NEW ADVANCES IN MICROPARTICLE RETENTION TECHNOLOGIES

Authors

Sal Mirza1, Mark Conyngham2 and Rosa M. Covarrubias1

Organisation and address

1Buckman Laboratories International, 1256 N. McLean Blvd., Memphis, TN 38108, US
2Buckman Laboratories Pty. Ltd., Buckman Boulevard, Hammarsdale, 3700, South Africa

email

s_mirza@buckman.com , mrconyngham@buckman.com and rmcovarrubias@buckman.com

Keywords

retention, drainage, formation, polymers, microparticle technology

ABSTRACT

The pulp and paper industry globally is facing growing demands for innovation and productivity within the context of ever increasing environmental restrictions and the challenge of the trend towards a paperless office. In order to maintain profitability, there have been tremendous advances in the sophistication of manufacturing equipment together with higher paper machine speeds. This has resulted in a requirement for more advanced wet-end management methods, and increasing performance from retention/drainage programmes. There has been a steady evolution of microparticle technology and wet-end management techniques over the past twenty years to meet this challenge.

Retention and drainage aid programs have evolved from the use of a single flocculant or conventional coagulant-flocculant program to include the use of anionic microparticles based on bentonite clay or colloidal silica chemistry. These anionic microparticles have been used along with cationic starches, coagulants, and acrylamide-based flocculants to achieve better retention, drainage, and formation. All-organic anionic micropolymers were recently developed that are based on branched and crosslinked polymers. All these programs have broadened the spectrum of wet-end management options available to papermakers.

Current microparticle systems, however, often have limitations in working effectively in highly contaminated systems. Buckman Laboratories has recently introduced three newly engineered colloidal materials to achieve improved drainage, retention, and formation in various papermaking furnishes under a wide range of wet-end conditions. This new, unique Mosaic.... system combines the strengths of the existing Bufloc technologies with performance-enhancing engineered colloidal components, resulting in superior performance.

This paper will present information on three newly engineered colloidal technologies. Laboratory evaluations and mill trial data for fine paper, board and newsprint will be discussed.

INTRODUCTION

Microparticle retention, drainage and formation programs have been used in the production of pulp and paper for over 25 years. Since the introduction of microparticle programs, several have been successful, but each has specific limitations. Several areas that were identified that impact retention and drainage program performances are:

1. System closure: Reuse of water builds up colloidal and dissolved substances resulting in processes with high conductivity and charge demand.

2. The increasing use of secondary and deinked fibres introduces chemical carryover, stickies, and potentially greater levels of fines.

3. The interaction of pigments, fillers, dyes, resins and coating binders in the wet end adds complexity to managing the wet end chemistry and impacts performance of functional additives.

4. Pitch, wood resins, and chemical carryover from the pulping process.

5. Paper machine speeds have increased considerably, and innovative headbox designs apply greater shear forces causing greater turbulence in the forming zone.

Over the past twenty years microparticle technologies have been developed to improve retention, drainage, and most important formation. Compared to conventional single and dual polymer retention systems, due to the small, tight flocs forms which adsorb strongly to the furnish components and leave the sheet structure open and uniform, microparticle systems have significant advantages. (1)

Advantages of microparticle systems include increased retention and drainage with no sacrifice in formation, and better performance in the presence of high concentrations of interfering substances (2). The microparticle retention system allows for the clean-up of the white water loop by effectively retaining the suspended and dissolved solids including fillers with wood fibres (3).

Papermakers have continued to seek even more advanced technologies that will allow them to meet the most stringent requirements for formation and opacity in light-weight fine paper grades as well as superior retention of fillers and fines. For heavier weight grades of paper and paperboard, increased or high response drainage is often key to keeping up consistent machine speeds without sacrificing paper and paperboard properties. This is especially true in furnishes with all or a high level of recycled fibres where drainage can often be a limiting factor.

Microparticle retention aid systems
Retention and drainage aid programs have evolved from the use of a single flocculant or conventional coagulant-flocculant program to include the use of anionic microparticles based on bentonite clays or silicas. These anionic microparticles have been used along with cationic starches, coagulants, and polyacrylamide-based flocculants to achieve higher benchmarks for retention, drainage, and formation.

