Date of Award
Bachelor of Science
Paper Science and Engineering
Wet strength papers are papers that retain 15% of their dry strength. Wet strength agents form non-hydrogen bonds with the cellulose so that the bonds are not broken when saturated with water. When these agents are used repulping of the product becomes very difficult. Therefore, a chemical treatment is necessary to break the bonds and disperse the fibers. Generally speaking a high pH and high temperature are desired to assist in breaking the bonds.
Chlorine dioxide and sodium borohydride were analyzed to determine the best repulping chemical. Success will be measured by several factors. These factors are: least amount of fiber degradation, speed of repulping, and least amount of chemical used.
This experiment was performed using beverage carriers as the wet strength paper. The beverage carriers were repulped in a Tappi disintegrator using chlorine dioxide and sodium borohydride at 1% concentration and 3% concentration levels. Three pulping times of ten, twenty, and thirty minutes, were used for the pulping runs. After the pulping runs were completed a shive count was taken and compared to the control run. Handsheets were made and tested for tear index, tensile index and burst index. A fiber length analysis was also performed to determine the amount of fiber damage.
The results of the testing gave acceptable numbers. The shive analysis showed the three percent sodium borohydride had the best fiber dispersion with one percent sodium borohydride having the second best. The chlorine dioxide failed to show acceptable degrees of fiber dispersion. The strength tests, tensile index, tear index, and burst index, showed that the strongest fibers were those pulped with sodium borohydride, at both concentration levels. The fiber length analysis showed that at thirty minutes the control run had the largest average fiber length. For shorter pulping times the sodium borohydride at both concentrations showed the largest average fiber length.
Barr, David S., "Repulping of Wet Strength Papers Using Chlorine Dioxide and Sodium Borohydride" (1996). Paper Engineering Senior Theses. 12.