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Paper for recycling is an important fiber source for the production of corrugated base paper. The change in production capacity toward more and more packaging papers affects the composition of paper for recycling and influences the paper quality. This research project investigated the influence of the multiple recycling of five different corrugated base papers (kraftliner, neutral sulfite semichemical [NSSC] fluting, corrugating medium, testliner 2, and testliner 3) on suspension and strength properties under laboratory conditions. The corrugated board base papers were repulped in a low consistency pulper and processed into Rapid-Köthen laboratory sheets. The sheets were then recycled up to 15 times in the same process. In each cycle, the suspension and the paper properties were recorded. In particular, the focus was on corrugated board-specific parameters, such as short-span compression test, ring crush test, corrugating medium test, and burst. The study results indicate how multiple recycling under laboratory conditions affects fiber and paper properties.

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Calcium carbonate provides good optical properties to graphic paper and is relatively inexpensive. Therefore, the use of calcium carbonate for the production of paper has steadily increased. But the high amount of calcium carbonate in paper for recycling and the closure of water circuits leads to a high concentration of calcium ions in the process water of paper mills. The consequence can be undesired precipitation and deposition of calcium carbonate in machines and plant components of the mills. Enhanced knowledge about the precipitation potential of calcium carbonate is needed to avoid or reduce undesired precipitation and deposition. The potential can be described using the Langelier saturation index (LSI). Our investigations showed that a deposition of calcium carbonate only happens if the LSI value is higher than 0.5. An LSI value above 0.5 often exists in process water that is treated in a biological effluent treatment plant. Reasons for such values are the increase in hydrogen carbonate concentration (m-alkalinity) by carbon dioxide production and the increase of the pH value by reduction of fatty acids. With the knowledge about the precipitation potential of calcium carbonate in a process water line, suitable measures could be implemented.

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