Abstract
Abstract The main objective of the current study was to demonstrate that it is possible to enhance strength properties of sheets from spruce HT-CTMP and CTMP furnishes up to the same level as is common on sheets from softwood kraft pulps by changing conditions in papermaking. To achieve that, sheets of spruce HT-CTMP and CTMP were consolidated at densities close to that of the reference bleach kraft pulp by pressing at press nip temperatures well above the tack and softening temperatures of lignin. On sheets from spruce CTMP (CSF 420 ml), where the fibers were surface treated with cationic starch, it was possible to reach tensile index at the same level as on sheets from the untreated reference kraft pulp. The compression strength (SCT) of CTMP and HT-CTMP sheets, which were achieved at the highest press nip temperature (200 °C) in the study, was equal to or higher than that of the reference kraft pulp sheets. The results show that there is a great yet unexploited potential in papermaking from spruce HT-CTMP and CTMP furnishes, which could be utilized in manufacturing of products where very high requirements upon strength is demanded.
Highlights
IntroductionVery high strength of papers from softwood CTMP can certainly be achieved at conventional papermaking conditions if its fibers are refined to sufficiently high flexibility, (Höglund and Bodin 1976)
The characteristic properties of softwood chemimechanical pulps (CTMP) are of special interest in manufacturing of high quality packaging board as this type of high yield pulps (HYP) can be formed in sheets with a higher bulk at a given internal bond strength thanVery high strength of papers from softwood CTMP can certainly be achieved at conventional papermaking conditions if its fibers are refined to sufficiently high flexibility, (Höglund and Bodin 1976)
Sheets of spruce HT-CTMP and CTMP were consolidated at densities close to that of the reference bleach kraft pulp by pressing at press nip temperatures well above the tack and softening temperatures of lignin
Summary
Very high strength of papers from softwood CTMP can certainly be achieved at conventional papermaking conditions if its fibers are refined to sufficiently high flexibility, (Höglund and Bodin 1976). This is, extremely energy demanding, (Klinga et al 2008). The energy consumption is on such high level that it up to now has not been of interest to use CTMP in paper products with very high requirements upon strength out of economical reasons. To be able to manufacture strong papers from HYP in an economical feasible way, the conventional conditions in papermaking have to be changed to take advantage of the specific characteristics of lignin rich fibers.
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