Condensed from "NISO Draft Standard Allows Significantly More Lignin," Alkaline Paper Advocate, Dec. 1990, p. 61-62.
The ANSI/NISO standard for permanent paper for library and archival use, Z39.48, is being revised to cover both coated and uncoated paper and to incorporate the results of recent research. A revised draft was made available in November for review by all interested persons. The review period ends February 28, 1991. The draft revision can be purchased for $30 from National Information Standards Organization, PO Box 1056, Bethesda, MD 20827.
The biggest surprise in this draft is an increase in the amount of allowable lignin, from 1% to 7.5%. The question of the permanence of recycled paper is dealt with indirectly by controlling lignin and specifying minim strength, as measured by the tear index. (The tear index is calculated by dividing the tear resistance in millinewtons by the grammage of the paper.)
The draft standard comes with a separate s of issues related to this revision. That summary is excerpted below, with the permission of Betsy Humphreys, chair of Standards Committee II (SCII), which is preparing the revision. For a similar discussion of the previous draft revision, see the June 1990 issue of this Newsletter, p. 37: "The February NISO Meeting on Z39.48."
... All data known to the Committee indicate that adherence to the criteria described in the proposed revision is a sure predictor of acceptable retention of durability after accelerated aging.
Given that fact and the number of questions about accelerated aging that remain unanswered, SCII has concluded that there is no need to add a requirement for artificial aging to this revision of Z39.48.
Since the current standard was developed, the paper industry has begun to use chemi-thermomechanical pulps. These pulps do not contain groundwood and therefore meet the paper stock requirement in the current standard. Such pulps do contain significant amounts of residual lignin. Paper tests commissioned by the Committee and conducted by other institutions confirmed that alkaline papers with up to 7.5% residual lignin exhibit retention of durability equivalent to alkaline papers with less than r/. lignin. For this reason, SCII has set a lignin percentage of 7% in the proposed revision. The specific prohibition against groundwood has been removed. Papers with significant groundwood cannot meet the tear resistance criterion in the standard.
... Alkaline papers containing recycled pulp can be suitable for long term retention in libraries and archives. ... Some alkaline recycled papers meet the tear resistance requirement and some don't. The proposed revision will also screen out recycled paper with very high amounts of residual lignin.
SCII received a few comments on the desirability of adding specific prohibitions against the use of certain sizing materials and of specifying that the paper must be made by certain processes. The Committee believes that, as much as possible, the standard must specify measurable attributes of finished paper and leave the selection of production methods and materials to paper manufacturers. To do otherwise could penalize the development of innovative ways to make permanent paper and have a negative effect an beneficial advances in paper technology.
The issues previously discussed apply to both coated and uncoated paper. Another set of questions applies to coated paper only.... Because of their coatings and adhesives, coated papers contain more different substances than uncoated papers. As slight differences in the makeup of coatings can affect the quality and cost of finished coated papers, paper manufacturers are naturally reluctant to provide information on the exact formulation of these papers.
The core of a coated paper may be alkaline, neutral, or acidic. Most coatings are alkaline at least at the time they are applied, although some owe their alkalinity to substances which quickly evaporate after the paper is made. If the coating is very alkaline, the extraction pH of the coated paper as a whole is likely to be alkaline even if the core paper is acidic. An initial question addressed by the Committee was whether an alkaline coating could, in effect, neutralize acid in the core paper.... Both the opinions of paper experts and the results of private studies done by paper manufacturers indicated that acid in the core of a coated paper would have a negative effect on permanence. Paper testing commissioned for SCII has corroborated the view that the core of a coated paper must be acid-free to ensure reasonable permanence. Standard tests for determining the pH of the core paper exclusive of its coating are yet to be developed. For this reason, the proposed revision specifies reliance on manufacturer's certification of the pH of the core paper as well as qualitative methods for determining the core pH of coated papers.
Comments received in response to the discussion draft of the revised standard pointed out that paper which is technically "uncoated" may have a very lightweight, but highly alkaline surface coating sufficient to yield an alkaline cold extraction pH for a paper that is actually acidic. SCII has therefore specified manufacturer's certification of the pH of the paper and qualitative methods for determining the underlying pH of the paper for uncoated papers as well.
Another question was whether a coated paper containing a neutral core and an alkaline coating could be as permanent as a coated paper with an alkaline core. The paper testing done for the Committee indicates that this may indeed be the case. Experts consulted agree that it is logical that an alkaline reserve in a coating could protect a neutral core from environmental pollutants.... Data currently available support a minimum required pH of 7 for the core of coated paper and an alkaline reserve for the paper as a whole of or more.
Because a significant part of its weight is coating rather than fiber, the results of physical tests on coated paper differ substantially from the results of the same tests performed on uncoated paper of equal basis weight.... The Committee found that almost none of the coated papers met the requirements as stated for uncoated paper [of equal weight] .... The alkaline 60 lb. coated papers generally did meet the standards for folding endurance and tear resistance for 40 lb. uncoated paper. Since the printing qualities of coated paper are essential for sane kinds of publications, it would serve no useful purpose to establish a standard for permanence of coated paper that excludes virtually all available alkaline coated paper. For this reason, SCII is proposing that requirements for initial durability of coated paper be based on the weight of the core of the paper.
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