Due to the ongoing closure of the water circuits in paper production and to the increasing amounts of waste paper there is an accumulation of so-called impurities. These impurities they can be distinguished by to their origin as well as by their chemical composition. However, for principle considerations, it is sufficient to distinguish between soluble and partially soluble or insoluble impurities.

Impurities are characterized by their fundamental physical / chemical parameters.

In this context the most important parameters are the weight-specific charge density and the particle size. Soluble impurities are molecules or macromolecules and therefore they have a size of less than one micrometre. Several studies in water circuits of numerous paper mills have shown that more than 90 percent of the partially soluble impurities have a particle size between 1 micron and 50 microns. (fig. 2)

For the treatment of impurities in paper production a clear distinction between charge neutralization and deposit control is important. For the treatment of insoluble impurities the focus usually is on charge neutralization, for the treatment of partially soluble impurities it is on the deposits. In aqueous media – during the stock preparation and in the wire section and press section -many partially soluble impurities have the tendency to deposit; that is closely related to their „stickiness”.

The deposition tendency of the impurity particles increases with an increasing particle size.

During long retention times even impurities, which initially have a low deposition potential due their small size coagulate with other particles and so their deposition potential can be increased. A now well-established method for the removal of impurity particles of this size is the fixation with cationic polymers. It is important that the particles are fixed in finely dispersed condition not to form coagulum.

Among others the cationic polymers of the Bond Star-series offer many chemical options for special applications.

The Chemistry of the Fixing Agents

The fixing agent acts as a link between fibre and impurity particles. This attractive forces act between polymer and fibre, as well as between the polymer and the impurity particles.

In the case of shearing of the impurity particles the polymer would remain on the fibre. To adjust the interactive forces several molecular parameters of the polymer can be optimized. The key parameters are the molecular weight, the charge density and the molecular structure. The molecule can be modified by the addition of functional groups.

The variety of material systems and the different applications require an ideal combinations of the different molecular parameters. The products of ACAT BondStar® series offer a high degree of flexibility.

Over a very wide pH range (3-10) the products of the BondStar® series have very high cationic charges (up to 15 meq /g). For a punctual fixation the BondStar® products can be optimally used for many different paper productions: in the production of wood free and fine papers up to papers that are produced from 100 percent recycled paper as well as in board production.

     Fig.5: Abietic

Practical Application

Problems in runnability with bright specks, holes, breaks and others on a paper machine, which produces standard newsprint (500 t/ day), were the reason to carry out various tests over a longer period to reduce hydrophobic particles originating from the resin acids of the TMP.

Several preliminary tests proved that Bond Star® reduces these particles efficiently.

Resin Acids:

Chemically resin acids are carboxylic acids based on terpenes. Typical representatives of resin acids are the abietic acid, the neoabietic acid, the levopimaric acid, the pimaric acid and palustric acid.

In addition to the conventional measurement methods for the analytical detection of impurities, such as

• COD measurement
• BOD measurement
• Turbidity measurement
• Measurements of pH value and conductivity
• PCD measurement (using the polyelectrolytetitration to determine the consumption of cationic aids)

ACAT pays special attention to the evaluations in

• FCM methodology (flow cytometer measurement) – Determination of particle number and size, for example, of the hydrophobic particles

• Microscopic evaluation of stickiness

Improvements by the Use of BondStar®:

The use of Bond Star shows a significant reduction of hydrophobic particles (Fig. 6).

Dosing point BondStar®: in the TMP unbleached to the blending chest Dosage  BondStar®: 0,5%

• Improvement of runnability (reduction  of standstills for cleaning per month)

• Significant reduction of sheet breaks
• Reduction in bright specks and holes

(Fig. 7)

• Relief of the paper machine circuit
• BondStar® supports the retention

(Savings of retention additives)

For decades, dry strength agents have been known in paper industry and literature. They can be both natural and synthetic products. Examples are especially starch or products based on polymers. ACAT BondStar® products are mainly based on polymers and they work by an interaction of aldehyde and hydroxyl groups. The strengths develop already in the press section and they are developing completely during drying. The massive bonds strengthen the sheet structure opening new possibilities and tools for papermaking. The BondStar® products made their breakthrough during the last few years. The paper production has changed rapidly and digitization is an ongoing process.

The increase of waste paper and the decreasing share of fresh fiber are a real challenge for the paper industry. Today, global and political influences play an increasingly important role in the procurement of waste paper. Naturally, this has an impact on quality and prices. In the packaging sector it is tried to produce the best possible end product with the lowest fiber quality. But that does not always succeed.

