4D Printing of Recyclable Lightweight Architectures Using High Recovery Stress Shape Memory Polymer

Ang Li,Guoqiang Li,Adithya Challapalli

doi:10.1038/s41598-019-44110-9

Ang Li, Guoqiang Li + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-44110-9

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Journal: Scientific Reports	Publication Date: May 20, 2019
Citations: 70	License type: open-access

Affiliation: Louisiana State University

Abstract

High-performance lightweight architectures, such as metallic microlattices with excellent mechanical properties have been 3D printed, but they do not possess shape memory effect (SME), limiting their usages for advanced engineering structures, such as serving as a core in multifunctional lightweight sandwich structures. 3D printable self-healing shape memory polymer (SMP) microlattices could be a solution. However, existing 3D printable thermoset SMPs are limited to either low strength, poor stress memory, or non-recyclability. To address this issue, a new thermoset polymer, integrated with high strength, high recovery stress, perfect shape recovery, good recyclability, and 3D printability using direct light printing, has been developed in this study. Lightweight microlattices with various unit cells and length scales were printed and tested. The results show that the cubic microlattice has mechanical strength comparable to or even greater than that of metallic microlattices, good SME, decent recovery stress, and recyclability, making it the first multifunctional lightweight architecture (MLA) for potential multifunctional lightweight load carrying structural applications.

Highlights

Where E is the Young’s modulus of the foam, Es is the Young’s modulus of the cell-wall material, ρ is the density of the foam, ρs is the density of the cell-wall material, σe is the elastic collapse stress of the foam, σp is the plastic collapse stress of the foam, σy is the yield strength of the cell-wall material, and n is the scaling factor
Bisphenol-A glycerolate diacrylate (BPAGA) or bisphenol-A glycerolate dimethacrylate (BPAGMA) have been widely used as a component in coatings, adhesives, and dental materials for decades, and lately they have been adopted as a component in 3D printing resin formulation due to their photo-sensitivity and good thermal and mechanical properties
It was shown that the UV-cured BPAGMA has good shape memory effect with high recovery stress and energy output

Summary

Introduction

Where E is the Young’s modulus of the foam, Es is the Young’s modulus of the cell-wall material (solid), ρ is the density of the foam, ρs is the density of the cell-wall material (solid), σe is the elastic collapse stress of the foam (cell wall buckles), σp is the plastic collapse stress of the foam (cell wall yields), σy is the yield strength of the cell-wall material (solid), and n is the scaling factor. Bent by the concentrated transverse load, and with additional axial load transferred from the nodes of the unit cell to the beam, can buckle, leading to lower collapse strength of the foam. With 3D printing, we can join all the beams at the nodes of the unit cell, thereby eliminating the concentrated bending load at the beam mid span, and leading to increased local buckling load and higher collapse strength in the foam or lattice. Current 3D printable materials cannot satisfy the desired properties for MLAs. various metallic microlattices with excellent mechanical strength have been 3D printed and shown as promising components for future engineering applications[23,24,25,26], shape memory metallic microlattices have not been developed. Most existing 3D printable vitrimers lack the mechanical strength and shape memory effect required for load carrying structures, such as space applications[45,46,47]

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