Developing Environmentally Friendly Repulping Methods For Recycled Papers Wet-Strengthened By Epoxy Resin

The using of recycled paper in our paper-making industry has been kept on increasing for decades, but there are often various kinds of wet-strength papers that are too hard to be disintegrated, especially the permanent wet-strength paper containing epoxy wet-strengthagents. Using hypochlorite can improve the effect of fiber disintegration, but it causes environmental pollution problems and damages fiber quality. In theory, some peroxides, either used alone, or with the help of activating agents, or with the combination of each other, can also improve the effect of fiber disintegration during repulping, while the pollution problems can be alleviated.Firstly, in this paper, hydrogen peroxide and sodium hypochlorite were used to treat respectively a fruit protecting paper, a lab-made wall base paper, and a lab-made decorative base paper. For the fruit protecting paper, the results of disintegrating ratio, Kappa number, brightness and mechanical strengthes of the pulp showed that hydrogen peroxide reacted much more with wet-strength agent, while sodium hypochlorite reacted much more with lignin; for the lab-made wall base paper and lab-made decorative base paper, there were less paper debris and more fines in the pulp treated with sodium hypochlorite, but sodium hypochlorite had much more damage to the fiber. In the meanwhile, sodium hypochlorite reacted much more with the chromophoric structures in the pulp, while hydrogen peroxide reacted much more with wet-strength agent.Then, in order to disclose the repulping effect of different repulping agents better, a model wet-strength paper contains bleached chemical pulp and polyamido-polyamine epichlorhydrin resin (PAE) only was made. The repulping differences of peroxides were studied. It was shown that hydrogen peroxide, potassium persulfate (KPS) and sodium percarbonate (PSC) had little effect on the length and the width of the fiber, and there were lots of fines in the pulp from the the lab-made recycled wet-strengthpaper. They all had some damage to the fiber, among which KPS had the most serious effect while PCS and hydrogen peroxide were similar. And they decreased the PAE residual content of the pulp, again KPS reacted the most with PAE of the pulp, followed by hydrogen peroxide and PCS.Finally, activating agents such as tetraacetylethylenediamine (TAED), sodium molybdate, and dicyandiamide, were used with peroxides to investigate their effects on the repulping of the model wet-strength recycled paper, so did the combination of different peroxides. It was shown that the repulping effect could be improved by adding the activating agent, the best one being TAED, followed by sodium molybdate and dicyandiamide; when hydrogen peroxide and other peroxides were combined to treat the model wet-strength paper, mixing H₂O₂ with KPS could improve the repulping effect, and increasing the ratio of KPS improved the repulping effect.