However, to achieve a better quality, it is possible to stabilize the end product in terms of strength with the ACAT dry strength agents. In recent years, especially the graphic paper sector has suffered considerably from sales losses, and this development is still ongoing. Continuous efforts are made to produce a low cost product for the market. To achieve this, even cheaper alternative fibers are sought or the amount of filler is increased. More and more dry strength agents must be used to achieve the necessary strength and printability properties of the final product, and therefore also our BondStar® dry strength products are requested. They are available as a commodity in various concentrations. In addition, we offer an on-site technology, where the production of the most cost-effective product takes place in the paper mill on site. ACAT has specialized in this on-site technology and on its base we have developed the BondStar® range.

Mostly new projects start with laboratory work laying the foundation for a successful machine trial. If the customer is convinced of the technology on the machine, a customized plant will be constructed. After the installation of the plant engineering, the application will be further optimized, also in terms of cost-effectiveness. State-of-the-art monitoring and maintenance systems guarantee a reliable application. In terms of logistics, we work with the utmost foresight and with telemetric monitoring.

LABORATORY WORK – THE BASIS FOR SUCCESS

Before we recommend a paper machine trial, we often start our work in the laboratory of the customer. We simulate the type of paper and the customer‘s process to determine in advance whether our BondStar® dry strength agents can meet the expectations and the effects that can be expected on the paper machine later. Of course, the results of the laboratory tests must convince the customer of our product. In the laboratory we can reproduce many types of paper on the sheet former and we can simulate the process of mixing and adding of the additives. We test the laboratory produced test sheets on strength parameters and also on some printability properties. The most common test methods for the strengths are: breaking load, breaking stretch, breaking length, SCT / RCT, bursting pressure, ply- bond strength and CMT. As an example for the increase of the ply-bond strength with BondStar®: we couch two wet lab sheets and this way we are simulating a double- or multi-layer paper machine. For the printability tests we closely work together with our customer and, among other things, we check the Dennison wax test, IGT, smoothness and roughness. An example of this could be the use of BondStar® to increase the amount of filler. It is important to comply with the printability requirements.

For example, the use of too much filler would cause problems on the offset blankets. The ash can be better fixed within the paper by using BondStar®.

THE MACHINE TRIAL WITH BONDSTAR® –ANOTHER MILESTONE

If the laboratory tests convince the customer and he agrees to a paper machine trial, we will organize the suitable equipment and the raw material. We have developed two methods to carry out a paper machine trial.

The first method is very simple and it is used for short tests lasting up to two days. We take the locally produced BondStar® from one of our customers and deliver the product to the trial

customer via IBC container or tank truck. The product is applied in the paper mill with the appropriate dosing technology. The second method is more complex. A manual Bond-Star® unit is installed, which is continuously supervised by

ACAT employees throughout the trial. In this case BondStar® is freshly made on-site. With this system a trial over several days is possible and it is the only method for long term trials. It offers more flexibility, but it requires a large amount of personnel.

All the time the machine trial is supervised by ACAT specialists and accompanied by the respective production management and the machine operators. Thanks to our numerous experiences we know exactly the screws we have to move on the paper machine, to make the trial a success and to exclude losses or damages. For many customers not only strength or printability properties are important, but increasingly the efficiency of the paper machine should also be optimized.

BondStar® is the ideal product for the papermaker. It offers some exciting possibilities, as the graph (Figure 3) shows.

The manufacturers of packaging papers expect from BondStar® the increase of strength, but sometimes in addition it can also increase production and improve runability. The runability is defined as the machine run without breaks and disruptions. The runability is particularly in demand for low basis weights. Dry strength agents, such as BondStar®, can significantly improve the production process using an ever deteriorating quality of waste paper resulting in stagnant strengths and increasing ash contents. In addition, BondStar® is often used to meet or to achieve the desired specification. Thus, very effectively lowers the costs of complaints and often new customers can be attracted.

oon after the addition of BondStar®, the first positive effects are to be seen and the improved strengths and surface properties are measurable in the laboratory. This gives the papermaker the opportunity to quickly influence the quality parameters. As a side effect in clean cycles retention increases and drainage improves and accordingly the specific steam input to dry the paper decreases. As a result, the draws in the dryer section can be loosened and the machine run can be improved. BondStar® offers the opportunity to perform faster grade changes to higher grades without intermediate grades.

