The passenger car industry has been trying to build a global standard to measure and assess the levels of VOCs and FOGs in the cabin for many years, and work continues. Simon Robinson and Sarah Houlton report.
The traditional smell of a new car quite often depends where you are from. It is either the smell of success, or something rather unpleasant. The molecules that make up the smell may be the same, but people’s perception of that smell will vary depending on where in the world they are.
James Paul, global marketing manager at Evonik, explained that odour is a big topic for his company. ‘People want to reduce the odour inside the cabin, with strong pressure coming from China and Japan,’ he said. ‘In Europe, if you buy a vehicle and the interior smells of leather, you think of it as prestigious. In China, the demand is for no odour at all.’
It’s also an important subject for Huntsman. ‘From our perspective, everything to do with emissions is not a nice to have it is a right-to-play issue,’ said Irina Bolshakova, the company’s market manager for automotive and transportation in EMAI.
Huntsman’s approach to reducing the chances of developing VOC in the seat moulding process, she said, is to look at everything they can control within the materials for polyol blends and MDI. ‘This means we have looked at impurities and compounds that were intentionally added, such as formulation components, or things which were not [added deliberately], like contamination,’ she said. ‘These are the areas where we are working to reduce everything to a reasonable minimum. We make sure that we use intermediates and materials that have the minimum or make a minimum contribution to VOC creation.’
Evonik’s Paul said that this was a fairly common approach. ‘To reduce odour, formulators typically start with the main components first, such as polyols, before trying to eradicate odour from every single component, including additives,’ he said. ‘There’s a lot involved in trying to take down the odour rating.’
According to Bolshakova, Huntsman has extended this concept. ‘We conducted research internally to ensure there is a clear understanding what the primary and secondary sources of emissions are, and what are the effects of material degradation on the foams,’ she said. ‘This has given us a high confidence how we can meet growing OEM specifications.’
A number of chemicals have to be controlled; these are primarily acetaldehyde and formaldehyde precursors, and some flame retardants. ‘Unfortunately, VOC and FOG chemicals are not all created during the moulding process,’ she added. ‘That could be hard to manage, but would be a single stage in the process; their precursors can develop over time.’
Huntsman is also looking into materials manufacturing, storage and raw materials, she said. The aim is to exclude the negative effects of storage, and the possibility of contamination of raw materials. All of these could lead to an increase in the emissions.
Driving down aldehydes
Additive manufacturers are already aware of the need to reduce VOC and FOG levels. ‘Formulators are placing an ever-increasing focus on emissions, with a continuing drive to lower aldehyde levels,’ Evonik’s Paul said. ‘We have projects in place to further optimise our established DABCO NE catalyst range, and are developing new scavengers that can remove acetaldehyde and formaldehyde from systems.’
His colleague Eva Emmrich-Smolczyk, senior technical manager for automotive in EMEA, said it is important to remember that the perception of odour is more complicated than it might first appear. ‘To significantly improve it, you have to reduce the amount of odour-bearing substances by about 95%,’ she said. ‘It is a logarithmic function, and not a linear function. This has a big impact on the odour improvement process.’
Another important factor in odour is not only the concentration, but the threshold, she claimed. ‘You might already achieve a very low concentration of a substance, but the smell is so intense that even with such a low threshold it can still be smelled at a very low concentration,’ she said.
However, if that substance is an additive that is an important component of the formulation, it may not be possible to eliminate it – and the associated odour – completely. Another approach is to neutralise unwanted molecules. Evonik is close to launching a second-generation product that will be much more capable of scavenging all aldehyde types including formaldehyde and acetaldehyde. This has been developed using technology that Evonik acquired with its purchase of AirProducts in 2017.
Scavengers are designed to be used in formulations at levels which are typically between 0.2 and 1.0 parts per hundred polyol (pphp), depending on the polyol being used, Emmrich-Smolczyk said. They need to react with the aldehyde, without influencing the reactivity profile. ‘Our latest development has involved finding a substance which is process friendly and does not interfere with the kinetics of the polyurethane reaction,’ she said.
Like comparing the comfort of the seats, comparing smell is a direct, simple comparison that consumers can make between brand. So car makers, seat makers and raw material suppliers are searching for a level playing field with the interior smell of cars reduced to a minimum.
