Making a car less heavy has many advantages. It can increase its range; it can give it a higher top speed. But lightweighting can also give carmakers more space to insert new components. Seats and composites, in particular, are areas where polyurethane can help OEMs meet their lightweighting goals
Reducing the weight of components that make up a vehicle has been a constant refrain of the European automotive industry over the past 30 years. Other parts of the world have now caught on to the concept, as regulations imposing lower levels of emissions or corporate fuel economy have become more widespread.
Polyurethane innovations in seating and composites can help OEMs rise to the challenge of maintaining comfort and lowering weight. Seats are the largest visible components in passenger cars, and this niche has been owned by moulded polyurethane for many years.
Foam density specifications change regularly, as Irina Bolshakova, market manager automotive and transportation at Huntsman EMAI explains. ‘If we look at the requests from the customers five to seven years ago, on top of the list was lower density to give a relevant reduction in weight,’ she said. ‘We eventually reached the situation where lower density meant less comfort. Over the past three years, we have seen a return to higher density formulations.’ However, she added, while light weight remains important technology advancement must also help simplify manufacturing and design.
This is echoed by Adient’s director of foam engineering, Brent Hodge. ‘Foams are getting thinner; the volume is falling, and the difference is being accounted for with more active suspension systems,’ he said. ‘But as the seats are getting thinner, then the density of the foam has to go up. Nobody has developed a magic formulation where 30 kg/m3 foam could support an occupant like a 65-70 kg/m3 density foam.’
Evonik’s senior technical manager for automotive in EMEA, Eva Emmrich-Smolczyk, said that thinner seat cushions means filling narrow moulds with high density foam, and this presents a number of technical challenges. ‘During filling, you have slow turbulences in the mould, and in most of them you have design elements like inserts in the seat pads,’ she said. ‘The foam has to flow over these.’ These could be clips, for example, that attach the textile to the seat. ‘All these parts have to be defect-free and sit in the foam, or they could be torn out,’ she said. ‘We are interested in maintaining the cell structure with silicone surfactants. The choice of the right surfactant is important to support flowability and reduce subsurface voiding.’
However, she explained, the thinner seat pads get, the more challenging liquid flowability becomes, and designs are also becoming more ambitious. ‘Silicone surfactants help improve the flowability in these parts, in combination with well-balanced catalysis gel and blow catalysts,’ she said.
Filling the mould is only one piece of the equation. When the part is moulded, it has to conform to the OEM’s specifications, and these are getting tighter. ‘We have so many requirements from OEMs who need to maintain heat and humidity ageing properties,’ Emmrich-Smolczyk said. ‘For this, we also have additives that help to improve and maintain the foam’s physical properties after ageing.’
Huntsman is interested in how the seat cushion and frame interact, and whether there is an opportunity to save weight here, too. ‘We are talking with the people who make the seat frames,’ said Bolshakova. ‘Seats are tremendously complicated parts of the vehicle. We want to see how the foam and the frame can work together to reduce the weight of the vehicle. Foam is important, but it is not the heaviest part of the seat.’
One way to reduce weight could be to replace dense metal springs with less dense polyurethane foam. Huntsman has a variable density technology that it plans to launch later this year. ‘We have technology where you can play with the hardness across and through depth of the seat profile,’ Bolshakova explained. ‘It is possible to make seats with a soft layer near the leather or fabric surface, and a hard layer at the bottom of the cushion. This is done by altering the formulation during the pour. It helps to simplify manufacturing process of more complex seats.’
Conventionally, a changing foam density through the depth of the seat is achieved by bonding two different foams together. ‘Moulding the seat cushions with different densities in one shot enables producers to reduce weight and simplify production. This is our GH, or gradient hardness, technology,’ she said.
Could lightweighting be improved or mitigated if the seats were made with recycled material, or with greenhouse gases as raw materials? Some producers think there could be useful trade-offs.
Esther Quintanilla, global & EMEAI mobility market segment leader at Dow Polyurethanes, suggested that polyols generated using the company’s Renuva programme for mattresses could, potentially, play a part. ‘There is nothing to stop us,’ she said. ‘Why not have that sort of solution for automotive seating or carpets?’ Dow also recently announced a partnership with France’s Eco-Mobilier to take foam from end-of-life mattresses to convert to polyols.
