4D printing: processability and measurement of recovery force in shape memory polymers

The fourth dimension in 4D printing refers to the ability of materials to alter its form after they are produced, thereby providing additional functional capabilities and performance-driven applications. Stimuli materials provide this capability through the use of shape memory polymers. For this research, the property of programming the determined shape is achieved through controlled heat under laboratory conditions. This paper shows the potential to process and experiment with thermoplastic polyurethane as a shape memory material. Taking a step further, we ascertain the properties of this material through extrusion-based additive manufacturing processes and produce parts for testing. The results show that the characteristics of the 3D printed parts successfully retain the property of the shape memory and the recovery force allows this to be utilised as a mechanical actuator. The recovery stress has been recorded to be between 0.45 and 0.61 MPa (at feed rate 990 mm/min). The maximum level of recovery stress is similar to the same material being processed through conventional compression moulding. Lastly, we designed and produced a coil as an actuator to demonstrate that the same material can be extended to other applications.