In the recently published study, “Investigating Closed-Loop Manufacturing with Acrylonitrile-Butadiene-Styrene (ABS) Over Generations Using Additive Manufacturing,” the authors investigate Mazher Iqbal Mohammed, Daniel Wilson, Eli Gomez-Kervin, Bin Tang, and Jinfeng Wang the effects of FFF 3D printing on acrylonitrile butadiene styrene (ABS) during multiple recycling processes.

As 3D printing grows in popularity, so does the amount of plastic discarded. And while PLA is biodegradable, ABS is a typical plastic that has no environmental issues. In this study, the researchers hoped to examine FFF systems in terms of their low power consumption, which could be a suitable path to more sustainability in manufacturing.

The researchers began using virgin ABS that went through two consecutive phases of filament extrusion and 3D printing. In this study, they used 100 percent recycled 3D printed ABS that was made into filament for reuse. This allowed them to study parameters and the potential for defects along the way.

“Studies have previously reported that changes in the melt index and mechanical properties of ABS occur after recycling through injection molding and casting,” the researchers said. “To the best of our knowledge, however, no study has investigated the impact of multiple closed-loop recycling phases using AM, where ABS quality and thermal process regimes differ from those made by molding processes.”

Virgin ABS pellets were extruded as filament and then 3D printed into parts. The researchers made sure that plastic was only used from a single source to ensure that differences are directly comparable. Granules were produced in a uniform size and separated with a sieve with a mesh size of 5 mm.

“To determine the average pellet / granule size, 20 ABS pellets or granules were randomly collected from the source batch and their longest lengths measured and averaged,” the researchers explained.

(a) Relative pressure orientations of the tensile and compression test certificates and (b) universal testing machine on which mechanical tests were carried out.

While the study focused on the use of virgin ABS, the research team also experimented with one-time, two-time recycled ABS as well as samples of 90, 80, 70, 60, 50, 40, 30, 20, and 10% virgin ABS. They assessed extrusion flow rate, 3D printing and characterization, polymer analysis and mechanical property characterization.

In some cases the “unevenness of the granules” leads to clogging as well as to “sticking” due to sharp edges. The researchers tried to stir granules during extrusion to maintain the correct filament flow. Ultimately, the research team found that the FFF 3D printer worked very well with recycled ABS and over several generations of recycling. They viewed the process as successful and as a process that could actually serve as a valid “multi-generation” manufacturing method.

(a) (i) A graph showing the change in extruded filament diameter for changes in extrusion temperature; For the sake of clarity, only results for virgin, 10% recycled, 50% recycled and 100% recycled ABS are shown. (a) (ii) Temperature differences when extruding a respective ABS mixture relative to a filament diameter of 1.75 mm. (b) (i) extrusion flow rate for different ABS blends comprising different percentages of recycled to virgin material; For the sake of clarity, only results for virgin, 10% recycled, 50% recycled and 100% recycled ABS are shown. (b) (ii) Extrusion flow rate for the various ABS blends in forming filaments with a diameter of 1.75 mm.

“FFF has arguably the greatest commercial success right now in the production of concept prototype devices by design firms or in the production of ornaments such as toys and models that generally do not have strict mechanical strength requirements. We therefore believe that using recycled ABS made from single or double recycled variants could potentially replace virgin polymer filaments in such applications, as the measured drop in mechanical strength would not affect the function of the end parts or prototypes. The researchers concluded.

“The FFF has significant potential for sustainable management of ABS plastics through their reintroduction into broader industrial manufacturing and potentially creating value from an otherwise growing burden on resource recovery sites and landfills.”

ABS is one of the most popular 3D printing materials for users of all levels, whether they are making new materials and composites, refining adhesion issues, or even creating jobs. What do you think of this news? Let us know your thoughts! Join the discussion on this and other 3D printing topics on 3DPrintBoard.com.

Compressive stress comparison for 3D printed samples printed using (a) virgin, (b) once recycled, and (c) twice recycled ABS. (d) Summary of the compressive stress for the various ABS samples printed in the two spatial orientations. (e) Summary table of results for all compression test samples.

[Source / Images: ‘Investigation of closed loop manufacturing with Acrylonitrile Butadiene Styrene (ABS) over multiple generations using Additive Manufacturing’]

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