PAPERMAKING CHEMISTRY in the 21^st CENTURY

 

John G. Penniman

 

 

Conceptual Elements

 

Stock components must be mixed thoroughly, until homogeneous.  The repulsive negative surface charge must be neutralized at the point of web formation.  Microflocculation accomplishes the best balance between formation and retention. 

 

 

Summary

 

First we show the sensitivity of retention, drainage and the physical property parameters to zeta potential.  Next, we provide machine data on the correlation between HST sizing and zeta potential, to validate the significance of process chemistry control on the machine.  Finally, we provide a study extract by Christian Pierre of Centre Technique, demonstrating the remarkable balance between formation and retention achievable with the microparticulate process.

 

The machine data reveals two important facts.  First is the high Correlation Coefficient of .71 between HST sizing and zeta potential, confirming the lab results.  Second is the otherwise unsatisfactory quality of the result.  Sizing quality varies by a factor of 5, and is from 3X to 15X higher than required to attain its intended purpose.

 

The point is that it is not possible, given current practices, to obtain the most cost-effective level of quality and of uniformity on a world-class paper machine.  Chemistry has evolved, but the paper machine has resisted accommodation.  Thoroughness of mixing of chemicals with stock needs to be embraced as an essential capability of a 21^st century machine.

 

 

Van der Waals Force

 

Reference is made to the presentation, Maximizing the Influence of van der Waals Force in Papermaking, on the Web Site

www.papermaking-chemistry.com The exhibits used in the balance of this article are taken from it, beginning with the following:

 

The x-axis shows incrementally increasing amounts of cationic chemical being added, and the y-axis that the zeta potential increases from -5mV to +9mV.  The z-axis shows that drainage increase, HST sizing, sheet ash and Scott Bond are all at maximum in the range +1 to +6mV zeta potential.

 

This is most remarkable.  We demonstrate that two key process parameters AND two key physical property parameters are both maximized in a clearly defined optimum zeta potential range.  It wasn't until after a lot more lab and machine experimentation that we realized the cationic decay of charge-neutralizing chemicals required a small positive headbox zeta potential in order to obtain zero charge at web formation.

 

HST sizing is shown to be especially sensitive to zeta potential in the graph.  The following example represents machine data, and has a Correlation Coefficient of 0.71 of HST sizing with zeta potential.  The importance of

Sizing Example
 

zeta potential control on the machine is clearly evident.

Reverting for a moment to the subject of thoroughness of mixing, sizing variation, from 100-500 Hercules Sizing Test seconds, does not seem an appropriate level of quality uniformity for a world-class machine (quite apart from 2 reels produced in late November with zero size.)

 

 

Microflocculation

 

To maximize both the process parameters:  retention and drainage, and the physical property parameters, one must obtain the best possible balance between retention and formation.  The Microparticulate Process makes this feasible.  In the illustration below, various charge-neutralizing cationic chemicals are added to the stock while their flocculation and retention are measured.

 

In the final instance, cationic starch is followed by a highly anionic microparticle in the form of colloidal silica.  (It is fashionable today to call it a "nanoparticle.")  The amount of the two components is carefully balanced in order to obtain zero charge at the point of web formation.