Curiously, I just realized I haven’t heard of clay-filled PLA filament before, but it turns out that it does exist; the clay increases shear thinning, thermal stability, crystallinity, and rigidity, and at 40% clay the print can be fired to ceramic, though melt viscosity increases. Other mineral fillers currently on sale include zircon and sapphire, both of which claim to be sinterable in the same way. I’d think that including clay would also lower the cost and increase strength without firing, but that doesn’t seem to be the case yet; in this experiment the clay actually decreased tensile strength in most cases by 5-20%.
They bought a prefunctionalized clay whose preparation I don’t understand at all:
For nanocomposites preparation, an organo-modified layered silicate (Cloisite 30B, Southern ClayProducts Inc., Gonzales, TX, USA), modified by methyl, tallow, bis-2-hydroxyethyl, and quaternary ammonium chloride, having a basal interlayer spacing d001 = 18.5 Å, was used.