funnel with 80 mesh copper at the bottom, wash it fully manually until the filtrate becomes clear, then collect the residual pulp sample, and filter it into a pulp cake with a quantitative amount of about 170 g/rn2 in the Buchner funnel (it is required that the pulp is also the foundation cake for the development of new generation biomedical materials, and the opacity of the cake is greater than 97%). Measure the Eric of the positive and negative sides of the pulp cake on the ctp-iso eric950 detector, and take the average value

1.2 over washing whiteness

the over washing whiteness of deinked pulp reflects the whiteness of the pulp, which excludes the influence of substances such as ink and filler in the pulp on the whiteness of the pulp. Under the same pulping conditions, the higher the over washing whiteness of the pulped pulp, the more the ink peels from the fiber. Measure the whiteness of washed deinked pulp on the whiteness meter with the suction filter cake with Eric knot value measured in 1.1. The whiteness of the washed pulp after crushing is not only related to Eric value, but also depends on the proportion of waste paper, the quality of waste paper, the amount of chemicals added, etc

1.3 total effective residual ink concentration

total effective residual ink concentration (Eric total) mainly includes the stripped free ink in the deinked pulp and the bonded ink still attached to the fiber. The total level of Eric is related to the amount of ink and the size of ink particles. The more ink, the larger Eric. Under the condition of a certain amount of ink, the higher the Eric, the smaller the ink particles in the slurry. Flotation deinking is different from washing deinking. The ink particles of flotation deinking are relatively small, which is conducive to washing deinking; In the flotation deinking process, the free ink particles are relatively large, which can be better separated from the slurry, and the fine ink content in the white water in the deinking workshop is less, which is conducive to the reuse of white water. Therefore, under the condition of a certain proportion of waste paper, the smaller the Eric of the pulped pulp is, the better. The general determination method of Eric has no detection standard yet. The key is how to keep the free ink in the slurry evenly in the slurry cake when pumping the slurry cake. The filtrate should be clear by visual inspection. Aluminum compounds, fixatives, CPAM, etc. can be added for retention before the pulp cake is formed. The Eric values of the positive and negative sides of the filtered pulp cake (the opacity is greater than 97% when the ration is about 170 years old) are measured on the ctp-iso eric950 detector, and the average value is taken

2 flotation

flotation is to separate different particles by using their different physical and chemical properties on the surface. In the flotation process, hydrophobic particles or particles that convert hydrophilicity into hydrophobicity with surfactants are adsorbed on the air bubbles in the pulp suspension, floating upward and then separated from the pulp. The flotation effect of deinked pulp is often evaluated by the increase of flotation whiteness, the removal rate of flotation ink, and the loss of flotation residue pulp

2.1 flotation whiteness increment

flotation whiteness increment refers to the difference between the whiteness of good flotation pulp and the whiteness of incoming pulp. The higher the whiteness increment, the better the flotation effect. It should be emphasized that because deinked pulp contains fibers, inks, fillers, pigments, etc., its whiteness measurement is different from other pulps. The whiteness measuring piece (pulp cake) should be filtered with a Buchner funnel, not with an ordinary tablet reader, and it should be uniformly specified that the amount and concentration of the pulp sample should be filtered before the pulp cake is formed. The whiteness of the front and back sides of the pulp cake is quite different, and the average value should be taken

2.2 flotation ink removal rate

flotation ink removal rate II [(total feed Eric - Total good pulp Eric)/(total feed Eric - total feed Eric junction)] x 100%. Generally speaking, the better the ink trapping during flotation, the greater the ink removal rate, and the higher the whiteness increment

2.3 flotation slag slurry

high solid content of flotation slag slurry will inevitably lead to low yield, especially when there is a large amount of fiber content, a large amount of fiber loss will increase the production cost. During flotation, the foam is too small and the amount of foam is too much, which is easy to be taken away by air bubbles and the loss increases. In actual production, for example, the long defoaming time of foam will not only make the overflow condition of foam in the flotation cell bad, resulting in some ink re entering the slurry and reducing the flotation effect, but also cause the flotation ink cell to be in an overflow state, increasing the loss of workshop trench and affecting the production environment in the workshop

3 comparison of deinking effects of several deinking agents

under the same pulping conditions, due to the large Eric, g of the pulped pulp, it indicates that deinking agents B and C will break the ink to a large extent. A reasonable amount of deinking agent (131) can obtain a better ink stripping effect, which is reflected in the washed whiteness of the pulp after crushing. During flotation, the flotation whiteness increment and ink removal rate of deinking agent B1 are higher than those of deinking agent a. With the increase of its dosage, the solid content and fiber content in flotation slag slurry increase. However, deinking agent B1 and deinking agent C are too rich in foam during flotation, and the defoaming time is long, so they are not suitable for use in actual production. Therefore, to select a suitable deinking agent, we need to comprehensively consider the effects of pulping and flotation

4 conclusion

4.1 in flotation deinking, the evaluation of deinking performance of deinking agent should be comprehensively considered from two aspects: pulping and flotation, in which the increase of flotation whiteness and the removal rate of flotation ink are the two main indicators

4.2 foaming property and foam defoaming time are important indicators for evaluating deinking agent in the flotation process. The distribution of foam size, the number of foam and foam defoaming time should be moderate to reduce the loss of flotation yield