The producer of graphic paper expect very different results from the use of BondStar®.

Their focus is on cost optimization and on the substitution of expensive raw materials with cheaper substitutes. One example is the sector of offset papers: here it is requested to increase the amount of filler while maintaining the printability and strength properties. Using BondStar®, it is possible to increase the amount of filler up to 34% while adhering to all parameters.

The use of BondStar® often causes an increase in retention and drainage as a side effect. At the same time, the formation can be slightly improved. By using more fillers, a better drying can be achieved. BondStar® is relatively neutral within the system and it is compatible with various commercial chemical additives. This gives the customer great confidence, because he does not have to adapt his system to BondStar®, or he cannot or he does not want to adapt it. For example, there is no negative influence on optical brighteners, on various sizing agents, retention aids or dyes.

INSTALLATION OF PLANT ENGINEERING – TAILOR-MADE SOLUTIONS FOR EACH CUSTOMER

After the successful paper machine test, the project planning of the plant engineering and its installation takes place. ACAT has its own mechanic workshop in Austria and all necessary facilities to build customized BondStar® units.

Before project planning, the ideal place for the installation of the system is determined together with the customer. With CAD plans, ACAT can draw the units in 3D into the planned location

and present it to the customer in advance. When installing a system, many factors must be considered, such as the unloading of the raw material and the proximity to the dosing point.

Usually the installation and commissioning of the BondStar® equipment takes not more than five working days.

START-UP AND OPTIMIZATION

The equipment is put into operation by the ACAT startup team. The product is supported both technically and technologically by the employees of ACAT for a longer period of time. During this time continuously the mill staff are trained and together they are optimizing the dosages and the product. During the start-up phase you get a feeling for the required dosages and for the ideal logistics timing of the raw materials. After some time, the customer often controls the BondStar® by himself.

Whenever BondStar® is needed, he starts the pumps. The units are always on standby and produces automatically when needed.

AFTER SALES SERVICE – CONTROL OF LOGISTICS

Regular visits and the maintenance of the system technology are part of the ACAT service. Via various telemetric services, we are able to monitor, control and maintain the equipment worldwide. In consultation with the customer, it also handles the entire raw material logistics.

BONDSTAR® – WORLDWIDE

ACAT is the world leader in BondStar® on-site production of synthetic dry strength agents because of its many years of experience. ACAT is represented with this technology from the USA to China. We look forward to new projects and we are really excited to see where the next trip will take us to.

About 40% of anaerobic industrial wastewater treatments in Germany are operated in the paper and pulp industry. The process is most commonly used by the manufacturers of packaging papers using waste paper, especially in the production of corrugated base paper, which is produced with low specific amounts of waste water due to the closed loops. As a result of

high recycling ratios, the waste paper fibers are becoming shorter and weaker leading to reduced paper strength. To counteract the resulting negative consequences, such as not achieving the required paper specifications or sheet break on the paper machine during the production process, a wide range of chemical additives are added, including dry strength agents.

With the BondStar® product range ACAT has developed synthetic dry strength additives used successfully worldwide. BondStar® is added to the stock suspension early in the wetend. Due to the very good absorption a very high proportion of BondStar® is remaining in the paper and only a very small amount is discharged to the anaerobic stage with the wastewater flow. The product is offered in various concentrations to the market. Glyoxalated polyacrylamides have only a very limited shelf life. To solve the shelf life problem, ACAT has also developed a cost-efficient on-site technology at the paper mill for the production of BondStar®.

The use of BondStar® results in increased dry strength, less breaks, higher paper machine speed and an increased filler content in the end product.  Similar to polymer flocculants used in sludge thickening and sludge dewatering in wastewater treatment plants, BondStar® has a cross-linking/ bonding effect between particles oppositely charged to the polymer.

As part of his master‘s thesis at the Upper Austria University of Applied Sciences, supervised by Dipl.Ing.Dr.nat.techn. Kiril Atanasoff, in cooperation with the Ostwestfahlen-Lippe University of Applied Sciences – Department of Civil Engineering, Laboratory for Urban Water Management, Lucas Wagner investigated the ques-

tion of whether the use of BondStar® can have negative effects on the anaerobic degradation of the wastewater. To this end, on one hand he carried out extensive batch tests and on the other hand continuous laboratory trials with two parallel operating UASB reactors on a laboratory scale.

