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

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.

Effect of Cellulose Nanofibers’ Structure and Incorporation Route in Waterborne Polyurethane–Urea Based Nanocomposite Inks

“…As can be observed, the differences in rheology translated in different printing capacities and precision, and the content, type and incorporation route of the reinforcement played a part in the printability of the materials, with systems with stronger gel-like behavior showing better results, as previously reported [ 6 , 44 ]. Overall, all systems showed a good extrusion process thanks to their shear-thinning behavior.…”

“…Among 3D printing techniques, direct ink writing (DIW) and specifically cold extrusion offer further advantages, such as the possibility of obtaining ready-to-use parts without the need for high temperatures or further processing [ 4 , 5 ], which is of special interest for the biomedical field, where the possibility of working at low processing temperatures and the lack of additional components or steps for shape stabilization could be extremely beneficial. However, inks for cold extrusion 3D printing must meet very specific rheological properties in order to allow good printability and show good shape fidelity [ 6 ]. For this, inks must show shear-thinning behavior and defined but not too high yield points in order to allow extrusion but retain the given shape.…”

Soft Mechanosensing via 3D Printing: A review

“…Usually, the printing of these materials goes through their dispersion in solutions, with the synthesis of waterborne PUs overcoming the issues related to the use of organic solvents. [74,75] In general, it can be stated that DIW offers the broadest selection of printable materials among the 3D-printing technologies, being suitable also for hydrogels, [76] ceramics, [77] epoxy resins, [78,79] photocurable resins, [80,81] and multi-material printing. [82] As for the composites, the problems are the same as the other extrusion technologies: for instance, the unsuitable size of the fillers and agglomeration can cause nozzle clogging.…”

“…Usually, the printing of these materials goes through their dispersion in solutions, with the synthesis of waterborne PUs overcoming the issues related to the use of organic solvents. [ 74,75 ]…”

Improved Sound Absorption Performance of Melamine/Waterborne Polyurethane Composite Foams Using Cyclic Freeze–Thawing

“…With increasing environmental awareness, water-based PU has attracted attractive attention from both the industrial and academic spheres. Waterborne polyurethane (WPU) is widely used in adhesives, ink printing, coatings, and other fields for its nontoxicity, environmental friendliness, good toughness, and strong adhesion . However, there are few reports on WPU in the field of sound absorption.…”