Quote:Printers that use a stereolithography process, also known as SLA, work slightly differently. Models are still built up layer by layer, but instead of extruding melted plastic, a high definition beam of light hardens a photosensitive liquid resin into thin layers. It allows for much higher detail given the precision of the beam of light, but it can still be a time-consuming process.

What the EPFL researchers are doing differently is, instead of using a single laser to build up a model layer by layer, they’re bombarding a vat of resin, or other photosensitive materials such as biological gels, with multiple lasers coming from several directions at the same time. By carefully controlling the direction of the beams and their intensity, a 3D model seemingly appears to materialise out of thin air, in a process that takes about 30 seconds.

Quote:To turn cooking oil into usable resin requires a fairly straightforward chemical process. Once the oil is filtered and cleaned (a rare time when overcooked, extra crispy french fry bits aren’t welcome) a photoinitiator is added which causes the oil to undergo a significant change in its physical properties when exposed to light. The resulting resin is then suitable for 3D printers that use stereolithography techniques to build up a 3D model. Instead of melting plastic that’s solid at room temperature and extruding thousands of thin layers to build up a model, stereolithography starts with a container filled with ever-increasing thin layers of liquid resin that are hardened with light until a model is finished.

A litre of cooking oil waste yielded 420 milliliters of resin, which is a little less than half of its original volume. One test involved 3D printing a plastic butterfly and the results included details as small as 100 micrometres in size, while the model itself was thermally stable meaning it wouldn’t melt or become structurally fragile at or above room temperature. Furthermore, the 3D printed models are completely biodegradable, with a sample that was buried in the ground losing 20 per cent of its overall weight after hungry microbes worked away at it for a period of two weeks.

Quote:ArticleVisible Light Photoinitiator for 3D-Printing of ToughMethacrylate Resins

Bernhard Steyrer1, Philipp Neubauer1, Robert Liska2and Jürgen Stampfl1,*1Institute of Materials Science and Technology, TU Wien, 1060 Wien, Austria;bernhard.steyrer@tuwien.ac.at (B.S.); e1328884@student.tuwien.ac.at (P.N.)2Institute of Applied Synthetic Chemistry, TU Wien, 1060 Wien, Austria; robert.liska@tuwien.ac.at*Correspondence: juergen.stampfl@tuwien.ac.at; Tel.: +43-1-588-013-0862Received: 28 November 2017; Accepted: 18 December 2017; Published: 19 December 2017

Abstract: Lithography-based additive manufacturing was introduced in the 1980s, and is still the method of choice for printing accurate plastic parts with high surface quality. Recent progress in this field has made tough photopolymer resins and cheap LED light engines available. This study presents the influence of photoinitiator selection and post-processing on the thermo-mechanical properties of various tough photopolymers. The influence of three photoinitiators (Ivocerin, BAPO,and TPO-L) on the double-bond conversion and mechanical properties was investigated by mid-infrared spectroscopy, dynamic mechanical analysis and tensile tests. It was found that 1.18 wt %TPO-L would provide the best overall results in terms of double-bond conversion and mechanical properties. A correlation between double-bond conversion, yield strength, and glass transition temperature was found. Elongation at break remained high after post-curing at about 80–100%, and was not influenced by higher photoinitiator concentration. Finally, functional parts with 41 MPa tensile strength, 82% elongation at break, and 112◦C glass transition temperature were printed on a405 nm DLP (digital light processing) printer.

Keywords: photopolymer; photoinitiator; additive manufacturing; digital light processing