We are looking for a simple method to separate compact bundles of (very fragile and stiff, not to be compared with mineral wool for example) chopped ceramic fibers. The fibers shall be dispersed in water (ideally without an additive, but if you have an idea with additive, we are also grateful). This task may seem simple, but the fibers are prone to break and if stirred using several methods, they accumulate at the front of the stirrer and thus filtrate themselves and form compact bundles.
Only by ultrasonication the fibers could be completely separated without damage. This is still unsatisfactory, as it needs a lot of time.
We would be grateful if you could provide any useful hint or experience.
While considering SiC dispersions in aqueous media, the following discussion may possibly help: https://www.researchgate.net/post/Which_is_the_suitable_binder_and_dispersant_for_making_SiC_slurry
Well, thanks for the answer. Meanwhile, I have solved the challenge in a quite easy way. But fracture of the fibers could not be completely prevented.
1. Dilute to a very low fiber concentration. This means: 0.5 g/L or lower. Yes, you read correctly. Higher fiber concentration lead to massive aggregation and self filtration. It´s not comparable to spherical particles and surprised me. Regarding that, this paper might help:
Mueller, S., Llewellin, E. W., & Mader, H. M. (2010, April). The rheology of suspensions of solid particles. In Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences (Vol. 466, No. 2116, pp. 1201-1228). The Royal Society.
2. Use a HIGH energy stirrer/disperser. We used a propeller mixer with chamfered edges (to prevent accumulation of fibers). A disc might work as well. Make sure that there are not sharp edges, because they are prone to form fiber agglomerations. Don´t worry, fibers need several minutes to fracture. Just don´t stir too long.
3. Prevent to fibers to settler or reagglomerate again. You can use a thickener based on cellulose for example.
4. Dispersants did not help. Neihter polyacrylates nor PDADMAC. The Zeta Potential changed or was reversed, but the overall Zeta-Potential in solely water was high enough. Note the following: fibers of said dimensions are no colloidal particles and the effect of surface area is very limited, which likely is the reason for the low effect of dispersants.
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