Silicone rubber which is originated from silicon is basically a synthetic polymer. Silicone rubber bears good durability and is also non reactive in nature. These characteristics make it suitable to be utilized in kitchen utensils and medical devices. The question about the safety of silicone rubber started a comprehensive scientific research. The results of the extensive research indicated that silicone rubber is biocompatible and non toxic in nature.
These properties are considered vital when applications include food industry and medical sector. The regulations and safety standards devised by regulatory bodies are implemented and followed to ensure safety. However, there are environmental concerns which need to be addressed when production and disposal of silicone rubber is carried out. Silicone rubber proved to be safe for utilization in numerous applications which eliminates the concerns about its leaching and stability.
Fundamentals of Silicone Rubber
Primarily silicone rubber is composed of following atoms.
- Silicon
- Carbon
- Oxygen
- Hydrogen
Silicone rubber is basically synthetic elastomers and is produced through polymerization processes. These processes involve the combination of silicones with different additives to acquire the required properties. These properties then depicts in the form of chemical resistance, flexibility and heat resistance. Silicon and oxygen bond exists in the molecular structure of silicone rubber. This bond provides the following two important properties.
- Elasticity
- Flexibility
These properties are the basic reason of its utilization in household items, kitchenware items, automotive seals and medical devices.
Understanding the Chemistry and composition of Silicone Rubber (Basics)
The composition and chemistry of silicone rubber varies from the following traditional rubber materials.
- Styrene butadiene rubber
- Natural rubber.
The characteristics and properties of silicone rubber are governed by its molecular structure.
Silicone rubber composition
There are three major portions which form the composition of silicone rubber.
- Silicone backbone
In silicone backbone a polymeric chain is formed by the alternating silicon and oxygen atoms. This backbone bears the following characteristics.
- Highly stable
- Resistant to chemical attack
- Provide silicone rubber durability
- Organic group
There are organic groups in the composition of silicone rubber which defines and impart the properties and characteristics to the silicone rubber. These groups include methyl groups and phenyl groups. These groups are attached to the silicon atoms in the atomic structure of silicone rubber. Each group offers particular capabilities as follows.
- Phenyl group increase the resistance to the oxidation and thermal stability
- Methyl group improves low temperature performance of silicone rubber and its flexibility
- Cross linking
Cross linking is a very important phenomenon in silicone rubber which is achieved during the curing process. So in silicone rubber individual polymer chains are interconnected by chemical bonding. The process of cross linking enhances the following aspects.
- Strength
- Elasticity
- Resistance to deformation when stress is applied
There are certain curing agents which are utilized to treat silicones during the curing process.
- Peroxides for peroxide cure silicones
- Platinum catalysts for addition cure silicones
Synthesis Process of Silicone Rubber
The synthesis process of silicone rubber involves following four steps.
- Raw materials
Silica sand is basic raw material which provides silicon dioxide. After that a chain of chemical reactions involve to retrieve silicon from silicon dioxide. This silicon is then further processed to produce siloxane units. Then ultimately the backbone of silicone polymers is formed by these siloxane units.
- Polymerization Process
In this process raw materials are transformed into polymers having long chains and cross linked structure. The oxygen atoms combine with silicone atoms to produce siloxane units. The phenyl or methyl organic groups which are attached with silicon atoms are used to carry out the modification in siloxane units. After that these siloxane units are polymerized to produce long chains which are in the form of network.
- Additives
The additives are added to get the required properties. However, carbon black and silica which are utilized as reinforcing filler provides following.
- Stabilizers for heat
- Resistance to ultra violet radiations
- To enhance mechanical strength
- Pigments for color
- Curing Stage
After the formulation of silicone rubber is completed the curing process is carried out. The curing process is performed to acquire the final elastomeric form of silicone rubber. There are two types of curing methods which are generally adopted.
- Heat curing method (Heat is applied on silicone mixture and as a result of that curing agents are activated)
- Room temperature vulcanization curing method (moisture of the air starts curing process).
Significant and Important Properties of Silicone Rubber
Silicone rubber offers very unique characteristics and properties. These properties make it very suitable to be utilized in numerous applications. Followings are the main properties of silicone rubber.
- Exhibits excellent resistance to chemical
- Non toxic and biocompatibility
- Excellent heat and temperature resistance
- Good resistance to weathering, ozone and ultraviolet radiations
- Highly elastic and flexible
- Excellent Electrical Insulator
- Excellent durability and high tear resistance
- Non sticking property because of low surface energy
- Ease of processing to form complex and intricate products
- Ability to be formulated to become transparent
Doubts about the Safety of Silicone Rubber- Is silicone safe?
Although silicone rubber is popular for its versatile characteristics including there are some concerns related to its safe usage. These doubts and concerns are associate with the followings.
Impurities and additives
There are certain additives and impurities which are added to achieve specific formulation of silicone rubber. This typical formulation is formed to enhance performance and to get the required properties. However, on the other hand these additives can be the reason of toxicity and adverse environmental impact. So it is important to ensure that safety regulations and standards are being followed by the manufacturers while handling these additives. The limits devised for the safe usage of these additives by the regulatory authority must be adhered. Generally following additives are used.
