Turning orange peel into plastic

British scientists are pioneering a novel way of recycling that turns orange peel into plastic.

The technique relies on high-powered microwaves that can degrade the tough cellulose molecules of plant matter so that they release volatile gases that can be collected and distilled into a liquid product.

These valuable biodegradable chemicals can then be used in water purifiers, cleaning agents and plastics. Researchers behind the process say it is 90 per cent efficient and works not just on orange peel but almost any plant-based waste such as straw or coffee grounds.

James Clark, professor of green chemistry at the University of York, said he is building a small demonstrator facility to show the novel recycling scheme can be scaled up in order to suit industrial applications.

"It will be able to cope with tens of kilograms an hour. We believe it is the right scale to prove to people that this is a viable technology," Professor Clark said.

"You dice the peel and put it into a microwave field. You then focus the microwaves as you would with a domestic microwave oven but at higher power," he said.

"The microwaves activate the cellulose and that triggers the release of chemicals or further chemical reactions inside the orange peel," he told the British Science Festival at Bradford University.

Volatile chemicals are released in the process, including d-limonene, which is responsible for the distinctive smell of citrus fruit and is used in cosmetics, the cleaning industry and as a biological insecticide.

"As you produce the volatiles you strip them off continuously. It's a continuous process. You feed the peel into a microwave zone and have a pipe that takes off the volatile fractions as they are produced," he said

"The unique feature of our microwave is that we work at deliberately low temperatures. We never go above 200C. You can take the limonene off or you can turn limonene into other chemicals," he said. "It works really well with waste paper. It can take a big range of bio-waste material."

York University has set up the Orange Peel Exploitation Company with Brazilian and Spanish partners to test the idea of using orange peel residue left behind from the juice-making industry in the two countries.

"There are eight million tonnes of orange residue in Brazil. For every orange that's squeezed to make juice, about half of it is wasted. What we've discovered is that you can release the chemical and energy potential of orange peel using microwaves," Professor Clark said.

"Orange peel is an excellent example of a wasted resource. Brazil is the largest producer of orange juice in the world," he said.

The idea is to take the technology to places where large amounts of plant waste are already collected, such as a power stations that collect biomass for burning or a farming district that packs or processes foodstuffs, Professor Clark said.

"We are talking to farmers who are already concentrating a lot of biomass for palletising before going to power stations about the possibility of locating a facility in one of these centralised units," he said.

"We're talking to power stations about materials that they are already bringing in for microwaving as well. If you put typical waste into our system before you burn it, the calorific value doubles compared to what it was before," Professor Clark told the meeting.