Silicone’s Properties and Advantages for Molded and Extruded Rubber

silicone propertiesSilicone is a versatile synthetic rubber used in nearly all industries for applications ranging from seals and tubing to insulating paints or films. Unlike similar organic materials such as natural rubber latex, which have a carbon-to-carbon backbone, silicone’s silicon-to-oxygen backbone makes it stable, resistant to damage, and flexible enough to be processed into end-use products with a variety of properties in a broad spectrum of temperatures from very high to very low.

Silicone can be processed into many forms, such as

  • Solid silicone rubbers
  • Liquids
  • Lubricants
  • Water-proofing agents
  • And more

Common silicone products stay stable elastically and mechanically across a wide range of temperatures from -60° C to +200° C. Specialty silicone products, such as certain types of silicone rubber and fluorosilicone, also possess a high tensile strength and extreme low and high temperature performance. For example, certain high-consistency rubber (HCR) silicone products have a tensile strength of more than 1800 psi., and are functional in temperature ranges from -75° C up to 220° C or higher.

Some of the most common types of manufactured silicone products include:

  • Adhesives, including both liquid adhesives and pressure sensitive tapes
  • Caulks, protective or waterproof coatings, and sealants
  • Electrical Insulation
  • Molds for fabrication
  • Silicone resins
  • Silicone rubbers tubing, profiles, and molded seals
  • Surfactants

These products and more are used across every industry, including but not limited to:

  • Food Preparation And Handling Equipment
  • Electronics
  • Healthcare
  • Transportation
  • Consumer goods

Before companies select the final type of silicone material for a product, it’s important to know the properties of silicone.

Properties of Silicone

silicone chemical properties

 

 

 

 

 

 

 

 

 

 

 

Silicone is the name for a general class of inorganic polymers that include materials both stable enough and flexible enough for industrial purposes. While there are several different types of silicone polymers, each one has a central strip, or backbone, of alternating silicon and oxygen.

Along the edges of this backbone are varying methyl groups that give silicone polymers their different properties and applications. Using organic methyl replacements can lead to unique properties, such as increasing the material’s flexibility at low temperatures or increasing solubility.

General silicone properties include:

  • Silicone polymers can be fabricated to remain soft and pliable throughout their lifetime without fatiguing, hardening, cracking, or requiring plasticizers. This makes this material optimal for products that undergo repeated loading/unloading, such as tubing in peristaltic pumps.

 

  • Hydrophobic properties.Silicone seals repel water to protect underlying materials without restricting breathability. This property is essential in waterproof coatings and films, and insulating components.

 

  • Low rotation barriers.Silicone’s molecular backbone has low rotation energy, which gives it greater rotational freedom that contributes to the material’s flexibility.

 

  • Resistance to aging.Silicone resists degradation caused by UV radiation, chemical exposure, and poor environmental conditions.

Physical Properties of Silicone

Silicones can be processed and formed into different shapes and sizes, which then retain properties such as:

Flexibility

Silicone’s silicon-oxygen chain backbone gives the material great flexibility, even once it’s been set and molded. Silicone components can be folded, bent, and twisted without suffering damage.

Hardness

Silicone materials use comparative scales called Shore hardnesses to characterize their hardness. The two commonly used Shore scales for silicones are Shore 00 for silicone sponge products and Shore A for dense products. Commonly used dense silicone materials typically have a Shore hardness of 30A-70A on a scale of 0-100A. Specialty grades can go as low as 10 Shore A to as high as 90 Shore A. For comparative purposes, 20 Shore A indicates a “feel” similar to a racquetball and 80 Shore A feels more like the tread on an automobile tire.

Color and Finish

Silicones in their original state are translucent white. Silicone polymers can be colored and finished to have different hues and surface textures.

Electrical Insulation and Conductivity

Silicones in their original state are highly insulative electrically. As such, they are often used in applications where high dielectric strength is needed. What is unique about silicone is that they accept high levels of fillers and retain processability. As a result, they are often filled with conductive fillers to achieve very low resistance and are used as seals on electronics to provide EMI/RFI shielding.

Thermal Insulation and Conductivity

Silicones in their original state are highly thermally electrically. As such, they are often used in applications where low heat transfer is needed, such as in tubing for fluid conveyance in food handling or oven applications. What is unique about silicone is that they accept high levels of fillers and retain processability. As a result, they are often filled with materials to increase their thermal insulation even more, or conversely, with thermally conductive fillers to achieve very high heat transfer, such as for thermal interface (TIM) materials in electronics.

Melting Point

Because silicone is a thermoset elastomer, it does not truly melt. It will continue to function and retain its elastic and mechanical properties to the point where enough energy is imparted to the polymer that the polymer chain starts to break down. In general, silicone rubber can withstand temperatures as high as 300° C.

Set Shapes

Silicone polymers can be fabricated into set shapes and dimensions that hold their form after crosslinking. These forms include:

  • Tubes
  • Gaskets
  • Sheets
  • Complex molded components

With these properties, silicone is the ideal material for manufacturing O-rings, gaskets, tubes, and solid seals. These silicone O-rings and other parts are thin, flexible, and resistant to temperature extremes and chemical damage.