- Pigments
- Catalysts
- Plasticizers
- Stabilizers
- Fillers
Release of organic compounds
It is important to note that certain compounds are released during the curing process. These compounds are organic and volatile in nature. These include the followings.
- Solvents
- By products of curing reactions
- Residuals of chemicals from manufacturing process
The release of these compounds during the manufacturing process can pose various risks to human health due to prolong exposure including the followings.
- Respiratory irritation
- Exacerbation of asthma
- Various potential long-term health effects
Extractables and Leachables
Silicone rubber is utilized to produce the items for food industry and medical sector. It is pertinent to mention that silicone rubber can release small quantity of the following substances into the surrounding environment.
- Un-reacted monomers
- Additives
- Impurities
These substances are termed as leachables or extractables.The safety of these substances is based on these two parameters.
- The chemical nature of released substances
- The level of exposure
Keeping in view the usage of silicone rubber in food and medical sector it is important to ensure that the exposure limits set by the regulatory authorities for these released substances are being followed.
Applicability as a biomaterial
Silicone rubber is biocompatible but still there are certain concerns regarding the usage of silicone rubber as a biomaterial as mentioned below.
- Potential for inflammation
- Potential for tissue reaction
- Immune response of the body to the silicone materials
In order to address the above mentioned doubts and concerns, medical grade silicone is subjected to series of testing and certifications are obtained to ensure the safe utilization of silicone rubber in biomaterial applications.
Impact on the Environmental
Generally, silicone rubber is considered non toxic and inert in nature but there are certain concerns which are related to its impact on environment. The major issue regarding this is the persistence of the wastage of the silicone in the environment because of the followings.
- Silicone rubber is stable
- Silicone rubber shows resistance to biodegradability
These adverse impacts on the environment can be prevented or minimized by ensuring the below mentioned steps.
- Optimizing the effective disposal practices
- Improving the recycling processes
Compliance of standards and regulations
This is the basic and most important concern which plays a vital role in the safe utilization of silicone rubber. The strict quality control of the silicone rubber products is necessary throughout the manufacturing process to make sure that required safety is being acquired. The standards and regulations devised by the regulatory authority need to be strictly implemented and followed. This is mandatory to ensure the followings.
- Impurities are not above the specified level
- Additive are not above specified quantity
- Emissions are not above the specified values
Safe Applications of Silicone Rubber
Silicone rubber provides safe utilization in many renowned sectors because of its unique characteristics. Major applications of silicone rubber are mentioned below.
Medical Sector
Silicone rubber is considered very suitable to be utilized in medical and healthcare sector because of its biocompatibility properties. There are two basic reasons behind this utilization.
- Human body tolerate silicone rubber well
- Immune response is not provoked
The utilization of silicone rubber in medical implants and medical devices is mentioned below.
- Joint replacements
- Pacemaker insulation
- Soft tissue implants such as breast implants
- Ocular implants such as intraocular lenses
- Catheters
- Tubing such as respiratory tubing
- Feeding tubes
- Wound drains
- Respiratory masks (Because of the properties of resistance to bacterial growth, flexibility and durability which silicone rubber provides)
Food industry and cooking sector
There are regulatory bodies such as FDA which has approved the silicone rubber to be utilized in applications which involve contact with food. This kind of authentic approvals has provided the base of silicone rubber usage in food related products and kitchenware.
Followings are the main applications of silicone rubber in cooking utensils, food storage and bake wares.
- Silicone spatulas
- whisks, baking molds
- Cooking brushes (Because they provide heat resistance, non-stick properties, and ease of cleaning as well)
- Silicone baking mats
- Cupcake liners
- Ice cube trays
- Food storage containers (They commonly used in households and commercial kitchens)
Consumer Products
Silicone rubber also finds its utilization in consumer goods because it offers durability along with safety. It is mainly used in personal care products, skin care items and baby products as mentioned below.
- Silicone baby bottle nipples
- Pacifiers
- Teething toys (They are selected for their safety because silicone is hypoallergenic and completely free from harmful and dangerous chemicals like BPA and phthalates)
- Facial cleansing brushes
- Makeup applicators (a variety of products)
- Hair care tools (Because it offers gentle touch and ease of cleaning)
Engineering and industrial applications
Silicone rubber bears excellent mechanical properties and is utilized in numerous industrial and engineering applications. Keeping in view the reliability and safety that silicone rubber offers, it is mainly utilized in following applications of automotive, insulation and sealing areas.
- Seals and gaskets
- O-rings
- Spark plug boots (because silicone rubber provide resistance to automotive fluids along with durability)
- Hoses
- Insulation for electrical components (Because silicone offers resilience to extreme temperatures, UV exposure, and weathering)
Conclusion
Silicone rubber is has certain critical and important properties and characteristics which enable it to be considered safe for many applications. These properties include durability, biocompatibility, ease of maintenance and resistance to the chemicals. The applications range of silicone rubber covers many sectors such as medical, food and automotives. Regulatory bodies ensure the safety of silicone rubber by implementation of safety standards and regulations in all stages. The proper formulation and compliance to the devised standards and guidelines result in the production of safe silicone rubber.
Final answer for the question “is silicone safe“, the answer is Yes, the silicone is safety materials, go to silicone molding parts page to know more.