Wood-based plastic made childproof

German researchers working on a plastic made from renewable raw materials instead of petroleum have optimised it in such a way that it is even suitable for toys and for products such as Nativity figurines.

The 'liquid wood' material, known as Arboform, has been developed by researchers at the Fraunhofer Institute for Chemical Technology ICT and the Fraunhofer spin-off Tecnaro.

"The cellulose industry separates wood into its three main components – lignin, cellulose and hemicellulose," said ICT team leader Emilia Regina Inone-Kauffmann. "The lignin is not needed in papermaking, however. Our colleagues at Tecnaro mix lignin with fine natural fibres made of wood, hemp or flax and natural additives such as wax. From this, they produce plastic granulate that can be melted and injection-moulded."

Car parts and urns made of this bio-plastic already exist, but it is not suitable for toys in this form. To separate the lignin from the cell fibres, the workers in the cellulose industry add sulphurous substances. However, children's toys should not contain sulphur because, for one reason, it can smell very unpleasant.

"We were able to reduce the sulphur content in Arboform by about 90 per cent, and produced Nativity figurines in cooperation with Schleich GmbH. Other products are now at the planning stage," says Tecnaro's managing director Helmut Nägele. This is a challenging task: Sulphur-free lignins are usually soluble in water – and therefore unsuitable for toys. On no account must they dissolve if they are left out in the rain or if children suck them. With the aid of suitable additives, the Tecnaro scientists were able to modify the bio-plastic to survive contact with water and saliva undamaged.

To ensure that the material is recyclable, the team produced components, broke them up into small pieces, and re-processed the broken pieces – ten times in all. "We did not detect any change in the material properties of the low-sulphur bio-plastic, so that means it can be recycled," said Inone-Kauffmann.

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