Elastomer Materials

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“Rubber” compounds are resilient (elastic) materials made from one or more cross-linked base polymers, reinforcing agents, processing aids, and performance-enhancing additives.

Polymer

Derived from Greek meaning "many units," polymers are long chains of repeating units. On the molecular level, they resemble extremely long spaghetti strands.

Monomer = the unit that repeats in a polymer
Isomer = polymer made from one monomer
Dimer or Copolymer = polymer with three monomers
Trimer or Terpolymer = polymer with three monomers

Polymers tangle themselves together like a large bowl of spaghetti.

Base polymer determines chemical resistance, rough temperature limits, and rebound resilience. In some materials, the high and low temperature limits can be modified by ingredients.

Polymers provide "baseline" for abrasion resistance, compression set resistance, and permeability. There can be (and almost always are) modified - up or down - by other compounding ingredients.

Polymer chains must be "glued" together (cross-linked) to achieve resilience and elasticity.
Sulfur: simplest cure system, used in nitrile and EP
Organic Peroxides: improved compression set in EP, improved compression set and high temperature limit in nitrile, standard cure system for silicone.
Bisphenol: best cure system available for fluorocarbon (specialty FKMs need to be perovide-cured, but it's not the first choice)
Others: specialty materials have special cure chemistry

Reinforcing agents add mechanical strength and resistance abrasion, permeation, and compression set.

Carbon black: standard for black
Silica: standard for non-black compounds

Fillers lower the cost of a compound but reduce compression set resistance and elongation.

Carbon black: lower grades or excessive amounts provide no performance benefit for seals.
Clay: Commonly used in "generic" seal compounds

Oils and/or polymers used to lower the low temperature limit of nitrile and make the material flow better (see Process Aids)

Reduce resistance to compression set
In "generic" materials, they are used to offset the hardening influence of high levels of filler.
Can extract into process fluids, resulting in seal shrinkage and hardening

• Nitrile (NBR)
• Hydrogenated Nitrile (HNBR)
• Polycrylate (ACM)
• Vamac (AEM)
• Neoprene (CR)
• Ethylene-Propylene (EPR,EPDM)
• Butyl (IIR)
• Polyurethane (AU, EU)
• Flourocarbom (FKM)
• Tetrafluoroethylene-Propylene (TFE/P)
• Perfluoroelastomer (FFKM)
• Hiflour (FKM)
• Silicone (VMQ)
• Fluorosilicone (FVMQ)

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