Wet-Web Strength and Pressability of Highly-Filled Sheets, 2011 PaperCon Conference

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Increasing filler content in paper could be an attractive strategy to improve paper quality and reduce fibre consumption and drying energy. However, filler addition reduces fibre-fibre bonding and hence tensile strength of paper and wet-web. Low wet-web strength leads to frequent sheet breaks and thus poor machine runnability. In this work, we have determined the impact of increasing filler content on the strength and pressability of wet web. The results indicate that addition of precipitated calcium carbonate (PCC) filler into sheets substantially reduced their wet web strength. At a PCC content of 50%, wet tensile energy absorption index decreased by about fivefold at a web solids content of 50%. Although the web was drier under constant drainage and press conditions, increasing PCC content actually reduced web pressability, and the fibre portion in the web became wetter in the presence of PCC. We have also found that wet-web strength is dependent on the filler type used. For instance, the PCC and GCC (ground calcium carbonate) reduced wet-web strength more than clay fillers. Therefore, manufacturing of highly filled paper requires developing strategies for improving wet-web strength to ensure adequate machine runnability.