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“There are many groups working on biodegradable
plastics, but we’re one of a few working on plastics that degrade in
seawater,” says study leader Robson F. Storey, Ph.D., a professor of
Polymer Science and Engineering at USM, located in Hattiesburg, Miss.
“We’re moving toward making plastics more sustainable, especially
those that are used at sea.”
Conventional plastics can take years to break down
and may result in byproducts that are harmful to the environment and
toxic to marine organisms, conditions that make their disposal at sea
hazardous. The new plastics are capable of degrading in as few as 20
days and result in natural byproducts that are nontoxic, Storey and
his associates say. Their study is funded by the Naval Sea Systems
Command (NAVSEA), which is supporting a number of ongoing research
projects aimed at reducing the environmental impact of marine waste.
The new plastics are made of polyurethane that has
been modified by the incorporation of PLGA [poly (D,L-lactide-co-glycolide)],
a known degradable polymer used in surgical sutures and controlled
drug-delivery applications. Through variations in the chemical
composition of the plastic, the researchers have achieved a wide range
of mechanical properties ranging from soft, rubber-like plastics to
hard, rigid structures, depending on their intended use.
When exposed to seawater, the plastics degrade via
hydrolysis into nontoxic products, according to the scientists.
Depending on the composition of the plastics, these compounds may
include water, carbon dioxide, lactic acid, glycolic acid, succinic
acid, caproic acid and L-lysine, all of which can be found in nature,
they add.
Because the new plastics are denser than saltwater,
they have a tendency to sink instead of float, Storey says. That
feature also could prevent them from washing up on shore and polluting
beaches, he notes.
The plastics are undergoing degradation testing at
the U.S. Army Natick Soldier Research, Development, and Engineering
Center in Natick, Mass., and in the Gulf of Mexico at the USM Gulf
Coast Research Laboratory in Ocean Springs, Miss. Initial results have
been favorable, Storey says.
The plastics are not quite ready for
commercialization. More studies are needed to optimize the plastics
for various environmental conditions they might encounter, including
changes in temperature, humidity and seawater composition, Storey says.
There also are legal hurdles to overcome, since international maritime
law currently forbids disposal of plastics at sea. |
