Breaking Down Silicone: A Comprehensive Overview

We are all aware of the devastating effect plastic has on our environment. So we are looking for alternatives. In clothing, polyester can be replaced by cotton or bamboo and your plastic kitchen tools can often be replaced with wood. But not every plastic item can easily be replaced with a sustainable alternative. Especially when you want something to remain flexible. Therefore, silicone has often been mentioned as a sustainable alternative to plastic but is this true? Let's take a closer look.

How is silicone made?

Silicone is a polymer made up of siloxane creating polysiloxane. Most of the time these are colorless rubber or oils-like substances. They have a multitude of uses including; sealants, adhesives, lubricants, medicine, cooking utensils, thermal insulation, and electrical insulation. They also come in lots of different forms like silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk.

The first step in making silicone is by isolating silicon from silica. This is done by heating a large amount of quartz sand to 1800˚C. The result is pure, isolated silicon. After cooling, this is ground into powder. Methyl chloride is added to the powder and the mixture is heated again forming methyl chlorosilane. As the latter is a mixture of several components, these need to be separated to extract silicone. Using a distillation method, polydimethylsiloxane is isolated which is the main component of silicone.

Is silicone sustainably produced?

The production of silicone is very cheap and fast, however, as you just read, extremely high temperatures need to be created so even though this is a very cheap process it has an enormous carbon footprint. Creating these extremely high temperatures requires immense amounts of energy and because it is heated multiple times, the amount of energy required increases with each step.

Let's not forget the amount of fuel that is required to transport all this sand to the factories. So, no, the production of silicone is not very eco-friendly.

Is silicone plastic?

No, silicone is not plastic as plastic has a completely different resource. Plastic is completely manmade from petroleum while silicone is also manmade but remains more of its original resource, quartz sand.

The end product may have a similarity in properties and functions like transparency, flexibility, and resistance to water and temperature. However, silicone is much more resilient due to its structure making it more long-lasting than its plastic. So the purposes of both are also completely different. Silicone is often made to last (as it is so resilient) while plastic is (too often) used for single-use products.

So even though silicone is more eco-friendly compared to plastic as it is made to last while plastic is often not, the production process is very polluting. Compared to single-use plastic it is definitely a more sustainable option while also being very budget friendly.

Is Silicone biodegradable?

We know plastic has the big downside of breaking down into microplastics instead of actually degrading. For silicone, the degradation process is completely different. As you will read below, silicone is a very resistant material. It can handle extreme cold and heat without much alteration of the material. It also has great resistance to UV and ozone degradation. Meaning it will not biodegrade under UV light or sunlight like plastic can.

This makes you think that silicon will not biodegrade. However, research has shown that silicone will break down naturally in soil. In the soil of this research, silicone polymers are broken down into Dimethylsilanediol.

This is also a compound that can be broken down naturally in the soil.

It needs to be noted that this research was done with very low concentrations of liquid silicone which does not mean that your (broken) silicone stasher bag will biodegrade in your compost bin as more research needs to be done on this topic.

Also, no research was done (yet) on the biodegradability of silicone in ocean water but as silicone is known to be very water-resistant, I don’t think silicone can biodegrade in ocean water.

Is Silicon recyclable?

Silicone is a rather new material that is different from all other materials we know. It is made from different sources and therefore it also receives a different treatment when it is at the end of its lifecycle.

Special recycling programs are created specifically for silicone as it is such a unique material however, the process itself is rather simple.

The recycling process for silicone starts by grinding or tearing the silicone material down. The shredded silicone granules are then poured into a prepared mold. Fresh silicone needs to be added to ensure the particles adhere to one another. The created end-product is then used to make cooking molds, shredded playground mulch, or water-resistant insulation.

Is silicone toxic?

Lots of research has been done on silicone but this is mostly about the safety of silicone in breast implants. Luckily I found 2 relevant and recent articles about the use of silicone rubber baking molds that tested whether or not these mold release toxic compounds while used. While the research shows that silicones are stable, they are not completely inert. This means that there is a possibility of leaching.

The first study researched silicone rubber baking molds under severe conditions like baking at 175 °C, microwaving at 800 W, and freezing at −18 °C. They found that the percentage of volatile organic compounds was about 2,5% higher than recommended by the Recommendations on Food Contact Materials. They found 18 different types of silicone oligomers indicating that the researched silicone rubber baking molds were badly tempered materials.

This second research has shown that octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane show migration behavior in silicone rubber baking mold when used at 175 °C for 30 min. This was however not the case when a cake was made that contained dairy products including milk and milk powder.

This confirms what was found in another study where they studied the release of siloxanes from 2 products, silicone nipples and bakeware, and whether they released siloxanes into milk, baby formula, and a solution of alcohol and water. Nothing was released into the milk or formula after six hours, but after 72 hours in the alcohol solution, several siloxanes were detected. It should be noted that siloxanes are known to be linked to cancers and are potential endocrine disrupters.

Both these studies indicate that silicone backing molds release compounds in the food when the molds are used under the given conditions. This is for me a reason to avoid silicone items that are made to be used for a longer time like in an oven. The silicone molds I have I use for making skin and hair care products like lotion bars, shampoo bars, and conditioner bars. Also, some of my kitchen utensils are made with silicone like my spatulas but again, these are not long in contact with hot food for a long time.

Tips for using silicone items safely

Choose silicone products of the highest grade possible. This should ideally be "medical grade" but "food grade” is still sufficient in most cases. If no grade is listed with the product, this is a bit of a red flag but always check with the manufacturer to be sure. Higher silicone quality reduces the possibility of chemicals leaching. Something you would like to avoid for say your menstrual cup.

A silicone product can be tested for chemicals fillers. Do this by twisting or pinching a flat surface to see if any white substance shows through. If you see anything white, a filler likely has been used. Pure silicone should not change color when under pressure. If a filler is present, the product is likely not uniformly heat resistant and may release a smell to your food.

What is most important is that you often have no idea what this filler is and it could leach unknown chemicals into your food.

Nipples from baby bottlers and pacifiers should be safe. It is advised to not put them in the dishwasher as silicone can release volatile compounds under heat. They should also be replaced when they get cloudy or are worn out. Ideally, they should be replaced a lot sooner like every six to eight weeks. Natural rubber is another great option, but your child should obviously not have an allergy to natural rubber latex.

In your kitchen for cooking, silicone can be avoided by choosing cookware made from glass, ceramic, and stainless steel. Although silicone is the best option for non-stick cookware.

Other kitchen utensils like silicone oven mitts, spatulas, spoons, splatter guards, and potholders should not be a problem because they are only in contact with food for a minimal amount of time. However, I try to avoid prolonged direct use of silicone on the food I prepare.