Misconceptions about Liquid Silicone Rubber (LSR)

The silicone family is made up of an enormous variety of compounds, and is perhaps the most widely used family of materials in the world. Liquid Silicone Rubber materials can be found in consumer products in applications such as appliances and electronics, in astronomy, biotechnology, and in the automotive, aviation, beverage, construction, paint, plumbing, textile, and toy industries.

There are some myths and misconceptions associated with silicone materials as a whole, including Liquid Silicone Rubber that prevent some practitioners from using these materials with full confidence. The following are the most common myths about the silicone family of materials, with a special focus on Liquid Silicone Rubber, and a simple explanation about why each are not accurate.

Misconception # 1: Silicone is a chemical element or ingredient

The silicone products that first come to mind are usually breast implants, lubricating oils, an ingredient in certain cosmetics, and may even be confused with silicon. The reality is that silicones are a family of chemicals with different states (liquid, gel, solid). Speaking specifically of silicone rubbers, they are long macromolecules formed by silicon (Si) and oxygen (O), and depending on the arrangement, they can have different properties and be used in different applications [3].

Misconception # 2: Silicone Rubbers are synthetic materials

Silicone rubbers, including LSRs, are synthetic from the perspective that their synthesis is created by humans. However, the raw material is completely natural: the sand or “silica” is formed by silicon and oxygen. In fact, for many years humans have used natural silicon materials in arrowheads and bowls. Although silicon, silica, and silicone are different, the confusion is understandable. To clarify: Silicon is a chemical element; Silica is a silicon dioxide (sand) that is used to produce the Silicone family of materials [3].

Misconception # 3: Silicone rubbers can only be processed and applied at high temperatures

There are different types of silicones, for example, Room Temperature Vulcanization (RTV) Silicone Rubbers that can be processed and applied at room temperature. If the application requires the use of Liquid Silicone Rubber (LSR), they can be modified in such a way that they can be molded and vulcanized at low temperatures. This is mainly used in electrical and electronic applications [2].

Misconception # 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 are sticky, however it depends on the processing and the application needs. For example, in cable insulation, or in medical applications using Liquid Silicone Rubber, the surface of the part must be as smooth as possible, without a sticky feel. The silicone rubber formulation can be modified to include Mica or the processing conditions can be changed [2].

Misconception # 5: Silicone rubbers are soft and flexible

Shore is the scale used to measure the silicone hardness, For instance, a rubber band has a 25 Shore, and roller or skate wheels a 100 Shore. It is commonly believed that all silicones have a hardness of less than 40 Shore, and therefore they are thought to 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 in hardness, and has almost no elasticity [5].

Misconception # 6: Silicone rubbers generate a lot of fumes when they burn

It is believed that burning a silicone rubber generates fumes and gases that would be a disadvantage for certain applications. Actually, silicone rubbers by nature are self-extinguishing, and depending on the compounding of silicone rubber, generation of gases and fumes can be completely eliminated by adding flame retardants, and complying with standard requirements [2].

Misconception # 7: Silicone rubbers contribute to atmospheric contamination

The chemicals that cause environmental contamination are volatile organic compounds (VOCs), such as acetones, alcohols, methacrylates, acetates, among others. Chlorofluorcarbon compounds (CFCs) have been identified has having an effect on the ozone layer [4]. Due to its inorganic nature, silicone compounds or mixtures do not contain these type of chemicals that contribute to contamination.

Misconception # 8: Silicone rubbers take thousands of years to degrade

From the literal definition of biodegradation, silicone rubber is not biodegradable. However, with certain environmental conditions, the silicon-oxygen backbone can be split into water, silic acid, and carbon dioxide. Sunlight and atmospheric oxygen create low molecular weight silicone chains (cyclopentasiloxane). When they are buried, soil minerals act as catalysts, accelerating the chain scission and degrading the silicone rubber in only days [6].

Misconception # 9: Silicone rubbers create allergies and irritations

Many studies have been conducted on this subject, and unlike other types of rubbers (i.e., natural latex rubber), silicone rubbers do not irritate the skin or create allergic reactions. In fact, the inherent biological inertness of silicone (including Liquid Silicone Rubber) is an advantage. [2].

Misconception # 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 rate of intake of the substances is greater than the rate of the excretion or metabolic transformation of the substance” [1]. In extensive testing, silicone rubbers have exhibited superior compatibility with human tissue and body fluids and an extremely low tissue response when implanted, compared with other elastomers. Odorless and tasteless, silicones do not support bacteria growth and will not stain or corrode other materials. They are often formulated to comply with FDA, ISO, and Tripartite biocompatibility guidelines for medical products [3}.

Misconception No. 11: Silicone rubbers cause diseases

Due to fact that many applications of silicone rubber are in contact with the human body or with food, there is a concern that the material can cause diseases. As far as the release of molecules during the application, they are too big to penetrate tissues. The Food and Drug Administration (FDA) is very strict about materials that contact human beings and has approved use with consumables such as food and beverages and food-safe silicone is also found in use in the cosmetics and pharmaceutical industries [7].

References

  1. http://www.dictionary.com
  2. http://www.calmont.com/blog/?p=908
  3. http://www.mddionline.com/article/silicone-rubber-medical-device-applications
  4. http://www.skininc.com/skinscience/ingredients/12-Silicone-Myths-Exploded-269445911.html?prodrefresh=
  5. http://www.ozone-hole.org.uk
  6. http://www.dowcorning.com
  7. http://www.rubbercal.com/industrial-rubber/fda-approved-rubber/