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Fascinating Silicone™ Chemistry Corner – Environmental Degradation

How polydimethylsiloxane degrades in the environment

When polydimethylsiloxane (PDMS) polymers contact clay minerals in the soil, their siloxane backbone depolymerizes into lower-molecular-weight materials – primarily Me2Si(OH)2. Depending on soil type, this dimethylsilanediol will undergo further degradation:

  • Either in the soil via biodegradation
  • Or through evaporation into the atmosphere, where it will degrade oxidatively via reaction with hydroxyl radicals

Whether degradation occurs in the soil or in the air, the result is the same. The PDMS polymer breaks down into naturally occurring materials:
  • Silicates that exist naturally in the soil
  • Amorphous silica
  • Carbon dioxide
  • Water vapor

How PDMS enters the environment

PDMS fluids – Low-molecular-weight PDMS polymers are primarily used in personal and household care products, like shampoos, conditioners, and detergent antifoams. These products are rinsed away after use and end up in municipal wastewater treatment plants. High-molecular-weight PDMS fluids used as process aids, or surface treatments in industrial applications also end up in wastewater treatment facilities.

High-molecular-weight PDMS molecules are virtually insoluble in water. This, combined with their tendency to bind with organic material, effectively removes them from the wastewater and onto the sludge during wastewater treatment. This sludge is either used as a soil conditioner or it is incinerated. Either way, the PDMS will break down into the same naturally occurring materials: silicates, amorphous silica, carbon dioxide, and water vapor.

Solid silicones – Solid silicones such as PDMS-based rubbers or sealants may be used in the home (as bathtub caulk or baby bottle nipples) or in industrial applications, such as textile coatings, electronics protection materials, moldmaking rubber, or rubber gaskets. They enter the environment as a component of domestic or industrial waste, where they will be either landfilled or incinerated. Many silicone rubber elastomers can be reclaimed and recycled into new materials. This not only keeps them out of the landfill, but extends their useful lives.

Learn how different types of silicones work.

 Did you know ... studies have shown that the application of sludge containing PDMS to the soil does not appear to affect crop growth or soil organisms.

Expand your understanding

Learn more about:
Silicones and their Impact on the Environment (PDF Size 56KB)
An Overview of PDMS in the Environment (PDF Size 35KB)
An Overview of VMS Fluids in the Environment (PDF Size 79KB)
Polydimethylsiloxanes Do Not Bioaccumulate (PDF Size 34KB)
Fate and Effects of Polydimethylsiloxane in Marine Environments - Article reprint from the Marine Pollution Bulletin (PDF Size 4.2MB)

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