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 fibres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fibre bonds made of springwood and summerwood fibres of refined 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 significant differences in the relative contact area between the bond types. This suggests that the effect of relative and absolute contact area on the strength differences between bond types seems to be minor.
Highlights
Fibre bonds play an essential role in various properties of paper
The difference in breaking strength and optically bonded area (OBA) between individual fibre bonds made from exclusively summerwood or exclusively springwood fibres has been recognised[4,5,6], as well as bonds made of a springwood and a summerwood fibre[7]
One of the earliest examples is the study conducted by Page et al.[3] where it was found via optical microscopy that refined spruce sulphite fibre bonds had an relative contact area (RCA) of 71.6%
Summary
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 provides a challenge. 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 fibres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fibre bonds made of springwood and summerwood fibres of refined bleached softwood kraft pulp. X-ray nanotomography is a non-invasive imaging method capable of resolutions up to tens of nanometres, greatly surpassing that of optical methods As such, it seems highly applicable in studying the contact areas of individual fibre bonds. In terms of the relative contact area (RCA) of individual fibre bonds, several different studies have been conducted over the years. In the previous study utilising X-ray nanotomography[8], the average RCA of refined softwood fibre bonds was found to be approximately 58%. An identical value was found in another www.nature.com/scientificreports/
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