VOC Content of Energy Curable Coatings by Static Headspace – FID Gas Chromatographic Analysis

Energy curable coatings possess several advantages over traditional coatings, including having low levels of volatile organic compounds (VOCs) compared to most traditional coatings. According to the U.S. Environmental Protection Agency (EPA), a VOC is any volatile compound of carbon, excluding methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, ammonium carbonate, and exempt compounds which participates in atmospheric photochemical reactions. Generally this is interpreted to mean VOCs are “solvents” which evaporate from a material during and after application, excluding exempt compounds.

In the U.S., the measurement of VOCs is specified in EPA Method 24 (ASTM Practice D3960). In general, the VOC content of coatings may be determined experimentally by heating a specified quantity of the coating for one hour at 110oC and measuring the weight loss. The procedure is described for specific coatings in ASTM Method 2369, Test Method for Volatile Content of Coatings. This method essentially defines a VOC as any substance, other than water or exempt solvents, that evaporates from a coating when a specified sample is heated for one hour at 110oC. This method as written is not suitable for use on energy curable coatings.

ASTM Method D 5403 was developed to measure the volatile content of radiation curable materials using a mass-loss method. However, the method has been found to be unreliable for coatings designed to be applied at thicknesses of 10 micrometers or less. Wright et al.1, have developed a variant of ASTM Method D 5403 for use on individual reactive components of an energy curable coating. In their method, a sample of the reactive component or blend of reactive components is combined with 2% TPO-L as the photoinitiator and the sample is cured, weighed, then heated for sixty minutes at 110oC and then reweighed. The fraction VOC in the reactive material can then be calculated. No identification of the VOCs produced is obtained.