High Consistency Refining of Kraft Pulp for Reinforcing Paper Based on TMP Furnishes, 2007 International Mechanical Pulping Conference

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This study evaluated whether there inforcement effect of bleached softwood kraft pulp fibres added to a thermomechanical pulp (TMP) based furnish for lightweight coated (LWC) paper could be improved by high consistency (HC) refining. There inforcement pulp was HC refined under various temperature and steam pressure conditions. Fibre and sheet properties, such as fibre length, fibre curl, tensile strength, strain at break and tensile energy absorption, of both isotropic handsheets and orthotropic paper were studied. There inforcement effect was estimated by fracture mechanics for a larger web containing a small crack. The critical force and critical elongation were calculated based on material parameters measured on laboratory made orthotropic papers.

The study revealed that HC refining did not significantly increase the final level of fibre curl of bleached softwood kraft fibres after a combination of high and low consistency refining. Despite this, testing of laboratory sheets indicated that the highest levels of tensile energy absorption and strain at break were achieved as a result of HC refining. The highest level being achieved with fibres refined in the pressurised refiner at high temperature.