Plastic coating traps indoor air pollutants.Plastic coating traps indoor air pollutants
A Canadian chemist has developed a plastic coating to filter several toxic pollutants, including formaldehyde and acidic gases, from indoor air. Air filters coated with the plastic might one day help furnaces, box fans and air conditioners remove some of the indoor air contaminants responsible for so-called sick-building syndrome (SN: 9/23/89, p.206), suggests Hyman D. Gesser of the University of Manitoba Location
The main Fort Garry campus is a complex on the Red River in south Winnipeg. It has an area of 2.74 square kilometres. More than 60 major buildings support the teaching and research programs of the university. in Winnipeg. In preliminary tests, the newly patented coating absorbed susceptible pollutants for at least one month -- the recommended life of most furnace filters.
Polyethyleneimine (PEI) is a water-soluble plastic used in applications ranging from adhesion and disinfection disinfection,
n the process of destroying pathogenic organisms or rendering them inert.
disinfection, full oral cavity,
n a procedure used to reduce active periodontal disease, usually completed within a certain short time frame. to carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. absorption. It comprises three types of amines--subunits derived from ammonia. These primary, secondary and tertiary amines amines (mēnz´),
n.pl organic compounds that contain nitrogen. are distinguished by whether one, two or all three of the hydrogens in ammonia have been replaced by a carbon-based molecular fragment.
Because amines bind aldehydes, Gesser reasoned that PEI might trap formaldehyde. Indeed, his first tests confirmed that PEI's primary and secondary amines would absorb the pollutant from air recirculating through a filter coated with the plastic. However, as soon as all molecules on the coating's surface reacted with formaldehyde -- within 10 days or so -- its pollutant-trapping activity ceased.
The problem, Gesser discovered, was that the originally gooey See GUI. PEI coating quickly dried and hardened, anchoring its molecules fairly firmly. So he added glycerol glycerol, glycerin, glycerine, or 1,2,3-propanetriol (prō`pāntrī'ŏl), CH2OHCHOHCH2OH, colorless, odorless, sweet-tasting, syrupy liquid. to soften the plastic. This allowed PEI molecules to remain mobile so that those on the surface could trade places with others underneath, effectively replenishing the surface until nearly every molecule had reacted. In the April ENVIRONMENTAL SCIENCE AND TECHNOLOGY, he and Shali Fu report filtering out roughly 96 percent of the formaldehyde in air (at concentrations of 2, 5 and 10 parts per million parts per million
mg/kg or ml/l; see ppm. ) by drawing the air through a PEI/glycerol-coated filter at 500 milliliters per minute.
Since PEI is alkaline, Gesser also tested the coating against three acidic gases: sulfur dioxide, nitrogen dioxide and hydrogen sulfide hydrogen sulfide, chemical compound, H2S, a colorless, extremely poisonous gas that has a very disagreeable odor, much like that of rotten eggs. It is slightly soluble in water and is soluble in carbon disulfide. . Again, it chemically neutralized 98 percent of them. Here, however, the tertiary amines proved not only active but also the most potent agents. Some of the acid also dissolved into the glycerol, becoming trapped there.
"An abatement technology like this is useful," comments George Semeniuk, who works in EPA's indoor chemical control division in Washington, D.C. However, he notes, materials that give off indoor gases will sometimes increase their emission rates to compensate, at least temporarily, for a lowering in their air concentrations. That's one reason why EPA's program to reduce indoor formaldehyde focuses on limiting emissions from their sources, such as pressed wood, Semeniuk says.
For a "few dollars" in material costs, Gesser says, "it looks like we can now develop a [filter] coating to work for up to six months." He is about to begin testing prototypes in homes insulated with ureaformaldehyde foam or containing new particle board particle board: see composition board. and other building materials that initially emit high levels of formaldehyde.