10 Misconceptions About Liquid Silicone Rubber

With Contributing Expertise From: simtec

The silicone family comprises an enormous variety of compounds and is the world’s most widely used family of materials. Liquid silicone rubber (LSR) materials are widely used in  consumer products such as appliances, shower and faucets, electronics, baby products, food and beverage products, and healthcare applications. It also finds extensive use in the automotive, aviation, industrial and construction, textile, and toys and recreational products industry.

Some myths and misconceptions associated with silicone materials, including Liquid Silicone Rubber, can prevent practitioners from using these materials with complete confidence. The following are the most common myths about the silicone family of materials, focusing on why each of these misconceptions of liquid silicone rubber is inaccurate.

1. Silicone Is a Chemical Element or Ingredient

Silicones are a family of chemicals with different states like liquid, gel, and solid. Silicone is a nonmetallic chemical element in the carbon family, part of group 14 on the periodic table of elements. Liquid silicone rubber uses two components to reinforce long polysiloxane chains with specially treated silica. The first component may contain a platinum catalyst that cross-links with the second component, a methyl hydrogen siloxane, and an alcohol inhibitor. Silicone rubbers are long macromolecules formed by silicon (Si) and oxygen (O), and depending on the arrangement, they can have different properties and for use in other applications.

2. Silicone Rubbers Are Synthetic Materials

Silicone rubbers, including LSRs, are synthetic from the perspective that humans create their synthesis by modifying the chemical element of silicon, which is naturally occurring. However, the raw material is completely natural. Sand, or “silica,” is formed by silicon and oxygen. In fact, for many years, humans have used natural silicon materials in arrowheads and bowls. Silicon is a chemical element — Silica is a silicon dioxide, or sand, used to produce the Silicone family of materials.

3. Silicone Rubbers Can Only Be Processed and Applied at High Temperatures

Different types of silicones, for example, Room Temperature Vulcanization (RTV) Silicone Rubbers, can be processed and applied at room temperature. If the application requires the use of Liquid Silicone Rubber (LSR), they can be modified so that they can be molded and vulcanized at low temperatures. This is mainly used in electrical and electronic applications. This high-performance elastomer has good low-temperature flexibility with notably high-temperature resistance too. There are three types of silicone rubber:

  • High-temperature vulcanized (HTV): HTV is a solid silicone rubber that must vulcanize under the same temperatures as traditional rubbers. It has high temperature and chemical resistance and acts as a good insulator.
  • LSR: We use LSR to inject into molds using specialized equipment to manufacture components for various industries.
  • Room temperature vulcanized (RTV): RTV is a silicone rubber that cures at room temperature with a soft to medium hardness. It works well as a sealant in the automotive, electronics, and aerospace industries.

4. Silicone Rubbers Are Tacky

This myth is related to the tactile feel of silicone rubber. Usually, people tend to think that all silicone rubber is sticky. However, it depends on the processing and the application needs. For example, in cable insulation or medical applications using Liquid Silicone Rubber, the part’s surface must be smooth, without a sticky feel. The silicone rubber formulation can include Mica, or the processing conditions can be changed.

5. Silicone Rubbers Are Soft and Flexible

The scale used to measure the silicone hardness is the shore scleroscope, so a rubber band likely has a 25 Shore and roller or skate wheels a 100 Shore. The hardness or durometer can range from 0 to 100 Shore A, from gel like to firm. A common belief is that all silicones have a hardness of less than 40 Shore. So, it may seem that they have low mechanical properties. However, this is not the case.

There are many ways to increase the hardness of silicone rubber, such as creating more crosslinks or adding fillers. For example, optical liquid silicone rubber has a 70 Shore hardness and almost no elasticity. It is worth noting that silicone rubbers also have a tensile strength of 1750 psi making this substrate very durable. LSR will maintain its flexibility throughout and extensive temperature range, which is a good characteristic for substrates operating in challenging environments.

6. Silicone Rubbers Generate a Lot of Fumes When They Burn

Some believe that burning silicone rubber generates fumes and gases that would be a disadvantage for certain applications. There are a variety of silicone rubbers, for example processing platinum-cured silicone rubber does not emit excessive gasses, however processing peroxide-cured silicone rubbers have certain ventilation requirements. By nature, silicone rubbers are self-extinguishing, and depending on the compounding of silicone rubber, generating gases and fumes can be eliminated by adding flame retardants and complying with standard requirements.

7. Silicone Rubbers Contribute to Atmospheric Contamination

The chemicals that cause environmental contamination are volatile organic compounds (VOCs), such as acetones, alcohols, methacrylates, and acetates, among others that are not present in silicone rubber and more common in plastic materials. Chlorofluorocarbon compounds (CFCs) have an effect on the ozone layer. Due to its inorganic nature, silicone compounds or mixtures do not contain these chemicals that contribute to contamination. The LSR molding process is highly efficient and produces minimal waste.

8. Silicone Rubbers Take Thousands of Years to Degrade

With certain environmental conditions, the silicon-oxygen backbone of LSR can split into water, silic acid, and carbon dioxide. Sunlight and atmospheric oxygen create low molecular-weight silicone chains or Cyclopentasiloxane. When buried, soil minerals act as catalysts, accelerating the chain scission and degrading the silicone rubber in days. LSR components are also recyclable and together with its minimum-waste benefit during production, this constituent can have a very environmentally friendly profile.

9. Silicone Rubbers Create Allergies and Irritations

This subject is studied closely, and unlike other types of rubbers like natural latex rubber, silicone rubbers do not irritate the skin or create allergic reactions. Silicone allergies are often due to contaminants or other materials in the production of components containing silicone rubbers. The inherent biological inertness of silicone, including Liquid Silicone Rubber, is an advantage, they are biocompatible and hypoallergenic. Those with a latex allergy are likely to find an allergy-free alternative in silicone rubbers.

10. Silicone Rubbers Bioaccumulate in the Human Body

Bioaccumulation is “the accumulation of a toxic substance in tissues of a living organism. It occurs when the intake rate of the substances is greater than the rate of the excretion or metabolic transformation of the substance”. Silicone rubbers have exhibited compatibility with body fluids and human tissue, with a deficient tissue response with implants, compared with other elastomers. Liquid silicone rubber may move through the human body if injected or somehow ingested. However, there are no applications that allow this substrate to be injected into a person. They must comply with guidelines set by the FDA, ISO, and Tripartite biocompatibility for medical products. Silicones do not support bacteria growth, feature stain and corrosion resistance advantages and are easy to clean.

Bonus Misconception: Silicone Rubbers Cause Disease

Because many silicone rubber applications are in contact with the human body or with food, there is a concern that the material can cause diseases. Regarding the release of molecules during the application, they are too big to penetrate tissues. The Food and Drug Administration (FDA) is strict about materials that contact human beings and has approved use with consumables such as food and beverages. Food-safe silicone also finds use in the cosmetics and pharmaceutical industries.

Choose SIMTEC for LSR Components

LSR is well-suited for a wide range of applications and can align with various materials and processes. It also has one of the most effective tooling processes for high-volume production, thanks to quick cycle times. Silicone rubber offers many optimizing loops, ensuring efficiency in the parts you need for your operations.

SIMTEC has over 20 years of knowledge and experience working with LSRs, advanced automation and technology, and a team of LSR and LIM (liquid injection molding) experts that have extensive technical capabilities. We are committed to delivering consistent quality LSR components with simple to complex part designs for a wide range of industris. We are ISO 9001, ISO 13485, and IATF 16949 certified, ensure your products meet stringent quality standards throughout the manufacturing process. Contact us today for more information on how we can help to optimize your products with LSR materials.



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