Date Published: February 7, 2017
Publisher: Public Library of Science
Author(s): Zhenhua Liu, Xinping Li, Wei Xie, David A Lightfoot.
Carrageenans are commercially important sulfated gums found in various species of red seaweeds (Rhodophyta), wherein they serve a structural function similar to that of pectins in land plants. In this study, carrageenan was used independently or in combination with cationic polyacrylamide (CPAM) and/or Al2(SO4)3 to explore its application as a dry strength additive in papermaking. Strength index determination, ash content detection, FTIR characterization and SEM observation were performed on prepared handsheets. The results showed that with 0.6% Al2(SO4)3 and 0.2% carrageenan as additives, the tensile index increased by 13.53% and precipitated calcium carbonate (PCC) retention increased by 57.06%. With 0.6% Al2(SO4)3, 0.2% carrageenan and 0.03% CPAM as additives, PCC retention increased by 121% while the tensile index did not fall compared to handsheets without additives, indicating that carrageenan could enhance the strength of handsheets and be used as an anionic dry strength agent.
Dry strength additives are important chemicals in the papermaking industry to increase paper strength. Many water-soluble polymers, which can form hydrogen bonds with cellulose fibres, can be used as dry strength additives. Dry strength additives are typically used to offset the decline of paper strength resulting from addition of fillers or secondary fibres (such as recycled fibres). Frequently used dry strength additives are natural or synthetic polymers. Natural polymers include starch (cationic/anionic starch) and gums (guar gum, for example). Synthetic polymers comprise polyacrylamide and its derivatives, polyvinyl alcohol, etc. In most cases, a mass fraction of 0.1%-0.35% of these substances can achieve an effective dry strengthening effect. Thus far, most studies focused on the use of synthetic polymers, starch or terrestrial plant gums in papermaking [1–5]. As a gum from marine plants, carrageenan used in papermaking has been reported rarely.
This study attempted to apply carrageenan in papermaking and extend the range of paper dry strength agents. Applied in papermaking, carrageenan can obviously improve paper strength by strengthening the bonding between cellulose fibres, which was confirmed through FTIR spectra and SEM images. As an anionic dry strength agent, carrageenan decreased the efficiency of some cationic retention aids such as CPAM, thus reducing filler retention. However, carrageenan is suitable for single use or in paper forming processes where Al2(SO4)3 is involved to enhance the strength of paper products and may be potentially used as a new additive in papermaking industry.