Design of a Waterborne Polyurethane-Urea Ink for Direct Ink Writing 3D Printing.

Julen Vadillo,Christophe Derail,Tamara Calvo-Correas,Izaskun Larraza,Nagore Gabilondo,Arantxa Eceiza

doi:10.3390/ma14123287

Abstract

In this work, polycaprolactone–polyethylene glycol (PCL–PEG) based waterborne polyurethane–urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink’s shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters.

Highlights

Direct ink writing (DIW) 3D printing is an additive manufacturing technique that has generated increasing interest in many fields in the last year, owing to the possibility of avoiding the limitations of other 3D printing techniques such as the use of volatile organic compounds or the need for high temperatures for its processing; this technique offers high resolution printing
waterborne polyurethane–urea (WBPUU) with low solid content presented a Newtonian plateau at very low shear rates, which was reduced in length and disappeared completely for WBPUU36 and WBPUU42
Inks based on a novel waterborne polyurethane urea combining in the soft segment of hydrophilic PEG and hydrophobic polycaprolaptone diol (PCL) were synthesized

Summary

Introduction

Direct ink writing (DIW) 3D printing is an additive manufacturing technique that has generated increasing interest in many fields in the last year, owing to the possibility of avoiding the limitations of other 3D printing techniques such as the use of volatile organic compounds or the need for high temperatures for its processing; this technique offers high resolution printing. This work focuses on understanding the relationship between rheological parameters and printing performance that can help with the design of suitable inks for DIW printing With this aim, novel waterborne polyurethane–urea (WBPUU) gels with different solid contents based on hydrophobic polycaprolaptone diol (PCL) and hydrophilic poly (ethylene glycol) (PEG) as soft segment, were synthesized and used as printing inks. The different synthesized inks were extensively characterized from the rheological viewpoint in order to establish a relationship between the structural parameters of the WBPUU based inks, their rheological properties, and their printing performance This would lead to an understanding of the complex behavior of physically crosslinked gel-based inks for DIW and establish valid criteria for designing inks with this novel technology

Materials

Synthesis of the WBPUU Inks

DIW 3D Printing of Prepared Inks

Characterization

Results and Discussion

Conclusions