Nigeria: Assessing Properties of Recycled PET Powder for 3D Printing Feedstock

The topic of recycling is anything but new, but today innovative methods must be applied to the reuse of an influx of plastics, powders, and other materials being discarded in volume during 3D printing. Now, Nigerian researchers are discussing recycling in relation to PET powders in the recently published ‘Characterization of Recycled Polyethylene Terephthalate Powder for 3D Printing Feedstock.’

Recycling crushed plastic bottles into 3D printing material, authors C.N. Nwogu, Remy Uche, J.O. Igobkwe, and A.C. Okoronkwo examine the following characteristics of the powder:

• Flow property
• Coefficient of friction
• Bulk density
• Flexural strength
• Tensile strength

They also compare the recycled powder, which stems from the most commonly used plastic (bearing a number 1), to ABS, PLA, PVA, nylon, and HDPE in 3D printing.

“Plastic recycling reduces the approximately eight million metric tons of waste plastic materials that enter the earth’s ocean every year especially as plastic is non-biodegradable,” state the authors. “Before now, injection molding was the most commonly used manufacturing process for the fabrication of plastic parts but challenges like: high cost of designing new molds, presence of defects (bubbles, unfilled sections, sink marks, etc.), difficulty in producing complex parts in one piece and color inconsistency of molded part led to the discovery of 3D printing.”

Experimental determination of angle of repose

Both grade 1 and grade 2 forms of PET bottles were used, with five different experimental runs for each sample. In examining mechanical properties and flow-ability, the authors considered influencing factors like particle size and shape, density, porosity, and moisture. To determine powder flow property, they focused on the following:

• Angle of repose
• Compressibility index
• Dispersibility
• Flow through an orifice

Coefficient of friction (the relationship between frictional force and the ‘normal reaction between two objects’) was evaluated, along with bulk density—the ratio of the mass of the material to the occupied volume. The researchers point out that because bulk density is dependent on specific handling, ‘it is not an intrinsic property.’

Flexural strength test arrangement

Flexural strength was tested via the three-point bending test, allowing for the highest stress possible, with plastic powder extruded and then assessed on a flexural test machine. Tensile strength was tested by recording and plotting stress versus strain—with the amount of load weight finally breaking the wire acting as breaking strength—with a larger wire taking longer to break.

Mechanical properties of the PET powder in comparison with other plastics used for 3D printing.

“Experimental results show that both PET1 and PET2 have very good flow property. Also, comparison with other 3D printing plastics like: ABS, PLA, PVA, Nylon and HDPE shows that the PET powder is suitable for 3D printing,” concluded the researchers. “This study solves two major problems: plastic waste management and availability of locally produced 3D printing feedstock, which is currently the greatest challenge of 3D printing in Nigeria.”

Environmental concerns continue around the world with an even greater sense of urgency and effort to reduce the human footprint. This includes many different aspects of the material realm in 3D printing as so many new techniques and textures are evolving. Researchers and users on nearly every level are working to recycle from simply converting recycled plastics into new filament, recycling powder, and more attention-getting programs like using weed containers to create prosthetics or creating manufacturing alternatives like wood.

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