Plastic That Degrades in Seawater a Boon for Cruise Industry, Others

Newswise — Large volumes of plastic waste generated aboard military, merchant and cruise ships must be stored onboard, often for prolonged periods, until they make port. In the future, a new type of environmentally friendly plastic that degrades in seawater may make it safe and practical to toss plastic waste overboard, freeing-up valuable storage space, according to scientists at The University of Southern Mississippi (USM).

The biodegradable plastics could replace conventional plastics that are used to make stretch wrap for large cargo items, food containers, eating utensils and other plastics used at sea, the researchers say. The biodegradable plastic has not yet been tested in freshwater. The development was described today at the 233rd national meeting of the American Chemical Society.

"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.

The American Chemical Society — the world's largest scientific society — is a nonprofit organization chartered by the U.S. Congress and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.

The paper on this research, POLY 207, will be presented at 9:00 a.m., Tuesday, March 27, at the McCormick Place Lakeside, Room E264, Level 2, during the symposium, "Polymer Performance, Degradation, and Materials Selection."

Robson F. Storey, Ph.D., is a professor of Polymer Science and Engineering in the School of Polymers and High Performance Materials, The University of Southern Mississippi, located in Hattiesburg, Miss.ALL PAPERS ARE EMBARGOED UNTIL DATE AND TIME OF PRESENTATION, UNLESS OTHERWISE NOTED

The paper on this research, POLY 207, will be presented at 9:00 AM, Tuesday, 27 March 2007, during the symposium, "Polymer Performance, Degradation, and Materials Selection."

POLY 207Marine-degradable thermoplastic polyurethanes

Program Selection: Division of Polymer ChemistryTopic Selection: Polymer Performance, Degradation, and Materials Selection: Environmental Degradation and Controlled Drug Release

Preprint submitted: YES!

Scott J. Moravek1, Tim R. Cooper1, Mohammad K. Hassan1, Jeffrey S. Wiggins1, Kenneth A. Mauritz1, and Robson F. Storey2. (1) School of Polymers and High Performance Materials, The University of Southern Mississippi, Polymer Science, 118 College Drive #10076, (2) School of Polymers and High Performance Materials, The University of Southern Mississippi, 118 College Drive #10076,

Abstract Large volumes of plastic waste are generated aboard military, merchant, and pleasure vessels at sea, and this waste currently must be stored onboard the ships until port is made. Biodegradable plastics that could be safely and ecologically disposed of at sea represent a strategic solution to this problem. Degradable thermoplastic polyurethanes (TPUs) based on methyl 2,6-diisocyantocaproate (LDI) or dicyclohexylmethane diisocyanate (H12MDI) were synthesized and characterized. Poly(D,L-lactide-co-glycolide) (PLGA) has been shown to be readily degradable and when incorporated into TPUs, contributes degradability to the TPU. The TPUs synthesized exhibit excellent tensile properties as compared to LLDPE stretch wrap. The TPUs were also characterized by dynamic mechanical analysis, which demonstrated the wide range of thermomechanical properties possible with varying compositions.

Researcher Provided Non-Technical Summary

Briefly explain in lay language what you have done, why it is significant and what are its implications (particularly to the general public)

Researchers at The University of Southern Mississippi are developing novel polyurethane-based plastics that are designed to degrade upon exposure to seawater. Large volumes of plastic waste are generated aboard military, merchant, and pleasure vessels at sea, and this waste currently must be stored onboard the ships until port is made. The new plastics, which could be safely and ecologically disposed of at sea, represent a strategic solution to this problem. Seawater degradability is imparted to the polyurethanes through the incorporation of poly(D,L-lactide-co-glycolide) (PLGA), which is a known degradable polymer used in controlled drug delivery and surgical suture applications. The new plastics exhibit excellent tensile properties as compared to common linear low-density polyethylene stretch wrap. Through variations in composition they can be designed to offer a wide range of mechanical and thermal properties. Degradation studies are currently underway in laboratory and marine environments.

How new is this work and how does it differ from that of others who may be doing similar research?

The development of these new plastics is ongoing. The novel property of these plastics is the ability to safely and ecologically be disposed of in a marine environment while also possessing excellent physical and thermal properties.