Five different gypsum products were tested and found to release 57 odor-active compounds; including some previously unknown sulfur-smelling odorants.
German scientists at the Fraunhofer Institute of Building Physics have completed the most extensive analytical effort to date, in order to identify odor-active organic sulfur compounds in gypsum products. It is these odor-active compounds that are responsible for the unpleasant emissions produced by Chinese drywall.
Ideally, gypsum has an unobtrusive odor. It is usually described as slightly milky and chalk-like. In the US, commercially-active gypsum deposits have monocline crystalline structure, are white in color and relatively pure, formed in strata under high pressure and temperature. Recent gypsum deposits found in China are more amorphous in structure, formed in sediment layers and less pure.
Five gypsum-based products were examined by the German research team: white gypsum board with an unpleasant odor; white gypsum board with a typical gypsum odor; white, commercially-available gypsum powder, with a typical gypsum odor; rock-layered, natural raw stone from a Chinese deposit, with a very unpleasant sulfur odor; unpurified, ground and burned product from the Chinese mine, with the same unpleasant sulfur odor, but more intense.
In their efforts to determine the compounds responsible for the odor of the gypsum products, the researchers placed 100 grams of each sample in a 4L headspace vessel which was sealed airtight; equilibration took place over 16-20 hours, a period previously identified as permitting a constant relative amount of odorants in the gas phase.
The five different gypsum products released 57 odor-active compounds. Thirty-four of these, more than half, were easily identified and included aldehydes (hexanal, octanal) and ketones (2,3-butadione, 1-octen-3-one), 2-acetyl-1-pyrroline and some known sulfur-containing odorants (diethyl sulfide, 2-methyl-3-furanthiol). Most of these odorants have been previously found in various building products: mortar, composites, flooring materials. All of the gypsum products tested released some previously-unknown sulfur-smelling odorants.
The unpurified, ground and burned product from the stone of Chinese mine released 42 intensely-detectable odorants. Thirty of these had a sulfur odor, including all eight of the unidentified sulfur compounds released by the rejected gypsum product. There were thirteen sulfur compounds found only in the burned product which were tentatively identified on the basis of odor.
The author's note, in conclusion, that sensory evaluation of gypsum products using an odor panel combined with a rapid method to measuring reduced sulfur compounds would enable the gypsum industry to select the raw material appropriate for the product needed. This would avoid both consumer complaints, as well as unintended property damage like corrosion.
A copy of my complete review of the research performed to date (October 2009) by the German scientists at the Fraunhofer Institute of Building Physics is available upon request. Please send your request to info@buildinghealthsciences.com with the subject line noted, "Dr. Manis review - FIBP."
