As part of Women's Month, the Council for Scientific and Industrial Research (CSIR) Centre for Nanostructures and Advanced Materials principal researcher Dr Maya John has showcased some of the plastics the centre has developed that are compostable or biodegradable and can be used by industry with their existing machinery and processes.

The CSIR bio-based plastic formulations meet technical and mechanical properties, are compostable and can be used in local manufacturing. The formulations can be considered viable alternatives for conventional single-use plastics, John says.

The formulations biodegrade within 120 days, have a shelf-life of two years, can help the plastics industry reduce its greenhouse-gas emissions and help create bio-based industries, she notes.

The aim of the work by the centre's bioplastic and advanced polymers research group was not to replace all plastics, but rather to replace single-use plastic products that are not recovered, recycled or that are contaminated, with compostable or biodegradable alternatives.

Further, bio-based polymers can be recycled like petroleum-based polymers and extruded as pellets to make new products; can be chemically recycled to get monomers to form new polymers; and can also be organically recycled or composted during which the product biodegrades to CO₂ and water, she adds.

The team tested the properties of the bio-based polymers, in terms of mechanical strength, stiffness and shelf-life, which were found to be comparable to petroleum-based products with the added advantage of biodegradability, John says.

As part of its research, the team developed compostable plastic single-use medical devices, including diagnostics kits, surgical aprons and angle connectors for oxygen masks in partnership with a company in Cape Town that produces medical devices and apparel using conventional medical-grade plastics.

The company manufactured the medical apparel and devices for the CSIR at its facility, which shows that these new bio-based materials can be used by existing local manufacturing companies to produce goods, she emphasises.

These bio-based medical plastic products were also tested, and the formulation was found to comply with strength, stiffness and toughness properties of the plastic the company currently uses.

"Our biodegradation tests showed that our formulation saw 93% biodegradation of carbon in the material to CO₂ in 120 days," John notes.

The bio-based medical products were also subjected to other tests to comply with medical uses, including human immunodeficiency virus tests, whether lateral-flows strips that were added to the material would have any effect, and tests over three days at 60 °C to see whether the material maintains its dimensions.

These tests were positive in terms of the usability of the material, she says.

The CSIR Nanostructures and Advanced Materials team developed a range of products, including three-dimensional- (3D-) printed biodegradable plastic espresso coffee pods, biomedical surgical aprons, plant-fibre reinforced composite panels for vehicles, bagasse-biopolymer cutlery, compostable mulch films for the agricultural sector, and other 3D-printed cellulose and biopolymer prototypes.

The team also reports that toys can be made from the new plastics and that bio-based polymers can serve as a future material that can be 3D-printed.

"These bio-based plastics are only a long-term solution if they are compostable or biodegradable into CO₂ and water, and leave non-toxic residues," says John.

The CSIR has a biodegradation testing facility where it tests the biodegradability of products under various atmospheric and environmental conditions in terms of biodegradability standards. The standards require at least 90% of the carbon in the material must biodegrade to CO₂ within six months.

"Merely claiming that a product is biodegradable is incomplete. It needs to state under what conditions it is biodegradable, such as in soil or compost, and what the timeframes are for biodegradation."

The team tested its bio-based plastic formulations and found that the material disintegrated completely within 70 days and biodegraded 93% to CO₂ and water within 120 days. The residues were analysed for the presence of toxic chemicals and whether they would be suitable for plant growth. Both tests were positive, she adds.

"We started with biomass- or plant-based sources, such as sawdust and post-harvest green agricultural waste, as alternative feedstocks to petroleum-based feedstocks."

Further, the production of virgin polymers from fossil sources is responsible for about 60% of the plastics industry's greenhouse-gas emissions. Biopolymers, in comparison, have a much lower carbon footprint; about 50% less than conventional plastics.

The main benefits of plant-based plastics include a reduced carbon footprint, that they are mechanically recyclable, biodegradable in suitable conditions, compliant in terms of strength and properties and are processable by local manufacturing companies, John says.

The team also developed bio-based plastics alternative products that have added functionality, such as improved fire resistance, reduced water absorption or not fracturing on impact. The aim was to ensure that the new materials can be used in advanced industrial sectors, she adds.

This project to develop an action plan to transition South Africa from conventional to more sustainable plastic alternatives was funded by the government of Japan through the United Nations Industrial Development Organisation.