Cellulose (2021) 28:5807–5826 https://doi.org/10.1007/s10570-021-03856-0 (0123456789().,-volV) ( 0123458697().,-volV)
ORIGINAL RESEARCH
Fractionation of pulp and precipitated CaCO 3 –pulp composites: effects on sheet properties of selective CaCO 3 precipitation onto fiber size fractions
. Kaj Backfolk . Isto Heiskanen
Teija Laukala
Received: 22 December 2020 / Accepted: 29 March 2021 / Published online: 11 May 2021 The Author(s) 2021
Abstract CaCO 3 -pulp composite was prepared via precipitation of calcium hydroxide in the presence of pulp. In order to investigate the precipitation selectiv- ity and mechanism, the substrate pulps and the obtained composites were fractionated (R30, R100, R200, R400 and a sedimented fraction that passed the 400 mesh wire) using a Bauer-McNett unit. The main fractionation criterion was therefore fiber length. The pulp used was CTMP (chemithermomechanical pulp), yielding a precipitated calcium carbonate-chemither- momechanical pulp (PCC-CTMP) composite with a targeted PCC-to-CTMP ratio of 1:1. The PCC con- sisted primarily of nano-sized primary particles which formed aggregates and clusters on the fibers. When the fiber morphology, zeta potential and surface charge density of the fractions were determined, a correlation was found between the surface charge density of the
CTMP and the ash content of the corresponding PCC- CTMP fractions. This supports the hypothesis that the precipitation on the CTMP fiber is driven by the charge interparticle interaction. The use of refined CTMP furnishes and fractionation of the PCC-CTMP furnishes demonstrates that PCC is preferably fixed on fines and fibrils since it appears at a higher content in the fines fractions. Fiber activation via fiber split, removal of primary wall and surface defibrillation enhanced the affinity of the PCC for the fibrils. The laboratory handsheets prepared from the material demonstrated the importance of controlling the sub- strate fiber properties for the mineral-fiber composite, e.g. via refining, as differences between the refining levels and fractions were found to lead to differences in both optical properties and bonding.
T. Laukala ( & ) Lappeenranta-Lahti University of Technology Packaging technology of LUT School of Energy Systems, P.O. Box 20, 53850 Lappeenranta, Finland e-mail: teija.laukala@lut.fi K. Backfolk I. Heiskanen Stora Enso OyjResearch Center Imatra, 55800 Imatra, Finland
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