Making good use of recycled plastics

Tom Shelley reports on the latest views on using recycled plastics in engineered products.

Making products and components out of polymers that are partly or wholly recycled is becoming a more and more commercially attractive option now that prices of virgin plastics continue to move upwards with the price of oil and recycling itself becomes more commonplace. However, some plastics recycle better than others, properties depend on grade, history, and possible contamination, and while some recycled plastics are getting into engineered products, they are not normally considered appropriate for critical applications requiring high mechanical performance. Alastair Green, in charge of research and development at AK Industries in Hereford, believes using recycled plastic in a design 'should certainly come out cheaper', adding that there is 'not a huge amount of difference' between the properties of virgin and recycled materials. He does point out, however, that 'you normally cannot run 100% recycled'. How easy it is to use recycled polymer depends on what the polymer is. Green says some, including polypropylene (PP), polystyrene (PS) and unfilled polyacetals (otherwise known as polyoxymethylene or POM), are relatively easy to use. He also points out that there is "close to 100%" of recycled PET (polyethylene terephthalate) in plastic bottles. However, he notes there are problems with some engineering polymers, especially when they contain fillers. At present, Green says his company is not producing many products made with recycled plastic due to customer and product requirements. The exception is a device called the 'Warmit', which uses waste water from domestic showers to warm incoming cold water. The heat exchanger for this, which was developed with Pera, is made from recycled Acrylonitrile Butadiene Styrene (ABS). It will eventually go on the commercial market after it has been approved by WRAS – the Water Regulations Advisory Scheme. Green claims that, as regards designing products to make use of recycled plastic, there little that designers had to worry about. A bigger issue in his opinion, was designing products made of plastic in such a way that the plastic parts could more easily be recovered for recycling. A company whose products are based on 100% recycled polymers is Trojan Services in Chichester, which makes cable troughs – including designs that can be walked on and driven over – for the UK rail and other industries. Managing director Stewart Wellens says that its 'TroTrof' and 'TroTred' products are made from 'post-industrial polyolefins'. Unlike traditional concrete products, the tops can be screwed down to resist vandals and cable thieves and the TrofTrof units can withstand loads of 25 tonnes and the TroTred units (pictured, left), 6 tonnes, without suffering damage. Off cuts resulting during installation are recycled back to production. Ford also uses recycled plastics but only in certain components. Post-consumer recycled polymers are used by them to make underbody parts such as aerodynamic shields, splash shields and radiator air deflector shields. In the US, the latest example is the engine cam cover on the 3 litre V6 2010 Ford Escape. Repurposed nylon carpeting made into nylon mesh is moulded into cylinder head covers for the Ford 3 litre 'Duratec' engine, as used in to 2010 Ford Fusion and Escape. In Europe, the Ford Focus uses recycled polymer in the battery tray and wheel arch liners. Materials engineers are in the process of determining whether recycled polymer can be used for similar components in the global Ford Focus coming to North America and Europe in 2011. "Sustainable materials need to meet the same high standards for quality, durability and performance as virgin material; there can be no compromise on product quality," said Valentina Cerato, Ford materials engineer in Europe.