The first commercial microparticle systems were based on cationic starch with colloidal silica, and bentonite in conjunction with a cationic polyacrylamide. (4)

Current microparticle retention systems can be classified into the following categories depending on the type of microparticle used:

  • Colloidal silica
  • Bentonite

The most recently developments include the use of an anionic micropolymer in a two or three component system that can produce results similar to the bentonite and colloidal silica programs.

These systems can be used in different combinations (5) as showed in Table 1.

Table 1

Table 1: Typical combinations of microparticle retention systems

Cationic Microparticles
All current commercial microparticles systems are based on anionic products. Little work has been done on the use of cationic microparticles.

In principle, cationic microparticles should be more effective than anionic microparticles in systems with higher levels of negatively charged fibre fines and waste solids. Surprisingly, little development work has been done or new products introduced that are based on cationic microparticle technology.

Buckman Laboratories has worked for the past several years with paper manufacturers and research institutes to further develop retention and drainage technologies, the result of this work is presented in this paper.

Buckman Laboratories has introduced the Mosaic™ System that includes two new inorganic microparticles and two new proprietary cationic polyacrylamides as well as advanced programs for their use in superior wet-end management. Three of these new, structured products carry a cationic charge.

The Mosaic™ System
This new system allows a papermaker to incorporate previously used coagulant and flocculant technologies with one of the new inorganic synthetic microparticles or engineered polymers.

Each new product can demonstrate improvements over existing technology and each is designed for particular applications.

Two of the new products are synthetic inorganic microparticles; one is anionic, the other is cationic.

The other two new products are structurally engineered cationic polyacrylamides that give superior performance compared to more traditional microparticles. They have a proprietary composition and structure that allows them to made down very easily with simple equipment and to be highly effective at economic dosages.

Figure 1

Figure 1: The Mosaic System

The Mosaic MP components
MP 810 is a unique anionic synthetic inorganic microparticle. MP 810 delivers excellent formation, drainage, and superior retention in all acid and alkaline systems.

MP 810 is iron free and has no negative impact on sheet brightness. It is typically used along with a flocculant or along with a coagulant and a flocculant. It has been especially effective in newsprint furnishes where the drainage profile on the machine improves and results in improved printability and z-directional filler distribution.

Table 2

Table 2: Typical combinations of the Mosaic System

MP 820 is a new cationic boehmite microparticle with unique chemistry and structure. This particle is highly charged, pH insensitive and has a high surface area. MP 820 is a freeze -thaw stable 35% sol with a particle size of 10-30 nm. It works especially well in high conductivity systems with a high cationic demand and anionic trash. It is used along with flocculants in a variety of paper grades.

MP 830 is a new, proprietary emulsion cationic polyacrylamide. Due to its unique structure and chemistry, MP 830 does not require complicated makedown or aging. It is effective over a wide pH, temperature and conductivity range. Its proprietary composition and structure facilitates excellent formation, drainage, and cost effectiveness with improved retention.

MP 830 may be used as a stand-alone program for retention, drainage, and formation or in combination with a traditional polyacrylamide. A very significant reduction in TiO2 usage for a fine paper grades has been seen in one of its applications where it replaced an organic micropolymer program.

MP 835 is much like MP 830 but has both a higher cationic charge and higher molecular weight. It also does not require complicated makedown or aging and also gives the desired small, tight flocs. It is especially effective on high-speed fine paper machines.

Table 3 compares various properties of these products against available microparticle products.

Table 3

Table 3 Comparison of MP products against current microparticle products

Mechanism of Action
The basic mechanism for all the microparticle programs is the same. The interactions involve all three fundamental mechanisms involving: coagulation, flocculation, and finally the formation of the micro or nano floc.

With the option of MP components available, the mode of action for the micro or supercoagulated floc formation follows well-acknowledged mechanisms that are fundamental for microparticle systems. The mechanisms of interaction are based upon the three fundamental mechanisms: charge neutralization, bridging, and patching.

Coagulation: To control the wet end chemistry balance, one of an available range of low molecular weight high charge polymers is used. This ensures that the stock characteristics are managed prior to the addition of other additives, resulting in optimum additive usage. The polymer interacts with dissolved and colloidal detrimental substances to reduce the charge so that agglomeration of the small or colloidal particles occurs.

Flocculation: Through correct selection of the polymer, bridging flocculation is induced, resulting in large flocs that are broken down under applied shear.

Microflocculation: Microflocs are formed as the stock approaches the headbox. The small, porous, and shear insensitive microflocs release water readily while maintaining the sheet formation characteristics.

