Liquid Silicone Rubber: What It Is, How It’s Used, and Where to Buy
Nowadays, we have no shortage of new and innovative manufacturing materials. However, it’s no longer enough for a material to be strong, chemical-resistant, or thermally stable. It also needs to be easy to handle, allows automation, and can be integrated into existing manufacturing processes.
One of the materials that seem to tick all these boxes is liquid silicone rubber. With material properties that make it reliable across different applications yet allows for versatile manufacturing processes, liquid silicone rubber has proven to be a valuable material for numerous industries. What is liquid silicone rubber and what makes it so useful?
What is liquid silicone rubber?
Silicone rubber is a widely used polymer containing silicon, carbon, hydrogen, and oxygen. It’s more specifically categorized as an elastomer or a rubber-like material. It is highly valued in several industries because of its chemical resistance and stability in extreme environments.
Silicone-based elastomers were first widely used in the 1940s by chemists in Corning Glass and General Electric because of their heat-resistant properties. They took the place for resin-impregnated glass fibers as the insulating material of choice for electric motors and generators. Not only were the elastomers superior in terms of heat resistance, but they were also more commercially viable because of their durability and ease of manufacturing.
The ease of manufacturing and shaping of this material comes from the use of liquid silicone rubber, a two-part thermoset elastomer. By separating the material into two components, the uncured material takes on gel-like properties. This can then be molded into the desired shape before it is cured or catalyzed, after which it takes on its final solid form.
At the molecular level, the silicone rubber polymer is made of a silica and oxygen backbone, in contrast to the usual carbon backbone of most polymers. This “polysiloxane” chain is what is more colloquially referred to as “silicone.” The silica and oxygen molecules create longer bonds than successive carbon molecules, resulting in a polymer that is much more flexible. This is the defining characteristic of silicone
Properties of liquid silicone rubber
1. Stable under extreme temperatures
Fully cured silicone rubber has a normal operating temperature of -100 °C to 300 °C. Within this range, the material retains its shape and other physical properties. Even at extreme temperatures, the thermal conductivity, tensile strength, dielectric strength, and tear strength remain superior to other organic rubbers. These characteristics make silicone rubber the material of choice for applications that require a material that retains stable properties even when exposed to extreme conditions.
2. Chemically resistant
The silicon-based backbone of silicone rubber makes it a highly inert material that does not react with other chemicals. This makes silicone rubber an excellent material for applications that call for constant exposure to oils, solvents, acids, and bases. It is safe for food contact.
In turn, this also means that silicone rubber is a bio-compatible material that is suitable for prosthesis and other medical tools. It is hypoallergenic enough to be used in products meant for baby care.
3. Superior electrical insulation
As with organic rubber, silicone rubber is a natural electrical insulator. It is an ideal material for the insulation of wires and other electrical components, enhanced further by high-precision manufacturing methods that allow the insulation of small parts.
In its base form, silicone rubber has a translucent to almost clear appearance. With pigment application, silicone rubber becomes a highly versatile material in terms of appearance and color requirement. Even skin tones can be easily simulated for prostheses.
5. Fast cure cycle
One of the more valuable characteristics of silicone rubber is that it lends itself well to rapid manufacturing processes. Upon combination of its components, the uncured gel-like polymer can be injection molded. This allows for large-batch processing, ensures repeatability, and can be adapted to automated processes. The suitability of liquid silicone rubber to fast-paced manufacturing is one of the main drivers of its commercial value.
Manufacturing methods for liquid silicone rubber
There are several methods for multi-component of liquid silicone rubber, but the most widely practiced relies on a platinum-based curing system. There are also two components to be mixed:
- Component A is made of the silicone base, a plasticizer compound, and the platinum catalysts
- Component B is made of linking and inhibitor compounds
Upon mixing and in the presence of the platinum catalyst, the hydride and vinyl functional groups in the separate components form ethyl bridges. The rate of curing can be controlled and inhibited by the presence of sulfur or amine compounds, but the curing typically still proceeds quickly.
Uses of liquid silicone rubber
Liquid silicone rubber is one of the most versatile manufacturing materials, both in the industrial and commercial settings. You might probably even have a handful of silicone rubber products in your home right now.
1. Medical applications
The biocompatibility of rubber silicone combined with its high-precision manufacturing methods makes it a perfect choice of material for the medical industry. The most popular medical use of silicone rubber is in the manufacture of prostheses. Rubber silicone is also durable enough to withstand the usual wear and tear that prostheses need to endure.
There are also smaller uses of silicone rubber in the medical field. From the pistons of syringes to cannula and other respiratory products, silicone rubber plays a crucial role in healthcare.
2. Food contact and kitchen items
Since silicone rubber is highly stable against chemical degradation, it is a suitable material for products that come into contact with food. The material is so safe that it is notably used for the nipples of baby bottles – a true testament to its being chemically inert and non-toxic. In recent years, baking pans, cupcake liners, spatulas, and other kitchen tools made from silicone rubber have become much more common. They are cheap, non-stick, pliable, and come in bright colors.
Food storage is one of the more long-standing applications of silicone rubber. Not only are they safe for food contact and don’t react chemically, but they also do a good job of maintaining the temperature of its contents.
3. High-precision industrial parts
Since silicone rubber parts can be reproduced very quickly and at a high level of precision, it’s an ideal material for performance parts using in industrial settings. Silicone rubber is widely used for sealants in valves and pipes connections in the form of O-rings, gaskets, and valve seals.
Rubber silicone can even be used to create very small components, such as the insulation liners of electrical connectors. By infusing rubber silicone with carbon black, a small amount of conductivity can be imparted into the material while still retaining its superior physical properties. Carbon-infused silicone rubber is preferred to meta-filled organic rubber because of overall better mechanical performance.
4. Cosmetic products
Silicone rubber is recognized as a hypoallergenic material. It is used widely as a container or delivery system for skincare or cosmetic products. Most makeup and lipstick are packaged using silicone rubber as it remains inert even when in contact with the product during long-term storage.
Silicone rubber is one of the more environment-friendly alternatives to natural animal hairs as material for makeup brushes. They are a little softer than nylon but are similarly cheap and gentle on the skin.
The strength, flexibility, and wear-resistance of silicone rubber make it an ideal material for clothes and shoes, particularly those that are used in active sports. From shoes to wetsuits and sports bands, silicone rubber has proven itself to be tough enough to go through the punishment that athletes subject it to. Outside of sports, silicone rubber has also found its way to one of the most demanding pieces of apparel we wear on the regular – underwear.
Silicone rubber is a versatile manufacturing material that has long been recognized in several industries as extremely valuable. However, it is only in recent times that the same material has found its way into our households in the form of tools in the kitchen and food containers. This only serves to reinforce the many applications of silicone rubber in key industries such as in healthcare, manufacturing, and energy.
A key characteristic of liquid silicone rubber is that its curing process provides a small window for shaping and customization. Injection molding is the go-to process for handling of uncured silicone rubber because of its speed. It also helps that the curing time of silicone rubber is so quick that some processes prefer delaying it to give them more time to work the material.
If you need a material that is stable in extreme temperatures, thermally and electrically insulating and has good flexibility, then silicone rubber is a prime candidate.