Recycling devices built with plastic cases and other components, such as mobile phones, mp3 players, and personal digital assistants, is difficult and requires repetitive manual labour. However, a new approach to creating the fastenings and tabs for such devices based on the shape-memory effect in plastics could mean that disassembling such devices at end of life could be automated.
The approach would allow valuable components and metals to be recovered more efficiently from the millions of devices discarded every year, according to research to be published in the International Journal of Product Development.
Habib Hussein and David Harrison of the School of Engineering and Design at Brunel University, UK, explain that Europe's WEEE regulations, the Waste Electrical and Electronic Equipment directive, are aimed at tackling the growing stream of waste electrical and electronic goods in order to reduce landfill usage and waste that is incinerated. The regulations mean that there are now incentives to design equipment that is more recyclable.
"Product disassembly offers one method for reducing the landfill and enabling compliance with legislative targets by optimising the recovery of hazardous and valuable components during the recycling process. However, manual disassembly is a time-consuming and thus costly process, in terms of either financial or social impact," the researchers say.
They have now investigated the possibility of Active Disassembly using Smart Materials (ADSM). ADSM uses materials that can act as fasteners within a product, which at product end of life, can be undone simply by direct heating. This releases the fasteners causing the device case to fall apart without screws having to be undone or stiff clasps opened manually. This is one important design feature that might make recycling electronic devices with plastic cases much easier.
Their concept relies on the so-called shape memory effect in engineering plastics, or polymers. Plastics can be fabricated in one shape - the unfastened state - and then moulded a second time into a new shape - the fastened state. When the fastened state version is heated, the plastic will revert to its original, unfastened state, as it retains a molecular memory of the form in which it was originally produced.
The researchers have developed a case-fastening device based on one such shape memory polymer. Their tests demonstrated that lowering the device at end of life into hot water, leads to the fasteners reverting to their unfastened state and the case falling apart, on agitation. They have also shown that the fasteners retain their integrity for at least two years without disassembling spontaneously.
"Standard-engineering polymers may be used to produce reliable long-term shape memory effect fastening devices to enable the efficient end of life treatment of WEEE," the researchers conclude.
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