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One critical challenge for commercial products manufactured via material extrusion 3D printing is their inferior mechanical properties in comparison to injection molding; in particular, 3D printing leads to weaker properties perpendicular to the plane of the printed roads (z-direction). Here, rapid (≤20 s) post-processing of 3D printed carbon- poly(ether ether ketone) (PEEK) with microwaves is demonstrated to dramatically increase the modulus, such that the z-direction after microwave processing (2.7–3.8 GPa) exhibits a higher elastic modulus than the maximum in any direction for the as-printed part (2.3 GPa). Additionally, the stress at break in the z-orientation is increased by an order of magnitude by microwaves to slign with the stress for other print orientations in the as-printed state. The rapid heating and cooling by coupling of the microwave energy with the carbon filler in the PEEK does not increase the crystallinity of the PEEK, so the increased mechanical properties are attributed to improved interfaces between printed roads. This simple microwave post-processing enables large increases in the elastic modulus of the printed parts and can be tuned by the microwave power. As PEEK is generally difficult to print, these concepts can likely be applied to other commercial engineering plastic filaments that contain carbon or other fillers that are microwave active to rapidly post process 3D printed thermoplastics without requiring modification of the filament with selective placement of microwave absorbers. Additionally, these results demonstrate that the average crystallinity does not necessarily correlate with the strength of 3D printed semicrystalline plastics due to the importance of the details of the interface between adjacent printed roads.
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Molecular Mass Engineering for Filaments in Material Extrusion Additive Manufacture
3D printing of thermoplastics through local melting and deposition via Material Extrusion Additive Manufacturing provides a simple route to the near net-shape manufacture of complex objects. However, the mechanical properties resulting from these 3D printed structures tend to be inferior when compared to traditionally manufactured thermoplastics. These unfavorable characteristics are generally attributed to the structure of the interface between printed roads. Here, we illustrate how the molecular mass distribution for a model thermoplastic, poly(methyl methacrylate) (PMMA), can be tuned to enhance the Young’s modulus of 3D printed plastics. Engineering the molecular mass distribution alters the entanglement density, which controls the strength of the PMMA in the solid state and the chain diffusion in the melt. Increasing the low molecular mass tail increases Young’s modulus and ultimate tensile strength of the printed parts. These changes in mechanical properties are comparable to more complex routes previously reported involving new chemistry or nanoparticles. Controlling the molecular mass distribution provides a simple route to improve the performance in 3D printing of thermoplastics that can be as effective as more complex approaches.
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- Award ID(s):
- 2011289
- PAR ID:
- 10463700
- Date Published:
- Journal Name:
- Journal of polymer science
- ISSN:
- 2642-4169
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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