Are you worried about the safety of the silicone in your products? Are you wondering if silicone contains ingredients that could affect its application? This article will show you what silicone is made of and how those ingredients affect it, to help you solve these doubts.
What Is Silicone
Silicone is not made from plastic or latex. It is a synthetic polymer material, formally known as polysiloxane. Silicone has a backbone composed of alternating silicon and oxygen atoms, to which organic groups such as methyl and phenyl groups are attached. This makes silicone a unique material, possessing characteristics of both organic and inorganic chemicals.
Depending on the length of these backbones, the types of organic groups, and the degree of cross-linking between the backbones, silicones can exist in many forms. Silicone rubber, or silicone elastomer, is one of the most common forms of silicone. In addition, it can also appear in liquid form or as a harder silicone resin.
Silicone’s unique structure gives it these characteristics:
- Wide temperature tolerance range: from 230°C to 60°C
- Chemically inert
- Biocompatibility
- Electrical insulation
- Weather resistance
What Is Silicone Made of
Silicone itself is safe and biocompatible, but silicone materials usually contain more than just polysiloxanes. During the manufacturing process, other chemicals may be mixed into the silicone material.
Raw Material
The entry of chemicals begins as early as the raw material stage. Silica, methanol, and water are the main raw materials for silicone. The purity of the silica material greatly affects the quality of the silicone. The silica material used in industrial silicone production is generally quartz sand. Unlike ordinary sand that you can see on the beach, quartz sand is high-purity silica that has undergone impurity removal and purification processes.
But even after purification, quartz sand inevitably contains impurities. High-quality silicone uses relatively clean quartz sand. Industrial-grade quartz sand, which focuses on cost-effectiveness, may contain more iron-containing minerals or elements such as aluminum and potassium, which can negatively impact quality.
Intermediate Products (D4, D5, D6)
After silica sand is initially heated to separate silicon, it undergoes hydrolysis, polymerization, vulcanization, and molding to obtain the silicone we know. During this processing, intermediates such as D4, D5, and D6 are produced. The reason for specifically mentioning these intermediates is that they may remain in the finished product, and intermediates D4, D5, and D6 are subject to strict regulation.
Studies have found that these three intermediates pose a risk of accumulating in organisms and producing persistent toxicity. What’s worse, they are volatile, and when excessive amounts remain within the silicone, they can slowly escape.
However, you don’t need to worry about the safety of high-quality silicone. The EU has already established regulations for them, including them in the list of chemicals to be tested in silicone for cosmetic, food-grade, and other applications. Manufacturers must control their content at very low levels.
Vulcanizing Agent
Another processing step that inevitably introduces impurities is vulcanization. During vulcanization, the silicone’s raw material is mixed with vulcanizing agents, fillers, pigments, additives, etc., ultimately forming an elastomer with a certain strength. Vulcanizing agents and vulcanization byproducts will mix into the silicone at this stage.
Silicone mainly has three vulcanization methods: peroxide vulcanization, platinum vulcanization, and condensation vulcanization. Their main characteristics are as follows.
| Characteristics | Peroxide Vulcanization | Platinum Vulcanization | Condensation Vulcanization |
| Vulcanizing Agent | peroxide | platinum catalyst | organotin |
| Toxicity of Vulcanizing Agents | toxic | harmless | toxic
|
| Potential for Toxic Byproducts | Yes | No | Yes |
| Odor | “rubber” odor
| odorless
| irritating odor
|
| Cost | cheap | expensive | moderate |
| Application Areas | ordinary silicone | food-grade silicone medical-grade silicone | silicone sealant |
Platinum curing is the primary curing method for liquid silicone rubber (LSR), a type of silicone rubber used in the food and medical fields. Even if platinum catalyst residues remain, they are harmless to the human body and don’t produce harmful byproducts, thus meeting safety requirements.
If you want to buy a safer silicone, choosing silicone that has been vulcanized with a platinum catalyst is a better choice.
In contrast, silicone rubber cured with peroxides and organotin generally has an odor, which is a key difference between high-quality and ordinary silicone rubber. During the catalytic process, they also produce byproducts such as acids and alcohols that are harmful to the human body. Unless they undergo secondary sulfidation, they are generally used in industrial-grade silicones.
Filler
In addition to residual vulcanizing agents, manufacturers also actively introduce fillers to improve the properties of silicone. The most important filler of silicone rubber is silica.
Silica, used as a filler, differs from quartz sand, a raw material, in that it is a finer nanomaterial. Sometimes it’s also called “white carbon black”.Adding silica to silicone transforms it from a material with extremely poor strength into a flexible yet relatively strong elastomer.
It can be said that silica filler is indispensable to silicone materials. Without it, silicone can’t have the wear resistance, tensile strength, and tear strength that make it widely applicable in various fields.
