Bulky Paper from Chemically Crosslinked Hardwood Kraft Pulp Fibers

There is a general interest among paper and board makers to produce lighter and bulkier paper and board products. The aim of the present study was to characterize chemically crosslinked hardwood kraft fibers regarding their potential in making bulky paper and board. Crosslinking agents are molecules that contain two or more reactive ends that form inter-chain covalent bonds with cellulosic hydroxyl groups. The formed water resistant crosslinks prevent mutual movement and relocation of cellulosic chains and further, changes in fibers physical shape and dimensions, as the fibers are wetted, mechanically stressed and dried. In paper and board making chemically crosslinked fibers are less prone to swelling and deformation. Blocking of fibers surface hydroxyl groups by reactions with crosslinking agents reduce fibres ability to form inter-fibre hydrogen bonds. In the present study the crosslinking treatments were carried out in laboratory scale. The used pulp was never-dried, bleached hardwood (Betula pendula) kraft pulp. Experiments were performed using various dosages of crosslinking agents followed by beating of the pulp and subsequent standard laboratory paper sheet making. The crosslinking treatments resulted in significantly increased paper sheet bulk. As expected, crosslinking decreased the dry strength of the sheets. However, after moderate refining, crosslinked pulps had much better tensile strength at constant bulk than never-dried or dried reference pulps. An additional advantage of crosslinking treatment is that it improves dewatering ability of the pulp significantly. Thus, use of chemically crosslinked pulp offers an attractive option for manufacture of bulky printing papers and paper boards.