Nitrosamine generation

Nitrosamine and Non-Nitrosamine Generating Accelerators and Sulfur Donors S. No. Particulars... 

Factors involved in the selection of vulcanization systems must include the type of elastomer, type and quantity of zinc oxide and fatty acid, rate of vulcanization, required resistance to fatigue, and service conditions. It is also recommended that use of nitrosamine-generating accelerators be avoided. 

Data obtained from the formulation ACS 2 (ASTM D3184-89, 2a) but containing 50 phr HAF. Use of nitrosamine-generating accelerators should be avoided. 

Nitrosamine-generating chemicals represent an area where suspect materials have been removed from rubber products, even though no governing legislation has yet been drafted. Nitrosamines can be formed when secondary amine accelerators are used to cure mbber. These accelerator changes have a very signiAcant effect on the total rubber industty. 

N-nitrosamines generated at low levels from secondary amines liberated from some of the accelerators can cause health concerns and have been subject to regulation. Volatile N-nitrosamines are quantified using GC with a thermal energy analyzer. 

Two workhorse members of the thiuram class, particularly active in cure rate as well as economical, are TMTD and TMTM (R= methyl, x = 2 and 1, respectively, in 2). Both TMTD and TMTM are stable nitrosamine generators, as they liberate the secondary amine, dimethyl amine, during vulcanization (12,13). Replacements for these rubber chemicals has been a target of considerable technical effort in the rubber industry. Several candidates have emerged, each with its own attributes. None is a direct substitute for either TMTD or TMTM but several have proven... 

Table 6. Low or Non-Nitrosamine-Generating Thiurams, Dithiocarbamates, and Guanidines...

Sulfur Donors. A fourth class of sulfur vulcanization chemicals has been affected by the move to non-nitrosamine generators the sulftir donors. These are organic chemicals which have a relatively high level by weight of sulfur atoms that are able to be donated in the vulcanization process to create sulfur crosslinks. Elemental sulfur is the material of choice as a source of the sulfur atoms which create these cross-links, but some articles cannot tolerate free sulfur for requirements of color, solubility, or performance. 

The rubber chemist has reacted vigorously to the challenge of eliminating volatile nitrosamine-generating chemicals in the workplace, even though many had been fixtures of the sulfiir vulcanization process. Non-nitrosamine primary and secondary accelerators and sulfur donors are now available and used extensively. 

Another commonly used sulfur donor is TMTD. However, TMTD can be used in some recipes as a sulfur donor, while in other recipes with sulfur present it functions as an accelerator. Just as with DTDM, the TMTD is also a nitrosamine generator during the curing process, which poses a health hazard to workers if air ventilation is not adequate. Therefore a large effort has been made by the rubber industry to find chemical substitutes that do not emit nitrosamines into the air. 

TMTD is under ever-increasing scrutiny because it is another toxic nitrosamine generator in the factory. 

MBSS is sometimes used as a primary accelerator by the tire industry, especially if its extra sulfur is needed for vulcanization efficiency. However, MBSS does have an environmental problem from excessive nitrosamine generation during cure, which has restricted its use. 

The international discussion about carcinogenic N-nitrosamines generated during or after vulcanisation of rubber products started in the late 1970s. It reached its... 

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