Years ago MRPRA published technical info bulletins titled "Natural Rubber Technical Information Sheet"s. Are these bulletins available anywhere on the web/Internet (preferably for free)?
I'm working with NR now, after being away from it for many years, and would welcome having these bulletins as...
I agree with Graham that properly formulated NR should be acceptable for 5 yr (+) service, although if longer lifetime is needed (10-20 yrs), EPDM would be desirable. There are published studies of EPDM aging, especially for the roof sheeting application, but I don't know of any that evaluated...
Depending on the formulation, you might be able to reduce the filler a little, which would have the same harness effect of increasing oil, and the less loading (i.e., higher polymer content) may not give a decrease in strength properties.
Your Mileage May Vary . . .
Another thought is to replace some of the 60 viscosity EPDM with lower viscosity EPDM (keeping the E/P ratio and ENB as similar as possible), which may improve flow of the rubber.
How are you vulcanizing? In a steam or hot air autoclave? If so, try increasing the amount of time at <110°C to give...
You would probably have similar types of emissions as you'd get with press curing of the rubber, and the emissions would depend a lot on the formulas you're curing. For example, you might have some ingredients in the formula that are somewhat volatile at the curing temperature (e.g., low...
Besides molding technique, the formulation and compound properties will also play a part in molding success, especiallyy for soft compounds. The compound should have as high viscosity as possible; low viscosity compounds will tend to trap air more than high viscosity compounds. Using a higher...
Increase the batch size a little? Very soft compounds probably have a lot of plasticizer which doesn't use up as much volume as polymer, so higher batch sizes are often needed.
This reference https://www.finemech.com/tech_resources/chemical_resistance.pdf suggests that PTFE should be good for caustic soda (sodium hydroxide) up to 50% and up to 120C.
If you're thinking polyurethanes, choose a polyether PU (ASTM designation EU), which is much more resistant to the effect of water than polyester polyurethanes (AU). Also, polyurethanes can be solid rubber materials ('millable polyurethane') as well as liquid, castable PU.
Sooner or later the discoloring ingredient will be diminished in the NBR (nitrile rubber) and there will be less and less ingredient to discolor the mineral oil. Depending on what the bad actor is and how much is in the formula, it may take a while (or not . . .).
I assume you just bought some...
It's likely that one of the ingredients in the nitrile rubber is leaching into the mineral oil. It could be a plasticizer (e.g., a yellow/darker oil-like material) or maybe an antioxidant or antiozonant (to protect the rubber from oxidation and ozone). It might even be a curatives, but I think...
FYI, with polyurethanes, most commonly used are castable (liquid) polyurethanes, but there are also millable (solid, rubber) polyurethanes. Millable PU's sweet spot (of best properties) are in intermediate hardnesses (50-75A); castables have better properties at 80+. MPU is very commonly used...
Assuming this isn't a mold part line, it sounds like a flow problem: not flowing enough before cure gets underway. Lowering viscosity and/or slowing the cure rate may help this. Or, it could be due to some mold release being trapped where the rubber flows together.
As Graham pointed out, a...
Try adding a small amount of an incompatible plasticizer, like a low viscosity silicone fluid (PDMS).
http://www.akrochem.com/pdf/product/silicone/silicone_fluids_df_55_series.pdf
