An inside job – automotive interiors

Materials World magazine
1 May 2010

The use of natural and recycled materials has increased significantly in the automotive industry, with a range of interior components being incorporated into vehicle models. Gary Price discovers the factors that have influenced their surge in popularity

Stepping beyond fuel efficiency and ‘what’s under the hood’, automakers are now looking behind the wheel to see how best to exploit natural and recycled materials.

Ford has announced that it will roll out more than one million Lincoln and Mercury vehicles that feature recycled plastic bottles and even worn-out jeans in their seat cushions and backs by the end of the year, while French carmaker Citroën has turned to natural materials derived from hemp, bamboo and kenaf for the door linings of its ‘premium’ models.

But why is the automotive industry actively making this shift away from existing materials, such as polypropylene, for their interior components?

The ‘party line’ is, of course, that natural and recycled materials are a far more sustainable resource, and, in this age of growing environmental-consciousness, is something that consumers factor in when making purchasing decisions.

‘If we have two parts, one is recycled, the other one is virgin, and they perform and cost the same, why wouldn’t we use the recycled one?’ says Valentina Cerato, Materials Engineer at Ford’s Dunton Technical Centre in Essex, UK, who has been heading up the company’s efforts to ‘green’ its materials.

In 2008, nine per cent of all high-density polyethylene recycled juice cartons, laundry detergent bottles and other materials were used in automotive parts in the USA, according to the Association of Postconsumer Plastic Recyclers. A decade ago, that percentage was negligible.

But getting recycled materials to perform like their virgin counterparts isn’t easy.
‘Customers expect suede to look and feel like suede, even if the base materials are
polymeric’, explains Cerato.

She says that this is achieved through careful engineering, and adds, ‘interior wood accents, a common luxury-car cue, must exhibit rich colours and textures, whether it’s derived from a natural veneer or a more eco-friendly reconstituted wood veneer.

‘The use of recycled content is certainly important to our environmentally conscious Government and corporate fleet customers. It is more difficult to generalise the rest of the consumer base, but the beauty of a good recycled compound or textile is that you cannot tell the difference because the quality, durability and performance are not affected by the carefully selected percentages of recycled content that is used in the component.’

Ford’s approach to selecting these materials and quantities is guided by its ‘Product Sustainability Index (PSI)’, which scores the environmental, economic and social impact of Ford cars.

‘All of the materials containing recycled content are validated to the same standard tests for virgin materials found in the PSI. These list the minimum values required for each material. All of our interiors are allergy tested and recycled materials are no exception. Recycled materials also need to comply with the same stringent volatile organic compound emission requirements we use for interior virgin materials’, Cerato explains.

Cerato stresses that, when it comes to processing, there are no specific allowances that need to be made for recycled materials.

‘Anytime that you change from one material to another, even if they are both virgin, all of the parameters during the manufacturing process need to be tailored’, she says. ‘Yes, you will have to modify the temperature or pressure requirements for recycled materials, but this is no different to processing virgin materials.’

Of course, the cost and energy of producing a recycled compound in the first place must be considered, but Cerato says that these are not a major concern. Firstly, she explains, there is a long-term ‘cost stability’ when using recycled materials, as crude oil prices continue to fluctuate. Secondly, the energy needed to process these materials is offset by the benefits of incorporating them into vehicle components, recapturing the resource of virgin materials and diverting waste from landfill.

Natural selection

While striving to become sustainable to please customers is an important issue for carmakers to take on board, the recent surge in activity could perhaps be better explained by looking at a key piece of European legislation that has compelled the industry to take a closer look at the materials they use.

The End of Life Vehicle (ELV) Directive, which came into force in October 2000, requires all Member States to de-pollute all scrapped vehicles, avoid hazardous
waste and reduce the amount of waste placed in landfill sites to a maximum of five
per cent per car by 2015.

One way to reduce the amount of scrap sent to landfill is to recycle. Another might be to make every component biodegradable.

The automotive sector occupies a 31% share of natural fibre usage, greater than any other industry, says Dr Brett Suddell, Senior Materials Scientist at ADAS UK in Preston Wynne.

‘The most important of the natural fibres in terms of automotive applications are the
bast fibre group, so called because they come from the bast part of the plant’, explains Suddell. ‘These include materials like hemp, flax and kenaf.’

