The impact of sulfonation and hot-pressing of low-energy high temperature chemi-thermomecanical pulp

• Published in: Holzforschung Vol. 76; no. 5; p. 463
• Main Authors: Joelsson, Tove, Persson, Erik, Pettersson, Gunilla, Norgren, Sven, Svedberg, Anna, Engstrand, Per
• Format: Journal Article
• Language: English
• Published: 2022
• Subjects: Chemi-thermomechanical pulp; high strength; hot-pressing; refining energy; sulfite
• ISSN: 0018-3830; 1437-434X
• DOI: 10.1515/hf-2021-0109

Hot-pressing high yield pulp-based paper, well above softening temperature of lignin, increases paper density and paper strength. It has been investigated whether improved paper strength can be achieved and if lower pressing temperatures can be used in combination with increased sulfonation of HTCTMP (high temperature chemi-thermomechanical pulp).Moist paper sheets from low-energy Norway Spruce HTCTMP were hot-pressed up to 270°C. Sulfite charges from 25 to 120 kg/bdt were used during impregnation, preheating, and refining at 180°C with an electric energy demand of 370–500 kWh/bdt to a shive content of 1%. The pulps were mixed with 20% bleached unrefined kraft pulp to ensure that the sheet formation would not be hampered by the coarseness of the pulps. A tensile index of 70 kNm/kg was reached with highest sulfite dosage at only 150°C in pressing temperature which can be compared to 60 kNm/kg for the corresponding market CTMP. To obtain high wet strength, the highest temperature was required, while the sulfite charge was found to be of minor importance. This study has shown that it is possible to obtain strong and wet-stable paper products from HTCTMP, having a yield of 94-96% and a low energy demand at reduced pressing temperature.