The Chemical Makeup and Properties of Liquid Silicone Rubber

The chemical makeup and characteristics of liquid silicone rubber (LSR) make it a versatile and desirable material for manufacturers across multiple industries. It’s used to create injection molded parts for many products and is especially beneficial for high-precision industrial items and consumer products.

The unique properties of LSR are a result of how the polymer is created and what types of additives are included in the mix. During the process of making an LSR, vinyl and methyl siloxane groups are polymerized to form long molecular chains that provide strength to the resulting elastomer. Adding different types of organic chemicals to the base mixture can also change its physical and mechanical characteristics.

Like other elastomeric materials, LSR is made up of a silicon polymer. At the molecular level, this polymer includes a silicon backbone with oxygen and hydrogen molecules added as side groups. In order to add different physical and mechanical properties to the base LSR, other types of organic chemicals are reacted to the silicon polymer during production. The resulting mix is then injected into a mold to form the desired part, which is then heat-cured for a finished product.

Injection molding is the most common method for manufacturing and using LSR. It involves injecting the liquid LSR into a pre-made mold and then applying a combination of heat and pressure until the LSR solidifies inside the mold cavity. Manufacturers use a variety of equipment and machinery to facilitate this process, including injection machines that have varying degrees of automation. This can significantly reduce the chance of human contamination and provide a more efficient and cost-effective way to produce parts.

A key benefit of using LSR for injection molding is its thermal stability. LSR maintains its physical and chemical properties in a wide range of temperatures, ranging from -40 degrees Celsius to 200 degrees Celsius. This property makes it an ideal choice for a wide variety of applications, from high-voltage line insulation to nipple protectors for nursing mothers.

Unlike thermoplastic and thermoset elastomers, which can be prone to dripping or loss of shape in the presence of high temperatures, LSR holds its shape even at elevated levels. This quality makes it an ideal material for a wide variety of applications, including electronics, automotive, baby products and medical devices.

Another reason that LSR is a great choice for injection molding is its resistance to corona discharge, which can be detrimental to electronic components and can disrupt electrical conductivity. In fact, LSR is one of the few elastomeric materials that can withstand corona discharge without impacting the conductivity of the finished product.

Liquid silicone rubber can be reacted to produce flame retardant grades, which is particularly important for manufacturers producing products that are exposed to high levels of electrical stress. There are several ways to achieve this, such as adding an organosilane, which can increase the amount of crosslinking in the resulting LSR polymer. Alternatively, fluorine can be added to the resulting polymer during the production process to produce FLSR, which is able to resist a much higher level of exposure to fire hazards.