Needle Punching of Wet Cellulose Fibre Structure

Needle punching of cellulose fibre structures was studied, in order to explore the possibility for a new method for bonding to be used in the paperboard industry. The interest in such subject was based on the need for stronger fibre-to-fibre bonding in the thickness direction of paperboard. The studied samples were prepared with a laboratory handsheet former, and the sheets were then couched to a three-ply paperboard. The middle layers were needled with and high (60 stitches/cm2) and low (40 stitches/cm2) needle stitch density at different needling depths, the different needling depths enabled the use of 0 to 3 barbs of the needle. The needling performed changed both the fibre orientation and the density of the fibre structure locally, i.e. close to the needled holes. For samples needled with two barbs, there were also some fibres tilted in the thickness direction. The local density was estimated to increase around 25% compared to the surrounding regions. Due to the needling, the peak bending moment was found to increase 8% and the peak bending angle increased 19 %, measured on three-ply paperboard samples having a middle layer needled with two barbs and the higher stitch density. The bending stiffness and the tensile and compression strength in the thickness direction were also measured, indicating no significant changes by the needling of the middle layer