UNFORCED CHEMISTRY ERRORS IN PAPERMAKING

PAPERMAKING CHEMISTRY IS 40% EFFICIENT

 

John G. Penniman

 

 

Preface

 

A Focus Group Study defined, for the author, the lack of interest and understanding of chemistry on the part of the papermaker.  Wet end chemistry is so complex, and there are so many simultaneous influences, that cause and effect relationships are often difficult to discern.  However, we owe it to the papermaker to identify and describe the key concepts. 

 

This narrative goes a step further and estimates the quality of execution, thereby providing an important perspective. Please do not simply dismiss the effort as controversial.  It is intended to lead to thoughtful consideration, debate; and much improved execution.  Your suggestions are earnestly solicited.  

 

 

Introduction

 

Our lab has been doing leading edge wet end chemistry experiments since 1970.  In early 1979, in a monthly column published as the Contributing Editor, Chemistry, of Paper Trade Journal, the author coined an expression that has become a part of the industry vernacular “anionic trash.”

 

Over a period of 6 years, beginning in the early 90’s, we conducted a series of 5000 well-instrumented, carefully controlled papermaking chemistry experiments.  Towards the end, we had learned to conduct each experiment at the zeta potential that maximizes drainage. 

 

This turned out to be a guiding principle because it maximizes both the process parameters and the physical properties.  It also ensures that the experiments are reproducible, both in the lab and on the machine. 

 

Contrary to conventional wisdom, the optimum headbox zeta potential turns out to be a slightly positive value.  After cationic decay has played its role, this enables sheet formation to occur at precisely the point of zero charge, thereby minimizing the normally repulsive inter-particle effect and maximizing the powerfully attractive van der Waals Force. 

 

Five specific principles emerge from a careful review of the data.  Each is given a weighting of 20, so that perfect execution would provide a score of 100.  The principles are listed below, together with a numerical value that represents the author’s estimate of how well each is executed in North America.  You are invited to make an estimate for your machine and to offer critical comment.

 

References are to publications on our Web Site, www.papermaking-chemistry.com  The reader is also encouraged to look over the technical papers and peruse the Newsletters, beginning with the most recent.

 

 

Applying 'Six Sigma' to Thoroughness of Mixing

 

After many years of on-line zeta potential headbox measurements, we concluded that zeta potential standard distribution correlates with thoroughness of mixing of stock with chemicals.  For example, we obtain a zeta potential standard deviation of 0.2mV in the lab, 0.2-0.5mV on an old, slow machine, 1.6mV on a modern high-speed tissue machine, and 2.9mV making alkaline fine paper with 6-10 breaks/day.

 

In our worst observed case, a recycle coated board machine had a headbox zeta potential standard deviation of about 4-5mV.  Wet web strength was so poor that many breaks were experienced and productivity was about 50%. 

 

Under the 'Six Sigma' doctrine, a zeta potential standard deviation range of 0.2mV to 1.2mV would be specified.  Utilizing the contemporary microparticle chemistry contemplated herein, it must be applied at two points on the machine:  after the addition of charge-neutralizing cationic chemical and following microparticle addition 

 

Web Site Reference:  Proceedings of the 1993 Papermakers Conference, MAXIMIZING MICROPARTICULATE PROCESS EFFICIENCY.

 

Execution Efficiency Estimate:  3 of 20

    

 

Respecting Nature and Using Natural Gum     

 

Galactomannon Gum is typically an important component of the liquid used by many plant species to extract moisture and nutrient from soil.  This results in a certain affinity of the gum, arising from similarity in molecular structure, for cellulose fiber. 

 

When used in papermaking, natural gum serves as a coupling agent to increase the attraction of starch to the cellulose.  A small amount can have a synergistic effect in increasing strength, where this purpose is intended; or greatly increasing sizing, when starch is used to emulsify AKD size.  

 

Web Site Reference:  Newsletter, January 1999, UBIQUITOUS GUAR

 

Execution Efficiency Estimate:  2 of 20

 

 

Following Common Sense to get Good Formation

 

Use of a microparticle, most commonly bentonite or colloidal silica, can lead to simultaneously high levels of formation, retention and drainage. It is of critical importance to maximize the microflocculation effect and minimize the MACROflocculation caused by use of a conventional “retention aid”.

 

A giant step in this direction can be taken by using an efficient charge neutralizing chemical.  Cationic starch is the best example, followed by polydadmac and polyethylenimine.  Should a higher sheet ash level be required, a small amount of cationic “retention aid” can be thoroughly blended prior to addition.  This enables the primary effect to be MICROflocculation and minimizes the poor formation and physical properties historically associated with high sheet ash.

