Navigating Materials Selection for Your Elastomeric Inflatable Seal

August 3, 2021

Elastomers are an incredibly diverse set of materials offering an ever-growing arsenal of properties engineered to meet the specific demands of a given application. Commonly used materials for most cases include:

  • Natural Rubber (NRx)
  • Styrene Butadiene (SBR)
  • Butyl (IIR)
  • Ethylene Propylene (EPDM)
  • Neoprene (CR)
  • Nitrile (NBR)
  • Epichlorohydrin (ECO)
  • Viton® (FKM)
  • Polyurethane (AU)/(EU)
  • Silicone

Many are also available in multiple configurations in which specific resistances have been further improved. Material selection is perhaps the most critical aspect of designing your elastomeric inflatable seal, so choosing the most suitable material for your application is paramount to a successful project. Here we explore many common materials used to manufacture inflatable seals and bags.

Natural Rubber (NRx)

Entering commercial use in the early 1900s, Hevea Rubber of the Hevea Brasiliensis tree is a naturally occurring substance that found widespread use for its unique properties of elasticity, electrical insulation, and water resistance. It is fully biodegradable and can be mixed with other compounds to further enhance the specific desired qualities of the material. Inexpensive and reliable, it performs consistently in situations where strength, elasticity, and abrasion resistance are required.

Natural operating temperatures are within the range of -50°C to +100°C, but the chemically similar synthetic polyisoprene can expand its utility further, particularly in low-temperature settings. Naturally occurring impurities impede the consistency of natural rubber, so that polyisoprene is the rubber of choice where consistency is vital. Due to differences in the microstructure, tensile strength and tear resistance are somewhat reduced in formulations of polyisoprene.

Typical uses:

  • Tires
  • Drive Couplings
  • Anti-vibration mounts
  • Bearings
  • Springs
  • Adhesives
  • Rubber bands

Styrene Butadiene (SBR)

SBR is an excellent inexpensive general-purpose elastomer and the highest volume synthetic rubber. Its standard operating temperatures are -25°C to +100°C and generally features inferior resistances to most other elastomers, though its heat-aging and abrasion resistances are better than natural rubber.

SBR finds use in many similar applications to NR except where its low fatigue resistance presents an issue, such as severe dynamic situations, and serves as a cheaper substitute. Degradation of this elastomer typically presents with a general stiffening of the material, called embrittlement.

Typical uses:

  • Drive Coupling
  • Conveyor belts
  • Car tires (Not truck tires)
  • Adhesives
  • Haul-off pads
  • Roll coverings
  • Shoe soles and heels
  • Various molded goods

Butyl (IIR)

Butyl rubbers are a versatile option with blends available to suit a variety of mechanical and thermophysical needs. Stable in dilute acid and alkali solutions, as well as extended periods of high heat and weather exposure, industrial applications are an excellent choice. Butyl has low gas and moisture permeability, making it an optimal choice for maintaining gas pressure. It also features good chemical resistance to organic and inorganic media, as well as ozone. Its weaknesses are compression, abrasion, and flame exposure. Operating temperatures are generally between -50°C to +120°C. Halogenation can further improve some chemical resistances at the expense of electrical and moisture resistance.

Typical uses:

Automotive

  • Inner Tubes or other high-pressure tubes
  • Diaphragms
  • Wire and cable insulation
  • Gaskets
  • Liners
  • Shock absorption
  • O-rings
  • Weatherstripping
  • Seals
  • Bottle closures
  • Insulation
  • Vibration damping

Liquid

  • Caulks
  • Sealants
  • Pressure-sensitive adhesives
  • Hot melts

Ethylene Propylene (EPDM)

EPDM elastomers offer similar properties to butyl rubber but provide additional advantages such as resistance to hot water, polar fluids, and steam up to 200°C. Like Butyl, EPDM rubbers perform exceptionally well under high thermal load, compression, and low temperatures but exhibit lower qualities of physical strength. In addition, they are some of the most water-resistant rubbers available.

Weaknesses include mineral and synthetic di-ester lubricants as well as hydrocarbon fuels and solvents. Standard operating temperatures are from -45°C to +150°C and up to +180°C in steam. The automotive industry sees the most extensive usage of EPDM.

Typical uses:

Automotive

  • O-rings
  • Gaskets
  • Radiator and heater hoses
  • Window seals, door seals
  • Accumulator bladders
  • Wires

Polymer Blends

  • Car Bumpers
  • Rub Strips
  • Fender extensions

Waterproofing

  • Facade and parapet sealants
  • Expansion joints
  • Roofing
  • Bitumen modifications
  • Pool and tank liners

Chloroprene (Neoprene) (CR)

Chloroprene Rubber (CR), chlorobutadiene rubber, or Neoprene®, a registered trademark of DuPont Performance Elastomers, is a diene-based elastomer. It has excellent chemical resistance in applications of chlorofluorocarbons, aliphatic hydrocarbons, mineral oils, greases, and ozone. It also has superior flame resistance as one of the few self-extinguishing rubbers and forms outstanding rubber-metal bonds.

