A biodiesel fuel byproduct called glycerol and an agricultural commodity called citric acid can be chemically combined to produce biodegradable polymers that could be used in produce packaging and other products, according to Agricultural Research Service scientists.
Justin Barone, a chemist at the ARS Environmental Quality Laboratory in Beltsville, Md., made the discovery while studying processes for improving the effectiveness of insecticides that contain citric acid as an active ingredient. Citric acid washes away very quickly in the environment, limiting its effectiveness.
Barone found that molecules containing hydrogen and oxygen--such as glycerol, sorbitol or polyethylene glycol--reacted with citric acid to produce polymers with citric acid groups in them. The materials formed are biodegradable polyesters. Further study showed that the viscosity of the material can range from the consistency of paint to a slow-to-dissolve, glasslike product, depending on how the chemical reaction takes place.
The new biodegradable polymers may provide the biodiesel industry with a new use for glycerol, which is now disposed of after the biodiesel is made. In addition, citric acid is used in the food industry as a retardant to browning in cut fruits and vegetables. The new citric acid-based polyesters may prove useful as a packaging material. Studies are under way to determine whether the new polymers would work as well as pure citric acid in these applications.
ARS is the U.S. Department of Agriculture's chief scientific research agency.