Silicone elastomers are thermoset polymers based on a siloxane (Si-O-Si) backbone, distinguishing them from organic rubbers with carbon-carbon backbones. This silicon-oxygen structure provides exceptional temperature stability from -60°C to 200°C continuous use, far exceeding EPDM, NBR, and natural rubber capabilities. Unlike thermoplastic elastomers (TPE, TPU) that can be remelted, silicone elastomers cure into permanent three-dimensional networks through platinum-catalyzed or peroxide-initiated crosslinking. Biocompatibility, purity (no plasticizers or phthalates), and sterilization compatibility enable medical device applications where organic rubbers cannot meet regulatory requirements. The siloxane backbone resists UV radiation, ozone, and moisture better than carbon-based elastomers, explaining their dominance in outdoor weatherstripping and long-term environmental exposure applications.

Silicone elastomers divide into two primary forms: liquid silicone rubber (LSR) and high-consistency rubber (HCR). LSR arrives as a two-part liquid system processing through liquid injection molding equipment, enabling complex geometries, tight tolerances, and automated production. HCR comes as a solid compound for extrusion, compression molding, and calendering, suited to simpler geometries and traditional rubber processing equipment. Within each form, grades span Shore A hardness from 10 (gel-like) to 80 (firm rubber). Medical-grade materials meet USP Class VI, ISO 10993, and FDA requirements with validated purity and biocompatibility testing. Industrial grades cost less but lack the documentation and extractables control medical applications demand. Self-lubricating grades incorporate additives reducing coefficient of friction, while electrically conductive formulations add carbon black or metal fillers for static dissipation.

Platinum-cured silicone elastomers use platinum catalyst to initiate hydrosilylation crosslinking between vinyl and hydride functional groups. This addition cure produces no byproducts, leaving no extractables or volatile compounds. Medical-grade purity, transparent formulations, and FDA compliance make platinum cure the standard for healthcare, food contact, and infant products. Cure occurs rapidly at 150-200°C, enabling fast injection molding cycles. Peroxide-cured systems initiate crosslinking through free radical mechanisms, generating volatile byproducts during cure that require post-cure baking to remove. Peroxide cure costs 20-40% less than platinum cure and provides higher tear strength and better compression set at elevated temperatures. Industrial gaskets, automotive components, and applications tolerating extractables benefit from peroxide cure economics. The choice depends on purity requirements, application regulations, and mechanical property priorities.

Most silicone elastomers maintain full mechanical properties through continuous use from -60°C to 200°C, with specialized high-temperature grades extending to 250°C. Below -60°C, the material stiffens and elongation decreases, though catastrophic failure does not occur. Short-term exposure to 300°C for minutes during sterilization or processing causes minimal property loss. Prolonged operation above rated temperature accelerates crosslink degradation, hardening, and eventual embrittlement. Heat aging at 200°C for 1,000 hours produces less than 10% tensile strength loss in properly formulated materials. Cold-temperature flexibility distinguishes silicone from organic rubbers that embrittle at -40°C. The broad operating range simplifies material selection across product lines and eliminates seasonal compound changes common with temperature-limited elastomers.

Silicone elastomers are thermosets and cannot be remelted or reformed like thermoplastics. Direct material recycling through reprocessing is not possible. Manufacturing scrap and end-of-life products go to landfill, incineration for energy recovery, or specialized downcycling processes. Pyrolysis at 500-700°C decomposes silicone elastomers into silica filler, hydrocarbon oils, and hydrogen gas. The recovered silica finds use in construction materials, though this downcycling represents value loss. Some manufacturers accept post-industrial scrap for grinding into filler material in lower-grade compounds, requiring clean, uncontaminated streams. The limited recyclability compared to thermoplastic elastomers represents an environmental trade-off against superior performance, durability, and biocompatibility. Extended product life and reduced replacement frequency partially offset end-of-life disposal concerns.