Ultrafiltrative Deinking of Flexographic ONP: The Role of Surfactants

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Ultrafiltration is a potentially viable method toremove dispersed flexographic pigments from the deinkingwater loop. This paper describes the role of surface active materials in the ultrafiltration of water based flexographicpigment dispersions. A logarithmic relationship between permeate flux and pigment concentration was demonstrated atink concentrations above .4%, with permeation rates becomingindependent of ink content at lower concentrations. Pressureindependent ultrafiltration permeation rates observed whenclarifying the more concentrated ink dispersions were shownto be limited by mass transfer effects, as predicted by theconcentration polarization model. The limit to permeate flux atlow ink concentration was due to membrane fouling resultingfrom the low concentration of surface active materials in the dilute ink dispersions. Increasing the concentration of urfactant in dilute ink dispersions was shown to decrease thedegree of membrane fouling. However excessive surfactantresulted in decreased permeation rates due to micelleformation. Clarification of more concentrated ink dispersions(greater than .4%) resulted in relatively stable permeation ratesand less fouling. The inherently higher concentrations ofsurface active materials in the concentrated ink dispersionsappeared to retard fouling.