Determination of Fibre Pore Structure: Influence of Salt,pH and Conventional Wet Strength Resins |
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Authors: | Email author" target="_blank">Bo?AndreassonEmail author Jennie?Forsstr?m Lars?W?gberg |
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Institution: | (1) SCA Graphic Research, AB, Box 716, 85121 Sundsvall, Sweden;(2) Fibre technology, Department of Fibre and Polymer Technology, Royal Institute of Technology, S-10044 Stockholm, Sweden;(3) Fibre Science and Communication Network, Midsweden University, 85170 Sundsvall, Sweden;(4) Department of Fibre and Polymer Technology, Royal Institute of Technology, S-10044 Stockholm, Sweden |
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Abstract: | It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached
chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average
pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity
of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results
when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with
both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However,
the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid
structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon
protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius
decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet
strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also
shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength,
measured as zero span-strength of the sheets. |
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Keywords: | Crosslinking Dry strength agents Fibres Fibre saturation point Pore size distribution Tensile strength Wet strength agents |
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