Batch trials

The batch trials were prepared in 2-liter glass bottles and carried out at a temperature of 37 °C ± 1 °C. In the first series of trials, waste water from the pre-acidification of the industrial wastewater treatment plant of a corrugated base paper mill in Bavaria was used as substrate. In a further series of trials a 0.5 % acetic acid solution with a pH value of 6.5. Pellet sludge from the mill‘s own anaerobic plant of the corrugated base paper mill in Bavaria was used as inoculation sludge. In the Bavarian mill a 2 % BondStar® solution is used, in a quantity of 66 l/m³ waste water.

It was assumed that different amounts of the dry strength additive remain on and in the end product paper. Conversely, this results in corresponding residual concentrations in the wastewater. These residual concentrations were
simulated by using different amounts of BondStar® 2 % in batch preparations.

Continuous laboratory trials

The laboratory tests carried out in the corrugated base paper mill were intended to simulate the effects of an incident at the production plant, for example in the case of a pipe burst or a leak in the storage tank. In the event of such an incident, different amounts of 2% BondStar® solution would be discharged directly into the waste water stream and thus into the anaerobic pre-treatment plant. The effects of higher BondStar® concentrations in the wastewater on the anaerobic degradation process in the UASB reactors should be analysed and documented. A continuous trial operation with abnormal high BondStar® addition levels was not carried out, because such an operating condition is far away from the reality and should already be avoided for cost reasons.

The pre-acidified waste water from a corrugated base paper mill’s sewage plant was used for the
trials. This wastewater already contained small amounts of BondStar® due to the mills operation with BondStar® in their production.

The laboratory reactors for the continuous experiments were borrowed from the Laboratory for Urban Water Management of the University of Applied Sciences Ostwestfalen-Lippe. Various BondStar® concentrations were used to simulate fictional incidents. In the trials it was assumed that a BondStar® inlet pipe would break and a significant amount of BondStar® solution would flow directly into the wastewater treatment plant. In the operation itself, approximately 208.5 ml of BondStar® are added to 5 l pulp suspension of base paper mash.

The assumption was that about 10 % – 100 % of the BondStar® solution is not absorbed by the paper and is in the waste water. In the simulation of the incidents, it was assumed, for example, that a BondStar® feed pipe would break and part or the whole BondStar® (100 %) solution would flow directly to the anaerobic stage.

The quantities of BondStar® (10 %, 50 %, 100 %) added to the waste water in the tests were intended to simulate that these percentages of the dry strength additive were not absorbed by the paper, but went into the waste water.

The quantity of dry strength additive for the respective incident simulation was always added once to the lab storage tank. The storage tank was filled daily with fresh waste water. The reactor was operated with wastewater without additional BondStar® for about 14 days.

In order to determine the effects of an additional quantity of BondStar® solution in the event of a malfunction, one of the two UASB reactors was operated only with pre-acidified raw wastewater, while a wastewater-BondStar® mixture with the respective BondStar® additives was added once to the second reactor. The two reactors were operated with almost the same COD loads and hydraulic retention times as in the anaerobic unit of the plant. The comparison should show whether and what effects occur in the event of an accident with BondStar®.

The following conclusions can be drawn from the trials:

In her review of Lucas Wagner‘s master‘s thesis Prof. Dr.Ing. Ute Austermann-Haun from the OWL University of Applied Sciences came to the following conclusions:

• BondStar® increases Chemical Oxygen Demand (COD) in wastewater. This COD is degraded, recognizable by the higher biogas production. The data show that BondStar® does not inhibit the biogas production, on the contrary, that both the BondStar® trials with pre-acidified wastewater and the BondStar® trials with acetic acid produce more biogas and even the methane concentration increases slightly.
• The batch trials clearly showed that with the increasing addition of BondStar® the COD degradation is delayed, maybe due to the hydrolysis required first. The same effect could not be found in the continuous tests.
• For 87 days the reactors ran in parallel. Reactor 1 was fed four times with wastewater containing high concentrations of BondStar®. Neither the COD elimination performance, nor the biogas production, the biogas composition, the organic acid content or the FOS/TAC ratio were negatively affected by the higher concentration of BondStar® in the anaerobic plant inlet.
• The trials showed that BondStar® is obviously degraded, which is shown by the increase of biogas production.

Result

With the presence of BondStar® in the waste water of a paper mill, no acute or incipient toxicity, no inhibition of biogas production and COD degradation were detected under the conditions described. No acute or long-term inhibition or toxicity occurred. On the basis of the tests, it can be ruled out that the correct use of BondStar® will not lead to any lasting inhibition of methanation, neither during operation nor in the event of malfunctions that may occur repeatedly during paper production.