Silicone Rubber Properties

silicone temperature range

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Silicone elastomers are one subgroup of silicone polymers. The material is stable, easy to handle, and usually formed into components through the extrusion or molding processes. Through a variety of fabrication processes, silicone rubbers can form custom rubber gaskets and seals, rubber tubing and silicone tubingrubber and silicone extrusions, and more.

Beneficial properties of silicone rubber include:

  • Flame retardancy and steam resistance. Silicone rubber’s general resilience to heat, steam, and flame damage make it a good material candidate for components in engines, processing plants, and cooking or food preparation industries. The material can be used safely across a wide range of temperatures. When it’s specially formulated for temperature extremes, it can be used at a low of -100° C to up to 250° C.
  • Food-grade materials rating. Silicone rubber seals and component extrusions are ideal for food production and handling. Food-grade silicone is ideal for fabricating cooking tools, conveyance tubing, oven/refrigeration seals and other parts or surfaces used during food production and handling. Because it does not require plasticizers to achieve flexibility, silicones do not impart taste or leach chemicals such as BPA into the food it contacts. Silicones are commonly available in grades consistent with FDA requirements for food contact detailed in 21CFR177.2600 and are available in NSF-51 listed compounds.
  • Good compression set. Silicone materials exhibit a high resistance to compression set after the curing process is complete. As a result, silicones retain consistent mechanical properties over their life.
  • UV resistance.While natural rubber is subject to aging over time due to sunlight exposure, silicone rubber’s silicon-oxygen composition makes it much better suited for prolonged UV exposure. This makes silicone rubber ideal for exterior applications featuring regular or prolonged sunlight exposure.
  • Resilience and rebound. Silicone materials are typically flexible and return to their original form after flexing or bending. The flexibility of the end product will ultimately depend on the hardness rating of the raw silicone material.
  • Strong adhesion to metals. Silicone adheres well to metal materials, such as during molding and extrusion
  • Tensile strength.Silicone rubber’s tensile strength ranges from 200-1,500 psi, depending on the fabrication process and compound formulation. Some grades of silicone rubber can also be stretched to 700% of its original dimensions before cracking or ripping under the tension.
  • Highly inert. Silicone rubber is considered an inert substance, meaning that it doesn’t react with many chemicals or biological elements. Further, it is considered hypoallergenic making an ideal replacement for natural rubber/latex in skin contact and medical applications. Many grades have been testing to requirements detailed in USP Class VI.

Fluorosilicone vs. Silicone

Fluorosilicone is a variant on the silicone polymer with unique characteristics that make it an ideal material for caustic conditions and environments that face temperature and pressure extremes. While both fluorosilicone and silicone are long-lasting and elastic materials, fluorosilicone has greater chemical resistance properties. It can better withstand damage from the following non-polar solvents:

  • Acids
  • Alkaline chemicals
  • Fuels
  • Oils and hydrocarbons

Fluorosilicones provide longer-lasting EMI/RFI shielding in exterior environments, environments with exposure to chemicals. This makes fluorosilicone ideal for components and seals in the following industries:

  • Aerospace and aviation
  • Automotive
  • Marine

Fluorosilicone is also commonly used for cushioning and static sealing applications, and for tubing to convey non-polar solvents.

Silicone vs. Natural Rubber/Latex

While both silicone and natural rubber are elastomers, their chemical compositions are very different. Unlike silicone’s inorganic silicon-oxygen backbone, rubber has a carbon-carbon bond backbone. Natural rubber is an organic compound, though it can also be synthesized.

Silicone is often considered to be ‘inorganic rubber’ due to many of the shared characteristics between the two materials. However, silicones can be created with a greater range of special properties so industry-specific parts can be customized for long-lasting use in adverse conditions.

Silicone’s superior strengths over natural rubber/latex include:

  • Greater resistance to heat damage.
  • Increased resistance to chemical attacks, corrosion, and degradation from prolonged exposure to caustic and acidic compounds.
  • Greater resistance to damage from fungus and organic buildup because the material itself is inorganic.
  • More resistant to ozone attacks.

Both materials can be used to create EPDM tubing for O-ring fabrication, seals, and more across multiple industries.

Silicone Temperature Ranges

One of silicone’s greatest strengths is its resistance to both heat damage and degradation of elastic properties in low temperatures. Silicone gaskets, for example, can weather temperature extremes of -50° C to 250° C (-60° F to 480° F). Different silicone polymers can be specially created and fabricated to withstand different ranges on this spectrum while retaining or enhancing additional qualities.

Industrial Silicone Products from Vanguard Products

Silicone is a versatile, stable synthetic rubber material that can be used across all industries. The material is easy to handle and can be formed to produce O-rings, gaskets, seals, complex components, and liquid adhesives and seals. Its many valuable properties include:

  • Ability to be chemically modified in fluorosilicones, organic-inorganic mixtures, and hundreds of varied polymers
  • Conductivity and use in electromagnetic interference shielding (EMI shielding) and RFI shielding gaskets . Silicone is also ideal for the fabrication of M83528 EMI/RFI shielding gaskets.
  • Flexibility
  • Food grade ratings
  • High tensile strength
  • Resilience
  • Resistance to chemical damage and corrosion
  • Water resistance and hydrophobic sealing

Silicone is the ideal material for extruded and molded parts for industrial, commercial, and consumer products. For more information about our expansive line of silicone-based industrial products, please contact us or request a quote.

 

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