The carcinogenic effect of N-nitrosamines was established back in the 1950s. Nitrosamines occur in many different walks of life, for example in foods, tobacco and cosmetics. They are also produced during the vulcanization of rubber containing nitrosamine-forming additives and are regulated by TRGS 552 (technical rules for hazardous substances).
The nitrosamine-free cross-linking of rubber products has now become established in many parts of the rubber industry, such as profile manufacture, but there is still a great need to replace cross-linking systems that generate carcinogenic nitrosamines. Rhein Chemie has made a major contribution to establishing nitrosamine-free rubber compounds by the use of dithiophosphates. In addition to containing no nitrosamines, this class of accelerators boasts many other technical benefits. They mainly comprise fast and moderately fast zinc dithiophosphate accelerators (e.g. Rhenogran® TP-50, Rhenogran ZAT-70, Rhenogran® ZBOP-50, Rhenogran® ZDT-50, Rhenogran® ZADT-50) and a moderately fast zinc-free accelerator and sulfur donor (Rhenogran® SDT-50). Depending on the dithiophosphate selected and in combination with other accelerators and retarders, a wide range of vulcanization speeds can be set.
Many of the dithiophosphates are liquids and - in polymer-bound form - can even be incorporated in soft rubber compounds quickly and free from pin holes. They work in synergy with sulfenamide accelerators to increase the level and speed of cross-linking. Dithiophosphates also improve the vulcanizates’ resistance to heat aging and reversion. The intelligent combination of Rhenogran SDT-50 with other additives results in optimum compression sets for vulcanizates and makes it possible to replace N-oxydiethylene thiocarbamyl-N’-oxydiethylene sufenamide (OTOS) as an accelerator in natural rubber, in particular in anti-vibration technology. OTOS is classified as toxic and carcinogenic and as a strong nitrosamine-generating additive.
In addition to dithiophosphates, Rhein Chemie offers other products that make it possible to dispense with cross-linking systems that can form carcinogenic nitrosamines. Rhenogran® CLD-80 can replace morpholine disulfide as a sulfur donor and has a comparable property profile. It is non-blooming and works in synergy with primary accelerators. Rhenogran® TBzTD-80 is known as a safe nitrosamine-generating accelerator and can replace critical thiuram accelerators in rubber compounds. This results in better solubility and thus good heat resistance, especially in EPDM and natural rubber. It has a positive effect on the physical and, in particular, the dynamic properties of vulcanizates.
Rhenogran® Geniplex-80 is an effective activator of accelerators and blowing agents, e.g. in foamed profiles. It also works on its own as a weak blowing agent and can thus be used in the manufacture of profiles with reduced densities.