KEE Roofing Membrane

KEE (ketone ethylene ester) membranes are thermoplastic single-ply roof sheets in which a high-molecular-weight KEE polymer acts as a permanent flexibiliser for PVC. The best-known KEE modifier was DuPont's Elvaloy. Because KEE and PVC are fully miscible and both have high molecular weights, the KEE does not migrate out of the sheet the way liquid plasticisers can. PVC in turn adds strength, abrasion resistance and flame retardancy.

History

The technology traces back to 1974, when a geomembrane using a KEE modifier was introduced for environmental containment. In the early 1980s roofing products based on it were called EIP (ethylene interpolymer), a term later recognised in the NRCA low-slope guide. An ASTM subcommittee for the product formed in 1987, and ASTM D6754, the standard specification for ketone ethylene ester based sheet roofing, was issued in 2002 and later revised.

Standard and terminology

ASTM D6754 assumes KEE is the primary polymer in the membrane. Many products sold as "PVC-KEE" or "KEE-enhanced PVC" contain only part KEE and are tested to the PVC standard, ASTM D4434, which requires PVC to exceed 50% of polymer content. Specifiers therefore check which standard a product meets.

Properties and uses

KEE membranes are hot-air fused like PVC, without torches or adhesives at seams, and are valued for chemical resistance and flexibility retained with age. Reported installations include mechanically fastened and adhered roofs and a large roof beneath a garden deck.

Naming in the market

Terms such as EIP, KEE, PVC-KEE and KEE-enhanced PVC are used for overlapping products. Some PVC membranes are also described by the type of plasticiser chemistry they use, such as CPA, EIP or NBP, so data sheets and the governing ASTM standard are the reliable guide to what a membrane contains.