Improving Paper Wet-strength by Means Hot-Pressing and Increased Lignin Content in Pulp Fibers, 19PaperCon
The research presented here show ways to improve wet strength by means of hot-pressing without strength additives when using lignin containing pulps as unbleached softwood chemical pulps (NSK) and lignin rich softwood chemi-thermomechanical pulps (CTMP). NSK (Northern Softwood kraft) laboratory scale produced pulps of 3 different levels of natural lignin (or kappa number) and two commercial pulps, NBSK (Northern Bleached Softwood kraft) and CTMP, were compared evaluating dry- and wet-strength properties. Staining methods and light microscope were used to study cross sections of paper sheets. The CTMP fibers collapse to an increasing degree with pressing temperature whereas NBSK/NSK do not change. The microscopy methods show the distribution of lignin within the paper structure. Sheets made from NSK show a significant increase in wet strength from 4kNm/kg to 23kNm/kg, when increasing temperature from 20°C to 200°C. CTMP show corresponding increase from 2kNm/kg to 16kNm/kg. No increase in dry strength or in density can be observed in case of NBSK/NSK, while the CTMP show an increase of 53% and 100% respectively. The SCT values show an increase up to 35% for lignin-rich NSK based paper sheets when hot-pressing.
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Improving Paper Wet-strength by Means Hot-Pressing and Increased Lignin Content in Pulp Fibers, 19Pa
