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Three-Dimensional Printed Shape Memory Objects Based on an Olefin Ionomer of Zinc-Neutralized Poly(ethylene-co-methacrylic acid)
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posted on 2017-07-25, 00:00 authored by Zhiyang Zhao, Fang Peng, Kevin A. Cavicchi, Mukerrem Cakmak, R. A. Weiss, Bryan D. VogtThree-dimensional
printing enables the net shape manufacturing of objects with minimal
material waste and low tooling costs, but the functionality is generally
limited by available materials, especially for extrusion-based printing,
such as fused deposition modeling (FDM). Here, we demonstrate shape
memory behavior of 3D printed objects with FDM using a commercially
available olefin ionomer, Surlyn 9520, which is zinc-neutralized poly(ethylene-co-methacrylic acid). The initial fixity for 3D printed
and compression-molded samples was similar, but the initial recovery
was much lower for the 3D printed sample (R = 58%)
than that for the compression-molded sample (R =
83%). The poor recovery in the first cycle is attributed to polyethylene crystals formed
during programming that act to resist the permanent network recovery.
This effect is magnified in the 3D printed part due to the higher
strain (lower modulus in the 3D printed part) at a fixed programming
stress. The fixity and recovery in subsequent shape memory cycles
are greater for the 3D printed part than for the 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. These characteristics enable the direct formation
of complex shapes of thermoplastic shape memory polymers that can
be recovered in three dimensions with the appropriate trigger, such
as heat, through the use of FDM as a 3D printing technology.