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How silicone water repellents work

Silicone water repellents or waterproofing agents generally come in two forms:

  1. Elastomeric polydimethylsiloxanes – elastomeric coatings that adhere to the substrate and cure to form a flexible, protective membrane.
  2. Penetrating water-repellent chemicals – reactive silanes and siloxane resins with crosslinkable side chains. These materials have smaller molecular structures, which enable them to penetrate deeply into the substrate, where they chemically bond with it.

Either of these materials can be delivered via solvent or aqueous emulsion.

Potential locations for functional groups on a silicone water repellent polymer.
 
Penetrating Water Repellent


Functional Groups for Penetrating Water Repellents

GroupPositionReactiveFunction
AlkylA or BNoWater repellency
AminoA or BNoCatalytic
AlkoxyA or BYesCrosslinking
HydroxylAYesCrosslinking
HydrogenBYesCrosslinking


The mechanics of waterproofing

Silicones have low surface tension, which enables them to spread and soak easily into a substrate’s pores. Their highly flexible and mobile siloxane backbone enables the water-repelling methyl groups to orient themselves toward the surface, creating a waterproof "umbrella."

What makes this "umbrella" unique is its ability to breathe. Because silicones have a very open molecular structure, water vapor trapped in the substrate can easily slip through. Water molecules, however, are too large to enter.

The creation of breathable water repellent "umbrella."

Silicone benefits for water repellency and waterproofing

  • High spreading and wetting capabilities – the ability to thoroughly cover a surface or penetrate a porous substrate
  • Permeability to gas and water vapor
  • Resistance to ultraviolet light (UV), heat, and oxidative degeneration
  • Durability, flexibility, and mechanical and chemical adhesion

Typical silicone water repellent and waterproofing applications

  • Water-repellent treatments for leather
  • Waterproof elastomeric coatings for industrial and fashion textiles
  • Integral additives or surface treatments for building materials
  • Waterproof elastomeric coatings for roofs, masonry, and other construction applications
  • Additives to improve the wash-off resistance of beauty and personal care products
  • Water-repellent additives for paints, inks, and protective coatings

Learn how other types of silicones work.

 

Did you know ... a waterproofing silicone helped save otters caught in an oil spill disaster!
Read the story.

 

Expand your understanding

Technical articles:
Silicones in Coatings (PDF Size  285 KB)
Silicones in the Construction Industry (PDF Size 89 KB)
Silicones in the Textile Industries (PDF Size 98 KB)

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