To meet the European Reach requirements, companies like German sealing and vibration control specialist Freudenberg have been eliminating harmful substances in rubber compounds by replacing with safer alternatives covering a variety of basic materials and additives, such as reinforcing fillers, plasticisers, anti-ageing agents, crosslinking agents, vulcanisation chemicals and others.
In 2009, a particularly problematic hazardous plasticiser, until then indispensible in vibration technology applications with high damping forces and limited ageing, was successfully replaced with harmless alternatives. In order to eliminate this “problem compound” from 48 rubber mixtures in 128 different applications, an alternative solution had to be found for each individual mixture, without any compromises concerning material characteristics.
This was achieved after five years of development activity and was only possible with cross-departmental co-operation between material and product developers, raw material managers, manufacturers and customers, says the company.
Part of this co-operation structure is an internal process called FSS 7, which aims to avoid particularly hazardous substances to protect purchasers and users of Freudenberg products. In this context, Freudenberg says it focuses particularly on substances with chronic hazard potential (suspected substances) even when they have not been classified as such by law. Examples are the handling of polycyclic aromatic hydrocarbons and the vulcanisation accelerator DOTG.
In the past, polycyclic aromatic hydrocarbons (PAHs) were found in many everyday products with plasticisers based on mineral oil. PAHs in such products are particularly relevant due to their frequent contact with skin.
Freudenberg is committed to eliminating the use of such PAH-containing plasticisers, but PAHs also occur in small amounts in carbon black. The PAHs are attached to the carbon surface and are, in addition, surrounded by an elastomer matrix.
Freudenberg has carried out internal research that shows there is no significant migration of carbon black PAH to the elastomer surface. Therefore, the PAH exposure does not pose a risk and is far below the legal limit requiring declaration, enabling the company to claim that PAH-containing plasticisers or rubbers are not used in any of its products and that carbon blacks used as reinforcing fillers do not pose a health risk.
Furthermore, Freudenberg has also developed rubber materials that use virtually PAH-free types of carbon black for use in special applications (such as in the food industry and medical technology).
Certain high temperature acrylate and ethylene-acrylate rubber compounds (HT-ACM and AEM) are processed using the vulcanisation accelerator DOTG (N,N’-Di-orthotoluylguanidin). Studies have shown that in certain thermal processes, such as vulcanisation or tempering, the degradation product o-toluidine is formed. In animal experiments this substance has been shown to be carcinogenic and is therefore classed as carcinogenic to animals under dangerous substances legislation.
Although no legal restriction has so far been imposed on the use of DOTG, Freudenberg says it is developing DOTG-free elastomer products. Alternative cross-linking chemicals make it possible to achieve nearly identical characteristics in the final product. Freudenberg’s target is the complete substitution of DOTG.
A current example is the new DOTG-free high-temperature ACM material HT ACM 380. Freudenberg says this is a safe and environmentally friendly material that does not release any problematic substances and hence, the sealing products made from it fulfill not only legal requirements but also all of the customer-specific demands, for example from the power tools sector or automotive industry.