The first phase of the study was focused on selecting a monomer that would act as the building block for the polymer resin. The monomer had to be UV-curable, have a relatively short cure time, and display desirable mechanical properties suitable for higher-stress applications. The team, after testing three potential candidates, eventually settled on 2-hydroxyethyl methacrylate (we’ll just call it HEMA).
Once the monomer was locked in, the researchers set out to find the optimal photoinitiator concentration along with an appropriate blowing agent to pair the HEMA to. Two photoinitiator species were tested for their willingness to cure under standard 405nm UV lights which are commonly found in most SLA systems. The photoinitiators were combined in a 1:1 ratio and mixed in at 5% by weight for the most optimal result. The blowing agent – which would be used to facilitate the expansion of the HEMA’s cellular structure, resulting in ‘foaming’ – was a little trickier to find. Many of the tested agents were insoluble or difficult to stabilize, but the team finally settled on a non-traditional blowing agent typically used with polystyrene-like polymers.
The complex mixture of ingredients was used to formulate the final photopolymer resin and the team got to work on 3D printing a few not-so-complex CAD designs. The models were 3D printed on an Anycubic Photon at 1x scale and heated at 200°C for up to ten minutes. The heat decomposed the blowing agent, activating the foaming action of the resin and expanding the size of the models. Upon comparing pre- and post-expansion dimensions, the researchers calculated volumetric expansions of up to 4000% (40x), pushing the 3D printed models past the dimensional limitations of the Photon’s build plate. The researchers believe this technology could be used for lightweight applications such as aerofoils or buoyancy aids due to the extremely low density of the expanded material.
Post time: Sep-30-2024
