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There is a couple of information online claiming that silicone is eco-friendly and is better than plastic because of its high quality, reusability, and temperature resistance. A lot of people are using food-grade silicone products because, accordingly, it is safe and non-toxic. However, is silicone biodegradable, bad for the environment, and is it better than plastic?
With the mission to go zero waste and to reduce single-use plastics, many people have become drawn into using silicone products. But after we have used it for some time and throw it, will it be part of the environment, or will it remain forever as waste like plastics?
This article will answer some common questions about using silicone, its difference from plastic and rubber, including its uses and impacts on humans and the earth.
Silicone types, uses, and biodegradability
Many are confused – is silicone plastic, or is silicon rubber? The answer is no for both. Silicone is made of silicon element, and silica is the raw material where silicon is derived. Silica is extracted from the sand. It also utilizes natural gas to process all elements needed to form silicone.
On the other hand, plastic is made from crude oil extracted under the earth, while rubber is made from the sap of a tree called Hevea brasiliensis.
Silicone (with an “e”) is technically defined as a synthetic polymer created from silicon (a chemical element), oxygen, and other elements such as carbon and hydrogen. It is under the functional group siloxanes – a group of low molecular weight compounds, organosilicon oligomers, and polymers. They are usually in the form of liquid or rubber-like plastic and have unique properties. It also has low toxicity, can withstand extreme temperatures, flexible like rubber, and has excellent insulation.
Because of this, silicone products gained popularity as an alternative to plastic. Its beneficial role in the medical, pharmaceutical, food, packaging, and cosmetic industry is widely recognized.
Around 150,000 practical silicone applications have been registered, including food-grade silicone, silicone lids, silicone bags, non-stick bakeware, sealants, silicone cup, and many others. You’ll be surprised to know the wide range of silicone for almost all household and industrial use.
Among the reputable institutions that endorse silicone’s safety for health and environment include:
- EU’s Scientific Committee on Consumer Safety (SCCS) tells us that silicones do not pose a risk for human health when used in cosmetic products.
- Cosmetic Ingredient Review (CIR) similarly concluded that silicones do not pose a risk to human health from their use in cosmetics.
- Health Canada vouched that there are no known health hazards associated with the use of silicone cookware. Silicone rubber does not react with food or beverages or produce any hazardous fumes.
Health Canada says this about silicone being used in consumer products. “[These products] are not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.”
Below are the different types of silicones and associated products:
- Organochlorosilane – frequently used as coatings for silicon and glass surfaces and in the production of silicone (polysiloxane) polymers.
- Hexamethyldisilazane (HMDS) – a colorless liquid, a reagent, and a precursor to bases popular in organic synthesis and organometallic chemistry. It is also being widely used in thin films or coatings.
- Polydimethylsiloxane (PDMS) – is a polymer widely used for the fabrication and prototyping of microfluidic chips. It is a mineral-organic polymer (a structure containing carbon and silicon) of the siloxane family (a word derived from silicon, oxygen, and alkane). Apart from microfluidics, it is used as a food additive (E900), in shampoos, and as an anti-foaming agent in beverages or lubricating oils.
- Dimethylpolysiloxane is an anti-foaming agent derived from silicone found in various foods, including cooking oil, vinegar, chewing gum, and chocolate. It is also added to the oil to prevent it from bubbling up when frozen ingredients are added, thus improving the product’s safety and life. While the risk of toxicity is considered low, this silicone is the same material used in non-edible stuff, such as shampoo.
- Volatile methyl siloxanes (VMS) – VMS compounds are low molecular weight materials primarily used in manufacturing higher molecular weight polydimethylsiloxanes. The cyclic VMS materials are also used in cosmetics and other personal care products as carriers and emollients. VMS volatilizes into the atmosphere from these consumer applications, and some even enter the surface waters through sewage treatment plants (STPs).
- Polyethermethylsiloxanes (PEMS) – are copolymers consisting of a siloxane backbone with one or more methyl groups on the silicon atom substituted with a polyoxyalkylene (i.e., polyether) group. Commercial PEMS materials are used for various applications, including the manufacture of polyurethane foams, textiles, personal care products, paints, and surface coatings.
- Silicone resins – are used to make paints and coatings and in electrical and many other applications, where they help to improve durability, safety, and reliability.
