Is Silicone Plastic or Rubber?

Silicone is an incredibly useful, versatile material found in many products we use every day. But there is often confusion about what exactly it is. Is silicone a plastic or a type of rubber? How does it compare to other polymers in toxicity and safety?

Here I'll cover the composition of silicone and how it differs from plastics and rubbers. I'll also explore the health and environmental impacts of silicone to help shed light on this unique substance.

Is Silicone Plastic or Rubber?

Silicone possesses properties of both plastics and rubber, but fits neatly into neither category. Chemically, silicone is very different from the hydrocarbon polymers that make up most plastics and rubber.
Plastics like polyethylene and polypropylene consist of long carbon-carbon backbone chains derived from petroleum. Rubber polymers like natural latex contain carbon-carbon double bonds that allow them to flex and recoil.

In contrast, silicones have a backbone of silicon-oxygen bonds, with side groups made up of carbon and hydrogen atoms. The unique chemistry gives silicones special attributes that set them apart from other polymers.
Like plastics, silicone can be easily fabricated into any shape. It has high heat resistance, low chemical reactivity, and high flexibility and resilience over a wide temperature range. Electrical insulating properties also resemble many plastics.

However, unlike hydrocarbon plastics, silicones have low intermolecular forces and friction. This results in an unusually slippery, smooth feel and makes silicone impermeable to gases and moisture. Silicones also remain flexible and stable at both high and low temperatures that would make plastics brittle.
Compared to natural and synthetic rubbers, silicone shares elasticity, bounce, and a rubbery texture. But silicone is more heat resistant and durable than rubbers. It also has higher gas permeability and chemical inertness compared to hydrocarbon elastomers.
So while sharing traits of both, silicone stands alone as a unique, high performance polymer. Its atypical chemistry allows properties not achievable with conventional plastics or rubber. This flexibility makes silicones invaluable across industries from medical to aerospace.

Is Silicone Toxic to Humans?

Silicone has a general reputation as a toxic material, but most medical and scientific evidence indicates human-grade silicones have very low toxicity and are harmless in typical exposures.
The silicon, oxygen and hydrocarbon components that make up silicone polymers are not considered hazardous or reactive in the human body. Unlike some problematic plastics, silicones do not degrade into toxic compounds over time or release traces monomers and plasticizers.

Studies have found that ingesting even substantial amounts of liquid silicones produces no acute or chronic toxicity in mammals. Some silicones are even used in FDA-approved implants and medical devices that reside in the body for years with local tissue reactions.
However, most toxicity data is based on medical-grade silicones designed specifically to be biologically inert. Some additives and lower purity industrial silicones may have more risks associated with them.

Overall, the bulk of research suggests properly formulated silicones exhibit very low toxicity even with significant exposure. More study is needed on subtype-specific effects, but silicones appear to pose little human health risk in typical consumer or industrial applications.

Is Silicone Biodegradable?

One downside to silicones compared to other polymers is that they are very difficult to break down in the natural environment. As a result, silicone materials tend to persist once discarded.
The high durability and chemical resistance that makes silicone so useful also means it resists natural degradation pathways. Silicone polymers are too large and stable for microbes and fungi to metabolize efficiently.

While some specialty biodegradable silicones have been synthesized, the vast majority of commercial silicones will not readily decompose in landfills, soil or water. Under ideal lab conditions, some degradation has been measured over the course of months or years.

Realistically however, most silicone objects, sealants, lubricants and coatings will persist for decades or longer with very little change in their polymer structure or properties. This contributes to the growing environmental presence of silicones as the usage increases worldwide.
Proper disposal and recycling is important to prevent environmental buildup. Incineration can fully decompose silicones at high temperatures. More green methods are also being developed such as chemical digestion and use of high pH fluids to accelerate breakdown.

Can Silicone Cause Cancer?

There is no good evidence that silicones themselves cause cancer or increase cancer risk. However, low purity grades may contain impurities that are carcinogenic concerns.