 

Execution Efficiency Estimate:  15 of 20 

 

Eliminating Alum and Switching to the Alkaline Process

 

When calcium carbonate is used in preference to the traditional acid alum rosin size, the pH changes from around 4.5-5.5 to the range 7.0 to 8.0 and the process is called “neutral” or “alkaline.”  The neutral/alkaline process is superior because:

 

1.  It is cleaner.  The Ca++ precipitates sufficient anionic trash on the fiber to significantly reduce BOD.  An unpublished study we did about 25 years ago showed a 20% reduction in the BOD of effluent from a recycle boxboard process.  (The other side of the coin is that it affords a more benign environment for microbiological growth.)

2.  It is stronger.  The neutral pH produces stronger fibers than an acid ph.

3.  It is cheaper.  Stronger fibers enable greater filler-for-fiber substitution.

4.  It is more stable.  The alum process changes pH as a function of concentration whereas calcium carbonate buffers out within a narrow range, and constitutes a stable process chemistry platform

 

Execution Efficiency Rating:  18 of 20

 

 

Minimizing Raw Material Costs and Maximizing Productivity

 

Maximum value is obtained from raw materials when sheet formation takes place at zero zeta potential.  In view of the lack of upstream electrokinetic measurement or control over process streams, it is necessary for maximum efficiency to automatically compensate by continuous closed loop computer control of chemical feed rates. 

 

During periods of transient instability such as start-up, grade change or re-start after a break, it is necessary to maintain a stable chemistry platform by automatic control of chemical feed rates, as stated immediately above, in order to minimize re-start time and the cost of off-grade product.

 

A major advantage of automatic control is that, on a machine unconstrained by mechanical water removal limitations, drainage can be increased by about 70% through automatic increase of cationic charge neutralizer and microparticle simultaneously, while maintaining the optimum zeta potential.  This option offers great potential for increased filler-for-fiber substitution or for substitution of fibers of reduced cost and quality.

 

Web Site Reference:  Technical Paper:  MAXIMIZING van der WAALS FORCE in PAPERMAKING

 

Execution Efficiency Estimate: 2 of 20

 

 

Summary and Discussion of Chemistry Efficiency Estimates

 

Total efficiency estimate is 40 on a scale of 100. 

 

Paper machine management normally grades the mechanical efficiency of each machine, on a periodic basis, and typically achieves ratings from the mid-80’s to mid-90.      

 

The primary reason why chemistry is not conducted more efficiently is that machine management is not currently measuring and closing the loop around key on-line parameters such as zeta potential and drainage.

 

Because of the rapidity of cationic decay, off-line data is relatively valueless for control purposes, although it can be helpful in stabilizing the process within broad limits and reducing upsets.

 

When paper machine management commits to automatic control of the wet end as fully as they have successfully committed to automatic control of the dry end, paper will be produced at lower raw material cost, higher productivity and improved quality.  Please let the author know if this holds interest, because we can help.

 

 

Who Created This Mess?

 

Several years ago, at a conference in Helsinki, the author sought out an absolutely brilliant Scandinavian professor to complain about a particularly egregious chemistry paper.  He looked me in the eye, reached up to put his hand on my shoulder, and said "John, everybody is partly right."

 

Several weeks ago, at a dinner that concluded a major annual paper science conference, I accused one of our North American academic stars (who has a dozen graduate students) of presenting a paper that held zero substantive value to the papermaker, when he should be making a real contribution.  He said, "John, I agree with you."

 

A senior North American papermaker called with the author on the Dean (a friend of 30 years) of one of our leading paper science institutions.  Our efforts to get the institution to play an appropriately pro-active role in paper chemistry were gently led in a different direction.   

 

After carefully re-reading a paper presented at a recent Papermakers Conference, the author found a point of inconsistency with our lab data.  A letter was written to the Darmstadt author.  It has not been acknowledged.

 

The worldwide academic fraternity seems to be accountable only to themselves.  When a written message makes them uncomfortable, they routinely ignore it.  A higher value is clearly placed on collegiality than on serving mankind.   

 

We need active academic leadership.  Our chemistry Professors need to serve the interests of the industry as well as they serve their own.  'The point is not to understand the world, but to change it.'    

 

 

What is the Role of the Chemical Supplier?

 

Paper machine management has delegated the responsibility for papermaking chemistry to the chemical supplier, but fails to provide appropriate compensation for doing the job properly.  The reality is that the cost of an on-line sensor, with related hardware, software, installation and start-up costs, is in the low six figures. 

 

The papermaker and the purchasing agent fail to understand that putting the machine on auto-pilot could, after the machine crew became comfortable with it, generate the large efficiencies discussed above.  Ultimately, it would greatly reduce the investment in expensive, dedicated manpower.  The final payback would be enormous.

 

The path forward is clear.  We need to:

…Use the most cost-effective chemicals

…Mix thoroughly to maximize value in use

…Control zeta potential to minimize raw materials cost, and

…Maximize physical properties

 …Automate chemical feed rates to maximize efficiency