Hydrogenated Nitrile (HNBR)

What the hydrogenation actually does

Standard nitrile has carbon-to-carbon double bonds left over in its backbone from polymerization. Those bonds are the material's weak points: they are where heat, ozone, and oxygen attack it. Hydrogenation saturates them. A fully hydrogenated HNBR has better than 99.5 percent of them converted, and what remains is a polymer that behaves like nitrile toward oil and like a far more expensive material toward heat.

The degree of hydrogenation is a real specification with real consequences. A partially hydrogenated grade is cheaper and cures faster, and it will age visibly worse in steam. When we develop an HNBR compound for a hot-wet application we specify the polymer at the high end deliberately.

Strengths

• Steam and hot-water resistance well beyond standard nitrile
• Keeps nitrile's oil and fuel resistance
• Very good ozone and weather resistance, unlike NBR
• Excellent abrasion resistance and mechanical strength
• No fluorine in the polymer, which matters increasingly for regulatory reasons
• A fraction of the material cost of FKM, FFKM, or AFLAS

Limitations

• Not a match for FKM or FFKM against aggressive chemicals or above about 150 °C
• Peroxide cure means sulfur-cured tooling and processes may need adjusting
• Costs more than standard nitrile, so it is not a drop-in for a cost-down
• Compression set can be worse than FKM's unless the compound is designed for it

HNBR as a PFAS-free alternative

Fluoroelastomers — FKM, FFKM, and AFLAS — all contain fluorine, which places them inside the PFAS definitions now being used in regulatory proposals. HNBR contains none. For programs that have to remove PFAS from a bill of materials, HNBR is the most credible candidate available to replace a fluoroelastomer in hot-wet service, because it is the only non-fluorinated family that gets close on steam performance.

"Close" has to be proven rather than assumed, and proving it means real time at temperature. We steam-age candidate compounds in our own autoclaves and pull specimens on a long schedule — hundreds of hours in, then thousands — because a compound that looks equivalent at 100 hours can separate badly from the incumbent at 1,600.

Read the case study

Typical uses

• Steam and sterilizer seals
• Timing belts and power-transmission parts
• Oilfield seals and packers
• Automotive under-hood seals, hoses, and gaskets
• Hot-water and heating-system components
• Rolls and pads needing abrasion resistance in a hot, wet environment

Developing an HNBR compound with us

HNBR rewards compounding work more than most families. The polymer grade, the acrylonitrile content, the peroxide and coagent levels, and the filler system all move the answer, and the difference between a competent HNBR and a good one shows up in aging rather than on an initial datasheet. We mix HNBR on our own floor and age it in our own accredited lab, so a formulation change and its verification are days apart rather than months.

Compound development