“Polymers remain the materials of the future for our industry”

About ten years ago, you told us about the decisive role that polymers played in the automotive industry. Have there been any notable developments in the field since that last interview?

First of all, it is important to understand how much our vision of cars has changed over the last ten years. Today, all manufacturers’ efforts are focused on developing increasingly connected vehicles and making all their models electric. We therefore need to invent new technologies, master them and make them reliable and, in the case of electric vehicles, implement those new technologies to further improve their efficiency. Naturally, polymers are more essential than ever! However, their applications are still limited in some areas, such as in combustion engines and, to a certain extent, electrical engines, where the heat is such that metals currently remain the materials of choice for the time being. There are of course high-performance polymers such as PEEK*, but their added value is still too low in relation to their cost. It is mainly for the same reason that carbon/resin composites are not used in structural bodywork components, although technically there is no reason why they should not be.

*PolyEtherEtherKetone, a very resistant polymer to extreme heat.

You mention connected cars but, unless I am mistaken, the advances made in this area are mainly electronic and therefore far removed from the world of polymers.

Electronics are crucial to the development of self-driving cars, but it is a mistake to think that polymers do not have a role to play in this area, for various reasons. There is nothing magical about self-driving cars; they rely on many technologies whose functioning is mostly based on the emission of various waves. To work effectively, these waves must be able to propagate without encountering any obstacles. It turns out that plastics are crucial in helping to prevent the waves from being disrupted by a barrier object; a phenomenon known as the ghost effect. In addition, aesthetic trends are evolving and our customers no longer want to see sensors that they deem unsightly. Therefore, we have to find solutions to hide them by covering the bumpers with a skin, for example. It goes without saying that metal is not a solution for obvious reasons, since the Faraday's cage effect must be avoided. As a result, we once again turn to polymers for an answer as they alone make it possible to let the radar operate unimpeded by the shielding effect.

Today's vehicles are so sophisticated that we might be tempted to transform the driver's cab into an Airbus cockpit. This is obviously something that we want to avoid for reasons of ergonomics and safety. The "everything tablet-operated" concept, while easy enough to implement, is not a miracle solution for the same reasons. We therefore need to develop new solutions and we are moving towards plastronics, a technology used to integrate electronic circuits into moulded plastic parts right from the design phase.

One of the most emblematic examples of this technology remains the steering wheel, which is often equipped with several buttons and an airbag. On this subject, although this is nothing new, we are constantly on the lookout for polymers that are pleasant to the touch and to the eye to manufacture buttons and other parts from. However, the design aspect is not the only consideration, as the buttons must be solid and offer a smoothness of operation while making a soft noise that is pleasant to the ear.

Finally, I would also like to talk about the growing phenomenon of car sharing, which is important in shaping our understanding of the vehicles of the future, especially the materials that will be used in them. These types of vehicles will certainly be put to the test and we are looking towards polymers to find materials that are resistant, that do not get dirty, that are easy to wash, but also pleasant from a sensory point of view. I cannot say any more at the moment, but this is one of our key areas of research.

Polymers have a busy time ahead of them. Some trade journals often mention electroactive polymers. Can you tell us more about them?

In short, they are polymers that can change shape when subjected to a stimulus, most often an electrical stimulus. This is the principle of piezoelectricity. Without delving too far into the details, various families of polymers fall under this category: ionic electroactive polymers, liquid-crystal polymers, ferroelectric polymers such as polyvinylidene fluoride (PVDF), and more. We use the latter to develop ways in which we can revolutionise acoustic speaker systems in vehicles by doing away with traditional speakers. The aim is to both improve sound quality and reduce their weight. In high-end vehicles, sound systems can weigh up to several dozen kilograms.

We are attempting to use the polymers to make vibrating surfaces for the dashboard or headrests, for instance. We are taking inspiration from stringed instruments whose wooden bodies vibrate and act as a resonance chamber. This technology is very promising as it would enable each seat to be independent and allow each of the vehicle’s occupants to listen to their own audio content. This would also be an avenue for improving the soundproofing of electric vehicles.