BENEFITS

Retention
The are several benefits to be derived from improved retention. Increased first pass retention of fibre, fines and colloidal material results in a significantly cleaner system. This in turn results in increased paper machine and additive efficiency, and reduced effluent loading (e.g. filler, starch).

The cost saving associated with a higher overall retention of additives can be significant. The use of microparticle/ microflocculant products promote improved z-direction filler distribution resulting in a less two-sided sheet with improved printing properties.

Dewatering
There are key advantages to the papermaker by improving total dewatering (free drainage, vacuum drainage and pressing), which is one of the major benefits associated with the use of a microparticle program. Better dewatering ensures that the sheet moisture entering the drying section is reduced with accompanying wet web strength/ runnability benefits. The higher drainage rates also allow the papermaker to increase the activity on the wire by opening the slice/ reducing the headbox solids to improve formation.

Formation
Formation is also enhanced significantly due to the microfloc structure imparted to the stock by the microparticle component. This translates to better sheet surface properties (strength , smoothness) with related printability benefits.

LABORATORY STUDIES

The Mosaic System components were extensively studied in the laboratory. Comparative testing against the available microparticle programs indicated that the MP technologies were unique.

Extensive work was carried out in all the major paper grades and under different papermaking conditions. In this article four short laboratory studies are reported demonstrating the diverse capability of the Mosaic system.

Standard laboratory techniques were applied in the studies to measure the parameters identified.

Retention
The vaned Dynamic Britt Jar was used to determine first pass total and filler retention. A 125P (200-micron) screen was used. Stock was taken and additives added in the correct sequencing, and with the appropriate mixing to provide the right shear. The final filtrate from the Britt Jar was collected at a agitator speed of 1200 rpm.

Free Drainage
A Canadian Standard Freeness (CSF) or Modified Schopper Riegler (MSR) tester was used to measure the free drainage. Stock was taken and additives added in the correct sequencing including the appropriate mixing to provide the right shear before the test was performed.

At least three factors impact the performance of a retention and drainage program:

a. Selection of the components

b. The chemistry balance: other additives and their interaction

c. Selection of the addition points

Each program evaluated was optimized for each product used and the correct amount of shear applied after each additive to simulate a fan pump or pressure screen.

Study 1: Newsprint
This laboratory study was carried out using mill furnish, and the Mosaic System was compared against the incumbent program, which comprised of a polyacrylamide and bentonite. The stock was characterized as shown in table 4. Retention tests were carried out using the Dynamic Britt Jar tester and drainage tests were carried out using a Canadian Standard Freeness Tester.

Table 4

Table 4. Furnish Characterization

Results
The system of choice was determined to be MP 810 in combination with a high molecular weight anionic polyacrylamide. A polyamine cationic coagulant was added first at 1.5 kg/t followed by MP 810 simulating a pre-fan pump addition point and finally by the polyacrylamide in a simulated post-screen addition. The results were significantly better than either coagulant/ cat PAM or coagulant/ an. PAM.

The results are shown in figures 1a and 2.

Figure 1a

Figure 1a: Britt Jar retention data

Figure 2

Figure 2: CSF drainage data

Study 2: Packaging
This laboratory study was carried out using mill furnish, and comparisons made against the incumbent program, which comprised of a coagulant, a polyacrylamide and colloidal silica. The stock was characterized as shown in table 5. Drainage tests were carried out using a modified Schopper Riegler and turbidity was measured on the final volume collected.

Table 5

Table 5. Furnish Characterization

Results
The system of choice was determined to be MP 820 in combination with a high molecular weight cationic polyacrylamide. MP 820 was added to the system first simulated addition pre-fan pump, followed by the polyacrylamide simulated post-screen addition. The results matching the silica system were obtained using 1.5 Kg/T as supplied of MP 820 and 0.2 Kg/T of the cationic polyacrylamide.

In the silica system the polyacrylamide was added first followed by the coagulant, adding the silica last. The best results with the silica system were obtained using 0.5 Kg/T of the polyacrylamide, 0.5 Kg/T of the coagulant and 5 Kg/T of silica. The results and shown in figures 3 and 4.

Figure 3

Figure 3: MSR drainage data

Figure 4

Figure 4: MSR Turbidity

CURRENT APPLICATIONS

Current Mosaic applications are in a range of grades including printing and writing, light-weight coated , newsprint, packaging, and tissue/towel grades. Three examples from this range of grades will show how application and control strategies are used.