The silica filler added to silicone can be classified into fumed silica and precipitated silica, depending on the synthesis method.
Fumed Silica(pyrogenic silica)
Fumed silica, or pyrogenic silica, is a type of silica produced in a flame. Its particles are extremely small, less than 50 nm in size, resulting in a very fluffy overall texture.
Due to the manufacturing process, it is relatively expensive, but it significantly improves the mechanical properties of silicone. Often, only a small amount needs to be added to increase the hardness of the silicone effectively.
What’s more, because of its very small particle size, silicone with added fumed silica still maintains high transparency. High-quality silicones almost exclusively use fumed silica as a filler.
Precipitated Silica
The manufacturing process of precipitated silica determines its lower price. Precipitated silica is formed in an aqueous solution, undergoing washing, drying, and pulverization to become a powder.
Precipitated silica particles are larger than those of fumed silica, its particle diameter is around 5-100 nm. The larger particle size makes it less effective at increasing silicone strength than fumed silica. However, precipitated silica is a cost-effective choice and is enough for ordinary silicone applications.
Other Additives
To control the bonding degree between silica filler and silicone, structural additives are often added to the silicone. Hexamethylsilazane is used in the manufacturing process of ordinary silicone, while medical-grade and food-grade silicone use more stable and safer hydroxyl silicone oil as a structural additive.
In addition, there are many additives used to improve or change certain properties of silicone. Their specific effects on silicone are as follows.
How Silicone Composition Affects Performance And Applications
Conductive Silicone
Silicone has a high dielectric constant and is often used as an electrical insulating material. Carbon black and silver powder can make silicone conductive, so they are added to conductive silicone. At the same time, carbon black also makes the silicone less prone to cracking due to external forces.
With its conductive properties, silicone can be used to make remote control buttons and EMI shielding gaskets.
Flame-retardant Silicone
Alumina trihydrate is a flame retardant and a component of silicone sealants used for fire or smoke protection. When exposed to high temperatures, it produces water to prevent the fire from spreading.
Thermal Conductive Silicone
To improve the thermal conductivity of silicone for use in heat dissipation pads, fillers such as boron nitride are added to the thermally conductive silicone. These help the silicone better transfer heat from components requiring heat dissipation, accelerating the cooling process.
Silicone with Stronger Weather Resistance
Titanium dioxide makes silicone more stable and durable under sunlight, which is undoubtedly important for outdoor applications that are frequently exposed to ultraviolet rays. Adding titanium dioxide also makes silicone less prone to yellowing, slowing down its aging process.
Fillers Are Used to Improve the Mechanical Strength of Silicone
Talc Powder
In the industrial sector, talc powder is a widely used filler. Its chemical composition is natural hydrated magnesium silicate, which can reduce costs while minimizing the permanent shape changes that occur to silicone after it has been compressed.
You may have heard its bad reputation. Talc may contain asbestos, a carcinogen, so industrial talc must never be found in standard medical-grade and food-grade silicone.
Glass Fiber
Glass fiber can improve the mechanical strength of silicone, making it more resistant to tension and impact, but it also affects the elasticity of silicone, making it less flexible. It is used in some silicone seals that require higher strength.
Calcium Carbonate
Like talc powder, calcium carbonate filler can also reduce the production cost of silicone. Its effect on silicone performance enhancement is minimal. In inferior silicone, its content may be relatively high.
It is worth noting that more filler is not always better. Appropriate amounts of filler and additives can improve the performance of silicone, but excessive filler can affect the transparency, flexibility, and other properties of silicone.
Food-grade Silicone
The U.S. Food and Drug Administration (FDA) and other agencies have imposed strict safety requirements on food-grade silicone. Food-grade silicone must be non-toxic and stable, and must not release harmful chemicals within a specified temperature range.
Many industrial fillers can’t be added to food-grade silicone. As an alternative, food-grade silicone uses safer, more stable fillers and additives. Except for platinum catalysts and fumed silica, the most variable additive in food-grade silicone is coloring.
Food Contact Pigments
Food-grade silicone doesn’t use industrial pigments that may contain heavy metals, but instead uses food-contact grade inorganic pigments such as iron oxide and titanium dioxide. They were chosen because of their stability, especially under conditions like high-temperature baking. You don’t need to worry about your colorful silicone utensils fading from hot soup. They also rarely react with chemicals in food.
Improvement Additives
Some of the additives mentioned earlier in the section on industrial silicone additives can also be used to improve the properties of food-grade silicone after certain processing. Food-grade alumina and boron nitride can enhance the thermal conductivity of silicone baking mats.
Antibacterial Agent
Because food production demands higher hygiene standards, some food-grade silicone products are added with antibacterial agents such as silver ions. Small amounts of silver ions are harmless to the body, making them a safe additive. By creating better hygiene conditions, antibacterial products that meet safety standards actually enhance the safety of food production.
