Date of Award
Bachelor of Science
Pulp and Paper Technology
Dr. Truman Pascoe
Dr. Stephen Kukolich
To improve the wet strength of paper, colloidal dispersions of thermosetting wet strength resins are added to the papermaking furnish. However, these resins show low efficiency when applyed to unwashed neutral sulfite semichemical corrugating medium. To determine the reason for this, experiments were made in which corrugating mill stock was made into handsheets using Paramel HE and Kymene 557 wet strength resins.
It was found that Kymene 557 gave poor wet strength when used at levels less than .67%, but that further addition brought increasingly larger gains. The wet strength attained with Paramel HE showed a rapid rise up to a .33% level of addition, but more resin gave smaller gains and the highest wet strength achieved was less than one third that obtained with Kymene. Hydrochloric acid, sulfuric acid and alum were used as pH adjusting agents with Paramel HE. Hydrochloric acid gave the best results and alum caused hard sizing of the sheet. Both Kymene and Paramel were tested on unwashed stock over a range of pH. It was found that Kymene and Paramel were tested on unwashed stock over a range of pH. It was found that Kymene gave best results at pH 8, while Paramel gave increasing wet strength with decreasing pH. Through experimentation, it was found that the amount of wood fines in the furnish had little effect on the development of wet strength. Wet strength increased rapidly, however, with washing of the stock. This indicates that the wet strength inhibiting material was part of the residual black liquor carried with the pulp. A list of the materials found in N.S.S.C. spent liquor was compiled, and these materials or representative model compounds were added to washed samples of pulp, which were tested for wet strength development. None of the compounds, except sodium sulfite and sodium lignosulfonate, exhibited an effect on wet strength resin efficiency. The sulfite was shown to be slightly detrimental while the lignosulfonate drastically reduced wet strength. As little as 3% sodium lignosulfonate reduced wet strength values by 80%. The lignosulfonate anion could be attracted to, and form a counterion layer around the cationic resin micelles, thus preventing them from being deposited on the fibers. This was believed to be the only major factor inhibiting wet strength on this grade. Wet strength resin was tried on a furnish loaded with calcium chloride in an attempt to change the sodium lignosulfonate into harmless calcium lignosulfonate, but it was found that to form the calcium precipitate, the calcium chloride requirements would be too high to be practical. It appears, that at present, the only way to get practical wet strength on this grade is to use a high level of resin addition or partially wash the pulp or both.
Latta, James L., "Investigation of Factors Influencing the Use of Wet Strength Resin on Unwashed NSSC Pulp" (1967). Paper Engineering Senior Theses. 356.