Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2001

Calculating VOCs for Two Component Coatings, Epoxy or Polyurethane

Q. Are all the VOCS in 2-part epoxy coatings emitted or are some reacted? I know, for example, that with fiberglass coatings only about 30% of styrene in the raw materials is actually emitted and EPA has a published emission factor for fiberglass. However, I have not found any similar information on epoxy coatings. Your help would be appreciated. Thanks.

A. You are correct that in fiberglass coatings the three components react. These are the polyester, styrene monomer and methyl ethyl ketone peroxide. Both the styrene and MEK peroxide are volatile and if left in the open would evaporate and would be considered VOCs. However, as soon as they are mixed these volatiles react with the polyester to form the solid coating. Some of the styrene does evaporate before it can react, and the EPA accepts this by providing a special emissions factor.

In the case of epoxy, polyurethane and most other two part paints, the solvents (volatiles) do not react with the resins to form part of the solid coating. From EPAs perspective ALL of the solvents evaporate and do not remain in the coating. Therefore, when you calculate the emissions for these coatings, you must assume that all of the VOC in each of the components will evaporate. You cannot take any credit for solvents that might be entrapped in the cured film, simply because they cannot get out fast enough.

For your information, I regularly run a 3 1/2 day training program on environmental compliance in the Paints and Coatings industry. Much of the class is devoted to calculations of VOCs from single and two part coatings. For more information please visit www.ronjoseph.com/compliancetraining/pcrc.htm