A rheological study of fiber suspension-impact of ionic form and fiber type on refining
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Helsinki University of Technology |
Diplomityö
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Date
2007
Department
Major/Subject
Paperi- ja painatustekniikka
Mcode
Puu-21
Degree programme
Language
en
Pages
104 s. + liitt. 7
Series
Abstract
This thesis investigates the effect of refining on fiber characteristics through the study and analysis of the rheological properties (deformation and flow) of different fiber suspensions. The main objective was to find a correlation between the refining results in terms of energy consumption and beatability with the rheological properties of fiber suspensions. The thesis was divided into 3 investigations lines, trial A Hardwood and Softwood suspensions, trial B ionic-exchanged suspensions and trial C chemical conditioned suspensions. In fiber suspensions, interconnected fibers create random networks. The fiber network strength in these interconnected systems was evaluated by deforming and disrupting the network structures. The storage modulus, the yield stress and the critical strain were employed to characterize the fiber network strength. Refining results showed that fibers in Na'-form presented a better beatability (measured as WRV at the same level of specific refining energy) in comparison to H' and Cat'-form due to higher fiber swelling. Addition of chemical deflocculants to fiber suspensions also improved the beatability of fibers. Suspensions previously treated with CMC and Guar gum presented higher values of WRV and °SR in comparison to standard softwood unbleached, A-Pam and C-Pam suspensions. The storage modulus was mainly affected by the suspension consistency. The fiber length reduction during refining also showed to have an effect on the storage modulus, as the fiber length was reduced the storage modulus decreased. The critical stain showed to be lower for unrefined suspensions in Na'-form than for other investigated ionic forms. As mechanical energy was applied during refining the critical strain increased for all the suspensions. Unrefined and refined fibers pre-treated with CMC and Guar gum presented lower values of critical strain in unrefined, low refined and high refined suspensions than fibers treated with A-Pam and C-Pam. The refining action, the type of counter ion and the addition of chemicals did not show a clear effect on the yield stressDescription
Supervisor
Paltakari, JouniThesis advisor
Bäckström, MarieKeywords
fiber network strength, fiber nätverks styrka, storage modulus, E-modul, critical strain, kritiska töjningsnivån, ionic-form, jonformer, refining, malning