Studies On Zinc-Oxide Free – Non Peroxide – Cross-Linking of Compounds Based On Acrylonitrile-Butadiene Polymers

Diene rubbers  are known to be  cross-linked  with sulphur and sulphur donors. These cross - linking agents are part of  a complex cross-linking system that includes for zinc-oxide,for example. Being evident in the published  literature (materials safety data sheet,for example)  zinc-oxides are dangerous for the environment  and, on top of this, very toxic for microorganisms in water”.

Therefore, cross- linking systems without zinc-oxide are of interest for environmental concerns.

In  this presentation  proposal are made  to cross-link acrylonitrile-butadien –rubbers (NBR)  with novel zinc-oxide-free systems which follow the principles of the general “cure site” technology for  speciality elastomers.

Carboxylated nitrile rubbers, e.g. Krynac® X ,  found numerous  applications.

In this class of polymer zinc-oxide is not just an auxiliary component of the cross-linking system but,  in addition to sulphur  a cross-linking agent as well. Polydispers zinc-oxide forms  three-dimensional clusters involving the carboxylic group of the polymer   to set up an elastomer network.

The zinc-oxide can be replaced by phenolic curing resins, as it was  found by us. Most likely , the hydroxy-methylene group of the resin give rise for ester-like structures between vicinal carboxylic functions.

Users of  that cross-linking systems will find very good abrasion  resistance which is known to be  unique for the traditional  zinc oxide cross-linking of these elastomers.

The second possibility is a specific one for some modified  acrylonitrile butadiene –rubbers in  which cross-linking is initiated by thermal and chemical activation.

The vulcanizates made thereof are characterized by a very good long-term high-temperature compression set the level of which is unique in NBR cross-linking technology.