Volume 5, Number 6
Dec 1992

ISO Responds to Claim that Lignin is Harmless

In Canada there are seven pulp mills that make CTMP, a relatively new kind of high-yield pulp that contains significant amounts of lignin, yet can be used to make paper of apparently high quality, provided it is filled with calcium carbonate to whiten it and stabilize it chemically. It is one of several types of pulp developed in recent years as a reaction to the growing shortage of trees, to get more usable pulp out of a given amount of wood. Paper made with carbonate-buffered CTMP pulp performs very well in the usual accelerated aging tests, though it has a tendency to yellow from light exposure. It has not undergone natural aging, of course, because it is too new, and it has not been age-tested under all conditions of storage and use that may affect its longevity.

These seven pulp mills are hurting not only from the recession, but from an unexpectedly low demand for their product. They have to export or die. They have been lobbying against permanence standards groups in this country because the standards limit the lignin content of permanent paper. The mills say this interferes with the free trade agreement between Canada and the United States.

It is not just the mills, and the pressure is not limited to the United States. In January the Standards Council of Canada forwarded to the ISO (International Organization for Standardization) a letter from the Canadian Pulp and Paper Association and two releases from the Pulp and Paper Research Institute of Canada on this issue. The ISO has been working on a standard for permanent paper (ISO DIS 9706) which is out for ballot. The votes arc in, but because of a recent extension, the official result will not be made public until July.

Per Olof Bethge, the convener of the working group that prepared the original draft of this standard, has replied to these communications in a letter reproduced in part below, reprinted with permission. It was addressed to Ivar Hoel, at the Secretariat of ISO/TC 46/SC 10 in Copenhagen.

The kappa number limit in DP 9706 was discussed thoroughly at the meetings of the WG [working group]. It was clearly understood that the limit proposed, 5.0, would discriminate fibers of mechanical pulps. It was recognized that there is an emerging technology including many new types of pulp and these should be allowed to show their possibilities, but this has to be deferred at least another five years (ISO standards are reviewed at 5 year intervals).

It has also been argued that the kappa number limit is not discriminating products on the basis of production process. The clause in which the kappa number limit is given is titled "Resistance to oxidation." The kappa number measures the tendency of the product to become oxidized. The oxidant used is an acid permanganate reagent, which has rather mild oxidizing power. The argument is that if the product is easily oxidized by permanganate, it cannot be excluded that in the long term it will be oxidized by the oxygen present in ambient air, in particular in the presence of various trace contaminants, like sulphur dioxide. And--if a product gets oxidized, it is not permanent.

The working group felt great responsibility to fulfil its task to specify papers with a high degree of permanence and which could be used faithfully for documents intended for long time storage. It was not felt sufficient that, for any particular paper type, there was no indication of deterioration under laboratory conditions. There should be not even a suspicion that the product may be unstable under the actual storage conditions to be expected.

[Signed by Per Olof Bethge, Convener, ISO/TC 46/SC 10/WG 1]

This story is reprinted and updated from the December 1992 issue of the Abbey Newsletter.