The Leading Journal for the Tyre Recycling Sector

The Leading Journal for the Tyre Recycling Sector

Wild Garlic for Devulcanisation

Wild garlic has been discovered to assist in devulcanisation, according to South African researcher Dr Jabulani Mnyango.

According to the South African Herald newspaper, Dr Jabulani Mnyango, a researcher at Nelson Mandela University, has found that using wild garlic in a devulcanisation process can assist in delivering a higher quality end product.

Nelson Mandela University scientist Dr Jabulani Mnyango has found an eco-friendly method to recover high-quality rubber from end-of-life tyres using wild garlic. 

Rubber has to be vulcanised (hardened) to make it usable in tyres. To retrieve and re-use the rubber, it needs to be devulcanised.

“The problem is that the current methods used for devulcanisation include chemical agents that are toxic to the environment and are expensive,” Mnyango said.

“What I did for my PhD research, starting in 2019, was to focus on an indigenous plant, Tulbaghia violacea, as a readily available and non-toxic agent to devulcanise waste tyre rubber in an eco-friendly manner.”

The wild garlic has a high level of sulphur compounds and Mnyango wondered if they could help with devulcanisation.

His PhD research was co-supervised by Professor Percy Hlangothi, director of the Centre for Rubber Science and Technology at NMU, and Prof Christopher Woolard, a chief researcher in renewable polymers and fuel and rubber chemistry at Stellenbosch University

For the first year of his PhD, Mnyango focused on understanding the chemical makeup of the plant to determine how stable its sulphur compounds were when subjected to heat in the thermochemical devulcanisation process.

He also needed to work out how to treat these sulphur compounds so that they did not degrade with heat before they could be used for devulcanisation. 

“In my second year, I started smearing the extract onto the rubber, and then put it in a reactor with CO² in the form of dry ice.

“I then had to work out the devulcanisation optimal conditions from the super critical point of CO², looking at the combination of temperature, pressure, time, and amount of extract.

“This required testing and retesting many times over. It took me a full three years to get it right and to achieve the product — devulcanised rubber.” 

Mnyango added; “However, while I have shown that there is an alternative form of devulcanisation that can be utilised in place of the commonly used toxic chemicals, the process still requires energy in the form of electricity to devulcanise.

“The gain is that the plant process requires far lower temperatures to achieve this than the common chemical process but to completely green the process would require addressing the electricity issue.” 

Source: Herald (South Africa)