Liquid Silicone Rubber Properties

Why Choose Liquid Silicone Rubber (LSR)?

When choosing materials to manufacture critical parts and components, consider Liquid Silicone Rubber (LSR). LSR is the primary material we process at SIMTEC — as a result, there’s no better partner for your manufacturing needs, and no one more experienced in helping customers make the most of it.

Liquid silicone rubber’s characteristics and chemical properties make it an ideal material for applications spanning several different industry verticals. Keep reading to learn more, or contact SIMTEC directly for more information.

Chemical Composition of Silicone Rubber

The unique physical properties of silicone rubber are a result of its chemical structure. Silicone rubber is an elastomer consisting primarily of a chain of molecules known as a siloxane bond (-Si-O-Si-). This chain is effectively silicone rubber’s “backbone,” to which a variety of organic chemical groups can be added, altering its mechanical and material characteristics.

Silicone rubber is distinguished from other elastomers by the strength of the siloxane bond. Whereas carbon bonds have a binding energy of 355 kJ/mol, the strength of the siloxane bond is 433 kJ/mol. This contributes to its greater heat resistance, chemical stability, and electrical insulation.

At the same time, silicone bonds also feature low intermolecular forces, which means that other chemical groups attached to them can rotate freely. Because of this, liquid silicone rubber possesses material properties such as a high degree of elasticity and compressibility, as well as water repellence and good releaseability.

Mechanical Properties of LSR

Various grades of silicone rubber have different material properties. This versatility is one of the reasons why LSR is used in so many diverse applications. Whether you require a medical- or food-grade product that offers superior resistance to bacteria, or an automotive component that can withstand excessive heat and vibration, liquid silicone’s mechanical properties make it an excellent starting point.

Key material properties of silicone rubber include its fast curing and low compression set, its resistance to tearing, heat, water and oil, its transparency and electrical conductivity, and its overall strength and long life. You can use LSR at temperatures between -100˚C and 200˚C, expose it to wind, rain and UV light for extended periods of time, or immerse it in water, oil or solvents. The various grades of LSR possess material properties that can stand up to even the most demanding applications.

Liquid Silicone Rubber Properties

How is Liquid Silicone Rubber Used?

The most common application for silicone rubber is the production of LSR parts. LSR parts are used in a range of different industries. Their steam resistance and low compression set make them an excellent choice for gaskets and hardware in consumer appliances such as microwaves. Their conductivity and fatigue resistance make them ideal for electronic interfaces on keyboards or touchpads. Their oil and heat resistance offers long-term durability in automotive components.

Properties of LSR Parts

LSR’s specific material properties are a result of its unique chemical structure. Its backbone is formed by a series of siloxane bonds which, compared to carbon bonds, are stronger and more stable. This allows liquid silicone rubber to be:

Chemically Inert

Liquid Silicone Rubber has an organic backbone and therefore inert, meaning it does not react chemically with others. LSR is also resistant to damage from water, oxidation, UV rays, ozone, and radiation, as well as a variety of alkali or acid products. For products subjected to frequent cleaning, exposed to water and moisture, used outdoors or in other harsh environments, LSR has the chemical properties to perform well in these conditions.

Hypoallergenic

Inherently hypoallergenic and non-toxic, LSR will not cause irritation or allergic reactions with contact, even in those with sensitive skin. For respiratory products such as oxygen and CPAP masks, or products like earbuds, hearing aids, or wearable monitoring devices worn for extended periods of time, LSR provides a safe and comfortable solution.

Biocompatible

LSR’s molecular structure also contributes to its biocompatibility. It is odorless and does not have a taste. Because it also complies with Food and Drug Administration (FDA) requirements, it is widely used in baby products and other food- and beverage- related products.

Physical Properties

LSRs physical and thermal stability properties are exceptional and the reason why LSR is the preferred choice over other elastomeric polymers. LSR maintains its physical properties in a wide range of temperatures – both high and low temperatures, ranging from -60 degrees Celsius to 180 degrees Celsius depending on the grade.

Additional physical characteristics include:

  • Compression set: LSR parts will retain their shape when compressed
  • Surface: LSR has a naturally smooth texture
  • Modulus: LSR offers flexibility and rigidity
  • Seals: LSRs are widely chosen for its sealing attributes
  • Responsive: Sensitive, responsive and ideal for delicate sensing membranes
  • Insulative: Naturally insulating – electrically and thermally
  • Hardness: Available in a range of durometers, most commonly used are 5 to 80 Shore A durometers

Liquid silicone rubber molded parts are odorless and tasteless. Unique colors and visual effects can be achieved through the use of pigments and master-batches. Parts are also ozone and UV safe. Other notable features of liquid silicone rubber parts include:

  • Resistance to steam and humidity
  • Flame retardancy
  • Low creep and compression set
  • Weatherability
  • Vibration absorption
  • Corrosion resistance
  • Resistance to mold, mildew, and bacteria growth
  • UL component recognition
  • And more

Many different variations of LSR are available to support potential applications in a wide range of industries. To learn more about the specific properties of different liquid silicone rubber products, contact SIMTEC to speak with one of our in-house engineers.

Liquid Silicone Rubber Applications

At this point, you may be asking what exactly silicone rubber is used for. Liquid silicone rubber is a highly versatile material, and new applications for it are discovered and tested every day. It is a mainstay in healthcare manufacturing, automotive component manufacturing, electronics and consumer products, gaskets and other hardware, and many other markets.

Typical liquid silicone rubber products manufactured by SIMTEC include:

  • Catheter tubing
  • Connectors/membranes
  • Gaskets, seals, and O-rings
  • Hand instruments
  • Lighted buttons
  • Needle-free valve sights
  • Pull rings
  • Skin contact devices
  • Soft-touch buttons/surfaces
  • Steam-sterilized parts
  • Syringe tips
  • Valve components
  • And much more

Contact SIMTEC To Discuss Your Project Today

At SIMTEC, we have one of the most advanced manufacturing facilities in the country, as well as a long history of helping our customers develop innovative solutions to the challenges that cost them money and affect their productivity.

Liquid silicone rubber isn’t the right choice for every application, but there’s a good chance it has applications you haven’t yet considered. For specific information regarding material and application alternatives, we recommend visiting our Technical Information page or contacting us directly.