Waterborne Polyurethane-Urea-Based Composite Inks for 3D Printing with Enhanced Properties

Composite inks valid for direct ink writing (DIW) three-dimensional (3D) printing have been prepared using a waterborne polyurethane-urea (WBPUU) as a matrix, κ-carrageenan as a rheological modulator, and graphene as a nanoreinforcement. The rheological characterization of the inks showed strong dependence on their formulation, with inks prepared with 2 wt % carrageenan presenting the most suitable properties for DIW, which was clearly evidenced by the high shape fidelity shown by the 3D printed parts obtained from these inks. Properties of the printed parts were related not only to their formulation but also to the additives' incorporation route. In this regard, inks prepared by in situ addition showed highly reinforced properties, signaling the favored formation of WBPUU/additive interactions by this method. For supplying electrical conductivity, the presence of graphene in the material was not sufficient since it seemed to remain embedded in the WBPUU matrix, and thus, the application of a graphene coating was necessary.