Date of Award
Bachelor of Science
Pulp and Paper Technology
Dr. A. H. Nadelman
A literature survey was prepared which covered the published information on the effects of ultraviolet light on the color of unbleached pulps.
Experiments were conducted with eight types of unbleached pulp which were converted into optical test pads under varying pH conditions, using sulphuric acid and caustic soda as well as alum and sodium aluminate for adjustment of the hydrogen ion concentration. The optical test pads were exposed to ultraviolet irradiation. Thereafter, reflectance measurements were taken, covering the range of visible light.
From the limited number of experiments which were conducted we can conclude that:
1. Unbleached coniferous kraft, unbleached hardwood, sulphite, and unbleached hardwood soda pulps brightened when exposed to ultraviolet light.
2. Unbleached hardwood H.S.S.C. (70% yield), unbleached hardwood N.S.S.C. (78% yield), unbleached coniferous sulphite, unbleached hardwood cold soda, and unbleached hardwood chemi-groundwood pulps yellowed when exposed to ultraviolet light.
3. Adjusting the pH four with sulphuric acid increased the reflectance of most pulps while adjusting the pH to ten with sodium hydroxide decreased the reflectance of the pulps. This was observed before irradiation with ultraviolet light.
4. When papermakers' alum was used to adjust the pH of the sheets to four, the reflectance values before irradiation decreased slightly in most cases. There was a larger drop in the reflectance value when the pH of the pulp is adjusted to the pH ten with sodium aluminate.
5. Both means of adjusting the pH to ten, namely sodium hydroxide and sodium aluminate, decreased the initial brightness of the pulp. However, there was little correlation between the effects of the two compounds used to adjust the pulp pH to four, namely sulphuric acid and papermakers' alum.
6. Experimental results showed that none of the compounds used in pH control stabilized consistently the color of unbleached pulp exposed to ultraviolet irradiation.
Brew, David L., "The Effect of Ultraviolet Light on the Color of Unbleached Pulps: Literature Survey" (1959). Paper Engineering Senior Theses. 87.