Cars have got to be one of the most emotive products around. Four wheels have come to represent all manner of characteristics from symbols of freedom through to wealth and status.
So with everyone involved in automotive design and manufacture, it's not surprising that a versatile material like plastics, which also has many different character profiles, is becoming increasingly important.
The absolute 'Holy Grail' of plastics in automotive design is metal replacement. The problem is that it's not usually a simple case of a straightforward swap and other aspects of the design often need to be altered. Counter intuitively, and despite looking lighter and sleeker, modern cars are getting heavier. Each extra bit of complicated kit adds up - whether it be airbags or engine parts. A 1966 Ford Mustang, for example, weighed around 1,100kg compared with 1,500kg of today's Toyota Prius.
Replacing metal parts with plastics helps reduce weight, thereby also minimising carbon footprint and increasing engine efficiency. In the case of electric vehicles lightweighting can also help them increase range. Most electric cars on the market have a range of around 100 miles. And although currently out of the 30 million vehicles in the
BASF, for example, has been working with Daimler on the development of the electric concept car Forvision. A breakthrough development with this smart car was the first ever all-plastic wheel made from BASF's high performance material Ultramid Structure 50% long glass fibre reinforced nylon 6. BASF says the material is as stable as metal and reduces weight by up to 30%. These lightweighting developments have helped the Forvision achieve a range of105 miles, up from 86 miles achieved by the Smart's third-generation electric car, which will be available next year.
Electronic-friendly polymers
But using plastics in electric cars requires the development of electronic-friendly polymers. In response DuPont has developed Zytel HTN PPA EF resins. DuPont automotive development consultant Rob Coates says the material could be used for metal replacement in electric vehicle motors or batteries. DuPont also supplies Vamac AEM, a halogen free flame retardant (HFFR) elastomer, for thin wall insulation in battery cables leading to weight reduction and operation at the high temperatures generated by high voltage electric currents.
Lightweighting vehicles also reduces carbon footprint. Coates adds: "We have European legislation coming in that governs the average C02 emissions of an OEM to around 130g of C02 per KM per vehicle. That's what a lot of the big manufacturers are moving towards."
Another key area that car manufacturers have been looking at is improving engine efficiency while simultaneously reducing the size of the engine. "A family vehicle two litre engine in the future might become 1.6 ltr 1.3 litre or even a 1 litre, engine potentially," says Coates. Due to the ease of moulding complex shapes, plastics are ideal materials for integrating several parts into one leading to weight savings.
"But a lot of these things put the temperature, and the thermal load, up in the engine bay," says Coates. Plastics companies have been working on polymers that can withstand these pressures. DuPont has responded with its Zytel PLUS range of polyamide based resins that have improved heat aging performance at over 200oC for 3,000 to 4,000 hours over vehicle life.
Many of the design trends within automotive interlink with sustainability - lightweighting, reducing carbon, developing electric cars - and there are also structural polymers with a green bent available. These are becoming popular in electric cars, for example.
DuPont offers a range of biobased materials launched in 2008. "Sorona EP is a polyester material that can be used for fibre production going into carpets and fabrics or it can be injection moulded," says Coates. "It can also be glass reinforced for use in more structural components."
Sorona EP has surface finish that doesn't require painting and for this reason was used in the heating and ventilation system of the Toyota Prius. DuPont also produces a renewably sourced (RS) version of its Hytrel TPC-ET family, which is a thermoplastic elastomer as well as RS versions of its Zytel PA range, which are ideal for use in more structural components.
Using plastics can be cheaper than using metals although 'green' materials are often more expensive than standard engineering plastics. However, these economics may change with the uptake of alternatives becoming more widespread. Oil-based plastics are also linked to the price of oil going up and as Coates points out, "with biomass derived materials the economic drivers are different to those of their oil based equivalents".