PHOTO: Performance overview of actual plasticizers
By JÜERGEN TRIMBACH,Hansen & Rosenthal, Hamburg, Germany
PLASTICIZERS comprise for up to 7% of a tyre’s weight. Depending on the individual structure, polarity and molecular weight, these plasticizers are interacting with all the major components of the different compounds and often are migrating through all parts of a tyre. That means that plasticizers form part of a complex puzzle comprising different rubbers, fillers and chemicals which have a major impact on the most important properties of a tyre, namely rolling resistance, durability and wear, on all the different types of surfaces.
However, the driving force behind the developments of plasticizers over the past decade has not been tyre performance, but rather new laws and regulations. The ban of polyaromatic hydrocarbons (PAH), for example, led to the development of oils such as TDAE, MES. RAE (residual aromatic extract) or ‘black oil’.
Nevertheless there are still some analytical problems to solve if the industry has to prove that RAE fulfils the required specifications. In North America the use of Heavy Naphthenic (HNAP) oil has been common for more than 50 years; however, that is not because it’s label-free, but due to the fact that it is the most available oil in the region. Outside North America, TDAE and MES are the most common oils.
The European tyre makers are world compliant with the PAH rules and tyre makers in China and other regions of the world who export to Europe that have little option but to comply with the relevant regulations.
With the recent implementation of the new norm EN 16143, a GC-MS (gas chromatography-mass spectrometry) method to determine the individual PAHs, an excellent tool has been implemented for the most of the analytical problems, while other methods such as ASTM E 1681 (a test to measure the mutagenic potential of oils) still have disadvantages.
In addition, the chemical-related legislation in the EU, known as REACH (Registration, Evaluation, Authorisation and restriction of Chemicals), will have a significant impact not only on tyre raw materials such as plasticizers, but also on other chemical substances for the whole rubber industry. With REACH all chemicals are restricted unless they can be shown to be toxicologically non-critical.
Because a tyre is an essential component determining the driver´s safety, the key properties of a tyre, namely wet grip; and since the tyre accounts for 20% of the car´s fuel consumption, also the rolling resistance have had to be included in labelling on new tyres since October 2012, according to the European Tyre Labelling Regulation (EC/1222/2009).
Similar regulations have been introduced in other regions like Japan, Korea and it is expected that such measures will also be introduced in the USA, Brazil and probably China.
With the introduction of this labelling regulation, besides having to fulfil toxicological requirements, it’s the first time that tyre raw materials now also have to show how they influence safety parameters such as grip and braking but also an economic and ecological parameter namely rolling resistance which can be directly translated to fuel consumption.
As a consequence we will see not only the end of plasticizers like DAE, containing high levels of PAH, but we will also expect to see a decline in the use of products which do not support the development of tyres with improved braking properties and reduced rolling resistance. This certainly points to increased demand in plasticizers such as MES, TDAE and HNAP which are non-carcinogenic and available globally in adequate supply volumes.
Parallel to these changes, we will certainly also see the development of new, more highly sophisticated, plasticizers which are today still in the development laboratories of the major plasticizer producers but which will be ready for launch phase shortly. Maybe these materials will in future help to produce tyres with properties far beyond those we know from today.
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