Silicone

Summary

Silicone is a polysiloxane with a silicon-oxygen backbone, supplied as oil, grease, rubber, resin, and caulk. It resists UV, ozone, and temperature extremes, which is why it is the standard for weather sealants, gaskets, and structural glazing.

Cols

Image

Siloxane: repeating Si-O unit; preferred term over silicone
One-part sealant: cures by absorbing atmospheric moisture
Structural silicone: adhesive-sealant carrying glazing loads
D4, D5: cyclic siloxanes of environmental concern

History and demand

Invention

1901: F. S. Kipping coined the term silicone
1930s: James Franklin Hyde launched the silicone industry

First uses in construction

Since 1974: structural silicone used in curtain wall facades
Silicone membranes restore industrial roofs

Sourcing

China held nearly 40 percent of global silicone capacity in 2014 (IHS); a 2024 analysis expected 83 percent that year and nearly 90 percent the next (SMM)

Demand trend

About 400,000 tonnes produced in 1991

Composition and production

Raw materials

Polysiloxanes with two organic groups on each silicon atom

Product forms

Oils, grease, rubber, resin, and caulk

Properties

Thermal and moisture

Service temperature: constant properties from -100 to 250°C (-148 to 482°F); aerospace grades -70 to 220°C
Gas permeability: oxygen permeability about 400 times that of butyl rubber at 25°C

Durability

Resists oxygen, ozone, and ultraviolet light

Uses in buildings

Building elements

Sealants and Flashing: weather sealants and gaskets
Curtain Wall Systems: structural glazing

Pros and cons

Pros

Stable from -100 to 250°C
Resists UV, ozone, and oxygen
One-part moisture-cure sealants

Cons

Some people develop silicone allergies
Cyclic siloxanes D4 and D5 are environmental pollutants

Sustainability

Health

Low toxicity and high biocompatibility; some sensitivity
At 250°C silicones release 1,200 to 4,600 µg formaldehyde per gram per hour

Manufacturing and cost

Main manufacturers and suppliers

Trade association: Silicones Environmental, Health and Safety Center.

Sources

Wikipedia: Silicone, https://en.wikipedia.org/wiki/Silicone
Wikimedia Commons: PS-151 1 big.jpg, photo by Sazanov111 (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:PS-151_1_big.jpg
SMM: overview of new DMC capacity in China in 2024, https://news.metal.com/newscontent/102874174-overview-of-new-dmc-capacity-in-china-in-2024
European Rubber Journal: IHS, silicones market at risk from expansions in China, https://www.european-rubber-journal.com/2014/04/16/ihs-silicones-market-at-risk-from-expansions-in-china