Wood chemistry turns nut shells into sunscreen

Monday, 19 August, 2019


A team of international scientists has found an eco-friendly way to produce potential sunscreens from cashew nut shells.

Via a chemical process called xylochemistry (wood chemistry), the team of ‘green chemists’ from the University of the Witwatersrand, Johannesburg — along with researchers from Universities in Germany, Malawi and Tanzania — is working on ways to produce useful compounds from wood and other fast-growing, non-edible plant waste.

From cashew nut shells, the team has produced new compounds that show good UVA and UVB absorbance, which may be applied to humans, livestock, polymers or coatings to protect them from sun damage. The research is published in the European Journal of Organic Chemistry.

UV rays are damaging to most materials, with exposure leading to the discolouration of dyes and pigments, weathering, yellowing of plastics, and loss of gloss and mechanical properties. In addition, UV exposure can lead to sunburn, premature ageing and the development of potentially lethal melanomas in humans and animals.

To mitigate UV damage, both organic and inorganic compounds are used as UV filters. Ideal organic UV filters display a high UV absorption of UVA rays (ranging from 315–400 nm) and UVB rays (280–315 nm). One important family of UV absorber molecules is derived from aromatic compounds known as phenols, which contain a hydrogen-bonded hydroxyl group that plays an important role in the dissipation of absorbed energy.

For example, an organic compound known as oxybenzone is a common ingredient that has also been added to plastics to limit UV degradation. Apart from their petrochemical origin, a major drawback of current UV protection agents is their negative effect on aquatic ecosystems associated with poor biodegradability.

As a result, there is growing attention from regulatory bodies and stricter regulations are being enforced on the production of sun-filtering products.

“With the current concerns over the use of fossil resources for chemical synthesis of functional molecules and the effect of current UV absorbers in sunscreens on the ecosystem, we aimed to find a way to produce new UV absorbers from cashew nut shell liquid (CNSL) as a non-edible, bio renewable carbon resource,” said lead author Professor Charles de Koning from the Wits School of Chemistry, together with Till Opatz from Johannes Gutenberg University in Mainz, Germany.

“Cashew nut shells are a waste product in the cashew-farming community, especially in Tanzania, so finding a useful, sustainable way to use these waste products can lead to completely new, environmentally friendly ways of doing things,” Prof. de Koning said.

The team has filed a patent application in order to commercialise the process in South Africa.

Image caption: A graphic representation of the international collaboration to find sustainable solutions to produce useful compounds. Image credit: Wits University.

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