The beginnings of ACAT’s BondStar® dry strength agents date back to 2010. “That was when e-commerce was really taking off, and the demand for packaging material was growing rapidly. The global COVID pandemic led to a surge in demand,” says Nuri Kerman, who heads the papertech division and has been instrumental in driving the development of the BondStar® products at ACAT.

To produce packaging cost-effectively and sustainably, waste paper is the primary raw material used. “It was foreseeable that the increased demand for waste paper would require a further increase in collection rates. However, extensive recycling had a significant impact on the quality of the fibres. The challenge was to compensate for the loss of strength, ensuring that the packaged goods could still be transported safely. This is where our polymer-based BondStar® dry strength agents came into play,” says Kerman. In 2017, a separate, globally valid patent was registered.

14 years of expertise

Years of experience with BondStar® dry strength agents have shown impressive results in daily practice, Kerman explains: “They lead to a significant increase in all strength values and greatly improve ply bond. They also boost the initial wet strength, making the paper more resistant to moisture.” In addition, BondStar® dry strength agents increase z-strength, which means less picking and dusting. Another positive effect is a more stable paper web, ensuring smoother feeding and higher production speeds. In addition, BondStar® dry strength agents offer the potential to replace primary fibres with recycled paper and reduce – or completely eliminate – the use of wet-end or surface starches. This leads to smoother operations and notable energy savings, including lower steam costs.

Advantages in black and white

All these benefits are also reflected in specific figures, as a look at a paper mill that relies on ACAT’s innovations shows. For example, 38 per cent less surface starch was required in the production process for the same strength. Steam consumption fell by 11 per cent, and the number of breaks dropped by 44 per cent. The downtime was reduced by half, and the need for retention agents by a fifth. Most importantly, production has increased by six per cent. Nuri Kerman (ACAT, Head of papertech): “We are committed to being very customer-oriented and providing the best solution for our customers. With BondStar®, we have been very successful in this, as the practical experience we have gained demonstrates.”

Production on site

ACAT BondStar® dry strength agents are in demand all over the world and can be used across a wide range of applications, including packaging papers, graphic papers and tissue. BondStar® is available in different concentrations as a commercial product. “We also specialise in on-site technology, where production takes place cost-effectively at the paper mill itself.” For this purpose, ACAT builds tailor-made systems directly at the customer’s location. ●

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)

In order not to affect adversely the optical properties and the printability of papers, primarily less costly fillers are used as fiber substitutes. Nowadays the quantities of fillers used are largely exhausted, because the paper industry has been particularly active in this area. Now a further increase of the quantities is attempted by using chemicals. Despite higher filler contents some strength parameters partially can be kept constant by using dry strength agents such as the ACAT BondStar® 289 L.

However, the increase of fillers often causes loss of bending stiffness that is of great importance for printing machines and copiers.

ACAT has expanded its portfolio to BondStar® 201 L, which has the ability to compensate the loss of stiffness. Test runs were carried out on a fine paper machine producing mainly copying paper with 60 and 90 g / m2. The retention aid system was a typical two component system using polymer and bentonite. The test run was carried out as follows:

• copying paper 80 g/m2
• PM speed: 850 m/min

First BondStar® 289 L was introduced into the filler pipe with a quantity of 3 kg / t. In a further step BondStar® 201 L was added at the output of the machine chest with 1.5 kg / t (see fig.)

With the addition of BondStar®289 L the filler content (GCC) increased from 22% up to 26%. This led to a 5% loss of stiffness.

To compensate the loss BondStar® 201 L was added and stiffness increased up to 5% above the initial value. To get to the bottom of the potential of this system, the filler content was increased again by a further 2% up to 28%. As a result the stiffness reached the initial value (see fig. below)

Conclusion: With the addition of 3 kg / t BondStar® 289 L and 1.5 kg / t BondStar® 201 L it is possible to increase filler content by 6% without losing bending stiffness.

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.

After the successful introduction of our dry strength agents based on GPAM (glyoxylated polyacrylamides) we add now two new products based on polyvinylamines (PVAm) to our portfolio of dry strength agents and additives to increase the efficiency. The products are:

BondStar® 206L und BondStar® 284L

 Mainly on older types of paper machines like four-drinier machines, top wire formers or paper machines equipped with a dandy rollthey can increase the dry content and they can deliver an increase of speed of up to ten percent. This effect is mainly due to the formation of a fine flock structure which has a positive impact on the vacuum dewatering and on the dewatering behavior at the press section. In addition to the side effect of increasing strengths the efficiency of the paper machine can be improved by the reduction of web breaks.

With the application of the new products in fine papers it is possible to produce papers with higher fillers content without significant loss of strength.

With the following case study we want to discuss this advantages in more detail:

Case study: packaging paper machine:

 Type of paper:

 Testliner 1-3

Paper machine:

 Top: top wire former, back: fourdrinier wire

• 170.000 t/a production
• speed 600 – 820 m/min
• 150 – 240 g/m²
• retention agent RetStar® 205P, 320 g/t

Dosing point and quantity:

 Test 1: Dosing between mixing and machine

chest

(high density pulp)

• Test 2: Dosing before the headbox pump

(low consistency pulp)

• dosing quantity: 9,5 kg/t BondStar® 206L

  Results test 1:

 increase of paper machine speed 3%

• increase of SCT: plus 15%, burst pressure:

plus 17%

• reduction of retention agent 30%
• reduction of vapour 2,5%
• reduction of breaks 37 %

Results test 2:

• increase of paper machine speed 7%
• increase of SCT : plus 8%, burst pressure:

plus 12%

• reduction of retention agent 50%
• reduction of vapour 4%
• reduction of breaks 26%

Conclusion:

If the focus is on the improvement of strength, it is better to dose the agent at the high density area. If the focus is on an increase of speed, it is better to dose the agent near the head box.

To prove this in practice the staff members of the ACAT application technology department would be happy to introduce the advantages of this specific development of the already known polyvinyl technology to interested customers in laboratory and machine tests.

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.