Retention of fatty acid soaps during recycling. Part I: A study using packed beds of pulp fibres

C. Fernandez, G. Garnier

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Paper made of recycled fibres often has different properties than paper made entirely of virgin pulp. A hypothetical mechanism for the loss of papermaking and printing potential of recycled paper is the adsorption and entrapment of molecules of low surface energy (such as oil and soap) on the wood fibres during recycling. This hypothesis was tested with a packed bed of wood fibres by following the dynamics of retention of a concentration pulse generated at the entrance (breakthrough curve, BTC). This study investigated the retention of model deinking chemicals in packed beds. The variables studied include the type of fibre (kraft, TMP), the type of adsorbate (calcium and sodium oleate), and the ionic strength. The objectives of this study were threefold: to develop a sensitive technique to quantify contaminant retention during recycling; to elucidate the mechanisms of soap retention by the fibres; and to assess the effects of soap retention on product quality. A sensitive technique to quantify the retention of contaminants on the pulp is to measure the area under a BTC of a packed bed of fibres. It was shown that sodium salts of fatty acids underwent ion exchange with the calcium present in the pulp. The availability of calcium and other ions within the pulp for ion exchange is diffusion controlled. When tap water was used during washing stages, calcium ions from the tap water were retained by the pulp, replacing some of the sodium ions. Soaps prepared by mixing equimolar amounts of sodium oleate and calcium chloride (1 meq) did not adsorb on pulp fibres. This behaviour goes according to theory as the negatively charged soap particles are repelled from the negatively charged fibre s. However, complete retention of the particles occurred at high excess calcium concentration (10 meq). Dynamic contact angle and surface tension experiments confirm the important role of soap retention in sizing and carry-over phenomena.

Original languageEnglish
JournalJournal of Pulp and Paper Science
Issue number4
Publication statusPublished - 1 Apr 1997
Externally publishedYes


  • Adsorption
  • Bogus papers
  • Calcium
  • Fatty acids
  • Impurities
  • Paper properties
  • Reclaimed fibers
  • Recycling
  • Retention
  • Soap

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