Additive manufacturing, otherwise known as three-dimensional (3D) printing, is a rapidly growing technique that is increasingly used for the production of polymer products, resulting in an associated increase in plastic waste generation. Waste from a particular class of 3D-printing, known as vat photopolymerization, is of particular concern, as these materials are typically thermosets that cannot be recycled or reused. Here, we report a mechanical recycling process that uses cryomilling to generate a thermoset powder from photocured parts that can be recycled back into the neat liquid monomer resin. Mechanical recycling with three different materials is demonstrated: two commercial resins with characteristic brittle and elastic mechanical properties and a third model material formulated in-house. Studies using photocured films showed that up to 30 wt% of the model material could be recycled producing a toughness of 2.01 ± 0.55 MJ/m3, within error of neat analogues (1.65 ± 0.27 MJ/m3). Using dynamic mechanical analysis and atomic force microscopy-based infrared spectroscopy, it was determined that monomers diffuse into the recycled powder particles, creating interpenetrating networks upon ultraviolet (UV) exposure. This process mechanically adheres the particles to the matrix, preventing them from acting as failure sites under a tensile load. Finally, 3D-printing of the commercial brittle material with 10 wt% recycle content produced high quality parts that were visually similar. The maximum stress (46.7 ± 6.2 MPa) and strain at break (11.6 ± 2.3%) of 3D-printed parts with recycle content were within error the same as neat analogues (52.0 ± 1.7 MPa; 13.4 ± 1.8%). Overall, this work demonstrates mechanical recycling of photopolymerized thermosets and shows promise for the reuse of photopolymerized 3D-printing waste.
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Mechanical behavior of bio‐inspired composites made of co‐continuous geopolymer and 3D‐printed polymer
Geopolymers (GPs) are emerging, low‐density ceramic materials that are simple to manufacture, with high elastic modulus and strength, albeit with low toughness. Fiber reinforcements have been used to achieve varied ductile behaviors, but little is known about the GP addition to polymeric frame structures. Thus, drawing inspiration from the nanostructure of bones, this paper investigated an interpenetrating, co‐continuous composite consisting of a GP as the stiff but brittle phase, and a 3D‐printed polymer (PA12 White) as the soft and deformable phase. The composite mechanical properties and failure modes were studied experimentally using uniaxial compression and four‐point bending tests. The co‐continuous network constrained brittle cracking within the GP and reduced strain localization in the polymer. The results showed that the composite had higher strength (56.11 ± 2.12 MPa) and elastic modulus (6.08 ± 1.37 GPa) than the 3D‐printed polymer and had higher toughness (5.98 ± 0.24 MJ/mm3) than the GP for the specific geometries examined. The shape effect study demonstrated that cubic structures had higher elastic modulus and strength but at the expense of lower toughness when compared to rectangular prism structures. The study of scale effects indicated that increasing the number of periodic unit cells while maintaining consistent bulk dimensions led to augmented strength and toughness, albeit without statistically significant alterations in elastic modulus. Thus, this paper presents an experimental realization of a novel, bio‐inspired, interpenetrating, GP–polymer composite design, offering improved strength and toughness. It also provides valuable insights into the shape and size effects on the mechanical properties of this new composite.
more » « less- NSF-PAR ID:
- 10495432
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Applied Research
- ISSN:
- 2702-4288
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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