If you think fillers are just ‘cheap bulk additives’ in the silicone manufacturing industry, you are wrong. Silicone rubber itself offers great chemical resistance, thermal stability, durability, and flexibility. But using pure silicone rubber for every product for commercial use is not efficient economically and may fall short in functionality and performance. That’s when filler comes in to increase the functionality, strength, and efficiency. Today, we’ll discuss everything about common fillers in silicone rubber, their usage, and their effects on the environment.
What Are Fillers in Silicone Rubber?
Fillers are mineral powders or other additives that are mixed with pure silicone rubber. This is a crucial component in the silicone product manufacturing industry for regulatory compliance, scalability, and performance consistency.
They can be made of different components depending on the product type. But usually fillers are mostly made of silica and calcium carbonate, and other organic and inorganic compounds. What fillers will be used depends on the required modification and final product.
A lot of crucial factors like cost optimization, desired performance, and functionality depend strictly on proper filler selection and adding them to pure silicone rubber in precise proportions.
Why Add Fillers to Silicone Rubber?
· Cost Optimization
Virgin silicone polymer is expensive than a silicone rubber compound. The mineral fillers are comparatively cheap. So if the polymer is partially substituted with mineral fillers, the raw material cost per part will decrease drastically.
So the manufacturers can produce with cost optimization while maintaining acceptable volume and mass. So, using fillers is crucial for reducing the usage of virgin silicone rubber in high-volume and price-sensitive products.
· Performance Enhancement
Filler compounds in pure silicone rubber may sound like they reduce the silicone quality, but in fact, fillers enhance the performance of the product. Pure silicone cannot be directly turned into a usable plate, cat toy, or collapsible water bottle.
Fillers are what give silicone its improvement in strength, hardness, and many other factors. They increase mechanical strength, thermal resistance, stability in environmental stress, tear resistance, high durability, etc, of the final product.
· Functionalization
Fillers have another reason to use other than cost optimization and strength. And that is for additional functionalities depending on the fillers. Carbon-based fillers like graphene, carbon black, and carbon nanotubes can alter thermal or electrical conductivity or insulation. A metallic or ceramic filler can also change electrical properties, thermal conductivity, EMI shielding, etc.
Some fillers, like alumina trihydrate, can be used to give the product functionality like fire safety or flame retardancy. Mineral fillers work as color for the silicone products. So different mineral filler is used as pigment to get the desired color in the product. Besides, they also determine the surface finish of the product. So specific filler is used to get a glossy or matte finish on the final product.
Detailed Types of Common Fillers in Silicone Rubber
Fillers in silicone rubber can be categorized by their intended effects. Common fillers can be broadly separated into three categories. These are:
1. Reinforcing Fillers
These types of fillers are used to enhance strength, stability, and durability. They can consist of different compounds.
· Precipitated Silica:
It’s a very common filler in silicone rubber. It is especially used for improving tensile strength, tear resistance, thermal, and environmental stability. In the chemical reaction with the pure silicone rubber, it interacts with silicone chains. It creates compounds through hydrogen bonding or silanol-siloxane interactions, which are more stable and stronger than pure silicone rubber.
· Fumed Silica:
This type of filler is used in the raw material of silicone products requiring high durability and performance. Fumed silica has a finer particle size and a higher surface area than precipitated silica, which leads to higher reinforcement. Due to its fine size, high surface, this type of filler improves stiffness and processing behavior.
Carbon-based Reinforcing Fillers:
These fillers are carbon black, carbon nanotubes (CNT), and graphene. These are used for properties like electrical conductivity, UV resistance, thermal conductivity, and EMI shielding.
· Glass Fibers/ Ceramic/ Metal-based Silicone:
These fillers commonly consist of alumina and metal oxides. They are used in specific applications in products that require high structural strength, thermal resistance, and rigidity.
2. Extending/Non-reinforcing Fillers
These are also known as cost-reducing fillers as they are primarily used in silicone rubber to reduce cost, increase volume, and modify density. They hardly have any effect on mechanical performance. Here are the common components in this kind of filler:
· Calcium Carbonate:
It is a very common extending filler that reduces the cost per part of a silicone product. It increases stiffness and is easy to process.
