Platinum Cured Silicones vs. Peroxide Cured Silicones

Curing is a chemical process that converts a material from a pliable gum or liquid state into a solid elastomer. Silicones use various curing systems, but platinum curing and peroxide curing are the most common. Each of these processes has its advantages, but there are also significant differences.

Stockwell Elastomerics inventories, fabricates and molds platinum cured silicones and peroxide cured silicones at our Philadelphia, Pennsylvania (USA) facility. The table below summarizes key differences between these two types of silicone rubber.

	Peroxide Cured Silicones	Platinum Cured Silicones
Curing Mechanism	Free radical polymerization using organic peroxides	Addition polymerization with a platinum catalyst
Purity	Contains byproducts that may affect odor and color	Little to no byproducts for high purity
Cost	Lower material and processing costs	Higher material and processing costs
Flexibility	Less flexible and stiffer	More flexible and elastic
Biocompatibility	Limited because of residual byproducts	Excellent for medical and food-grade use
Thermal Stability	Superior resistance to high temperatures	Slightly less thermal stability but still supports autoclaving
Processing	Less sensitive to environmental factors	Requires precise control of curing conditions

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Platinum Cured Silicones

Platinum cured silicones use platinum-based catalysts to initiate crosslinking, a chemical process that joins two or more molecules together. Because a silicone hydride is added across a double bond, platinum cured silicones are also known as addition-cured. Platinum curing can begin at room temperature, but heat between 120° and 200°C is used to accelerate and control this process.

Advantages and Disadvantages of Platinum Cured Silicones

Platinum cured silicones have better tensile strength and better elongation properties than peroxide-cured silicones. They also maintain their mechanical properties over a wide temperature range, resist degradation, and are translucent in appearance (unless pigmented). Because they contain little to no byproducts, platinum cured silicones are higher purity materials.

The main disadvantage of platinum cured silicones is their higher cost. There’s also a risk of greater material waste because once the catalyst is added, the compound begins to cure, thereby reducing its shelf life in its uncured state. Platinum cured silicones are available in biocompatible USP Class VI formulations, but this designation generally applies to translucent compounds. If pigments are added, each color must be tested separately. Stockwell Elastomerics’ platinum cured SSP4749 high performance high consistency rubber (HCR) (request SSP4749 touch brochure) is an example of a medical grade, platinum cured silicone.

Applications for Platinum Cured Silicones

Platinum cured silicones are used in these and other applications.

• Medical and Healthcare: Sealing gaskets in applications requiring medical-grade material
• Pharmaceuticals: Drug delivery systems and specialty seals for sterile environments
• Food and Beverage: Seals and gaskets for food contact applications

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Peroxide Cured Silicones

Peroxide cured silicones use organic peroxides instead of platinum catalysts. When heated, organic peroxides decompose and generate free radicals that initiate the cross-linking of polymer chains. Typically, the temperature needed to initiate this process ranges from 150° to 200°C. Post-baking or post-curing removes some residues and odors, but peroxide cured silicones are not high purity materials.

Advantages and Disadvantages of Peroxide Cured Silicones

Peroxide cured silicones are generally more cost-effective, both in terms of raw materials and processing costs. They also provide better compression set properties for gaskets that need long-term sealing at elevated temperatures. In addition, peroxide cured silicones can resist harsh chemicals, oils, and solvents for long-term performance in challenging environments.

Most of Stockwell Elastomerics’ closed cell silicone sponge materials are produced from peroxide cured silicone rubber compounds in molded sheets or in continuous rolls. These compressible cushioning and gasketing materials withstand the same temperatures ranges as solid silicone rubber materials.

Among their disadvantages, peroxide cured silicones contain byproducts that can be released through outgassing, especially under low pressures or high temperatures. For example, in the vacuum of outer space, silicone outgassing can cloud the lenses on satellite optics. In medical applications, the high temperatures associated with autoclaving can also cause offgassing. Peroxide cured silicones can be ‘post-baked’ after curing to help drive off volatiles and reduce outgassing – Stockwell Elastomerics offers this service for applications that require it.

Applications for Peroxide Cured Silicones

Applications for peroxide cured silicones include:

• Aerospace and Defense: Seals, gaskets and cushioning pads that need to perform in low and high temperature extremes.
• Industrial: Gaskets requiring excellent compression set properties in high temperatures.
• Electrical Equipment: Gaskets and pads needing broad temperature range, electrical insulation and UL 94HB and UL 94 V-0 flame ratings.

Contact Stockwell Elastomerics for Platinum Cured Silicones and Peroxide Cured Silicones

Stockwell Elastomerics inventories, fabricates and molds many silicone materials and offers manufacturing processes processes include die cutting, waterjet cutting, flash cutting, strip slitting, molding and adhesive lamination. Contact us for further assistance with platinum cured silicones and peroxide cured silicones.