WET END CHEMISTRY NEWS LETTER FOR OCTOBER, 1998

(Editor's Note: Following are summary reports on significant developments reported at the Symposium or in private discussion. For details, contact the respective authors.)

Dr. Detlev Glittenberg et al, Cerestar Starch Co.

A unique new nonionic starch is reported to replace anionic starch in paper coatings with 2% higher coating solids, reduced WRV, and improved surface strength. Runnability and blade pressure OK, printability maintained. Savings resulting from decreased scavenger usage and reduction of cobinder amount to $7.40/T. (Editor's Note: Cerestar has an important presence in North America).

Max Laufmann et al, Pluss-Staufer AG (Omya)

To emphasize Pluss-Staufer's recently acquired credentials as a PCC supplier, Max provided a comparison of papermaking properties using both GCC and PCC. He also reported on the interesting properties obtainable with a blend of GCC and PCC. A unique new pigment is announced, GCC with talc stuck to the surface. Description of properties (reported to be exciting) not yet available.

Peter Rohringer, Ciba Specialtychemicals

(Editor's Note: The following report also represents the results of lengthy private conversations with Dr. Rohringer and others.)

The conventional paper mill OBAs, disulfur stilbenes, have optimum affinity for fibers. Fluorescence is the difference between brightness measured with and without UV light. OBA can increase mechanical fiber brightness by 3-10% depending on bleaching.

Monosulfur stilbene is not subject to cationic quenching. However, it is made by a different, more expensive process, provides a greenish cast at relatively low concentration and has limited water solubility. Ciba discontinued 10 years ago. (BASF may offer).

Avoiding cationic quenching on wet end addition is most efficiently accomplished, in principle, by adding the OBA as far removed as possible from the cationic chemical addition points. This ensures that the two do not come into contact as free chemicals. Ciba has "excellent" cationic OBAs developed for textiles, but 10 to 15X more expensive. Size press addition rule of thumb is 2/3 applied there and 1/3 at the wet end. The scientist's typical caveat is invoked: optimum relative amounts depend on circumstances.

Comment from the floor: 'good results are obtained when addition points are separated and the cationic chemical has a low charge level, like starch.' (Editor's Note: This may reflect a beneficial influence from the structural similarity of starch and cellulose. In this case, use of a natural gum could be even more helpful.)

A scientist from SCA Fine Paper, Hallein GMBH, reported to me privately that they changed to adding "most" of the OBA at the size press. This action resulted in reducing OBA usage by 40%.

Prof. Dr. Ing. Elena Bobu, Technical University of Iasi, Romania

Successful enzyme treatment during beating of OCC-pulp indicates that biological degradation of the colloidal dissolved hemicelluloses could be an alternative solution to reduce the usage of cationic chemicals in papermaking systems with a high content of secondary fibers.

E. Zeyringer, Sappi Gratkom GMBH

Coated broke dwell time increases anionic trash as a function of temperature. Nonionic starch increases microbiological problems. Anaerobic bacteria can be quantified by redox measurement. ON-LINE MEASUREMENTS OF ZETA POTENTIAL IS NECESSARY. A new gas analyzer measures both free and dissolved gas. Fluctuations from 0.5-5% have been observed within one hour. 8-9% gas can be measured in the headbox as CO2. It is released by high turbulence, and can lead to holes whose source is difficult to identify.

(Editor's Note: Mutek now offers what appears to be such a gas analyzer. The emphasis attached to on-line zeta potential measurement is, of course, the Editor's.)

Robert J. Proverb, PhD, Cytec Industries, Stamford, CT.

An excellent, persuasive review of ASA technology and Cytec success, which has stemmed importantly from reducing the emulsion particle size and thereby improving effective reactivity; and from increasing retention and thereby decreasing hydrolysis. The big advantage over AKD is 100% complete reactivity before the size press.

B. Ullman, Dresden Papier AG, Langenbach

Better sizing leads to increased stiffness by decreasing starch penetration. .015% PEI is added upstream to "fix" anionic trash. A total of 1.2% PAC is added at three carefully selected points NOT DILUTED, in the middle of the pipe to avoid deposits on the walls.

Voigt (did work) N. O. Bergh (made presentation) Cerestar Starch Co. (again).

Production of coated papers for ink jet printers will increase at the rate of 20%/year, as more and better printers become available.

Cationic calcium carbonate fillers in the coating improved ink jet printability, assessed by color intensity increase, as follows:

Black 1.48 to 1.78

Magenta 1.26 to 1.4

The range of cationicity most appropriate in the coating for ink jet printing has been determined.

(Editor's Note: Finally having some measure of quantification of the printability improvement afforded by cationic coating is highly gratifying.)

Lydia Bley, Mutek Analytic GMBH, Herrsching

I told Lydia privately that this was the first paper I had ever heard her give that I understood, and also the first one that I did not disagree with. I did comment from the floor that her highly variable headbox cationic demand data, which was associated with a high incidence of machine breaks, was similar to my headbox zeta potential standard deviation data. We believe that headbox zeta potential standard deviation correlates with thoroughness of chemical mixing, and we have observed that a high standard deviation is associated with a high incidence of breaks. I have personally observed a zeta potential standard deviation of 2.5mV on a coated recycled board machine that had so many breaks the machine efficiency was below 50%.

Many wet end chemists share the opinion that, as an industry, we do a poor job of thoroughly and efficiently mixing chemicals with stock. On-line zeta potential measurement affords a means of quantifying this important dimension.

From the floor, I continued by saying we found that the optimum headbox zeta potential was a narrowly defined value, and our data clearly shows that operating just a few mV on either side of optimum can decrease process chemistry efficiency by 20-30%. MISS BLEY AGREED, AND WENT ON TO SAY THAT SHE IS TRYING TO DEVELOP AN ON-LINE ZETA POTENTIAL INSTRUMENT. After receiving so much static, over such a long period of time, on the subject of the superiority of the cationic demand measurement, the Mutek change in position, to endorse headbox measurement of zeta potential, was practically worth the entire trip!

John G. Penniman

Munich, September 18, 1998

P. S. As a courtesy, I sent a copy of the Munich report to Miss. Bley for her comment, which I quote below in total. I do concur that systems high in anionic trash, which cannot use charge neutralizing chemicals economically, are not appropriate candidates for zeta potential measurement. Beyond that, as a further courtesy, I allow her the last word. JGP