Manufacturers of products incorporating plastics are finding recycled materials increasingly attractive, both for economic and marketing reasons. Alistair Rae looks at the options available and the latest developments in recycled post-consumer plastic waste.
Modern life would be impossible without the features and versatility plastics bring to products and packaging, but a lot of resources are consumed in their manufacture and they are often disposed of inefficiently. Fortunately designers now have more opportunities to select materials that incorporate recycled materials. It makes economic sense, reduces the need for crude oil and, consequently, reduces greenhouse gas emissions.
There are five high-volume families of plastics. These are the polyethylene family (low-density and high-density PE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (solid PS and expandable EPS) and polyethylene terephthalate (PET). Between them they account for about 75 per cent of all plastics demand (Fig.1).
For post-consumer recycling, plastic types are usually referred to using the Society of Plastics Industry (SPI) resin identification codes (Table 1). Most plastics can be recycled, but they have to be separated into their different polymer types. Furthermore, while thermoplastics can be remelted, thermosetting plastics need to be reprocessed in other ways.
Polyethylene (resin codes 2 and 4) is widely used in domestic and industrial applications and its typical uses are crates, containers and drainage pipes. It is fully recyclable, though any contaminants and hazardous substances have first to be removed.
Polypropylene (resin code 5) is widely used for engineering products, especially in the automotive sector, and can be recycled up to 50 times without any reduction in strength.
Polyvinylchloride (resin code 3) is used in the construction industry and for packaging. PVC is recyclable unless this is prevented by the presence of other polymers.
Polystyrene (resin code 6) is an excellent packaging and insulation material, but it is difficult to recycle. However, it can be reprocessed into new plastics for use in the building industry.
Polyethylene terephthalate (resin code 1) is commonly used for lightweight plastic bottles and (depending on purity) can be recycled into new PET products or processed into other polyester products and fibres/fabrics.
When recycled, plastics are often used in lower-grade products than their first use (sometimes referred to as downcycling) but high-purity recycled material can be added to virgin polymer when making new products. Known as 'closed loop recycling', this is also the name of a UK company that reprocesses plastic bottles to create food-grade quality material (see panel).
"Separating of waste into different polymer types used to be an issue, along with the quality of material being recycled, but techniques have improved," says Stuart Foster, business development director for Recoup (Recycling of Used Plastics Limited), an independent organisation devoted to developing plastics recycling in the UK, promoting best practices and providing educational and training tools. "The situation in the UK at the moment is that bottle recycling capacity exceeds the amount being recycled, although domestic mixed plastic is the opposite, with sorting and reprocessing at an early stage of development. The commercial sector is very much dependent on the quality of material being recycled. In the end it is entirely down to economics whether recycled material can compete with virgin polymer."
There is more to recycling than just getting more use out of waste material, as the market is driven by consumers who make selections based partly on environmental impact and manufacturers who recognise the need to demonstrate their 'green' credentials as part of their marketing mix.
The EU's Waste Electrical and Electronic Equipment (WEEE) Directive sets recycling and recovery targets for all types of electrical goods, and this is now resulting in large volumes of post-consumer plastic materials becoming available for recycling rather than being sent to landfill (Fig. 2). Plastic re-processors like Axion Polymers take this waste from the electrical and electronics sector for recycling.
"We start with untreated waste, which includes a whole range of plastic materials and contaminants, and using the factory process we have developed we remove the impurities and produce high-grade polymer resin for use in injection moulding," says Keith Freegard, director of Axion Polymers. "Production batches are traceable back to the origin of the raw material as part of the certified manufacturing process."
This material is used by European injection moulders and extruders looking for economies, where the value of using recycled material is, in itself, low. It is also used by brand-leading OEMs wishing to promote themselves as users of closed-loop recycled raw materials.
From fridges to washing machines
A project run by Axion and the Waste & Resources Action Programme (WRAP) has helped Indesit to introduce recycled content into its Hotpoint Aquarius and Ultima washing machines. The back access ports of the washing machines are now covered with a plate made of recycled ABS that was produced from shredded plastic waste recovered from fridges.
"This groundbreaking project shows that closed-loop recycling in electrical equipment from UK WEEE is commercially viable on a large scale," says Peter Maddox, Head of manufacturing at WRAP. "We encourage other manufacturers to follow this example."
Mike Birch, environment manager at Indesit Company, states: "We now plan to roll out the innovation to a range of our washing machines and washer dryers that are produced each year. The cumulative cost and raw material savings will be significant and the improved price helps to deliver a project with environmental benefits, which we felt was the right thing to do."
Freegard adds: "The important thing is for us to make designers aware of these recycled material sources so they know that they are available to be used."
Mobile phones have recently been launched by manufacturers such as Sony Ericsson (C901), Nokia (3310 Evolve) and Motorola (Moto W233 Renew) incorporating recycled plastics; one of their marketing messages is that these products are more environmentally friendly than earlier models (Fig.3). This is a worldwide market in which CO2 reduction and recycling are seen as important by many customers.
Low-grade mixed waste is the most difficult to recycle, and this has resulted in new technologies being developed. Powder impression moulding (PIM) is a patented process that allows products to be made from mixed low-grade waste plastics that would otherwise be sent to landfill. For example, 2k Manufacturing produces Eco-Sheet for use as an alternative to plywood in the building industry. "Eco-Sheet has replaced plywood on the site hoarding for St David's retail development in Cardiff," says Matthew Locke, innovation manager at Bovis Lend Lease. "The boards have survived the Cardiff weather for two years now with no water damage. This material reduces the risk of injury, is easier to use than plywood and will reduce the carbon footprint of our temporary works."
Another approach is that taken by Plastinum Polymer Technologies, which has developed the proprietary Blendymer mechanically-induced process and two new types of plastic, Infinymer and Ultrymer.
Infinymer is supplied in pellet form ready for processing with standard plastic manufacturing techniques (Fig.4). SenterNoven, an agency of the Dutch Ministry of Economic Affairs, evaluated this material and concluded that it should be considered as a new material, rather than waste.
Ultrymer is a high-tech hybrid plastic in which several polymers previously considered incompatible are linked using the Blendymer process. Plastinum says that using the Blendymer technology enables high-performance plastics to be developed to match specific criteria.
Whatever the source of the recycled material or the way in which it is handled, there are opportunities for engineers and designers to incorporate them within their products and processes. The amount of scarce resources saved (energy and oil) and the environmental benefits (reduced landfill and CO2 emissions) would be a good justification, but the marketing advantages can also be significant, with both manufacturers and consumers seeking ways to show that they are behaving responsibly. Washing machines, mobile phone cases, building components and packaging are just a few examples of reuse in an industry that will grow as pressure increases to recycle more materials.