Study on the Dispersion Stability of the Two Components Slurry, Composing from SAP and MFC (Part III)

Abstract

A dispersion liquid can be obtained exhibiting a high viscosity at a low concentration by uniformly dispersing microfibrillated cellulose (MFC) or bacterial cellulose (BC) in a mixed medium of water and hydrophilic organic solvent.Particulate SAP as dispersed in this dispersion liquid, SAP particles can be stably dispersed with a high concentration in the dispersion liquid by virtue of the viscosity exhibited by MFC. In addition, possible coagulation and recoagulation to be caused with SAP particles otherwise coming near to each other can be almost entirely prevented by the SAP particles being dispersed in the dispersion liquid by the action of the dispersion of MFC, so that a dispersion slurry of a long and stable pot life can now be prepared.The respective behaviors of SAP and MFC in such mixed medium have been reported in Part I of “Study on the Composite Structure of SAP and Microfibrillated Cellulose”, “Swelling & Coagulation Behaviors of Acrylic Acid Base SAP in Water & Water Miscible Organic Solvent Mixture” and in Part II “Study on the Dispersion Stability of the MFC or the BC in a Solvent Mixture of Water and Organic Solvent” in this Journal.As reported previously, the authors believe that they have made clear the nearly whole picture of the conditions for stably dispersing each component, SAP and MFC, alone in a dispersion medium. When it comes to a two component slurry system of SAP and MFC in coexistence, various unexpected phenomenon come to take place caused by the concentrations and concentration ratio of SAP and MFC, their different mixing mechanisms, changes with time, coating conditions, etc. In this report, studies have been made on the process flow of SAP and MFC being added and mixed, their dispersion limits, stability with time of their mixed slurry, stability at their temperatures, etc. so that the following results have been obtained:1) It is found that MFC has the following effects in the slurry of SAP and MFC in coexistence:MFC even if At low concentrations prevents coagulation and re-coagulation of SAP by virtue of its high viscosity;MFC being dispersed keeping a finely particulate shape prevents bonding in groups of SAP particles to each other;While SAP tends normally to swell to 1.5 to 2.2 times larger than its original form as it selectively absorbs water in a dispersion medium, it is prevented by MFC in coexistence from swelling with MFC retaining water out of the dispersion medium by virtue of its high hydrating property; andMFC prevents the selective water absorption of SAP so as to cause the dispersion medium not to undergo changes in composition for a long period of time.2) The optimization of the preparation conditions of subject slurry contemplated in a commercial process:In a procedure of preparing a slurry, a dispersion liquid of MFC should be first prepared and then SAP is to be added;SAP has been found to be wide in its stable dispersion region if it is such as cross linked on the surface, of spherical shape, of small particle diameter and is obtained by being reversed phase suspension polymerization;The limit concentration of SAP in coexistence with MFC is 20 to 40%;The limit concentration of MFC in coexistence with SAP is 0.4 to 1.0%;Possible change with time of the slurry with MFC in coexistence can be prevented by properly selecting SAP and the water content of the dispersion medium and keeping the concentration of around 15°C3) It has been found that the conditions of stably forming sheets can be established by defining a range of conditions for stabilizing the slurry.