PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 2, Number 1, 2016
papermakers should monitor the yield or retention of fibre fines and filler fines when the amount of white ledger increases in the top ply of a duplex board.
Fig. 3. Freeness (left) and average fibre length (right) of recycled and virgin pulp (W/L = white ledger)
Fig. 4. Ash content (left) and fines content (right) of recycled and virgin pulp (W/L = white ledger) Figures 5 and 6 show the physical properties of the handsheets, which consist of recycled and virgin pulps. The bulk of the white ledger handsheets was similar to that of the OCC and ONP handsheets, and lower than that of the BCTMP and BKP handsheets (Seo et al. 2014). The strength of the white ledger handsheets was greater than the strength of ONP and OCC. However, the strength of the white ledger handsheets was lower than the strength of the BCTMP and BKP handsheets. The low strength of the white ledger handsheets in comparison with those made exclusively with virgin pulp is directly related to its low average fibre length (Retulainen et al. 1997) and high ash content (Kroguerus 1997; Lee et al. 2014b). In addition, the changes in the fibre properties reduced the paper strength during the recycling process (Hubbe et al. 2007; Gulsoy et al. 2013). The white ledger slurry produced handsheets that were lower in strength compared with BKP handsheets. The slurry contained fillers, pigments, and short fibres. Therefore, it is necessary to improve the first-pass retention and paper strength of white ledger handsheets. However, improving first-pass retention tends to result in increased ash content in sheets made from white ledger. Therefore, it is very important to select a proper retention aid that improves both first-pass retention and paper strength.
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Article 1 – Improving Retention and Strength
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