Researchers recycle 3D printing waste to develop carbon fiber reinforced PLA

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Researchers from the University of the United Arab Emirates are exploring the development of recycled composite materials using leftover 3D-printed PLA and carbon fiber waste.

Plastic consumption has been on the rise since its invention over a century ago, resulting in polluting waste that poses a challenge to both humanity and the rest of the earth’s ecosystem. In recent years in particular, there has been a push towards “green initiatives” that work to achieve a more sustainable society. One such initiative is recycling, where polymers such as 3D printed PLA waste are repurposed for new applications.

Similarly, composite materials have also seen increased demand over the years, with carbon fiber reinforcements having applications in both conventional manufacturing and 3D printing. Like polymers, the widespread use of carbon fibers in industries such as automotive and aerospace is fueling a growing waste problem.

Seizing the opportunity to kill two birds with one stone, researchers in the United Arab Emirates have found a way to reuse two different waste streams and meet the material needs of the composites sector.

A carbon fiber composite sheet. Image via Furo Systems.

Carbon fiber reinforced PLA

Polylactic acid, or PLA, is a bio-based polymer created from lactic acid from the sugar fermentation process. It was originally designed as a more environmentally friendly alternative to crude oil-based polymers and is technically biodegradable (albeit under industrial composting conditions). Besides being the most widely used polymer in the desktop 3D printing space, PLA also has a variety of applications in packaging, disposable cups, and more.

Although very cost effective, easy to process and easy to 3D print, PLA in its pure form offers poor thermal and mechanical stability, so it is not suitable for any high performance applications.

One way to improve material characteristics is to use additives such as carbon fiber reinforcements, as carbon fiber composites can offer an excellent mix of mechanical properties and heat resistance.

Carbon fiber scraps (a, c) were mixed with 3D printed PLA scraps (b) in a twin-screw extruder (d) to create recycled composite formulations.  Image via United Arab Emirates University.
Carbon fiber scraps (a, c) were mixed with 3D printed PLA scraps (b) in a twin-screw extruder (d) to create recycled composite formulations. Image via United Arab Emirates University.

How did recycled composites perform?

To create their recycled composite materials, the UAE team collected leftover 3D-printed PLA from the university’s prototyping labs. To obtain the carbon fiber element of the composites, scrap CF prepreg sheets and carbon fiber sheets were used. PLA and carbon fiber scraps were shredded, ground, blended, and melt-blended in varying percentages of additives.

The team then heat-pressed the formulations into dog bone specimens and used a universal testing machine to characterize the mechanical performance of the recycled composites.

Interestingly, the researchers found that the percentage of additive and the type of filler impacted mechanical performance. For example, the 20% carbon fiber composite had a higher modulus of elasticity than the 20% carbon fiber composite and prepreg sheets.

Overall, carbon fiber reinforcements generally improved the strength of PLA, with the 20% carbon fiber composite providing the highest yield strength. However, higher percentages of reinforcement have also been shown to have greater negative effects on the ductility of the material.

The work demonstrated that it is possible to recycle both PLA and carbon fiber to develop green composites with adjustable properties. The authors hope their project can serve as a springboard for others to investigate more efficient methods of creating recycled composites for industry.

Further details of the study can be found in the article titled “Carbon Fiber/PLA Recycled Composite”.

Stress-strain curves of recycled composite materials.  Image via United Arab Emirates University.
Stress-strain curves of recycled composite materials. Image via United Arab Emirates University.

There is an active market for environmentally friendly materials in 3D printing. This month, Brazilian petrochemical company Braskem launched its first line of sustainable 3D printing filaments. The launch includes the FL600EVA-BIO, a bio-based EVA filament derived from raw sugar cane, as well as recycled polyethylene (PE) and polypropylene (PP) offerings.

Elsewhere, at the University of Bath, researchers have recently developed a new way to decompose PLA material using only UV light. By adding sugar to its composition, scientists at the university’s Center for Sustainable and Circular Technologies (CSCT) have shown that PLA can actually degrade under natural conditions within hours.

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Featured image shows carbon fiber composite sheet. Image via Furo Systems.

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