Growing a solution to plastic waste

Polymers made from crops could provide an answer to increasingly tough environmental legislation governing the disposal of plastics in carrier bags and car interiors.

Engineers and chemists at Warwick Advanced Sustainable Technologies (WASTe), part of the Warwick Manufacturing Group, are developing plastics from triglycerides, the oil extracted from crops such as rape, flax and hemp.

These sustainable plastics could have an array of applications, said Malcolm Harold, senior fellow at the WMG. ‘They have a range of properties, the full breadth of which has not yet been established. Initial studies show the polymers are very versatile, and are suitable for uses ranging from fire-retardant foams to flexible plastics,’ he said.

Demand for sustainable polymers is likely to grow rapidly as governments worldwide impose taxes on the use of plastic, and strict regulations on its disposal. Bangladesh last week banned all plastic carrier bags, while Ireland imposed a e0.15 (9p) tax on every bag used in supermarkets.

The UK government is now considering what measures it should adopt, and there is increasing pressure on supermarkets to come up with viable solutions, said Harold. ‘If we can make carrier bags out of sustainable-origin plastic that is tough enough to be reused for about a month, we would have a completely environmentally friendly bag,’ he said.

The plastics could also come to the rescue of car makers, due to be hit later this year by the EU’s end of vehicle life directive.

The directive, which will make manufacturers responsible for recycling cars at the end of their working lives, is due to be introduced for new vehicles this year, and for all cars in 2007. ‘Cars have not been designed for disassembly in the past, so this is a nightmare for the manufacturers,’ said Harold.

In the case of flax and hemp it is not just the oil that can be extracted, but also a fibre crop. The plastic made from the oil can then be reconverged with this fibre to make composites, which could offer a replacement for glass-reinforced polyester, used as seat backs and bases within cars. ‘Glass does not break down very easily, but if car makers could use sustainable-origin plastic and fibre, it could be composted at the end of vehicle’s life.’

Sustainable-origin plastics are seen as the next step beyond recycling. Growing the crops would offer a financial lifeline to some farmers, and at the end of the product’s life it is simply broken down naturally with other biodegradable waste.

The plastics can be made out of a range of materials, including starch from potato crops. But while scientists have been aware of this for a number of years, producing plastic in this way has never been commercially viable because the processing costs have historically been too high.

Work now needs to be done to reduce these costs and develop markets for the polymers before they can be commercialised, said Harold. The government should also consider imposing a tax on non-sustainable plastics in order to encourage more firms to use the environmentally friendly polymers, he said.