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With all these new materials 3D printing is expanding into, it’s easy to forget the work done with the basics. Take PLA, for example: probably the most common and easy to use material on the market. There’s been a trend of taking PLA and giving it novel new characteristics and today’s story is no different. Thai researchers have developed luminescent PLA composites that display desirable heating and mechanical characteristics. The findings could be crucial in the development of tools for dark environments, in toy manufacturing or art installations.

The research is a joint project between the Rajamangala University of Technology and Kasetsart University in Bangkok. The study focused on the fabrication of luminescent PLA composite filaments for 3D printing applications, looking into ceramic phosphor as the ideal candidate due to its small particle sizes. This effectively makes it suitable for blending with polymer matrices.

The group found that novel Sm3+ doped MgAl2O4 phosphor not only improved luminescence but a range of other characteristics as well. The material displayed lowered glass-transition, crystallisation and melting temperatures for the PLA. Luminescent intensity was heightened with the increasing ratio of phosphors. The researchers also detected strengthened mechanical properties in composites with surface modification and better mechanical properties of the composite filaments as evident in a series of mechanical tests.

Creating Luminescent Filaments

Luminescent PLA Composite Filaments Display Improved Characteristics

Making the filament required a series of processes. Firstly, they had to prepare the phosphor itself using a laborious multi-step approach. They dissolved a coupling agent (3-aminopropyltriethoxysilane, 2 wt%) in deionized water and stirred it for 5 min, allowing hydrolysis reactions. Then, they added the phosphor in the solution, feeding it continuous heat and stirring it at 80 °C for an hour. This aided in surface modification. Then, they washed and dried the final powder at 80 °C for 6 h.

Making the material and filament is the next step. Combining polylactic acid (PLA) pellets and fillers requires extrusion into filaments using a twin-screw extruder. These filaments are then to be cut into master-batch pellets. Next, they mixed the PLA pellets and the master-batch pellets with a single-screw extruder into the composites with final compositions of 0, 1, 2, 3 and 4 phr. They were then ready to print the neat PLA and the composite filaments using a Wanhao Duplicator i3 plus 3D printer.

Next, the resulting Luminescent PLA Composite needed testing and measuring. PL measurements showed luminescent properties of 3D printed samples resembling those of phosphor powders. Additional tests included Fourier- Transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Differential scanning calorimetry. Standard procedures, ASTM D638, ASTM D790, ASTM D2240 and ASTM D256 tested tensile strength, flexural strength, hardness and izod impact strength, respectively.

Images courtesy of researchers, retrieved via Research Gate. The full paper is also available here

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