Putting the wattle to work

It’s not often that a tree gets a bad rap, but that certainly seems the case with the Australian black wattle.

Feared as an alien invader, a non-indigenous tree species, which represents a major threat to our environment, the black wattle left unchecked certainly poses a problem as an ecosystem wrecker. But farmed under carefully controlled conditions, the black wattle’s bark produces high quantities of tannin for use in the leather tanning industry.

It’s a curious dichotomy—on the one hand, black wattles are the equivalent of tree insurgents and are being removed across the country and, on the other hand, there are more than 120 000ha of the species under formal cultivation, yielding a lucrative crop. But, there is a drawback.

The tannin produced from wattle bark is not perfect, but thanks to a Thripfunded programme, scientists at the University of the Free State (UFS) are tackling the problem head-on, using chemistry and some serious brain power to unravel the complexities of wattle tannin.

‘Chemistry is an applied science,” says Professor Jan van der Westhuizen of UFS’s department of chemistry. ‘Most of the progress we have made in chemistry over the years is based on a specific application—solving problems. And most of the problems we have solved and are currently working on solving are industry-related problems.”

Van der Westhuizen’s take on chemistry is that because of its ability to find cures for the world’s industrial headaches, it is a major wealth creator. ‘It’s true: chemistry creates wealth,” he says. ‘We, the chemists, are the people who design new systems and new products. The problems that we solve have to do with improving the quality of life. We invent new drugs and organic chemists find ways to produce these in large quantities. And the world’s polymer scientists make plastics and synthetic cloth for clothing. A large majority of the everyday things we buy have been created from polymers.”

Which is a good thing, because tannin is a polymer. And a complex one at that. ‘Our tannin project aims to improve the quality of tannin extracts from black wattle and provide a better material, which will ultimately benefit society—creating wealth, jobs and stimulating the economy,” says Van der Westhuizen.

‘To do this we need to implicitly understand exactly what black wattle tannin is. We need to use chemistry to unravel it, unlock its secrets and find ways to improve it,” he says. There is something in black wattle tannin that causes a problem when it comes to the colour of leather.

‘The tanned leather can turn a reddish colour, particularly if the leather is left in the sun,” says Dr Neville Slabbert, general manager of Mimosa Central Cooperative in Pietermaritzburg—Van der Westhuizen’s industry partner in the black wattle project. ‘When it comes to products such as leather clothing and leather for car seats, which are often produced in light colours, this change in colour is unacceptable.”

Although MCC’s main customers use traditional methods of tanning to produce mainly sole, bag, belt and shoe-upper leathers, Mimosa also wants to improve on these tanning methods and expand opportunities, especially for rural farming communities.

‘Besides yielding particularly high amounts of tannin from the bark, black wattle wood is a good source of fibre for paper manufacture and this means that very little of the harvested trees is wasted,” says Slabbert.

The MCC has enjoyed a long association with the research department at the UFS, which was revitalised at the beginning of this year when Van der Westhuizen and his team came on board. Between five and 10 students are offered on-the-job research training on the project each year, using groundbreaking chemistry techniques, such as mass spectrometry, counter-current chromatography and solid state nuclear magnetic resonance to understand fully the behaviour of the polymers produced from the wattle bark.

‘If we get our chemistry right, we will be able to control the colour variations and other chemical reactions in the wattle tannin,” says Van der Westhuizen.

The need to move back to using more natural vegetable extracts (including wattle extract, or mimosa extract, as it is known commercially) has never been more relevant because the alternative method—using chromium salts—is less environmentally friendly.

Black wattle bark contains extremely high quantities of tannin and represents the perfect opportunity to produce a safe, sustainable source for the leather industry worldwide. ‘The world is moving away from oil-based products such as plastics and focusing more on agriculturally based raw materials such as tannin,” says Van der Westhuizen.

‘But while they are more environmentally friendly, they are generally more complex and harder to standardise,” he says, adding that, as a result, the chemistry involved in understanding them is a lot more difficult.

‘In the case of tannin there are two applications we focus on. The first is the tanning of leather in which you take a piece of skin and treat it with tannin so that its properties change—it becomes non-putrifiable, waterproof, durable and soft to the touch. The other application we look at is in adhesives. Tannin, as a polymer and treated with a cross-linking agent, can be gelled and used in the manufacture of panel products such as chipboard and plywood.” Van der Westhuizen says that his work is exciting and cutting-edge.

‘Applied research of this nature is far from mundane and boring. You cannot innovate or make a contribution unless your research is the best. Research is imperative. It must be novel, new and innovative. This innovation can be used to make new products or improve existing ones. Chemistry is therefore crucial. And if your chemistry is good, you can go far.”

The black wattle tannin industry is a case in point. It’s doing remarkably well—besides the leather that is used locally in shoes, clothing, furniture and by vehicle manufacturers, up to 98% of the 35 000 tonnes of tanning products that MCC’s members—NTE Company and UCL Company—produce are exported.

‘There is significant international demand for wattle-based tanning products,” says Slabbert. ‘Black wattles are a sustainable crop and grow fairly easily. This means there is a huge opportunity for rural and small-scale farmers, especially in far-flung parts of KwaZulu-Natal and the Eastern Cape, who could benefit from renewed global tannin demand,” he says.

Black wattle trees are typically harvested after 10 years of growth. Because it is a legume, the wattle naturally enriches the soil with nitrogen and new saplings can be planted soon after the adult trees have been felled.

Cash crops such as maize also thrive between planting seasons. Animals can browse between the trees, thus giving farmers multiple earning opportunities from the land under their control.

‘Once the team at UFS have used their innovative processes to resolve the chemical problems that still exist, I am confident that our production methods—and the tanning compounds we produce—will go from strength to strength.”

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