· Kaolin Clay:
Kaolin clay, or China clay, is used as a filler for silicone goods with lower specifications of rubber. In these products, high tensile strength is not necessary. So, China clay, talc, or clay-like minerals offer good enough hardness and reinforcement.
· Ground Silica:
Some extender-filled silicone compounds contain filler like ground quartz or diatomaceous earth. Though they are semi-reinforcing, most of the time these fillers are used as cost optimization for silicone products.
3. Special Functional Fillers
Special functional fillers are used in silicone rubbers for products that require special functions other than common features like strength.
· Flame Retardant Fillers:
These fillers contain alumina trihydrate, mineral powders that work as fire-resistant or reduce flammability. These fillers are used in parts of electrical or household products to ensure the safety of the users.
· Thermal or Electrical Fillers:
These kinds of fillers are carbon-based, made of metal particles or any other conductive or semiconducting particles. They increase electrical and thermal conductivity, which is used to manufacture products used in industrial applications.
· Color Fillers:
To get satisfactory color and opacity, color fillers or pigments are used in products like kitchenware, household goods, wearable products, etc. These fillers not only give desirable color, but also help to achieve the desired opacity, surface finish, or texture.
Are Fillers Harmful to Human Health?
There’s no doubt about the economic and performance benefits of using fillers in silicone rubber. But the chemical nature of the filler itself may have harmful effects on human health. Harmful substances can disrupt health if not used in limited quantities.
A responsible manufacturer must consider the effects on human health and produce silicone products with appropriate fillers. Specifically, for sensitive use markets like baby products, kitchenwares, food storage items, and medical devices, manufacturers must be extremely careful to avoid harmful substances.
A study showed that common fillers like amorphous silica and carbon black have no evidence of harming human health if used in standard applications. The exposure of these compounds to humans must remain within regulatory limits.
When fillers are used in silicone rubber, they are typically embedded in the cross-link of the polymer chain. They are not present in the raw material compound as free nanoparticles. So it is highly unlikely to get exposed to them through breathing or touching the finished product.
Even after that, avoiding harmful substances such as heavy metal particles is a must for all silicone product manufacturers. The best way to ensure the safety of human health while using silicone products is to be compliant with regulations by organizations like LFGB, FDA, CE, ISO, Sedex, etc
Are Fillers Harmful to the Environment?
Biodegradability Analysis
Compared to pure silicone rubber, silicone with filler is more durable and stronger. This makes it resistant to degradation. This cured silicone has fillers embedded in its cross-links in the polymer chain, generating an inert nature. So it gets difficult for these silicone products to be recycled or biodegraded.
Considering this, along with all the benefits, using fillers comes with its own limitations in terms of the circular economy and global sustainability. So, using fillers that will not affect the products’ biodegradability is necessary.
Microplastics
We got to know that fillers are usually embedded in the polymer chain in its cross-link link making it inert. This indicates that no free nanoparticles are exposed from touch or inhalation. However, concerns will arise if the nanoparticles in the fillers somehow start leaching out. In most cases, this doesn’t happen. So, usually, fillers are safe for the environment in terms of free microelements.
Chemical Inertness
Fillers show chemical inertness once they’re mixed with silicone rubber. So it doesn’t easily react with another substance. This makes disposal options limited. The filler-filled silicone products become a part of persistent waste.
So it is very clear that fillers don't magically make silicone rubber ‘green’. It surely gives a lot of benefits. So manufacturers can pick more environmentally friendly fillers to reduce their carbon footprint on the environment.
KEAN Production Assurance
When selecting a manufacturing partner, one with a proper filler strategy is crucial. As a silicone manufacturing company, KEAN does careful filler selection, high-quality compounding, compliance oversight, and sustainable end-of-life management. Besides, they offer high-quality performance and durable products that are tear-resistant, stiff, and stable.
· KEAN does the cost optimization by properly using certain fillers in the proper ratio. This can reduce the production cost while keeping the quality almost the same.
· They are capable of adding diverse fillers to the silicone rubber depending on the desired final product functionality.
· KEAN gives consistent raw material supply, quality assurance, and compliance verification for all products.
· They understand the importance of global sustainability in the long run. So KEAN offers more environmentally friendly fillers according to clients' demands.
So, a knowledgeable partner like KEAN in the silicone manufacturing industry, offering diverse filler compounds and precise formulation, is what your brand or business needs to be successful.