Evaluating Methods to Increase the Compressive Strength of Recycled Linerboard, 1993 Recycling Symposium Proceedings

Edward L. Springer, Richard J. Spangenberg, Freya Tan, John H. Klungness, James L. Minor

The compressive strength of handsheets produced by re-slushing dried linerboard is significantly less than that of hand-sheets made from original never-dried pulp. This is also true for tensile and burst strengths. Tensile and burst strengths of re-slushed linerboard can be significantly improved by chemical and mechanical treatments. The objective of this study was to determine whether compressive strength could be improved by chemical treatment. Several potential treatments were performed on repulped material. No treatment was effective in increasing compressive strength. The simplest and least expensive way of initially increasing compressive strength at high freeness levels is by beating the pulp. For additional compressive strength, a sodium hydroxide treatment was selected for use with alkaline beating. Although this combination significantly

increased tensile and burst strengths, it had no effect on compressive strength. The effect of increased wet pressing followed by restraint drying (IPD) on the best combination of alkaline treatment and alkaline beating was evaluated. The sequence of alkaline treatment, followed by alkaline beating, followed by IPD treatment produced an increase in compressive

strength. The improvement in strength was about 11% greater than that for handsheets made from never-dried pulp. Further study is needed to determine whether or not alkaline beating is required.