High strength paper from high yield pulps by means of hot-pressing

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 y...

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Bibliographic Details
Published inNordic pulp & paper research Vol. 35; no. 2; pp. 195 - 204
Main Authors Joelsson, Tove, Pettersson, Gunilla, Norgren, Sven, Svedberg, Anna, Höglund, Hans, Engstrand, Per
Format Journal Article
LanguageEnglish
Published De Gruyter 25.06.2020
Subjects
Bleached kraft pulps
Bleaching
Chemical pulp
Chemithermomechanical pulps
Cleaning
Compression strength
high yield pulp
High-tensile strength
Hot pressing
Increased temperature
Kraft pulp
lignin
paper properties
Tensile strength
Thermomechanical pulp
Thermomechanical pulping process
wet strength
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Summary: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 spruce-pine based bleached kraft pulp as reference. Rapid Köhten sheets of and 50 % dryness were hot-pressed in a cylinder-press at 20–200 °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.
ISSN:0283-2631
2000-0669
2000-0669
DOI:10.1515/npprj-2019-0087