This third in our series of blogs discusses road transport emissions, and how brake emissions contribute.
Road traffic has long been recognized as a major source of air pollution due to emissions of gaseous pollutants like CO, NOx, VOCs and Particulate Matter.
EU regulations have significantly reduced emissions from the exhausts of new cars, but non-exhaust emissions are currently not included. The proportion of non-exhaust emissions has consequently increased and become more significant.
Non-exhaust road traffic emissions include particles released into the air from brake wear, tyre wear, road surface wear and resuspended road dust. These types of emissions therefore contribute to the total particulate matter in the environment and are associated with human health problems and mortality.
Emissions of non-exhaust particles from vehicles may already exceed those from exhausts, and will likely increase in the future. However, quantitative data on the magnitude of non-exhaust emissions are limited and uncertain, also because the proper measurements and standards have not yet been validated.
The exact contribution of non-exhaust emissions to local and national air quality is therefore currently under discussion. Emissions vary widely according to brake, tyre and road surface material, and driving style. Existing emission factors therefore have a wide range of uncertainty and show significant variations between PM10, PM2.5 and PM1 size fractions.
Non-exhaust emissions particles are also an important source of metals to the atmosphere. Among others, Zn and Cu are highly associated with brake- and tire wear from cars in urban environments.
Besides a lack of approved legislation covering non-exhaust emissions, there are no product standards for the composition of brake pads and brake systems to limit air pollution. Methods of measuring non-exhaust emissions so far lack international consistency. Several testing institutes, and also brake pad manufacturers, are developing testing and analysis approaches that reflect real-world driving conditions. These are measuring particulate matter and particle numbers for emissions from brake wear, but there is no clear view on when a proposal can be expected.
Electric and hybrid vehicles are heavier than conventional cars because of the battery mass, and this will tend to increase non-exhaust emissions. Regenerative braking of electric cars is initially based on energy recovery rather than the frictional wear of brake materials. That should instead reduce brake wear emissions. However, the net balance between these two factors remains unquantified.
Both brake pad and disc manufacturers can have a major impact on particulate matter emissions. The friction industry is conservative, but in the last decades dangerous raw materials like asbestos have been banned, and there have been strict legislations for copper and copper-containing materials.
Antimony Trisulfide is also not forbidden by regulation, but in the last 10 years has not been accepted by most car manufacturers. Materials such as Potassium Titanate with high fibrous content are similarly under discussion as they bring potential health risks. Fortunately, more and more hazardous materials are being banned, and this will continue in near future.
Disc manufacturers are also focusing on materials that result in fewer emissions during braking. The newest technical developments focus on extremely durable coatings that prevent wear, and special temperature- or chemical treatments for the wear-resistant surface layer of the disc. Together with the focus on more sustainable and greener brake pads, this is a significant step towards reduced brake dust emissions.
As a raw material supplier and knowledge provider for the friction industry, Lapinus is also contributing to this challenge. Lapinus’ mineral fibres are used in nearly half of all passenger car disc pads, as they improve the friction performance and reinforcement properties of the friction material. The fibre products are sustainable and safe for humans and the environment. Lapinus’ fibres are certified bio-soluble due to their unique chemical composition and strict process control. Studies have shown that this important bio-solubility remains unchanged even in wear debris, demonstrated by Dynamometer testing in the Lapinus laboratory.
Lapinus already has a broad portfolio of mineral fibres that are specially engineered for friction materials like brake pads. Our “low shot” and “extra low shot” (ELS) products contribute greatly to reduced wear during braking and so reduce brake dust emissions. Production of these products is critical since consistent braking performance is not only related to low shot content, but also on the specific shot fractions and narrow distribution. Decades of expertise enable Lapinus to guarantee a high quality and consistent product every time.
Because we follow the automotive and friction industry closely, we have a good overview of the latest trends, challenges and new types of (for example Global-NAO) brake pads. This is critical as it allows us to align our internal development innovations with the needs of the brake pad manufacturers. For reducing wear, brake pad manufacturers use a principle called nest formation or reservoir effect. Long mineral fibres form nests, introducing voids in the friction matrix. When the voids reach the external surface of the brake pad and enter into contact with the disc during the braking event, wear debris is generated and accumulates inside the voids. These voids act as a reservoir for wear debris.
Based on this principle and with the focus on emissions we have developed a novel spherical mineral fibre product (fibre sphere). Fibre spheres are pre-made nests of fibres with voids to collect wear debris. Test results have shown significant reductions in brake pad- and disc wear during braking. The prototype is now being screened and analyzed by selected OEM brake pad manufacturers, and initial indications are promising.
Other innovations are based on high temperature performance of our fibres and increased mechanical strength for better matrix reinforcement under extreme braking conditions (high temperature, high speed, fading). This could eventually result in fibres that improve overall brake pad reinforcement, and consequently enhance bonding on a surface level. That will result in less wear debris, and thus decreased emissions.
Eventually, we expect all these improvements to result in truly “green” friction materials.
This is just a small glance at current development studies. Our upcoming blogs will provide further insights.
We develop innovative products used in a wide range of applications, including automotive friction, urban climate adaptation, urban acoustics, gaskets and coatings.
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