Pulling their weight: how minerals contribute to lightweighting vehicles

If you’ve ever had to push start a vehicle, you’ll be pleased to know that cars are getting lighter. But spare a thought for Reverend Kevin Fast (pictured), who has built his strongman reputation on pushing and pulling the heaviest modes of transport he can find. Among the multiple Guinness World Records he holds, the Canadian pastor has pulled the most cars (15) by an individual and the heaviest vehicle (a 99,060kg/218,389lbs truck) over 100 feet.

In 1977, when the World’s Strongest Man tournament introduced the vehicle pull event, cars were weighed down by bodies and parts made almost entirely of aluminium, iron and steel. It wasn’t until the following decade that the trend for lightweighting and the use of polymers for external car parts took off.

Imerys’ Leonardo Cunha, Marketing Manager for polymers, explains: “Car manufacturers were looking for lighter materials in order to increase vehicle efficiency and reduce energy consumption – and emit less CO2 emissions per kilo of car. They also wanted to be able to produce more sophisticated designs.”

Soon, polymers replaced many metal parts, such as bumpers, spoilers, trims, tailgates and interior parts. 

Manufacturers could reduce the weight of the car, without necessarily reducing the size of the car, because the density of materials used is lower. The lightweight vehicle consumes less fuel because it needs less energy to get from point A to point B. 

Gilles Meli, Imerys Senior Science & Technology Development Manager for polymers, says: “It is commonly agreed that reducing the car weight by 100kg/220lbs. leads to a reduction of 4g/km CO2 for a thermal engine.” 

These traditionally metal parts that have been replaced with lighter polymers are as important in electric cars, as they counterbalance the batteries, which are heavier than an internal combustion engine. Plug-in cars, which, over their lifetime, are expected to have a lower carbon footprint than non-electric cars, can further benefit the environment if they are also lighter and, therefore, consume less energy on journeys.

Talc improves stiffness and impact resistance

Safety regulation continues to evolve to make sure that the polymer elements replacing steel plates in these fuel-efficient cars do not put drivers or passengers at greater risk.

Automotive plastic parts can only be used because the right additive minerals bring the best rigidity, which, therefore, means there is a minimum impact. In the event of an accident, the energy is dispersed; because of its flexibility, plastic is better than metal for absorbing the shock, preventing the energy from transmitting to the driver or passenger.

As well as being naturally lighter than metal, plastic is more malleable and easier to mould into thin and complex parts that are not possible with steel. Talc is blended with polypropylene to provide the necessary stiffness, and the melted compound is injected into moulds. 

Gilles Meli says: “Designers and engineers can rethink the geometry of car parts and develop solutions that are more efficient at absorbing shocks. Plastic enables manufacturers to make compositions of different elements or create smaller interior parts that you cannot see – that fill small gaps – that further help absorb the impact. If you can reduce the thickness of parts, that also makes cars lighter.”

 “Additionally,” says Leonardo, “the flexibility of plastic has given car designers greater freedom. The futuristic cars we have today have only been possible because polymers have allowed us to move out of square metal box shapes. Not only have we enabled metal replacement in the past, but we are also enabling the usage of less mineral loading and the replacement of more expensive polymers solutions.”

High-performing minerals make fuel-efficient cars even lighter

Premium talc means compounders can use less quantities of mineral to get the desired stiffness, which further lowers the overall weight of the car.

Imerys has a technological advantage being the first supplier to develop a high aspect ratio talc, named HAR®. This engineered mineral has enhanced properties, meaning car manufacturers can use a lower charge of talc in order to achieve or exceed a specific performance.

“We have innovated in this market, and we will keep investing and bringing new products to the marketplace,” says Leonardo.

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Graphite and conductive carbon blacks provide thermal and electrical conductivity 

Traditionally, metal parts were also used to make components for cars to allow for thermal management. Lighter plastic polymers can now be used instead, thanks to thermally conductive fillers – notably graphite-based fillers – that allow them to conduct heat.

Conductive carbon blacks can also be added to polymer compounds to make these plastic components electrically conductive and prevent the build-up and discharge of static electricity, giving auto manufacturers further weight saving opportunities.  

Minerals give recycled plastic a second life in car manufacturing

Supporting the automotive sector’s environmental ambitions, car manufacturers are including more recycled polymers in cars. Again, minerals play a key role in guaranteeing the performance is in line with regulation. 

Used plastic is ground and reprocessed, which makes it less performing than virgin plastic.

Minerals restore the properties of the degraded polymer to give the recycled plastic a second life. Imerys supplies minerals depending on the planned use for the recycled plastic and whether compounders are using a mix of recycled and virgin plastic, though typically talc is used.

“Recycled plastic is more expensive, as there are two processes,” says Gilles. “However, car manufacturers are taking the initiative and are able to reformulate polymers with the right minerals to achieve the same performance as virgin plastic. This is a growing trend and regulation will change in the near future.”

Picture credits: Ranald Mackechnie/Guinness World Records.