IISc researchers extend recycled plastic life with upcycle twist

Researchers at the Indian Institute of Science (IISc) have developed a new procedure that tries to address one of the thorniest problems plaguing recycled plastic waste — increasing the derived product's life.

As a solution to a global environment problem, recycling of plastic waste has been limited in its recovery scope and applications, with studies showing that only 12 per cent of the waste generated worldwide is recycled; and the plastic also loses strength and quality with recycling, shortening the derived product’s life.

Now, IISc researchers have devised an upcycling process that could offset this quality depletion and transform disposed plastics into tougher, mechanically stronger versions, with the development having the potential to reduce the "burden on landfills".

Prof Suryasarathi Bose and his research group at IISc’s Materials Engineering Department converted post-consumer recycled acrylonitrile-butadiene-styrene copolymer, or PCR ABS plastic, into ABS Vitrimer, which retains the qualities of the plastic even after multiple recycling runs.

The group has filed an application for patenting the conversion process.

ABS is extensively used in trolley bags, helmet casings, Lego toys, automobile bumpers, keyboard keys, switchboards, shells of appliances like water purifiers, mixers, and grinders.

Noted for its toughness and cost-efficiency, ABS is a popular choice for applications that involve high-impact resistance. “Like many conventional thermoplastics, ABS loses its strength and toughness after multiple recycling. The upcycling of ABS using this unique strategy helps retain, even improve, its properties like tensile strength and elasticity,” Prof Bose told DH.

Vitrimers are a novel class of polymeric materials that contain thermally reversible covalent bonds. At elevated temperatures, these bonds can rearrange themselves, helping the materials retain their mechanical strength.

The researchers cut used trolley bags and, with “a little chemistry”, were able to upcycle the ABS. They synthesised a dynamic crosslinker — that binds together different polymer chains in the PCR ABS — from an FDA-approved, bio-based non-edible oil. It was then used to convert PCR ABS into ABS Vitrimer, through conventional reactive extrusion, an eco-friendly processing technique that does not involve the use of solvents.

According to market and consumer research firm Statista, the production volume of the global ABS plastic recycling market was 2.6 million metric tons in 2022 and is forecast to reach more than 4 million metric tons by 2028.

Upcycled, upgraded

A recycler, typically, shreds ABS into small pieces and places them in an extruder where the polymer is melted again to make wires that are chopped into pellets. The new technology does not require additional infrastructure. The manufacturers can buy back these pellets and mould them into new products. The upcycled ABS displays only “negligible change” in mechanical properties even after five cycles of reprocessing.

“The manufacturer can use the upcycled ABS and make the same product with improved properties. If it comes back to the recycler, it can be upcycled back into the market, ensuring a closed-loop, circular economy. This lessens the burden on landfills where the ABS is left to become microplastics, eventually,” Prof Bose said.

The findings open possibilities for advanced research on the applications of ABS Vitrimers, including upcycling of ABS blended with other polymers. The researchers are also studying if the technology enables the production of smart polymers through 3D printing of upcycled PCR ABS.