(777d) 3D Printed Shape Memory Objects Based on Olefin Ionomer of Zinc-Neutralized Poly(ethylene-co-methacrylic acid)

3D printing enables the net shape manufacturing of objects with minimal material waste and low tooling costs, but the functionality in these objects is generally limited by available materials, especially for extrusion based printing such as Fused Deposition Modeling (FDM). Here we demonstrate shape memory behavior in a complex object, a helix, fabricated by 3D printing with FDM using a commercially available olefin ionomer, Surlyn 9520, which is zinc neutralized poly(ethylene-co-methacrylic acid). The spring-like helix can be mostly straightened to a temporary shape and then recover in 3 dimensions to the initial shape on heating to 70 °C. The performance of 3D printed samples were compared to compression molded analogs using standard shape memory cycles using dynamic mechanical analysis (DMA) with a constant 1 MPa stress for generating the temporary shape. The initial fixity was similar between the printed and compression molded sample, but the recovery was much lower for the 3D printed sample due to the higher strain (lower modulus in the 3D printed part) and higher residual stress. Interestingly, the fixity and recovery on subsequent cycles to the initially recovered permanent shape is greater for the 3D printed than compression molded part. Moreover, the programmed strain can be systematically modulated by inclusion of porosity in the printed part without adversely impacting the fixity or recovery. FDM can be used to directly form thermoplastic shape memory polymers into complex shapes that can be recovered with the appropriate trigger.