Date of Award
Bachelor of Science
Pulp and Paper Technology
Dr. Ellsworth Shriver
Loss of strength is one of the worst aspects of recycled papers. Even though several factors are responsible for this phenomenon, loss of fiber swelling and inter fiber bonding are believed to be the main contributors. Therefore, prevention of loss in swelling and inter fiber bonding of recycled pup should result in the minimum strength loss of recycled papers.
Chemicals with hydroxyl group such as NaOH are known to provide superior swelling power to.pulp, and their swelling power might be utilized to minimize the strength loss of recycled paper.
In this study, batches of bleached kraft paper were repulped at varying NaOH charge levels and recycled, and effects of NaOH addition on freeness, tensile strength, and tear resistance of recycled paper in successive recycling were observed. The NaOH charge levels used in this experiment were 0%, 5%, 10%, and 20% by weight.
Large fluctuation in freeness of stocks with NaOH was observed, and freeness values of these stocks did not correlate to strength of papers.
The 5% NaOH paper showed higher tensile strength than regular recycled paper (paper with no NaOH) at the first recycling, but the regular recycled paper outperformed other papers in tensile strength at every recycling level.
Recycled papers with NaOH demonstrated reduction in tear strength in successive recycling while tear strength of regular recycled paper increased. The 5% NaOH paper showed the least deviation of tear index from that of the virgin paper. Deterioration of inter fiber bonding and fiber structures were detected at all the NaOH charge levels except 0%, and the degree of deterioration was greater at higher NaOH levels.
The amount of NaOH relative to the amount of pulp present during repulping appeared to be too much in this experiment, and the positive effects of NaOH on recycled paper as anticipated were not obtained at these NaOH charge levels. However, since the 5% NaOH recycled paper showed positive results in tensile strength and tear strength, lower NaOH charge level might provide better results in strength of recycled papers.
Suga, Satoshi, "Treating Recycled Papers with NaOH for Strength Improvement" (1996). Paper Engineering Senior Theses. 522.