Green nanocomposite gels based on binary network of sodium alginate and percolating halloysite clay nanotubes for 3D printing.

Alginate hydrogels with embedded rigid percolating network of halloysite clay nanotubes were evaluated as a novel ink for 3D printing. Hydrophilic alginate macromolecules adsorbing on halloysite stabilize the network of the nanotubes and form their own network of interlaced polymer chains. The effect of halloysite content on the structure and properties of the hydrogels was studied by rheometry, thermogravimetric analysis, FTIR-spectroscopy, dynamic light scattering, transmission electron microscopy, and 3D cryo-electron microscopy. Hydrogels demonstrate a very pronounced shear-thinning at extrusion and rather quick viscosity recovery after extrusion assigned to rapid rearrangement of the network structure promoted by mobile alginate chains. Even at low volume fractions (up to 0.054) the nanotubes reinforce the hydrogel increasing its storage modulus up to 650 Pa and inducing the appearance of yield stress. These properties make the alginate/halloysite hydrogels promising for the application in 3D printing for fabrication of green and sustainable nanocomposite materials made from natural components.