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PEER-REVIEWED ARTICLE
Increase of Paper Strength and Bulk by Co-Flocculation of Fines and Fly Ash-based Calcium Silicate Meiyun Zhang, a, * Qiumei Li, a Shunxi Song, a,b, * Ning Hao, a and Guodong Liu a
Fly ash-based calcium silicate (FACS), which has a large surface area (121 m 2 /g) and porous structure, has the potential to be used as a filler for the production of high-bulk paper. In theory, paper with a higher bulk has a lower strength. This work explores the possibility of improving paper strength without compromising its bulk through co-flocculation of cellulosic fines and FACS. To investigate the effect of co-flocculation on paper properties, composites made with various ratios of fines to FACS were studied. Results showed that paper bulk and tensile strength increased with increasing ratio of fines to FACS, up to 0.3 at 17% filler content. To further confirm these findings, the structures of composites were studied with a light microscope and scanning electronic microscope (SEM). Images showed that the composite formed at the ratio of 0.3 exhibited a larger size and looser structure than other composites, which can be attributed to the improvement of the paper ’s strength and bulk. Schemes for the composite formation process and its interactions with fibers were also proposed.
Keywords: Bulk, strength; Composite; Fines; Fly ash based calcium silicate; Co-flocculation Contact information: a: Shaanxi Province Key Laboratory of Papermaking Technology and Specialty Paper, College of Light Industry and Energy, Shaanxi University of Science & Technology, Xi’an 710021, China; b: State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, 510640, China; *Corresponding authors: myzhang@sust.edu.cn; songshunxi@sust.edu.cn INTRODUCTION Fine paper, especially printing paper, with low cost, high strength, and high bulk, is ceaselessly pursued by papermakers. For many paper grades, filler is used to decrease production costs and improve paper properties ( e.g. , brightness, printability). However, paper strength can be negatively affected because the filler impedes the inter-fiber hydrogen bonding. To improve the strength of filled paper, many methods have been tried, such as strength additives (Hamzeha et al. 2013), lumen loading (Miller and Paliwal 1985), filler pre-flocculation (Sang et al. 2012; Chauhan and Bhardwaj 2014), and filler modification (Yan et al. 2005; Zhao et al. 2005; Yoon and Deng 2007; Shen et al. 2009, 2010). Among those methods, filler pre-flocculation and modification are of great interest. In the pre-flocculation process, filler aggregates are formed by polymers. Chauhan and Bhardwaj (2014) pre-flocculated talc with cationic starch, resulting in a 7% to 15% increase in tensile index with 24% filler content. Yan et al. (2005) showed a significant improvement in the strength of paper filled with starch-coated clay compared with that filled with unmodified clay. Bulk is another important paper parameter, particularly for printing, because it affects printability and runnability. For printing-grade paper, high bulk is preferred, which correlates with high stiffness. Paper with a higher stiffness can make the printers work more smoothly (Gao et al. 2009; Chen et al. 2013). Moreover, improving paper bulk is a
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Zhang et al . (2016 ). “ Coflocculated fines & CaSiO 4 ,” B io R esources 11(3), 7406-7415.
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