X-Ray Nanotomography of Individual Pulp Fibre Bonds Reveals the Effect of Wall Thickness on Contact Area

Abstract

Fibre bonds play an essential role in various properties of paper. Much research has focused on their strength, but the determination of the actual contact area also provides a challenge. Many of the research methods rely on optical tools, which are restricted by the wavelength of light that is utilised. Novel X-ray computed tomography devices utilise X-rays in studying the inner structure of materials, and surpass the optical methods in terms of resolution, allowing detection of even smaller details and variations in distance between the fbres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fbre bonds made of springwood and summerwood fbres of refned bleached softwood kraft pulp. Various dimensional properties of the bonds were measured, most importantly the relative contact area (apparent contact area/intersection area), whose values showed wide variation from 6.4 to 85% with an average of 57.7%. Although the summerwood bonds had a somewhat smaller intersection and contact area than springwood bonds, there were no signifcant diferences in the relative contact area between the bond types. This suggests that the efect of relative and absolute contact area on the strength diferences between bond types seems to be minor.