This thesis examines the applicability of the CEPI recyclability method for evaluating wet-strength papers. The CEPI method is a standardised laboratory procedure that determines the recyclable fraction of paper products through numerical assessment. According to this method, wet-strength papers are generally classified as non-recyclable, although industrial practice shows that recycling such papers is possible. The aim of this thesis was to assess the method’s suitability for practical use in the paper industry and to investigate potential adaptations for wet-strength papers.
The theoretical section presents the characteristics of wet-strength papers, the function of wet-strength resins, and paper recycling processes, with emphasis on the repulping of papers containing polyamide-epichlorohydrin resins. In the experimental section, the CEPI method was applied and partially modified to compare the recyclability of wet-strength and non-wet-strength papers. The effects of extended repulping time, increased temperature, and the addition of sodium hydroxide on fibre yield were examined.
The results showed that the standard implementation of the CEPI method does not fully reflect the actual recyclability of wet-strength papers, whereas modified repulping conditions enable a significant improvement in fibre yield. The thesis highlights the limitations of the method and provides a basis for its further development and better adaptation to industrial practice.
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