Talking about the synergistic effect of various functional additives in papermaking process

Since these functional additives are rarely used on their own, it is essential to have a clear understanding of the synergy between them. The information provided below should provide some help for you to better use various additives. Before we begin, let us review together what are the functional additives and synergies. The so-called functional additives means that by using these products, users can provide the desired function. From a different point of view, this applies to all additives. Synergy is a proprietary term that indicates that when two or more additives are used together, the effect is different from the additive effect of using the additives alone. In general, synergy is a positive effect, but this synergy sometimes becomes negative.

1. Coagulants and retention aids Coagulants (catches) are commonly used in breakage and other waste paper pulps to neutralize system charges or to dispose of waste in the pulp. Such auxiliaries, when properly controlled for application, will reduce the demand for short-term retention aids for ton of pulp. The decrease in the amount of high-molecular-weight retention aids will significantly improve the formation and tightness of the resulting paper compared to the initial dosage. However, when the coagulant makes the system charge again excessive, it will also have a negative effect, leading to retention agent desorption on the slurry, reducing the efficiency of use.

Coagulants or low-molecular-weight retention aids are used in the factory to improve the drainage of the forming zone for optimum results. This also applies to the coagulation of pulp and pulp.

2. Starch and retention aids The addition of starch to the wet end can impart strength to the paper. It is also a good source of cationic charge and is generally beneficial to the retention and filtration of the slurry. In the production process of high-grade printing writing paper, it is often seen that the addition of starch in the wet part can significantly reduce the amount of retention aids, and at this time its main role is to help retain the internal sizing agent. With the development of high cationic substitution starch, some manufacturers are trying to use it to make the system clean to facilitate the improvement of strength, retention and drainage. Similarly, starch can also cause excessive cationization of the system, making the use of other auxiliaries less efficient.

3. The interaction between the two dispersants and retention aids will have an adverse effect. During use, dispersants are used to remove system waste or assist germicides in the diagnosis and killing of bacteria. Here the dispersion process will react to the retention of the slurry. When manufacturers use dispersants, it is always observed that the use of retention aids has decreased.

The example also demonstrates the importance of this synergy and the use of an on-line inspection device with an on-line monitor. The technicians observed that the retention rate will always decrease periodically after returning to normal. Further studies revealed that this reduction is directly related to the intermittent addition of bactericidal agents. Dispersants used in sterilizing treatments in bactericides are detrimental to the use of retention aids. The paper mill reduced the rate of slurry retention to normal by replacing the faster bactericide feed switching system and changing feed points.

4, particulate retention agent

Microparticle retention aids mainly include silica sol, bentonite and synthetic products. Paper mills use them together with starch and retention aids to improve slurry retention, drainage, forming, and paper machine operations. With the merger of some chemical companies, many of these technologies have been controlled by a single supplier. By intensively mastering these technologies, the paper industry began to develop a particle retention system that can simultaneously improve slurry retention and paper formation. This combination allows the slurry drainage to be improved while maintaining normal formation, changing the paper formation profile without losing slurry retention and drainage. These collaborative systems are still in their infancy, but their potential for development is enormous for users. The problem here is that its increased costs must be consistent with the benefits generated.

5, defoamers and wet add additives

Paper mills often use defoamers or degassing agents to prevent foam and deposits. However, they also have a positive effect on the addition of additives to the wet end. The use of adjuvants requires a clean, properly charged slurry fiber or surface of fine fibers to be absorbed and combined. If there is too much air in the slurry system, the surface of the pulp fibers or fine fibers will cover a large number of microbubbles, and these air bubbles will make the additives unable to make good contact with the fibers.

European paper mills usually pay more attention to the control of defoaming and degassing measures in the slurry system than American paper mills. Therefore, with the appropriate defoamers and degasifiers added monitoring measures, the chemical utilization efficiency and the paper machine operating conditions Relatively better.

6, starch and added sizing agent

Sizing agents such as alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD) are added internally and are difficult to retain on the fibers when used alone. Cationic starch can be used to increase the retention of the sizing agent on the fibers. In some cases, manufacturers use starch as an emulsifier for the sizing agent. Some sizing agents also use it as a sizing booster. In addition, these two chemicals act synergistically to improve the strength of the paper while improving the sizing efficiency.

7. Coagulant and internal sizing agent

Coagulants and trapping agents can help keep the sizing agent in two ways. The coagulant is added to the internal sizing agent to make it more favorable for adsorption onto fibers and fine fibers. It also removes wet rubbish, which provides a cleaner fiber or fine fiber surface for sizing agent adsorption. The technical difficulty exists in controlling the balance of charge in the system. System over cationization will result in desorption of other auxiliaries and sizing agents.

