How to minimize biodegradability of Natural Rubber?

Manufacturer:We are producing rubber products based on Natural Rubber. Some of these products must be "submerged" in the soil for many years. Since NR is well known to be biodegradable, we need to prevent this as far as practically possible. For reason we cannot reveal, switching to synthetic polymer is not acceptable. Your assistance would be appreciated.

JohnWoon:Unvulcanized NR would biodegrade faster than vulcanized NR and among the vulcanized NR products, those with better protection against oxidation would be more resistant to biodegradation.

I suggest you try the following ideas:

1) Use an EV system for your vulcanization recipe. EV stands for Efficient Vulcanisation based on sulphur-donor in the absence of sulphur or at very low level of sulphur. The resultant mono-sulphidic cross-links, as opposed to polysulphidic ones from the conventional cure system, offers good resistance to oxidation especially at elevated temperatures.

Research done indicates that while giving low stress relaxation, such formulation also enhance the resistance to biodegradation.

2) As normal organic waxes would trigger and increase biodradability, this material must be avoided or replaced with chlorinated wax.

3) Use a strong anti-degradation system. One possible combination is p-phenylene diamine antioxidant with chlorinated wax. Phenolic type of antioxidants such as butylated phenols, would not be strong enough.