Softwood kraft pulp fines: application and impact on specific refining energy and strength properties
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ORIGINAL RESEARCH
Softwood kraft pulp fines: application and impact on specific refining energy and strength properties Daniel Mandlez . Lukas Zangl-Jagiello . Rene Eckhart
. Wolfgang Bauer
Received: 3 July 2020 / Accepted: 15 September 2020 Ó The Author(s) 2020
Abstract Along with the emergence of micro and nanofibrillated celluloses and their application in papermaking, the influence of the so called fines fraction of pulps on both process and product properties has received increasing research interest in recent years. Several researchers have experimented with primary and/or secondary pulp fines to assess their effects on paper properties with not always consistent results. Our work focuses on the targeted application of the primary fines fraction of an unbleached softwood kraft pulp. The primary fines are separated from the pulp to be subsequently added to achieve blends of 5%; 9% and 12% primary fines content. These blends were then refined in a PFI mill to evaluate the effect of the primary fines on refining as well as on paper properties of hand sheets prepared from these pulps. It is shown that the addition of primary fines enhances tensile strength in the unrefined and slightly refined state, while the maximum tensile strength of the highly refined reference pulp is not increased. A slightly increased dewatering resistance (Schopper Riegler) at comparable air D. Mandlez R. Eckhart (&) W. Bauer Institute of Bioproducts and Paper Technology, Graz University of Technology, Inffeldgasse 23, Graz 8010, Austria e-mail: [email protected] L. Zangl-Jagiello Zellstoff Po¨ls AG, Dr. Luigi-Angeli-Str. 9, Po¨ls 8761, Austria
permeability (Gurley) for a given tensile strength was also observed. The linear relationship between tensile index and apparent sheet density seems to be affected in the unrefined and slightly refined state where the breaking length of the fines enriched samples is higher for a given apparent density. Keywords Fines Pulp Softwood Refining Beating PFI
Introduction In the evaluation of fibre morphological properties of any given pulp it is standard to differentiate between the coarse and the fines fraction. The fines fraction is commonly either defined as material passing a 76 lm screen (200 mesh) in a Britt Dynamic Drainage Jar Device (according to SCAN-CM 66:05), or particles smaller than 200 lm in case of determination by automated optical analysis (according to ISO 16065-2) (Mayr et al. 2017b). Depending on their origin, pulp fines have different morphological character and are usually divided in primary and secondary fines (Odabas et al. 2016). Primary fines are produced during the pulping process and mainly consist of blocky or flake like material, which is mostly ray cells, parenchyma cells, pores and fragmental parts from the middle lamella (Odabas et al. 2016). Secondary fines
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Cellulose
are generated during refining in the stock preparation process and have a strong fibrillar character, as they mainly consist o
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