The silicone polymer molecules are non-reactive and considered non-mutagenic and non-carcinogenic by themselves. Studies injecting or implanting silicones in animals have found no increase in tumors or other cancers.

However, industrial silicone oils made for non-medical uses can contain toxic residuals and byproducts from manufacturing. One family called polycyclic siloxanes has been linked to uterine and liver tumors in rodents, for example.

Strict regulations limit toxic impurities allowable in medical and food-grade silicones, making them highly pure. But other grades have less stringent requirements, so quality control is important for consumer and environmental safety.

While silicones themselves appear non-carcinogenic, the presence of unfavorable residues in some products would warrant caution until further toxicity evaluations are done.

Is Silicone Better Than Plastic for Health?

In terms of human health impact, silicone has clear advantages over many common plastics when purity is accounted for.
Plastics like PVC, polystyrene, and plasticized PVC can leach residual chemicals and plasticizers that have been linked to endocrine disruption and developmental issues. Low grade or degraded plastics can also grow bacteria and mold.

In contrast, medical and food-grade silicones have virtually no leaching or outgassing of harmful chemicals when used properly. Their non-porous surface also resists microbial growth and biofilm formation. No negative health effects are observed from silicone cookware, implants, sealants, etc. in the vast majority of cases.
Industrial and commercial silicones would need to be evaluated for specific impurities that could leach out and cause health concerns. Overall though, human toxicity and bio-uptake is extremely low, even compared to many widely used plastics.

So while plastics negatively impact human health in various ways, high purity silicones exhibit excellent biological inertness and negligible toxicity, making them a better choice for items in prolonged contact with the body. Proper testing of grades and formulations is still prudent however.

Which is Safer - Silicone or Rubber?

When it comes to safety for human health and the environment, medical grade silicone generally has advantages over both natural and synthetic rubbers as well.
Natural rubber latex poses allergy risks and can trigger potentially severe immune reactions in those with sensitivity. Chemicals in natural latex like proteins and accelerators can also leach out and be absorbed through skin.

Synthetic rubbers often incorporate plasticizers and chemical curatives that can migrate out over time. Traces may be emitted into air or transferred to skin. Some synthetic rubber chemicals are known carcinogens and toxicants as well.
In comparison, purified silicones contain virtually no problematic additives or residuals that can leach out or cause health issues. They are intrinsically non-reactive and non-allergenic. Food and medical silicones have no measurable toxicity when used as intended.

So while important uses exist for plastic and natural and synthetic rubbers, human-grade silicones offer a safer alternative for items in close contact since they are proven biologically inert and non-allergenic.

Is Silicone Good or Bad For You?

The unique properties of silicone make it a versatile material that provides benefits across many industries and applications. When properly formulated, silicones pose negligible toxicity risk and are "good" for general use and human health.

However, the inability of silicones to biodegrade can be considered "bad" for the environment if disposal and recycling are not addressed responsibly. More study is also needed on subtype-specific toxicity.

In summary:

Good:

Non-toxic, inert in human body
No harmful chemicals leach out
Doesn't promote microbial growth
Temperature and chemical resistant
Stable and durable for long-term use

Bad:

Persists indefinitely in landfills and ocean
Accumulates in environment since non-biodegradable
Lower grade varieties may contain toxic impurities
Long-term ecosystem effects still not fully known

So while crucial differences between grades exist, medical and high purity silicones offer unique performance and safety that benefit many facets of the economy and human health. But environmentally safe design, use and disposal practices are equally important to prevent unintended consequences.

Conclusion

Silicone stands uniquely between plastics and rubber with a set of properties all its own. When produced to medical and food standards, silicones exhibit almost no toxicity and are non-allergenic and non-carcinogenic, making them very safe for human use and health. However, their environmental persistence is problematic. Overall, silicones are neither universally good or bad, but remain indispensable materials that require responsible manufacturing, application, and disposal.

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