Greek researchers decide the impact of recycling on ABS filament

Recycling method flowchart.  Image via HMU.

New research from Greek Mediterranean University studies the change in mechanical properties of ABS filaments in response to recycling. The scientists created an experimental simulation of the recycling process, focusing on the thermomechanical treatments and running a series of mechanical tests on FFF printed parts. As a result, they were able to quantify the impact of repeated recycling at every stage of the process.

Recycling method flowchart. Image via HMU.

Non-biodegradable filaments

Materials science plays an important role in 3D printing, as the raw material used is often as important as the machine in the manufacture of high-performance parts. With the most popular 3D printers – FFF systems – the thermoplastic filaments used can be very damaging to the environment and are mostly not biodegradable. ABS, the second most popular filament after PLA, is one such material. The next best option is to recycle, reuse and reuse ABS parts to keep them out of the landfill for as long as possible.

According to the researchers, several studies on the recyclability of 3D printing polymers have already been carried out. One of the methods tested was to extrude the plastics and inject them into new parts before testing their properties. Another method mentioned involved blending natural biodegradable materials into the polymer matrix to effectively reduce the raw amount of wasted polymer. However, a common theme is that the mechanical properties tend to deteriorate as the number of recycling stages increases. This can lead researchers to find a delicate “sweet spot” between the number of reuse cycles and maintaining the desired mechanical properties.

Recycled acrylonitrile butadiene styrene

Looking at the sweet spot, the researchers went out and bought a vat of fine ABS powder. The powder was drawn into virgin filament 1.75 mm in diameter and a Flashforge Inventor was used to 3D print a set of test samples. Tensile, compression, flexural, impact strength and microhardness tests were carried out on the initial samples and the results recorded. Any remaining filaments were recycled using a polymer grinder and re-extruded, monitoring mechanical properties at each stage. The ABS samples underwent a total of six reuse cycles.

Test device for the various mechanical tests.  Photos via HMU.Test device for the various mechanical tests. Photos via HMU.

Interestingly, the researchers found that the mechanical properties improve by around 30% by the fifth stage of recycling. The first few thermal cycles of the polymer realign the amorphous polymer chain links in the matrix and increase the existing molecular interactions. This improves the stability and the overall mechanical properties of the ABS. After the fifth cycle, chemical degradation begins to take hold and the polymer chains begin to decompose. The ABS chains are no longer as flexible and the glass transition temperature of the polymer increases. In addition to the environmental benefits, the results also demonstrate a “significant positive influence” of the ABS recycling process.

Mechanical test results.  Image via HMU.Mechanical test results. Image via HMU.

For more details, see the article entitled ‘Sustainable additive manufacturing: Mechanical reaction of acrylonitrile-butadiene-styrene via several recycling processes‘. It was co-authored by Nectarios Vidakis, Markos Petousis, Athena Maniadi, Emmanuel Koudoumas, Achilles Vairis and John Kechagias.

The investigation of FFF filaments is one of the most common in 3D printing raw material research. Last month the US Army unveiled a new one high strength Multipolymer filament It had worked on it, consisting of an ABS shell and a polycarbonate core. The filament is expected to help on the battlefield, producing business critical parts in a timely manner at a fraction of the cost of traditional parts. Elsewhere in Beijing, researchers have one Polycaprolactone (PCL) -based composite filament infused with starch with antibacterial properties.

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The picture shown shows SEM images of the tensile breaks. Image via HMU.

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