Why is that? Silent operation is one of the most vaunted features of electric vehicles.

It is true that their engines are silent, but all noise caused by the interaction of the tires with the roadway, and any noise from air friction, is amplified for the vehicle’s occupants. We therefore have to develop new types of foams, often polyurethane-based, and study the sound frequency of the noise in order to find the material that will best soundproof the driver’s cab. Fortunately, the foams are lightweight and easy to insert between two parts or panels. All that is left is to find the right composition and the right density.

 Speaking of electric vehicles, has ongoing research into batteries caused new polymers to emerge?

I will not mince words. An electric vehicle’s weight is decisive; the more its mass can be reduced, the better the vehicle’s autonomy. We always use the same materials for all parts other than batteries: polyamide, polypropylene, ABS, polyurethane and polyethylene or polycarbonate. As a result of doing away with fuel tanks, we certainly use less PEHD since they are usually made from that polyethylene. However, we use more polyamide for the hot parts found in the Zoé, our first 100% electric vehicle, but frankly the quantity is very small.

Then there are the batteries. Batteries are mostly made up of metals, rare-earth elements and insulators. Plastics, by their very nature, are excellent insulators, which is why they are found in large quantities in batteries. Among them, polymer papers are becoming essential. They are called "paper" because they resemble cardboard sheets but are actually aramid fibres.

In addition to their very good ability to insulate the electrical current, they are very thermally stable (from -200 to 300°), mechanically stable and flame-resistant. In addition, they can be easily dyed, not to make them prettier but to colour code them, in this case using orange, to indicate that there is a danger of high voltage. This is very convenient for those who have to perform maintenance on these vehicles.

Finally, there are other polymers, whose names I cannot mention for reasons of business secrecy, that improve or reduce electrical conductivity. Some also play a role in lowering engine temperature, enabling us to reduce the size of the radiators and thus reduce the vehicle’s weight.

What about fuel cells?

Of course we have also looked into them, and today we offer commercial vehicles using this technology. However, compared to the yield of a traditional battery the performance of fuel cells have yet to be improved. Fuel cells give off a lot of heat, and most of it is lost since their yield is only 30% compared to the 96% of a polymer battery.
That being said, all of these technologies, including fuel cells, traditional batteries and hybrid systems, are emerging. We, and other major manufacturers such as us, are paying close attention as we are seeking the best solution to balance efficiency, autonomy and CO2 emissions. It is only a matter of a few years before we can achieve this.

Is recycling a priority for RENAULT?

Of course, and not only because European legislation requires us to recycle 85% of our vehicles (the same legislation also requires a cumulative recycling and recovery rate of 95%). We aim to make our vehicles as neutral as possible. To achieve this, we believe that reducing CO2 emissions, although very important, is not the only way in which we can make a difference. Environmental quality also involves the particles from wear on the tires and brakes, all other polluting emissions and air quality inside the vehicles.
Coming back to recycling, we are making progress every year. Our main focus today is on recycling our own materials before reintroducing them into our vehicles. It is for this reason that we have entered into a major joint venture with TOTAL-SYNOVA.
However, I would like to recall that recycling is not a new phenomenon in the automotive industry. For many years, various casings have been made using recycled plastics. What is new is that we now introduce recycled polymers into parts that are visible and no longer hidden. We started timidly with door sill plates and then moved on to designing a seat fabric made from textile scraps from the automotive sector, seatbelts and bottles. We had previously done this for the floor mats.

Our aim is to use the same method for other parts, although we do not want them to be considered as being made from cheap materials. We want to reproduce what we have achieved with the seats in the Zoé in other places, including in our high-end vehicles. Although it is too early to unveil all the details, we are testing new textures for the luxury ranges every day. When the time is right, we will unveil the details of our achievements, as we know that the users of our vehicles expect as much.

There are many details that still need to be ironed out, but we are rapidly approaching our objective. It is not possible to accurately predict what the car of tomorrow will look like, but one thing is certain: it will have to be part of an ecosystem that takes into account its environmental impact, its autonomy and its power. This is ambitious, but also exciting because there is still so much to be invented.