Medical-grade Silicone
Due to strict safety requirements, medical-grade silicone rarely contains additional fillers or additives. The fumed silica in medical-grade silicone must meet USP requirements and pass a series of medical-related safety tests. Because of its safety profile, platinum-cured silicone rubber is the primary curing method for silicone used in medical applications.
Barium Sulfate
Because some silicone instruments require X-ray imaging, barium sulfate is added to the silicone as a component to increase its density. This additive undergoes rigorous testing before official use, ensuring its safety.
Antibacterial Agent
Similar to food-grade silicone, some medical-grade silicone also contains silver ions, an antibacterial ingredient. The difference is that medical-grade silicone with added silver ions needs to pass cytotoxicity and irritation tests.
Is Silicone Safe?
If you are referring to food-grade and medical-grade silicone and their products, they are safe as long as they have passed safety certifications and are used appropriately. Industrial-grade silicone, due to its manufacturing process and the additives it contains, can’t ensure safety for the body.
High-quality silicone products that meet standards are free of toxic chemicals such as BPA and phthalates. Their safety is guaranteed not only by their inherent stability but also by national regulations.
For food-grade silicone, this standard could be FDA 21 CFR Part 177.2600 or the stricter LFGB. Medical-grade silicone must comply with USP Class VI, ISO 10993, ISO 13485, and pass a series of tests.
If you would like to learn more about the safety of silicone, please read Is Silicone Toxic: Silicone Safety Guide.
FAQ
Can I Customize Silicone with a Specific Formula or Needs?
Some manufacturers offer customized silicone formulations, although there is usually a minimum order quantity. You can provide an existing formula directly or provide specific requirements for customization. A professional R&D team will first experiment with formulations based on your needs and then send samples for testing.
Customizable components include pigments for color matching, fillers and additives to improve or alter conductivity and transparency, or components that affect the curing time of the silicone sealant.
How Can I Confirm Whether the Silicone I Purchased Is Safe?
First, when purchasing silicone, please confirm whether the silicone product meets FDA, USP, and other standards.
After receiving the product, you can first smell it to see if it has any odor. Food-grade and medical-grade silicone, because they use a platinum vulcanization process, generally don’t have an odor.
You can also observe the transparency of the silicone after it has been stretched. Silicone containing a large amount of inferior fillers, silicone using precipitated silica, and silicone without structural stabilizers generally have low transparency and will become white.
Why Doesn’t Food-grade Silicone Use Edible Pigments Like Allura Red?
For food-grade silicone, edible synthetic organic pigments like Allura Red are not safe additives. Firstly, regulations prohibit the use of these pigments in food-grade silicone.
Secondly, food-grade doesn’t equal edible. Edible silicone products are more commonly used in baking and processing. Allura Red, which bleeds color, is unacceptable for silicone that requires its internal chemicals not to be released at high temperatures. What’s more, the color-bleeding process is uncontrollable, and excessive amounts of edible pigments may be harmful.
Will Silicone Rubber Melt When Heated Like Plastic？
Unlike plastic, silicone doesn’t truly melt, but it ages and decomposes rapidly when exposed to excessively high temperatures. You can observe that when overheated, its surface ages and turns yellow, or even carbonizes and turns black, and its hardness also changes.As long as you use certified silicone products within the specified temperature range, you don’t need to worry about these issues.
Read Silicone Melting Temperature: A Deep Guide to learn more.
Is Silicone an Environmentally Friendly Material?
Compared to materials like plastic that produce microplastics, silicone is undoubtedly an environmentally friendly material.
While it’s true that silicone production consumes a significant amount of energy and it’s difficult to decompose in the natural environment, using durable silicone products can greatly reduce the use of disposable materials and plastics. Silicone also doesn’t drop microplastics, which are tiny particles that are very harmful to the environment. And it can be recycled through specialized recycling facilities.
What Types of Silicone Rubbers Are There?
- High-Temperature Vulcanizing Silicone Rubber (HTV): A type of silicone rubber typically sold in sheet or block form, requiring high temperatures for curing and molding. Due to its good mechanical properties, it’s often used to make O-rings and gaskets.
- Room-Temperature Vulcanizing Silicone Rubber (RTV): A silicone rubber sold in a viscous liquid form that cures easily at room temperature and is the main component of silicone sealants.
- Liquid Silicone Rubber (LSR): Famous for safety, its excellent fluidity makes it suitable for use in precision products.
Here is more information about different types of silicone rubber: A Simple Guide to Silicone Rubber Types and Applications.
Final Thoughts
A stable and efficient formula is the guarantee of high-quality silicone products. Legensilico provides more details and one-stop silicone solutions, manufacturing a wide range of high-quality products from industrial to medical-grade silicone. We have a professional team that can assess the feasibility of your custom project and provide comprehensive services from initial sketches to the final product. Take action now to meet your needs!
