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DISPERSION GUIDE FOR GRAPHISTRENGTH® CW2-45 into aqueous based formulations
Introduction Optimal properties of the final part are achieved only with high quality dispersions. In order to ensure consistent performances, MWCNT are pre-dispersed in CMC matrix during the production of the Master-Batch Graphistrength® CW2-45. Naturally, it is also important to disperse properly Graphistrength® CW2-45 in the final formulation. This paper gives information about the key recommended procedure for the dispersion steps for this Master-Batch.
Benefits and applications Graphistrength® CW2-45 can be diluted in various water-based formulations. Typical final MWCNT loadings in the final formulations are in the range of 1 to 6 wt% (2 to 12 wt% of CW2-45 concentrate) depending on the active material characteristics, the targeted performances, processing methods and conditions. Graphistrength® CW2-45 offers particular advantages for the formulation control due to high concentration of MWCNT. It also offers a process advantage, with the possibility to efficiently introduce MWCNT using conventional mixing equipment, such as high-shear mixers: dissolver disc, rotor stator and ball mill:
Dissolver disc
Rotor–stator
Ball Mill
Dispersion guide For optimal dispersion, the CW2-45 pellets should be added progressively in water under a certain agitation (1000-1500 rpm). After a few minutes, this dispersion is homogeneous but contains some aggregates. The dispersion can be optimized by high shear mixing. A detailed procedure is indicated below: Dispersion CW2-45 step by step: 1.
2.
3.
4. 5.
Introduce CW2-45 pellets progressively in hot water (70 – 90 °C) at least for 15 min or in water at ambient temperature at least for 2 hours with a dissolver disc at 1000-1500 rpm (peripheral speed around 3 m/s) to obtain the desired MWCNT concentration. Apply high-shear mixing to the dispersion produced in the step 1 for at least 30 min. (for instance for 500-1000ml solution). A dissolver disc (peripheral speed between 15 and 20 m/s) or a rotor-stator mixer (e.g. Silverson L4RT at 6,000 rpm or higher) can be used. Viscosifiers can be added prior to high shear mixing to increase viscosity and thus shear. This will result in better dispersion qualities or reduced dispersing times. High shear mixing will result in water evaporation. We suggest, to limit the water evaporation to put the flask in an iced batch, if possible put a top on the flask. Therefore, it is recommended to monitor and adjust the amount of water after the dispersion step if necessary. Note that a minimal amount of water is required to achieve efficient solvation of MWCNT. Add the remaining components of the formulation, e.g. binder, filler, latex... Final dispersion will more or less stable during storage at room temperature: more stable with high concentration of MWCNT like 4% and more. Versus the final % of MWCNT in the dispersion, we recommend a minimum duration of storage (maximum of one month) and apply a certain agitation with dissolver disk tool if storage of the dispersion during a certain time before use.
Quality Control of the dispersion of the master-batch into water •
The quality of the dispersion can be controlled using a North Bar tool. The picture below shows examples of satisfactory versus non-satisfactory dispersions. If the quality of the dispersion is not good, the product can be placed back in the chamber for an additional cycle.
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Second method suitable for the control of the quality of the dispersion is the visual control: o Dilution with final content of MWCNT at 1% of the produced dispersion has to be prepared for the control. o Put a micro-drop between two glass slides
Poor dispersion
Good dispersion
Safety and Handling Graphistrength® CW2-45 must be handled according to the Safety Data Sheet recommendations. Personal protection equipment includes: Dust mask FFP3, gloves, safety glasses and protective suit. Graphistrength® CW2-45 is provided in dried pellet form. Graphistrength® CW2-45 is provided in plastic drums of 5 kg and carton drum with PE bag of 50 kg net. Graphistrength® CW2-45 should be stored in dry place, preferably in its sealed original container, at temperatures between 0 and 45°C. In these storage c onditions, shelf life is more than one year. Dispersion produced with this master-batch has to be stored in plastic drum. Consult the product’s safety data sheet for additional information on properties, hazards and handling.
Arkema – 420, rue d’Estienne d’Orves – 92705 COLOMBES Cedex – FranceTel.: + 33 1 49 00 80 80 - Fax: 33 1 49 00 83 96
www.arkema.com
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