Silicone is a family of synthetic polymers found in countless products, ranging from cosmetics and cookware to advanced electronics and medical devices. Its unique chemical backbone, composed of silicon and oxygen atoms, gives it properties unmatched by traditional organic rubbers. While silicone comes in many forms, Liquid Silicone Rubber (LSR) is one of the most transformative. This article explores the nature of LSR and why it has become the material of choice for many modern consumer and industrial goods.
Defining Liquid Silicone Rubber (LSR)
Liquid Silicone Rubber is a high-purity, two-part elastomer supplied as two separate liquid components that cure into a flexible, solid material. These components are mixed immediately before processing. The base polymer is typically a vinyl-terminated polydimethylsiloxane (PDMS) combined with reinforcing fillers like fumed silica to enhance mechanical strength.
The curing process relies on an addition-cure system where a platinum catalyst in one part reacts with a cross-linker in the other. This reaction, accelerated by heat, creates a three-dimensional network structure that quickly transforms the low-viscosity liquid into a durable rubber. The defining characteristic separating LSR from other silicone types, such as High Consistency Rubber (HCR), is its low viscosity, which allows it to be pumped and injected into molds.
Essential Material Characteristics
One of LSR’s distinct performance advantages is its exceptional thermal stability, maintaining properties across a wide temperature spectrum. It can withstand continuous use from approximately -50°C up to 200°C, and certain grades tolerate short peaks of 250°C without degradation.
The material exhibits a low compression set, which is the ability to return to its original thickness after being compressed for a prolonged period. For seals and gaskets, this low compression set ensures a tight, long-lasting seal, even after years of continuous pressure and temperature cycling. Furthermore, the siloxane backbone provides superior resistance to aging factors like UV radiation, ozone, and weathering, making it suitable for outdoor applications. LSR’s inherent electrical insulating properties also make it an excellent choice for protecting sensitive electronics from electrical malfunctions.
Primary Applications Across Industries
The unique blend of flexibility, durability, and processing ease has made LSR a fixture in diverse manufacturing sectors.
Consumer Goods
In the consumer products space, LSR is widely used for items requiring direct skin contact, such as wearable technology bands and soft-touch buttons on electronics. Its durability and ability to be easily cleaned also lead to its use in kitchenware, including baking molds and spatulas. It is also used extensively in infant care products like bottle nipples and pacifiers.
Electronics and Automotive
In electronics, LSR is valued for its ability to create hermetic seals and provide excellent insulation for sensitive components. It is frequently molded into precise gaskets for water and dust-proofing connectors, sensors, and enclosures in devices like smartphones and outdoor lighting systems. The automotive industry relies on LSR for under-the-hood applications that demand performance in extreme conditions. This includes gaskets and O-rings for engines and transmissions, as well as sensor encapsulation that must withstand high heat, vibration, and exposure to oils and fuels.
Biocompatibility and Safety Profile
LSR is highly valued for its safety profile, especially for applications involving human contact. The material is chemically inert, meaning it does not readily react with other substances or body fluids.
This non-reactive nature means that LSR does not leach harmful substances, plasticizers, or byproducts into the surrounding environment, which is a requirement for regulated applications. High-purity, platinum-cured LSR is the preferred material for long-term skin contact and is often compliant with standards from regulatory bodies like the U.S. Food and Drug Administration (FDA) for food and medical grades. Its ability to withstand repeated sterilization methods, such as autoclaving, without degradation also makes it indispensable for medical devices, including tubing, seals, and components in implants.