The annual Papermakers Conference was held this year in Seattle, April 7-10. This time,- there were 66 papers and 11 posters, not to mention panels and round tables. Novel developments in a number of areas were reported, including the use of calcium carbonate in groundwood papers and the effect of alum and lignin on permanence. In addition, there was a panel on alkaline conversions at three mills, and sessions on permanence and acid/alkaline sizing. Committees, including the Paper Permanence Committee (Ad Hoc), net the day before the conference.
Max of Pluess-Staufer AG, a Swiss supplier of calcium carbonate, gave a paper on the manufacture of neutral groundwood-containing papers. He said 70% of all European freesheet (groundwood-free) papers were alkaline in 1989, and predicted that all of them would be alkaline by 1995. Furthermore, about 38% of all coated groundwood paper over there is produced under neutral or "pseudo-neutral" conditions. Groundwood paper production at a neutral pH was not adopted in the U.S. until late last year, but interest is high and the paper is well received on the market. It was not attempted earlier, as Bruce Evans of Pfizer said in his paper, because of pitch problem, darkening of the paper, and a "mind-barrier" about any pH over 6. Two secrets of success in making neutral groundwood papers: 1) control of anionic trash (an excess of miscellaneous particles with the wrong charge), which was the main focus of the Laufmann paper, and 2) choice of point of addition for the calcium carbonate (and for alum too, if it is used) so as to minimize the opportunity for the carbonate to interact with the low-pH alum and groundwood.
Speakers from two companies gave papers on what was called acid-tolerant or acid-resistant precipitated calcium carbonate (PCC). This is a recent development, which permits the use of the bright white PCC near or below the neutral point in groundwood (mechanical) papers, to make them whiter without triggering alkaline darkening. Apparently the PCC particles are coated with something that keeps them from interacting so readily with their environment, particularly while the paper is in the wet end of the machine. There was no discussion of whether acid-resistant PCC acts as a true alkaline reserve in the finished paper, able to neutralize acidic gases and retard deterioration. Perhaps this is a moot point if it will only be used in groundwood.
Gerard Rose of Nalco presented a paper entitled "The Effect of Aluminum on the Permanence of Papers" in the Session sponsored by the Paper Permanence Committee. It described changing trends in the use of alum, reviewed the scant literature on aluminum's effect on permanence, and found a preponderance of evidence suggesting that al in an alkaline sheet will not affect its permanence. He summarized scan recent German work comparing the effect of alum and polyaluminum chloride (PAC) on permanence: alum, with its lower pH, had a worse effect than the PAC, even though PAC contains twice the aluminum.
In the discussion afterwards, Chandru Shahani of the Library of Congress pointed out that deacidified papers containing high levels of alum aged very well in the oven.
Betsy Humphreys of the National Library of Medicine described the latest reversion of the American National Standard for the Permanence of Paper (Z39.48, the standard developed by the National Information Standards Organization or NISO), including its controversial specification for a of 7.5% lignin. This specification was based on testing of several sets of paper done for the Committee. If the papers were carbonate-filled, they probably performed very well, because alkaline buffered lignin-containing papers have been tested at the Library of Congress and are known to perform well under accelerated aging. However--and this is a major difference between accelerated and natural aging--the oven does not duplicate the effect of air pollutants over a long period of time.
Two recent studies, one French and one Swedish, suggest that accelerated aging with pollutants uses up the alkaline reserve in paper rather quickly. This is a new line of investigation. Its findings will be hard to translate into guidelines for policy or practice until natural aging with pollutants is systematically correlated with corresponding accelerated aging conditions.
Robert Johnson of DuPont gave two papers on permanence and color reversion (darkening) of MT in fine papers. Only the one on permanence will be described here. CTMP, or chemithermomechanical pulp, is a new kind of very high-yield (i.e., high-lignin) pulp that can be blended in a 1:2 or 1:1 ratio with chemical pulps to make commercially acceptable printing and writing papers. Color reversion is a problem because of the lignin, but it can be reduced substantially by the use of calcium carbonate fillers.
Papers containing up to 45% CTMP and up to 25% calcium carbonate filler were compared with unbuffered groundwood and with buffered and unbuffered freesheet. No unbuffered CTMP paper was included in the study. Both dry and moist aging were done for up to 50 days, and changes in fold, tear and brightness were measured. Both brightness and strength were retained well by the 30% CTMP, which kept its brightness just as well as the unbuffered freesheet, and retained its strength even better than the buffered freesheet. This was mainly a function of pH. Fiber type and presence of calcium carbonate had little effect.
Johnson's results confirm previous reports in the literature that color-causing reactions are not the same as those causing loss of strength: the rate of yellowing, but not the rate of loss of fold, is directly related to the percent of groundwood pulp. In this literature review he cites a study by LeThi reporting that rapid aging of acidic groundwood is largely due to the fines (fiber fragments, hemicelluloses and ray cells) produced during the pulping process. State-of-the-art CTMP pulps, Johnson says, have much lower levels of such fiber fragments.
(The effects of fines on aging is well documented in the literature, by the way, as shown by a 79-page literature review published in 1985 as a bound-in supplement to Art & Archaeology Technical Abstracts: "Three Fundamental Aspects of Cellulose Deterioration," three annotated bibliographies prepared by Robert L. Feller, Sang B. Lee, and Mary Curran. The stapled binding makes it almost unreadable close to the binding edge; rebinding is advised. But the paper, editing and printing are excellent. The second bibliography of the three is "hemicelluloses: Their Influence on Paper Permanence.")
Charles Farley of American Cyanamid (which has been making alkaline size since the fifties) spoke on the use of alum and several other aluminum compounds to improve the sizing efficiency of ASA (alkenyl succinic anhydride, a widely used neutral/alkaline size). ASA must be used very some after being emulsified, or it loses all its sizing effect; but if you add a very small amount of alum, it regains it, at least for a short while. Alum, which in-creases the sizing efficiency of ASA, is best added early in the system, where it can be well dispersed before the ASA is added. This brings it in contact with the carbonate, and lowers the pH, but the effect is only temporary.
Mike Williams (Boise Cascade/Wallula), Scott Fruhwirth (E.B. Eddy/Port Huron) and Rick Glisson (Simpson Pasadena/ San Jacinto mill) gave accounts of their mills' alkaline conversions, with the obstacles they met and overcame or learned to live with. The first two accounts are in the proceedings.
The San Jacinto mill, Glisson said, completed its conversion to alkaline in May 1990. They did not decide on AKD (alkyl ketene dimer, another widely used alkaline size) until after several three-day trials. One surprise was the importance of addition points for size and other additives. Another was the emergence of problems (e.g. slip and occasional size fugitivity), sometimes three or four months later, that had not been apparent in the three-day trials. Most problem were solved or reduced.
The Committee, which was formed two years age, had a productive meeting with about a dozen members present. Two subcommittees were formed, one to coordinate the Committee with a new joint task group to produce a trouble-shooting guide for printing and on alkaline paper, and one to nominate candidates for TAPPI awards for early work related to alkaline size. Reports were heard from Chandru Shahani on the Library of Congress's research on lignin (even 1% was found to affect permanence) and from Rolland Aubey on the work of the permanence standards Committees in ISO, ASTM and NISO. Members decided to include all permanent papers within the scope of the committee, whether they ,were alkaline or not. The Committee meets again next September in Las Vegas.
(Condensed from the report in the May 1991 Alkaline Paper Advocate)
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