Typical uses:

  • Gaskets
  • Cable jackets
  • Tire-sidewalls
  • Gasoline hoses
  • Tubing
  • Seals
  • O-rings
  • Weather-resistant products like orthopedic braces and wetsuits

Nitrile (NBR)

Acrylonitrile butadiene rubber (NBR), more commonly known as simply nitrile, is the rubber of choice for applications requiring oil and hydrocarbon solvent resistance. Formulations vary in acrylonitrile content, with higher quantities conferring better oil and abrasion resistance, while lower content formulations have improved low-temperature resilience flexibility. Carboxylation may also be performed to enhance temperature resistance. Standard operating temperatures are between -25°C and +100°C, but low nitrile rubbers can bring the lower bound to -50°C, while carboxylated nitriles are stable up to +150°C. For most applications, a medium nitrile content maximizes the benefits of both ends of the spectrum.

Typical uses:

  • Oil and gas sealing
  • Tubing
  • O-rings
  • Cable jacketing
  • Seals
  • Diaphragms
  • Gaskets
  • Gasoline hoses
  • Liners
  • Carboxylated grades also find use in epoxy formulations as rubber tougheners

Epichlorohydrin (ECO)

With properties similar to nitrile, ECO features improved heat and ozone resistance and enhanced flexibility in lower temperatures. Low gas permeability, excellent weather resistance, good compression set, and mineral oil resistance, as well as hydrogen peroxide and alkali resistance, confer several suitable applications, especially in the automotive industry.

ECO’s standard operating temperatures are between -35°C and +120°C but will perform short term up to 150°C. Limitations of this rubber are its poor abrasion resistance and electrical properties and its susceptibility to strong acids and many common polar solvents such as alcohols and phosphate ester-based hydraulic fluids.

Typical uses:

  • Gaskets
  • O-rings
  • Cable jackets
  • Seals
  • Hoses
  • Belts
  • Rubber Glues (Corrosive to metals, however)

Fluorocarbon (Viton®)(FKM)

Fluoroelastomers, more commonly known as Viton®, are best suited for continuous use at high temperatures. Many different grades are available to suit a host of applications. FKM features excellent heat and flame resistance, alongside resistance to aging, ozone, oxidizers, oils, and chemicals. They also have low gas permeability, a low compression set, and limited resistance to steam, hot water, and very polar fluids such as strong acids. Typical operation temperatures are between -20°C and +230°C but can withstand temperatures up to 300°C for short periods. They are expensive and best suited to applications in very harsh environments.

Typical uses: (In harsh environments)

  • Hoses
  • Gaskets
  • Seals
  • O-rings
  • Diaphragms
  • Accumulator bladders

Polyurethane (AU) (EU)

Polyurethane elastomers are broadly divided into two primary classes of polyester (AU) and polyether (EU) urethanes. EU elastomers are also more expensive and sensitive to UV light. High tear and abrasion resistance, tensile strength, and good resistance to oxidation, ozone, aliphatics, petroleum-based oils, and fuels lend themselves to many applications.

AU elastomers feature better physical properties, while EU elastomers have better chemical resistance. AU elastomers are sensitive to hot water, humidity, acids, and alkalis, as well as microbial attack. EU elastomers are susceptible to oxidation and heat. With operating temperatures between -40°C and +90°C, polyurethane elastomers are favored for their abrasion resistance, strength, oil, and solvent resistance.

Typical uses:

  • Gaskets
  • Hydraulic and reciprocating seals
  • Hoses
  • Diaphragms
  • Conveyor belts
  • Haul-off pads
  • Skateboard and roller-skate wheels
  • Many sporting goods
  • Abrasion-resistant linings and coatings

Silicone (SI)

Silicone elastomers are favored for their stability at high temperatures and oxidation resistance. Standard operating temperatures are from -70°C to +250°C, but some formulations are stable at temperatures up to +500°C for short periods. They also feature high resistance to UV, ozone, many chemicals and have excellent low-temperature flexibility. While their mechanical properties are relatively low, they are maintained at high temperatures. Their gas permeability is poor, and they have a low resistance to mineral oils and hydrocarbons.

Generally more expensive than most other elastomers, their use is typically reserved for when their excellent resistance, flexibility at low temperatures, or bio-compatibility are needed. Available in solid or liquid forms, silicones find broad uses in the pharmaceutical, medical, electrical, automotive, and aerospace industries.

Typical uses:

  • Wound dressings
  • Surgical implants
  • Seals
  • Tubing
  • Mold making
  • Wire and electrical insulation
  • Gaskets

Partner with the Seal Master Design & Engineering Team

Choosing a suitable material for your application requirements can be a daunting process. The Seal Master team is ready to assist you in finding the right elastomeric inflatable seal solution for your project. If you have any questions, please reach out and an expert will contact you to discuss your project.

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