The last test approach, in which 208ml BondStar® were added directly into the reactor, simulated a very unrealistic scenario. However, it was still carried out to observe and describe possible effects. The addition of 208 ml to 3.75 l reactor volume corresponds to an amount of 55 ml/l corresponding to 55 l/m³ reactor volume.

In real operation, this would mean, for example, for a paper production facility for corrugated base paper, that approximately 70 m³, i.e. more than three tankers of 20 m³ each of BondStar® 2 %, would be added directly to the wastewater stream and would immediately reach the wastewater treatment plant and subsequently the methane reactors.

During this experiment Lucas Wagner could observe that the sludge formed a massive floating layer.

In other industrial plants Prof.Dr.Ing. Ute Austermann-Haun has observed that if a too large amount of polymer flocculants is added, the pellets are not able to remove the biogas produced due to the change in viscosity. As a consequence, the biomass floats in this case as well. The microscopic pictures showed massive sticking of the pellets and a binding of fine materials to the pellets. However, the pellets were still functional, i.e. their degradation behaviour was
not affected. In summary, it can be said that BondStar® is a sustainable product. Especially using waste paper for the paper production, it improves significantly production conditions.

In the laboratory tests, simulations of malfunctions with large quantities of BondStar® entering the wastewater showed no acute toxic or mid-term negative effects on anaerobic degradation.

Our special thanks go to Prof. Ute Austermann-Haun and Dipl.Ing. Heike Witte from the Technical University of East Westphalia-Lippe, Germany and Dr. Alexander Jäger from the University of Applied Sciences Wels, Austria for their technical and practical support in carrying out the batch and laboratory tests.

Our practical experience so far is that in Fine Paper, BondStar® provides the opportunity of improved machine runnability, filler increase and long fibre reduction. In Newsprint we have applications which have resulted in filler

increase and yield improvement, while in Tissue we are running applications showing improvements in runnability and fibre yield increases.

Application knowledge, addition point optimization and working closely with the customer are essential to maximise the customer return and get the best cost performance from the product.

Increasing ash levels in Fine Paper will normally result in poorer runnability, reduction in sheet strength properties and more deposition in the machine system.

Applications currently running with BondStar® 206L in Asia have demonstrated the ability to improve first pass and ash retention, increase drainage, give more wet web strength to the sheet, reduce energy costs and maintain sheet strength properties.

Results are from a number of different current applications.

The enormous cost pressure on graphic paper manufacturers in recent years has resulted in the fact that more expensive fibers have been partly replaced by fillers, in stock as well as in coating.

This trend is currently continuing as some new developments are still in the experimental stage. Different concepts – either by dry strength agents, improved fillers or optimized coating color additives – have already been a success, but within a short time the increasing content has led to an increasing fillers content in waste paper. Due to this fact some paper manufacturers, who process especially ordinary grades of waste paper such as 1.01, now have problems with their water circulation systems and with strength values. Mainly these are the producers of newsprint paper and packaging paper. Some producers try to discharge the ash selectively with mechanical devices for example with flotation plants. This succeeds to a certain degree and provides relaxation for a limited period of time.

Quote Mr. Michael Habeck plant manager of the Adolf Jass GmbH paper mill: „We have become a waste disposing company for Rügen chalk.”

But the packaging paper producers currently have to deal with several trends: increasing fillers content, decreasing quality of waste paper due to the high demand and multiple recycling, as well as the trend towards low basis weights. Meanwhile, 80 g/m² are the standard grades for fluting paper. In the graph on the left above the average ash content of a packaging paper maker is shown as an example.

ACAT now offers different synthetic dry strength agents – the BondStar® series. With these dry strength agents it is possible to replace fresh fibers or higher quality recycled fibers with lower quality recycled fibers and therefore with cheaper waste paper grades, without a negative influence on the required features. Furthermore, it is possible to keep strength properties stable despite higher ash content in the paper. As a side effect in some systems these chemicals can significantly improve the efficiency of paper mills.

This effect causes especially a more stable and stronger paper web whereby the speed can be increased and the breaks caused especially by edge defects are reduced. Our synthetic dry strength agents keep their characteristics also in closed systems with high conductivity, where the wet-end strength is no longer working.

For the future a market is created for synthetic dry strength agents that will partly be in competition – but mostly they will be a complement- to conventional dry agents such as starch. For ACAT this area is a number one research and development project.