Although the trend towards elemental chlorine-free (ECF) bleaching poses no problems to the production of permanent paper, other new technologies may. Driven by the rising cost of pulp, manufacturers are looking towards thermomechanical and chemithermomechanical pulping processes to increase yield and lower costs. At least for the short term, these new pulping processes pose a threat to the legibility of books and documents because much of the original lignin remains in the pulp, even after bleaching. The lignin causes the resulting papers to darken upon artificial aging by light or heat. Such discoloration is unacceptable in a paper used for printing or writing that is to be retained indefinitely.
With this knowledge, manufacturers of these pulps are researching additives that will prevent the pulps from darkening. This work is still in the research stage, but no doubt in the next few years chemicals will be found which, when added to these pulps, retard the color change. Some of the compounds currently under investigation are sulfur-containing, which could pose a problem to photographic records. The presence of increased amounts of reducible sulfur are excluded by some box and board specifications, but are not currently addressed in the existing specifications for permanent paper.
Continue to Cost Issues
Go back to Environmental Issues
Return to the Table of Contents