For many of us, the easiest place to find liquid silicone rubber (LSR) is at the auto store. It comes in a tube and can be used to create flexible, formed-in-place gaskets that cure with the heat of an operating engine. In its extreme form, LSR can withstand constant temperatures of up to 316°C and intermittent temperatures of 371°C.

To those more familiar with ordinary thermoplastics, it may seem counterintuitive that such a rubbery material can be used in high-temperature applications, but LSR is actually made to take the heat. Unlike thermoplastics, which soften when heated, thermosets like LSR are created in high heat and, in their various forms, can easily withstand temperatures that would melt thermoplastics. This suits them well for a variety of high-heat automotive and industrial applications and for medical products that are sterilized with high heat.

In addition to high heat, LSR can typically handle low temperatures, well into double digits below 0°C, while maintaining its flexibility. The exact degree of flexibility varies with the compound, but can be very high; LR3003/50, for example, has an elongation at break of 480 percent. LSR compounds are available in varying durometer (hardness) and can be selected to match the requirements of the application.

The material has excellent thermal, electrical, and chemical resistance properties, although it can be attacked by certain solvents such as gasoline or mineral spirits, which is why it can be used in high-temperature automotive applications but not for fuel lines. And it has low compression set—low permanent deformation when a force is applied and removed—making it ideal for elastomers. In comparing LSR to thermoplastic elastomers (TPEs) like Santoprene, LSR has been described as “TPE on steroids.”

LSR is also approved for medical applications where it will be in contact with skin. Its stability prevents it from affecting skin or, in turn, being affected by skin contact. Some grades of LSR, when combined with the appropriate manufacturing environment can be used in implantable applications. Its hydrophobic (water-repellent) properties make it ideal for water-handling applications. And the fact that it is fire-retardant and does not emit toxins or halogens when burned suits it well for a variety of safety applications. Reviewing material specifications or consulting your moulder for more details is generally recommended.

Continue reading ->