Epichlorohydrin (1-chloro-2,3-epoxypropane)
Epichlorohydrin never reaches the jobsite as such, but almost every epoxy coating starts with it: it supplies the glycidyl groups that make epoxy resins reactive.
Epichlorohydrin is a three-carbon molecule that combines an epoxide ring with a chloromethyl group (molecular weight 92.52 g/mol). It is a colorless, volatile liquid with a chloroform-like odor that boils at about 116 °C.
ECH is an upstream raw material. Reacted with bisphenol A it gives DGEBA liquid epoxy resins; with bisphenol F, phenol novolacs, alcohols or amines it gives other epoxy resins and reactive diluents. Outside coatings it is used for epichlorohydrin elastomers, paper wet-strength resins and water-treatment chemicals.
In resin manufacture, a phenol or alcohol opens the ECH epoxide ring, and sodium hydroxide then removes HCl to close a new glycidyl (epoxide) ring on the product.
Epichlorohydrin is highly hazardous: flammable, toxic by inhalation, skin contact and ingestion, corrosive, a skin sensitizer and classified as a presumed human carcinogen in the EU. It is handled only in closed industrial systems with strict exposure controls. Coating applicators do not handle ECH directly, but resin SDSs report any residual content.
Commercial epoxy resins contain only trace residual epichlorohydrin, and it is consumed or bound during manufacture. Check the resin SDS for the stated residual content of a specific product.
ECH made from glycerol, a by-product of biodiesel production, instead of from propylene. The chemistry of the final resin is the same, but part of the carbon is renewable.
Chlorine remaining in an epoxy resin from incomplete ring closure during manufacture. It is listed on data sheets because high levels can affect electrical properties and corrosion performance.
