The effect of air pollutants on paper stability

The Canadian Go-operative Permanent Paper Research examined, besides others , the impact of air pollutants on the permanence of handsheets from six pul p types and four alkaline commercial papers. The pollution results confirm that sheets from mechanical pulps absorb more air pollutants and show a gre ater brightness loss than lignin-free sheets. However, this does not necess arily result in greeter deterioration of strength properties. A four-day ex posure to 10 ppm SO2 and 20 ppm NOx causes a significant acidification and degradation of all papers containing no alkaline reserve. The addition of c alcium carbonate as an alkaline reserve is very effective in reducing the n egative effect of air pollutants on both lignin-containing and lignin-free sheets.