Application 1
A North American mill currently uses the MP 830 for printing and writing grades.

Former Type: Fourdrinier
Speed: 460 m/min
Production: 135-216 tpd
Grade: Speciality lightweight opaque
Furnish: 60% HWK, 30% SWK, and 10% machine broke
Headbox pH: 8.2
Fillers: PCC and TiO2. Sheet ash is 19%.

The former program was alum with an anionic organic micropolymer.

The mill defined problems with high TiO2 usage, poor formation, excessive curl, and poor filler distribution. The MP 830 cationic polyacrylamide was chosen as a single product with addition prior to the fan pump.

Results
Alum was discontinued. TiO2 usage decreased 8-15 kg per ton -- opacity was maintained. Formation maintained, and retention of both TiO2 and PCC improved.

Figure 5 shows results for TiO2 usage and MK formation data in the lightest basis weight over the four weights that were run.

Figure 5

Figure 5. Titanium Usage and MK Formation
Grade: 24.5 lb

Figure 6 shows the first pass retention during the trial over a range of basis weight grades.

Figure 6

Figure 6: Printing & Writing

Application 2
A North American mill currently uses the MP 810 for newsprint grades.

Former Type: Valmet Gap Former
Speed: 1370 m/min
Production: 630 tpd
Grade: Newsprint
Furnish: 75% TMP, 25% DIP
Headbox pH: 5.1

In an ongoing newsprint application on a modern, high-speed twin-wire former in North America uses MP 810 along with a cationic polyacrylamide. A coagulant is also applied early in the system for colloidal substances management. MP 810 is applied pre-screen and the cationic polyacrylamide is applied post-screen to give the desired bridging of flocs. In other applications, the MP 810 is applied after the polyacrylamide. Application strategy for this machine was based on the desired mill control strategy for balancing of retention, drainage, and formation.

Benefits to the mill include:

  • Improved retention (up 6%),
  • Reduced bleaching costs (down 5%)
  • Reduced wet-end breaks (1-2 per day vs. previous 3-5 per day)
  • Increased press solids (up 1%),
  • Increased former solids (up 2%).

Application 3
Former Type: Voith Fourdrinier
Speed: 1400 m/min
Production: 350 tpd
Grade: Coated Freesheet
Furnish: 60% Softwood, 30% Hardwood, 10% CTMP
Filler: 6-17%
Headbox pH: 7.2

The third current application is the ongoing use of the MP 835 in a European mill producing coated free sheet grades. The former program was a two-part cationic starch - anionic silica microparticle program. Production was limited by drainage, formation was often unacceptable , and there were substantial periodic variations in retention.

After testing at the mill, the MP 835 was selected for use by itself with post-screen application.

Results
First pass retention values have increased from 65-75% to 70-80%
Ash retention has increased from 38-65% to 50-75%
ABB formation values have improved
Overall machine speed has increased by 1% across the range of basis weights.

Added advantage is that the 835 makedown system is very simple with direct feed of the polymer after dilution. There is no requirement for aging of the polymer after primary makedown.

CONCLUSION

All current commercial microparticle systems are based on anionic products. Little work has been done on the use of cationic microparticle products.

In principle, cationic microparticles should be more effective than anionic microparticles in systems with higher levels of negatively charged fibre fines and waste solids.

These examples of mills currently using these new technologies are representative of the benefits of using this next step approach in wet-end management with the linking of various facets of the papermaking process. These chemistries, in combination with polyacrylamide and coagulant technologies, have shown superior performance over existing conventional microparticle systems.

By viewing each application as a combined approach -- through total wet end management - - we have shown how to use the strengths of existing polymer technologies along with the newest engineered MP components. This allows us to use the Mosaic system to maximize retention, drainage, formation, and paper properties by using application and control strategies tailored to specific process parameters.

REFERENCES

1 Ovenden C, Xiao H and Wiseman N. UMIST. (1999)

2 Alexander SD & Dobbs RJ. Tappi Journal. 60(12):117-220 (1987)

3 Urbantas, R. PIMA Magazine. 78(5), 50-51 (1996)

4 Breese, J & Nilsson, L. Papermaker. Feb 1995, 43-45 (1995)

5 Lio, J. Paper Technology. April 1999, 41-42 (1999)

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