- Silicone elastomers – are made with linear polymers, reinforcing agents, a crosslinker, and a catalyst. They are mainly used to produce various electrical insulation materials like the insulating layers and high-temperature air ducts of airplanes. Likewise, they are a significant component of manufacturing sealants. The physiological inertness of silicone elastomers makes it possible to be used in medicine such as tubes for blood transfusions, artificial heart valves, and various prosthetic devices.
Out of the 8 classes of silicone described above, extensive studies on biodegradation focus on PDMS and its associated product from its degradation. PDMS was previously believed to be inert, but some studies show it is biodegradable.
One of the leading proponents of its biodegradability is Dow Corning – is a registered trademark of The Dow Chemical Company. A study by Lehmann and his team from the Health and Environmental Sciences Unit of the Dow Corning Corporation in Midland, Michigan, in 1998 shows that low-molecular-weight PDMSs are biodegraded in sewage sludge under anaerobic conditions. According to this, when PDMS is disposed of down the drain, it spreads to the soil forming a sludge.
This allows the catalysts in the form of microorganisms or soil enzymes to conduct depolymerization and convert the silicone to natural elements.
In the same year, Lehmann and his team published a study on how PDMS degradation is influenced by soil factors such as clay content and clay type. Results showed that PDMS degradation products are bound more strongly to goethite and smectite types of clay soils.
This supports General Electric Corporate Research and Development’s findings in 1996 that the hydrolyzed product of PDMS, i.e., dimethyl silane diol, is biodegradable. The study concluded that dimethyl silane diol degrades in soils under environmentally attainable conditions better than its parent polymer compounds, PDMS.
In 1999, further studies were pointing toward the positive biodegradation of silicone. One of the microbial degradation of silicone oils (i.e., particularly low-molecular-weight PDMSs) using mixed cultures of sewage bacteria Pseudomonas fluorescens and Pseudomonas putida under aerobic conditions were successful.
A study by Dr. Lukasiak and his team in 2005 tells otherwise. According to them, PDMSs have very low water solubility (usually 1 part per million), especially its version of high-molecular-weight (1 part per trillion). Because of this, the biodegradation of this silicon type is very hard to test. Although, the study did not further discuss whether the degraded or hydrolyzed product of PDMS exhibits the same.
In a more recent study in 2018, a silicone-containing high-molecular-weight thermoplastic polyurethane elastomer was explored. The material shows promising results such as exceptional flexibility, high toughness, high thermal, UV, and chemical resistance, as well as self-healing, shape memory, self-cleaning ability, and, more importantly, biodegradability.
From these studies, it can be concluded that silicone has a lot of potential for biodegradability, particularly its PDMS class. More research is needed to confirm the biodegradability potential of all silicone types.
Is silicone better than plastic?
Silicone is a better alternative than plastic as it does not leaches out or degrades into microplastics. However, since silicone is not biodegradable, it would typically take 500 years before it decomposed. This is good news for marine organisms but has some downsides as well.
For years, silicone has been regarded as having no known health hazards, unlike the vast array of health problems associated with BPA found in plastics. However, research made by Debra Lynn Dadd shows that a “methyl” type of silicone releases formaldehyde at high temperatures starting from 200°C (392°F). She claims that “the problem is that we do not know what type of silicone was used in our food-grade silicone products.”
A European Union report also presented that certain types of silicone such as organosiloxanes are endocrine disrupters. Endocrine disrupters are substances that can alter the endocrine functions and harm the individual and its reproductive ability. Endocrine disrupters are similarly present in plastics.
Concerning durability, food-grade silicone and other silicone products can last up to 10 years compared to plastics that easily cracks and melts under high temperatures. Silicone products are dishwasher, freezer, and microwave oven safe. A plastic subjected to these conditions would easily crack or turn cloudy.
But it is easier to find a recycling facility for plastic than with silicone when it comes to recyclability. Used silicone products need a particular recycling facility, which is not available in most areas.
Is Silicone Biodegradable?
There are many opposing views concerning the pros and cons of silicone use. But if I would have to conclude between plastic and silicone, I would probably choose neither.
For zero waste or plastic-free objectives, I would probably encourage you to use other containers such as stainless steel or glass. If you will use a silicone product, be sure to use high quality, food-grade, or medical grade and that it does not contain any chemical fillers.
In the end, as a group of consumers looking for a better plastic alternative for our home and personal use, we should opt for those with the least chemicals. These food-grade applications have no side effects on health or the environment.