Covestro marketing manager Galen Greene explains that his company has brought a number of sustainability developments to the automotive industry. ‘These include CO2 Cardyon technology; we’re working on that when looking at alternatives in the short term,’ he said. They also have some upstream projects looking at bio-sources, and chemical waste recycling. ‘These are very important topics for us as a company,’ he claimed.
In the matrix
The polyurethane industry has been pushing the change from traditional materials to composites with apolyurethane matrix as a way that the car makers can reduce weight in a number of parts. This is an area where some Tier 1 manufacturers very much rely on their suppliers. As Adient’s director of design Q& technology, Thomas Gould explains, ‘We are not going to develop a level of expertise in composites. We will work with suppliers. In the lightweighting area, composites are interesting, and they creep in through niche areas. Recaro, which was part of Adient from 2010 to 2020, did a lot of work with composites.’
He added that Adient has looked for opportunities in more mainstream uses. ‘There are limitations,’ he said. ‘A lot of the composites we use tend to be lay-ups, and we have hybrid approaches using long strand composites. You can get some great strength out of those, and they could be alternatives to steel structures.’
Huntsman’s Bolshakova believes that glass fibre composite structure are gaining huge recognition in the interior of the vehicles, particularly in the trunk area as spare wheel covers. ‘These are widely used parts now ,and OEMs are comfortable to have parts made like this with polyurethane matrix materials,’ she said. ‘The technology is well developed, and there are advantages of bringing this composite technology into other areas such as headliners, instrument panels and door trims.’
Polyurethane composites are now being tested in new areas, she added. These include dashboards, instrument panels, back seat plates, side pillars, and covers for electric and electronics components.
Covestro’s Greene agrees. ‘Polyurethane composites can help companies support their lightweight initiatives,’ he said. ‘The industry has been addressing lightweighting for a period of time, and we have made a lot of progress over the years.’ His company’s Baypreg polyurethane honeycomb floor panel materials is heavily used in the boot area, for example. Investigations are under way to see where else it might be used, such as the bulkhead between the boot and the rear seats.
This is also of interest to Huntsman. ‘The backseat plate sits between the rear seat and the boot,’ Bolshakova said. ‘[This is] one of the applications where PU is trying to enable the concept and composite technology.’
Other established applications for polyurethane include sun visors and parts in the trunk, she added. ‘These are honeycomb structures made using a resin spray process and compression moulding,’ she said. ‘This can be done quickly, accurately and at high volume and at the costs which the automotive industry likes. This area is where PU has gained significant recognition. However, in the more complex part of the composites world, structural and semi-structural parts, a lot of work has been done with epoxy-based matrix materials. ‘PU is gaining wider recognition, but it is still not widely adopted,’ she said. ‘But when we look at processability, PU is good choice for high pressure resin transfer moulding, wet compression moulding and pultrusion.’
A metal part cannot simply be replaced with a composite part as a one-to-one swap, she explained. ‘It requires a redesign, and this makes the thinking and development process more complex,’ she said. ‘The lightweight contribution is significant, but it needs to be combined with design for manufacturing and part simplification or consolidation to make parts production faster, and lower the total cost.’
Jump the barriers
Adient’s Gould said that, aside from design, there can be other barriers to overcome. ‘When you have industries that are really set up to manufacture in a specific way, be it auto bodies or seat structures, making a switch is a big deal,’ he said. ‘This applies not just to the product, but the infrastructure and legacy methods are really difficult to displace. When new materials come into the automotive industry it is often through niche products. Production runs [for these] are often much smaller, so the commitment is less. If we decided to make a seat back in a composite and if it did not meet expectations or failed, the cost to backtrack is huge.’
It’s important to remember that a seat is a safety product, he added. ‘It has to keep people safe and comfortable,’ he said. ‘Seats cannot endanger anyone and, as we have seen over the past few years, when a safety item goes wrong it has a devastating effect. The last thing car makers need is recalls.’
This explains the rate of adoption of polyurethane composites in automotive applications. Not only do the materials have to prove themselves in a wide range of non-safety critical products like parcel shelves, a well-understood manufacturing infrastructure needs to be in place so that car makers feel confident in specifying them in high-volume, safety-critical applications.