8, internal sizing and surface sizing sizing

The required degree of sizing of the paper can be achieved through refining, internal sizing and surface sizing. Paper mills usually add sizing agents to achieve sizing requirements after the refining has been optimized. The paper mill can do this by adding a sizing agent in the wet or in the size press section or both. The simultaneous addition of the wet part and the size press part at both places can increase the sizing efficiency, reduce the cost and reduce the phenomenon of deposition of charge in the wet part. How to correctly use this cooperative sizing method depends on the paper machine structure and process parameters, but as long as more attention is paid, this method is still very feasible.

9, Alum in alkaline papermaking

In the past few years, the use of alum in the alkaline papermaking system to improve papermaking performance is one of the hottest positive synergies. Alum Retention chemistry theory shows that it cannot work effectively under alkaline pH conditions. However, in reality it can indeed improve the alkaline sizing efficiency and slurry retention. At the beginning of the conversion to the alkaline papermaking system, alum was often added to the ASA emulsion to stabilize its emulsion particles. When such ASA-Alum emulsions are used for papermaking, the slurry retention rate and the cleanliness of the machine are significantly improved. Then people used the Ming dynasty again and they also obtained similar favorable results. Alum is now commonly used as a retention aid and sizing booster in paper mills. The problem is that when at alkaline pH, excess alum tends to form precipitates and cannot be used normally.

10, alum and rosin gum

Over the years, people have reached a consensus that alum can form a rosin alum complex with rosin gum at acidic pH to give the paper a good degree of sizing. This is also a typical example of the active synergy between two different chemicals. Regardless of the combination, it should pay attention to the proportion of additives, the way of adding and the place of addition, otherwise it may cause deposition, resulting in a decrease in the use efficiency.

11, the resin control of a talcum powder

Pulp mills generally use talcum powder to control resin barriers and other stickies. What is often forgotten is that it can also be used as a paper filler. Although the whiteness and opacity of talc is lower than that of ground calcium carbonate GCC and precipitated calcium carbonate PCC, it is still a good pulp filler. Therefore, talc can be used as both a resin barrier control agent and a filler. When the talc powder in the pulp mill is used as a resin control agent and the dosage is 4.5 to 6.8 kg/t, no side effects occur during the papermaking process.

12. Precipitated calcium carbonate (PCC) and ground calcium carbonate (GCC)

The market competition for these two types of calcium carbonate has been going on for many years, but many examples show that they share a positive synergy.

Each product has its own advantages and disadvantages, and it can weigh the pros and cons to meet the papermaking needs. Combining the advantages of each technology and selecting the right packing, the manufacturers will get the best cost performance, paper machine efficiency, physical performance and optical performance.

13. Titanium dioxide (TiO2) pigment blends

Titanium dioxide is often used as a high-performance pigment in wet parts and coatings to impart excellent opacity and whiteness to paper. Due to its high price, some alternatives and titanium dioxide have emerged in the market, and the required optical properties have been achieved at lower cost. Because they have lower dispersant requirements, these alternatives are usually easier to keep than titanium dioxide. Because the dispersant has a negative charge effect on the slurry, the paper mill should pay attention to the range of dispersants used in these pigments.

14, coloring agent and pink agent

This title seems strange, but in fact, the role of colorants can have both beneficial and negative aspects. Mixing dyes and brighteners can meet the paper's expected color, hue, color density, whiteness, and opacity. When operators properly mix colorants, they can achieve the desired results with less adverse effects. Only by exerting a synergy between various colorants can one obtain the desired paper performance index, which cannot be achieved with only one or two dyes.

These dyes can also be mutually exclusive. The order of adding them is very important when they are shared. Never add them in a random order. Some dyes are cationic and some may be anionic. Note that the oppositely charged dyes should not be added too close when they are added, otherwise they will interact before they adsorb onto the fiber. Even if they are all anionic, since they can form hydrogen bonds with each other and affect their adsorption, they are also preferably added separately to promote their adsorption on the fibers.

15. Colorants and other additives

The interaction between dyes and other wet end additives is also bidirectional. Dye fixatives and coagulants are often used to fix anionic dyes and their interaction with each other is positive. Anionic dyes and pigments give a large amount of negative charge to the wet portion, which will have an adverse effect on the use of a cationic additive to the wet end. Even if the anionic dye has been uniformly coated on the surface of the fiber overnight, the increased negative charge will increase the additional burden of traditional cationic retention aids and coagulants.

16, softener and defoamer

Softeners are often used in the production of toilet paper and facial tissue to increase their softness, bulk and absorbency. Such auxiliaries are usually surfactants and are prone to foaming. This requires increasing the use of defoamers and degassing agents. The advantage of using a softener is that it can meet consumer requirements for bulk, softness, and absorbency. The disadvantage is the increased consumption of defoaming chemicals.

17. Possible effects

The examples listed above give the possible synergies between papermaking auxiliaries, both positive and negative. There may be more examples. It is important that pulp mills and paper mills should take stronger measures for the use of functional auxiliaries so that these auxiliaries (whether individually or in several types) can better meet paper performance. And cost requirements. Paper mills should pay close attention to the interactions of various additives when they are used, and optimize their application processes to achieve optimal cost performance.