Plant bast is composed of an inner wood core surrounded by bundles of long hollow fibres and an outer protective skin. It is the bast that stabilises the plant and provides plant fibres with good mechanical properties. ‘They exhibit the greatest strength so it is only logical that these fibres are used for the more demanding composite applications,’ he adds.

While the so-called benefits of biodegradable materials have come into question recently, with regards to end-of-life disposal within a composite, Suddell argues that natural fibres are carbon neutral, meaning that they do not return excess CO2 into the atmosphere once they have been composted.

Market value

Tokyo, Japan-based chemical maker Toray Industries has begun mass production of its plant-and-petroleum fibres for use in automobiles.

The firm has developed various technologies for compounding plant-derived
polyesters with petroleum-based products, including a proprietary hydrolysis control technology and fibre spinning. The company says it expects to sell 200t of plant-based items such as door trims and ceiling upholstery in their first year of mass production, and has already begun supplying Toyota with materials, used most recently in the trunk and floor carpeting for the hybrid Lexus HS 250h. Toyota has also used a bio-based plastic to make spare tire covers, floor mats and vehicle trims.

‘There are two main production techniques for press moulding natural fibre composites used in automobile components,’ says Suddell. ‘The first technique involves blending natural fibres with polypropylene fibres or polyethylene to form mats that are then used in a number of different layers. Alternatively, non-woven mats are interspersed with a layer of polypropylene fibres that are then hot pressed, causing the polypropylene to bind the layers of non-woven materials together’, he adds.

‘The second production method involves using thermoset resins such as polyurethane or epoxy, which are sprayed or allowed to soak into natural fibre mats’, continues Suddell. ‘These are then press moulded to produce the final component shape. The composite is created as a result of polymerisation and subsequent hardening.’

Trash to cash

A team at Baylor University in the USA has made trunk liners, floorboards and car-door interior covers using fibres from the outer husks of coconuts, replacing the synthetic polyester fibres typically used.

‘This approach has potential because coconuts are an abundant, renewable resource in all countries near the equator,’ explains Walter Bradley, an engineering
professor who is leading the project.

A coconut’s husk is made of fibre and coconut dust, or pith. The pith is spongy at first, but dries and contracts into dirt-like particles. The Baylor researchers claim that it has the capacity to absorb 10 times its weight in water.

The husk fibres are blended with polypropylene before being compression-moulded into the required shape. The fibre provides a rigid architecture for the lightweight, yet stiff, composite.

‘Of course, natural materials will always depend on the weather and growing
conditions in relation to quality of fibre and yield and this will ultimately affect the supply and price,’ says Bradley.

All in the process

Suddell argues that natural fibres not only perform on par with manmade components, but they are also, in fact, easier to process. ‘Natural fibres are easier to cut and are also non-abrasive to processing equipment, so the life of the equipment is prolonged,’ he says. ‘The natural fibre products exhibit excellent formability and negate any irritation or respiratory problems associated with glass fibres. The components are generally produced using standard compression moulding techniques, meaning that manufacturers do not have to make any extra allowances for processing.’

So, the main driving forces for the adoption of natural materials in the automotive industry are reductions in vehicle cost and weight, and ‘sustainability’. It would seem, at least on the surface, that there are no real barriers preventing their widespread use.

But Mark Ellis, Manager of Materials Design and Test at the Nissan Technical Centre Europe, based in Cranfield, UK, argues that it is not quite that simple.
‘The single biggest barrier to widespread use of both recycled and natural materials is odour,’ he explains.

‘This continues to be a problem and a number of companies, including ourselves, are attempting to overcome this by mixing natural fibres with those that are less “odorous”.’

General Motors is having the same problem with some of its recycled content. ‘One nut we have yet to crack is using recycled milk cartons for use in interior components, because those cartons retain that milk odour,’ says Lora Herron, Materials Engineer overseeing the company’s recycled and bio-based materials efforts. ‘Of course, you do not want to make interior parts that smell like sour milk. But we think that as we keep developing the technology, this is something that we will be able to overcome.’

However, Cerato says that the use of recycled content in polymers does not cause Ford any major concerns in terms of odour and if the material does not meet the requirements for interior use it is simply not selected.

So while car makers and researchers argue that they are taking huge steps towards a motorised society that coexists with nature, there are still some big issues to be tackled. Not least the argument for sustainability, which is always subject to lifecycle assessment.

Further information: Ford, ADAS, Toray and Nissan