To do this the industry needs some common ground: You need good regulations like a bedrock across the industry,’ said Brent Hodge director of foam engineering at Adient. ‘That is really needed right now, he added.
The current situation, where there are up to 150 different OEM standards in the area, is complex. This complexity leads to high testing burdens, complicated raw materials and parts logistics, and potentially higher costs.
For Tier 1 suppliers like Adient, which are at the interface between chemistry and car makers this is important. ‘You end up with custom tailored chemistry which does not suit a large manufacturing plant that supports multiple customers. It is very difficult to meet all of the requirements, Hodge explained.
But, help could be at hand. Work is underway in the US to help forge a global consensus on VOC and FOG. The independent Molded Polyurethane Foam Industry Panel’s VOC workgroup is in the process of developing a roadmap as an industry standard to guide companies testing PU foam emissions. The plan is that this will provide detailed protocols for best practice across all the steps involved. These include demould, sample preparation and harvesting, packaging, shipping to the analytical lab, which analytical method to select, and how the results should be expressed.
Importantly, it will provide a proposed industry standard that will address the needs of OEMs across all three of the major markets: Europe, North America and Asia. It will make use of existing consensus standards from ASTM International, ISO, SAE International and VDA, alongside existing automotive test methods.
Since the group’s presentation at the 2019 CPI meeting in Orlando, significant progress has been made. ‘We have collected and categorised more than 50 VOC standards,’ said John Sebroski, who is a principal scientist in environmental analytics at Covestro, and chairs the VOC committee at SAE International. This committee supports the development of global specifications and procedures for the determination of volatile organic compounds from road vehicle interior materials, components and vehicle cabin air.
The panel has now developed a protocol for a comprehensive review of the standards, and also a template containing key parameters for review, to identify similarities, conflicts and potential areas that might require further clarification or research.
Work in progress
SAE Work Item J3233 has been created. This is a standard that is now under development, and will describe a harmonised approach to measuring VOCs from polyurethane foam used in automotive seating. ‘The standard will address the interests and requirements of OEMs and other stakeholders,’ said panel member Jennifer Holtz, an analytical chemist in the advanced materials and system research group at BASF.
It will leverage existing consensus standards combined with current automotive OEM test methods to address four important points. The first of these is foam processing and handling, sample production, conditioning, packaging, storage, shipment, and specimen preparation. Secondly, there will be test methods to measure VOC emissions, such as chambers, air sampling and analytical methods. The third point includes data analysis and expression of results. Finally, there will be a unification document, including a description and flowchart of combined documents. The result will be a comprehensive VOC roadmap.
The foundation for building the new roadmap is SAE J2989, Handling and Packaging of Materials and Components for Emissions Testing. This is a general standard applicable to a variety of materials, and the panel is working to create a document specific to polyurethane foams. ‘To accomplish that, we are reviewing existing standards to identify similarities and derive best practices. Sebroski said.
The process has had its issues. ‘It was challenging to identify and collect the various VOC standards in use from consensus organisations or OEMs, but a collaborative effort was made by the industry panel and the OEMs,’ said Kelly Kiszka, a PU applications development chemist at Dow, and another panel member. ‘Publicising the effort and soliciting feedback was accomplished by participating in conferences, distributing surveys, and publishing scientific papers and journal articles.’
Representatives from the industry have expressed concerns, too. ‘[Some have said] they do not want to write material specific standards for evaluating every material used in the interior of a vehicle cabin,’ Holtz added. ‘And it may be difficult to change standards because it would cause difficulties with comparison to historical data.’
The roadmap is an ongoing endeavour, and the target date for publishing this SAE standard is 2022, Kiszka explained. ‘Progress has been made towards the harmonisation of global VOC standards, and collaborative efforts by global automotive manufacturers and suppliers continue,’ he said.
The panel continues to work with OEMs, suppliers, and key contributors to the industry to communicate the importance of harmonisation of VOC standards and relevance to the business. And they are optimistic that harmonised specifications that are acceptable across all three regions will be achievable. ‘Results from the survey showed overwhelming support for harmonising standards,’ Sebroski said. ‘We are optimistic because we see a strong interest across the industry.’