3D reactive inkjet printing of aliphatic polyureas using in-air coalescence technique

An in-flight coalescence reactive inkjet printer has been developed to facilitate the in-air collision of two reactive microdroplets. This way precise volumes of reactive inks can be mixed and subsequently deposited on the substrate to produce the desired product by polymer synthesis and patterning in a single step. In this work, we validate the printer capabilities by fabrication of a series of 3D structures using an aliphatic polyurea system (isophorone diisocyanate IPDI and poly(propylene glycol) bis(2-aminopropyl ether) PEA-400). The influence of temperature and ink ratio on the material properties has been investigated. An increase in both IPDI and temperature facilitates the production of materials with higher Young's Modulus E and higher ultimate strength U. The possibility of printing different materials i.e. ductile (U = 2 MPa, ε _B = 450%), quasi-brittle (U = 14 MPa, ε _B = 350%), and brittle (U = 10 MPa, ε _B = 11%) by varying the printing process parameters using one set of inks has been presented. The anisotropy of the material properties arising from different printing directions is at the 20% level.