Journal
NORDIC PULP & PAPER RESEARCH JOURNAL
Volume 35, Issue 2, Pages 195-204Publisher
WALTER DE GRUYTER GMBH
DOI: 10.1515/npprj-2019-0087
Keywords
high yield pulp; hot-pressing; lignin; paper properties; wet strength
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Funding
- Knowledge Foundation (KKS)
- FORIC (Forest as Resource Industrial Research College)
- Kempe Foundation
- IPCO AB
- Mid Sweden University
- MoRe Research Ornskoldsvik AB
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The hypothesis is that it should be possible to modify papermaking conditions in line with the softening properties of high yield pulp fibres and achieve similar strength properties to conventional chemical pulp based paper. We therefore investigated the rheological and physical properties of high yield pulp based papers during hot-pressing. Our results confirm that increased temperature combined with sufficient pressure enables permanent densification by softening of lignin, producing very high tensile strength. This treatment also significantly improved the wet tensile strength in comparison to bleached kraft pulp without using wet strength agents. The high yield pulps used here were spruce based thermomechanical pulp, chemi-thermomechanical pulp, and high temperature chemi-thermomechanical pulp, and birch-aspen based neutral sulphite semi chemical pulp, with sprucepine based bleached kraft pulp as reference. Rapid Kohten sheets of 150 g/m(2) and 50 % dryness were hot-pressed in a cylinder-press at 20-200 degrees C, 7 MPa, and 1 m/min. The mechanical properties showed great improvements in these high yield pulp papers, with tensile index increased to 75 kNm/kg and compression strength index to 45 kNm/kg; levels close to and better than bleached kraft. Wet strength increased to 16 Nm/g compared to 5 Nm/g for bleached kraft.
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