- Basic Concepts of Rubber
- Medical Ethylene-Propylene
- Fluorocarbon (Viton®)
- Medical Fluorocarbon (Viton®)
- Natural Rubber
- Neoprene® (Chloroprene)
- Nitrile (Buna-N)
- Hydrogenated Nitrile
- Perfluoroelastomer (Kalrez®)
- Polyurethane, Cast
- Polyurethane, Millable
- Liquid Silicone Rubber
- Medical Grade Silicone
- Styrene Butadiene
- Teflon® Virgin
- Vamac® [Ethylene / Acrylic]
- Thermoplastic Elastomers
- Cautionary Note
“Rubber” refers to elastomeric compounds that consist of various monomer units forming polymers that are heat cured (vulcanized). Polymers are long molecular chains and are derived from the Greek “poly” (many) and “meros” (parts). The base monomer or monomers is used to classify the type of rubber, for example: Nitrile, Silicone or Neoprene.
Rubber Compound is:
Rubber is composed of many different ingredients that include the base elastomer, vulcanization agents, fillers and plasticizers. For example, the addition of fillers can reinforce or modify properties, or additional plasticizer can increase elongation and lower durometer.
Rubber manufacturing process:
The elastomer is the basic component of all rubber recipes and is selected in order to obtain specific physical properties in the final product. Processing aids and softeners, such as oils and plasticizers, modify rubber to aid in mixing or molding operations. The fillers like carbon black and sulfur is used in the making of rubber.
Rubber has “Rubbery Behavior” because:
A polymer is considered a very viscous liquid or an elastic solid (i.e. rubber). The polymeric chains in rubber tend to be very long and flexible by nature and can rotate about their axis, which results in an entangled mass of contorted chains.
When a deformation of the rubber occurs, these tangled chains uncoil and recoil when the force is released. Therefore, elastic rebound or rubbery behavior is possible due to contortions of long, flexible polymeric chains, which allows rubber to be so resilient.
The long, flexible polymeric chains of rubber, when heated, react with vulcanizing agents to form three-dimensional structures. These vulcanizing agents (usually sulfur or peroxide) are necessary to facilitate chemical crosslinking of polymeric chains. Once the rubber has been vulcanized or “cured”, physical properties are enhanced and the compound is more resistant to deterioration.
Elastic recovery is a measure of the elastomer’s ability to return to its original shape once a compressive force has been removed. Failure of the seal to return to its original shape after compression is the condition termed “compression set” and all seals exhibit some degree of compression set.
Difference between a Thermoset and Thermoplastic:
One classification method of polymeric materials is according to physical properties at elevated temperatures. Thermoset polymers become permanently “set” in the presence of heat and do not soften in the presence of subsequent heating. Conversely, a thermoplastic material will soften when heated (and eventually liquefy) and harden when cooled. This process is reversible and repeatable, as opposed to thermosetting polymers where the process is irreversible. Also, thermoset polymers possess superior mechanical, thermal, and chemical properties as well as better dimensional stability than thermoplastics.